Publications

2008

  • [PDF] [DOI] P. Kluth, C. S. Schnohr, O. H. Pakarinen, F. Djurabekova, D. J. Sprouster, R. Giulian, M. C. Ridgway, A. P. Byrne, C. Trautmann, D. J. Cookson, K. Nordlund, and M. Toulemonde, “Fine structure in swift heavy ion tracks in amorphous sio$_2$,” Physical review letters, vol. 101, p. 175503, 2008.
    [Bibtex]
    @Article{Klut08,
    author = "P. Kluth and C. S. Schnohr and
    O. H. Pakarinen and F. Djurabekova and
    D. J. Sprouster and R. Giulian and M. C. Ridgway and
    A. P. Byrne and C. Trautmann and D. J. Cookson and
    K. Nordlund and M. Toulemonde",
    title = "Fine structure in swift heavy ion tracks in amorphous
    SiO$_2$",
    journal = " Physical Review Letters",
    year = 2008,
    volume = 101,
    pages = 175503,
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Kluth_tracks_PRL_2008.pdf",
    DOI = {10.1103/PhysRevLett.101.175503},
    note = {also availalbe at \url
    {http://dx.doi.org/10.1103/PhysRevLett.101.175503}},
    abstract = {We report on the observation of a fine structure in ion
    tracks in amorphous SiO2 using small angle x-ray
    scattering measurements. Tracks were generated by
    high energy ion irradiation with Au and Xe between
    27 MeV and 1.43 GeV. In agreement with molecular
    dynamics simulations, the tracks consist of a core
    characterized by a significant density deficit
    compared to unirradiated material, surrounded by a
    high density shell. The structure is consistent with
    a frozen-in pressure wave originating from the
    center of the ion track as a result of a thermal
    spike.}
    }
  • [PDF] [DOI] F. Djurabekova, C. Björkas, and K. Nordlund, “Atomistic modelling of the interface structure of si nanocrystals in silica,” Journal of physics: conference series, vol. 100, p. 52023, 2008.
    [Bibtex]
    @Article{Djur08a,
    author = {F. Djurabekova and C. Bj\"orkas and K. Nordlund},
    title = "Atomistic modelling of the interface structure of Si
    nanocrystals in silica",
    journal = "Journal of Physics: Conference Series" ,
    year = 2008,
    volume = 100,
    pages = 052023,
    doi = "10.1088/1742-6596/100/5/052023",
    pdf =
    {http://www.acclab.helsinki.fi/~djurabek/pubs/ICN_T_conf_Sweden_2008.pdf},
    project = {NC}
    }
  • [PDF] [DOI] F. Djurabekova, M. Backman, and K. Nordlund, “Atomistic modelling of the interface of si nanocrystal structures in a-sio2 before and after ion irradiation,” Nuclear instruments and methods in physics research b, vol. 266, p. 2683, 2008.
    [Bibtex]
    @Article{Djur08b,
    author = "F. Djurabekova and M. Backman and K. Nordlund",
    title = "Atomistic modelling of the interface of Si nanocrystal
    structures in a-SiO2 before and after ion irradiation",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2008,
    volume = 266,
    pages = 2683,
    doi = "10.1016/j.nimb.2008.03.099",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Djurabekova_SiNC_interface_NIMB.
    pdf",
    abstract = {As the basis of the conventional microelectronics
    industry, silicon is the most appropriate material
    for integration of electronic and optical
    functionalities in the same chips. Recent
    investigations in the field have lead to a drive to
    overcome the problem of poor light amplification
    properties of silicon. It has been shown that Si
    nanocrystals (Si-nc) embedded into a dielectric
    matrix emit light with a wavelength in the visible
    range. Ion implantation is widely used to form
    nanocrystals, and a subsequent step of inverse
    Oswald ripening can be used to control their size
    uniformity and flat space distribution. By means of
    molecular dynamics, atomistic models of Si-nc
    inserted into amorphous silica (a-SiO$_2$) have been
    constructed. The defect structure of the interface
    region is discussed. The influence of ion
    implantation on the Si-nc atom distribution is
    analyzed and compared to binary collision
    approximation simulation results. The amorphization
    of Si-nc’s due to high-dose ion implantation is also
    discussed.},
    project = {NC}
    }
  • [PDF] [DOI] F. Djurabekova and K. Nordlund, “Atomistic simulation of the interface structure of si nanocrystals embedded into amorphous silica,” Physical review b, vol. 77, p. 115325, 2008.
    [Bibtex]
    @Article{Djur08c,
    author = "F. Djurabekova and K. Nordlund",
    title = "Atomistic simulation of the interface structure of
    Si nanocrystals embedded into amorphous silica",
    journal = "Physical Review B",
    year = 2008,
    volume = 77,
    pages = 115325,
    note = "also selected to Virtual Journal of Nanoscale
    Science \& Technology Vol. 17 Issue 13 (2008).",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Djurabekova_Si_SiO2_PRB_2008.pdf",
    myfile = "Publications/final_papers/2008/Djurabekova_Si_SiO2_PRB_2008.pdf",
    DOI = {10.1103/PhysRevB.77.115325},
    abstract = {An efficient means to obtain light emission from a
    silicon-based material would enable integrating both
    optical and electronic functionalities on the same
    silicon chips. The long radiative lifetimes have
    until recently obstructed efficient light emission
    from Si. A nanocrystalline approach has opened up a
    prospect for silicon in the optoelectronics
    application field. However, the structure of the
    nanocrystal-matrix interface, which appears to be
    important for the light emission, remains
    unclear. In the present work, by means of molecular
    dynamics atomistic models, small nc-Si embedded into
    defect-free a-SiO$_2$ are constructed using two
    different classical interatomic potentials. The
    models allow analysis of the defects at the
    interface which may serve as radiative and
    nonradiative recombination centers for excitons
    formed in nc’s and, thus, be responsible for the
    optical properties of the structure. We analyzed the
    interface structures after a series of
    high-temperature annealing runs and subsequent
    relaxation at room temperature. The results show
    that the nc-Si/SiO$_2$ interface is organized by
    means of a thin suboxide layer (SiO$_{2−x}$), which
    contains a considerable amount of undercoordinated
    defects as well. We also observed the spontaneous
    formation of silanone bonds (Si=O), frequently
    discussed in the literature to be centers with an
    important role on the optical properties of the nc
    structures.}
    }
  • [PDF] E. Holmström, A. Kuronen, and K. Nordlund, “Threshold defect production in silicon determined by density functional theory molecular dynamics simulations,” Physical review b, vol. 78, iss. 4, p. 45202, 2008.
    [Bibtex]
    @Article{Hol08a,
    author = "E. Holmström and A. Kuronen and K. Nordlund",
    title = "Threshold defect production in silicon determined by
    density functional theory molecular dynamics simulations",
    journal = "Physical Review B",
    year = 2008,
    volume = 78,
    number = 4,
    pages = 045202,
    pdf = "http://www.acclab.helsinki.fi/~knordlun/pub/Hol08a.pdf",
    project = {Si}
    }

2009

  • [PDF] [DOI] M. Backman, F. Djurabekova, O. H. Pakarinen, K. Nordlund, L. L. Araujo, and M. C. Ridgway, “Amorphization of ge and si nanocrystals embedded in amorphous sio$_2$ by ion irradiation,” Physical review b, vol. 80, p. 144109, 2009.
    [Bibtex]
    @Article{Back09,
    author = "M. Backman and F. Djurabekova and O. H. Pakarinen and K.
    Nordlund and L. L. Araujo and M. C. Ridgway",
    title = "Amorphization of Ge and Si nanocrystals embedded in amorphous
    SiO$_2$ by ion irradiation",
    journal = "Physical Review B",
    year = 2009,
    volume = 80,
    pages = 144109,
    pdf = "http://www.acclab.helsinki.fi/~djurabek/pubs/Backman_GeNC_PRB.pdf",
    DOI = {10.1103/PhysRevB.80.144109},
    abstract = {Finite-size effects become significant in nanoscale
    materials. When a nanocrystal is surrounded by a
    host matrix of a different nature, the perfection of
    the crystal structure is distorted by the interface
    formed between the nanocrystal and the matrix. The
    larger the surface-to-volume ratio of the
    nanocrystal, the higher the influence of the
    interface defect states on its properties. The
    presence of defect states in the interface can also
    explain the different responses of the nanocrystals
    (NCs) on external influences. By the combination of
    molecular-dynamics simulations and x-ray absorption
    spectroscopy measurements, we show that the
    amorphization of Si and Ge nanocrystals is reached
    at doses roughly one order of magnitude lower than
    those for the bulk crystals. Examining nanocrystals
    in the size range from 2.4 to 9 nm, we also show
    that the susceptibility to the amorphization
    decreases with increasing nanocrystal size. The
    finite-size effect remains significant also for the
    largest nanocrystals of 9 nm.},
    project = {NC}
    }
  • [PDF] [DOI] O. H. Pakarinen, F. Djurabekova, K. Nordlund, P. Kluth, and M. Ridgway, “Molecular dynamics simulations of the structure of latent tracks in quartz and amorphous sio$_{2}$,” Nuclear instruments and methods in physics research b, vol. 267, p. 1456 – 1459, 2009.
    [Bibtex]
    @Article{Paka09a,
    author = "O. H. Pakarinen and F. Djurabekova and
    K. Nordlund and P. Kluth and M. Ridgway",
    title = "Molecular dynamics simulations of the structure of
    latent tracks in quartz and amorphous SiO$_{2}$",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2009,
    volume = 267,
    pages = {1456 -- 1459},
    DOI = {10.1016/j.nimb.2009.01.071},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Pakarinen_latenttracks_NIMB_2009.
    pdf",
    abstract = {Swift heavy ion irradiation (SHII) can leave a latent
    ion track around the ion path. Tracks in amorphous
    silicon dioxide (a-SiO2) and quartz are interesting
    due to applications in nanofabrication, for
    example. In recent experiments, a previously
    unresolved fine structure in latent ion tracks in
    a-SiO2 was found comprising a lower density core and
    a higher density shell. We model the formation of
    latent ion tracks in crystalline quartz and
    amorphous SiO2 using classical molecular dynamics
    (MD) to simulate the irradiation at the atomistic
    level, and compare the results to small angle X-ray
    scattering (SAXS) experiments on amorphous, 2 $\mu$m
    thick SiO2 layers. Electronic energy deposition of
    $^{197}$Au ions corresponding to experiments is used in
    the simulations, to allow direct comparison between
    simulations and existing experiments. We explain
    the formation of the experimentally observed
    cylindrical core–shell structure with the dynamic
    simulations, and compare the obtained track
    dimensions and threshold energies with the
    experiment.},
    project = {FAIR}
    }
  • [PDF] [DOI] F. Djurabekova, M. Backman, O. H. Pakarinen, K. Nordlund, L. L. Araujo, and M. C. Ridgway, “Amorphization of ge nanocrystals embedded in amorphous silica under ion irradiation,” Nuclear instruments and methods in physics research b, vol. 267, p. 1235 – 1238, 2009.
    [Bibtex]
    @Article{Djur09a,
    author = "F. Djurabekova and M. Backman and O. H. Pakarinen and K.
    Nordlund and L. L. Araujo and M. C. Ridgway",
    title = "Amorphization of Ge nanocrystals embedded in amorphous silica
    under ion irradiation",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2009,
    volume = 267,
    pages = "1235 -- 1238",
    DOI = {10.1016/j.nimb.2009.01.022},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2009_Djurabekova_amorph_GeNC.pdf",
    abstract = {One of the key reasons why nanoscale materials behave
    differently from their bulk counterparts is that a
    large fraction of atoms reside at surfaces or
    interfaces. For instance, the melting point,
    hardness and even crystal structure of a nanocrystal
    can be dramatically different from that of the same
    element or compound in its conventional phase. Of
    particular interest from an ion-beam modification
    point of view is how much the structural
    transformations induced by energetic ions in
    nanocrystals differ from those in the bulk
    phase. Using a combination of molecular dynamics
    (MD) computer simulations and Extended X-ray
    Absorption Fine Structure (EXAFS) experiments, we
    show that the crystalline-to-amorphous transition in
    Ge nanocrystals occurs at a dose which is
    significantly (more than an order of magnitude)
    lower than that in the bulk phase. The MD
    simulations indicate that this is related to the
    outermost part of a structured nanocrystal being
    subjected to an additional stress delivered by the
    amorphous surroundings. These results show that
    conventional models based on irradiation of bulk
    materials can not be used to estimate the
    susceptibility of nanocrystals to phase
    transitions.},
    project = {NC}
    }
  • [PDF] [DOI] J. A. Pakarinen, M. Backman, F. Djurabekova, and K. Nordlund, “Partial melting mechanisms of embedded nanocrystals,” Physical review b, vol. 79, p. 85426, 2009.
    [Bibtex]
    @Article{Paka09b,
    author = "J. A. Pakarinen and M. Backman and F. Djurabekova
    and K. Nordlund",
    title = "Partial melting mechanisms of embedded nanocrystals",
    journal = " Physical Review B",
    year = 2009,
    volume = 79,
    pages = 085426,
    DOI = {10.1103/PhysRevB.79.085426},
    myfile = "Publications/final_papers/2009/Pakarinen_NCmelting_PRB.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Pakarinen_NCmelting_PRB.pdf",
    abstract = {Understanding the melting mechanisms of nanocrystals
    embedded in solids is of great current interest
    since both the synthesis and modification of such
    systems frequently involve the use of high
    temperatures. Using molecular-dynamics computer
    simulations we study the melting mechanisms of Cu,
    Ag, and Au nanoclusters embedded in metal matrices
    and Si nanocrystals in amorphous silica. The results
    show that nanocrystals embedded in a solid bulk
    material with a higher melting temperature exhibit
    complex melting behavior and can even, in the same
    system, exhibit four distinct stages prior to full
    melting of the system.},
    project = {NC}
    }
  • F. Djurabekova, M. Backman, O. H. Pakarinen, K. Nordlund, L. L. Araujo, and M. C. Ridgway, “Energetic ion modification of semiconductor nanocrystals embedded in silica: simulation and experiments,” in Proceedings of the 2009 ion-solid interactions conference, Moscow, Russia: Moscow aviation institute publisher, 2009, vol. 2, p. 149 – 152.
    [Bibtex]
    @InCollection{Djur09b,
    title = "Energetic ion modification of semiconductor
    nanocrystals embedded in silica: simulation and
    experiments",
    author = "F. Djurabekova and M. Backman and O. H. Pakarinen
    and K. Nordlund and L. L. Araujo and M. C. Ridgway",
    booktitle = "Proceedings of the 2009 Ion-Solid Interactions
    conference",
    year = 2009,
    volume = 2,
    publisher = "Moscow aviation institute publisher",
    address = "Moscow, Russia",
    pages = "149 -- 152",
    project = {NC}
    }

2010

  • [PDF] D. J. Sprouster, R. Giulian, L. L. Araujo, P. Kluth, B. Johannessen, K. Nordlund, and M. C. Ridgway, “Ion irradiation induced amorphization of cobalt nanoparticles,” Physical review b, vol. 81, p. 155414, 2010.
    [Bibtex]
    @Article{Spr09,
    author = "D. J. Sprouster and R. Giulian and L. L. Araujo and
    P. Kluth and B. Johannessen and K. Nordlund and
    M. C. Ridgway",
    title = "Ion Irradiation Induced Amorphization of Cobalt
    Nanoparticles",
    journal = " Physical Review B",
    year = 2010,
    volume = 81,
    pages = 155414,
    pdf = "http://www.acclab.helsinki.fi/~knordlun/pub/Spr09.pdf",
    file = "pub/concamo",
    project = {NC}
    }
  • E. Holmström, A. V. Krasheninnikov, and K. Nordlund, “Quantum and classical molecular dynamics studies of the threshold displacement energy in si bulk and nanowire,” in Ion beams and nano-engineering, D. Ila, J. K. N. Lindner, P. K. Chu, J. Baglin, and N. Kishimoto, Eds., Warrendale, PA, USA: Mrs, 2010, vol. 1181, pp. 111-122.
    [Bibtex]
    @InCollection{Hol09a,
    author = "E. Holmström and A. V. Krasheninnikov and K. Nordlund",
    title = "Quantum and Classical Molecular Dynamics Studies of
    the Threshold Displacement Energy in Si Bulk and Nanowire",
    booktitle = "Ion Beams and Nano-Engineering",
    publisher = "MRS",
    address = "Warrendale, PA, USA",
    year = 2010,
    editor = "D. Ila and J. K. N. Lindner and P. K. Chu and J. Baglin and
    N.
    Kishimoto",
    series = "MRS Symposium Proceedings",
    volume = 1181,
    pages = "111-122",
    file = "pub/mrsspring2009_kai",
    project = {Si}
    }
  • [PDF] E. Holmström, K. Nordlund, and A. Kuronen, “Threshold defect production in germanium determined by density functional theory molecular dynamics simulations,” Physica scripta, vol. 81, p. 35601, 2010.
    [Bibtex]
    @Article{Hol10a,
    title = "Threshold defect production in germanium determined by density
    functional theory molecular dynamics simulations",
    author = "E. Holmstr\"om and K. Nordlund and A. Kuronen",
    journal = "Physica Scripta",
    volume = 81,
    pages = 035601,
    year = 2010,
    file = "pub/gethres_siesta/",
    pdf = "http://www.acclab.helsinki.fi/~knordlun/pub/Hol10a.pdf",
    project = {Si}
    }
  • M. Backman, F. Djurabekova, O. H. Pakarinen, K. Nordlund, and M. Toulemonde, “Contribution of electronic energy deposition to the atomic cascade damage in nanocrystals,” in Basic actinide science and materials for nuclear applications, Warrendale, PA, USA, 2010.
    [Bibtex]
    @InProceedings{Back10,
    author = "M. Backman and F. Djurabekova and O. H. Pakarinen
    and K. Nordlund and M. Toulemonde",
    title = "Contribution of Electronic Energy Deposition to the
    Atomic Cascade Damage in Nanocrystals",
    booktitle = "Basic Actinide Science and Materials for Nuclear
    Applications",
    year = 2010,
    editor = "J.K. Gibson and S.K. McCall and E.D. Bauer and L.
    Soderholm and T. Fanghaenel and R. Devanthan and
    A. Misra and C. Trautmann and B.D. Wirth",
    volume = 1264,
    series = "Mater. Res. Soc. Symp. Proc.",
    address = "Warrendale, PA, USA",
    number = "1264-BB02-07",
    myfile =
    "Publications/final_papers/2010/Backman_MRS10_proceedings.pdf",
    project = {FAIR}
    }
  • [PDF] A. Descoeudres, F. Djurabekova, and K. Nordlund, “Dc breakdown experiments with cobalt electrodes,” Clic-note, vol. 875, pp. 1-6, 2010.
    [Bibtex]
    @Article{Desc10,
    author = "A. Descoeudres and F. Djurabekova and K. Nordlund",
    title = "DC Breakdown experiments with cobalt electrodes",
    journal = "CLIC-Note",
    volume = "875",
    year = 2010,
    pages = "1-6",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Descoeudres_CLIC_Note_Cobalt.pdf",
    myfile =
    "Publications/final_papers/2010/Descoeudres_CLIC_Note_Cobalt.pdf",
    project = {CLIC}
    }
  • [PDF] E. Holmström, M. Hakala, and K. Nordlund, “Amorphous defect clusters of pure si and the type inversion in si detectors,” Physical review b, vol. 82, p. 94102, 2010.
    [Bibtex]
    @Article{Hol09b,
    title = "Amorphous defect clusters of pure Si and the type inversion
    in Si detectors",
    author = "E. Holmström and M. Hakala and K. Nordlund",
    journal = " Physical Review B",
    year = 2010,
    volume = 82,
    pages = 094102,
    pdf = "http://www.acclab.helsinki.fi/~knordlun/pub/Hol09b.pdf",
    file = "pub/asi_detectors/",
    project = {Si}
    }
  • [PDF] S. Calatroni, A. Descoeudres, A. Hansen, J. W. Kovermann, M. Taborelli, H. Timko, W. Wuensch, F. Djurabekova, K. Nordlund, A. Pohjonen, and A. Kuronen, “Breakdown studies for the clic accelerating structures,” in Proceedings of 2010 linac conference, http://epaper.kek.jp/index.html: Joint accelerator conference website, 2010.
    [Bibtex]
    @InCollection{Cala10,
    author = "S. Calatroni and A. Descoeudres and A. Hansen and
    J. W. Kovermann and M. Taborelli and H. Timko and
    W. Wuensch and F. Djurabekova and K. Nordlund and
    A. Pohjonen and A. Kuronen",
    title = "Breakdown Studies for the CLIC Accelerating
    Structures",
    booktitle = "Proceedings of 2010 LINAC conference",
    publisher = "Joint Accelerator Conference Website",
    address = "http://epaper.kek.jp/index.html",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Calatroni_BDR_CLIC_proceedings.
    pdf",
    year = "2010",
    myfile =
    "Publications/final_papers/Calatroni_BDR_CLIC_proceedings.pdf",
    abstract = {Optimizing the design and the manufacturing of the CLIC
    RF accelerating structures for achieving the target
    value of breakdown rate at the nominal accelerating
    gradient of 100 MV/m requires a detailed
    understanding of all the steps involved in the
    mechanism of breakdown. These include surface
    modification under RF fields, electron emission and
    neutral evaporation in the vacuum, arc ignition and
    consequent surface modification due to plasma
    bombardment. Together with RF tests, experiments are
    conducted in a simple DC test set-up instrumented
    with electrical diagnostics and optical
    spectroscopy. The results are also used for
    validating simulations which are performed using a
    wide range of numerical tools (MD coupled to
    electrostatic codes, PIC plasma simulations) able to
    include all the above phenomena. Some recent results
    are presented in this paper.},
    project = {CLIC}
    }
  • [DOI] O. H. Pakarinen, F. Djurabekova, and K. Nordlund, “Density evolution in formation of swift heavy ion tracks in insulators,” Nuclear instruments and methods in physics research b, vol. 268, p. 3163, 2010.
    [Bibtex]
    @Article{Paka10,
    author = "O. H. Pakarinen and F. Djurabekova and K. Nordlund",
    title = "Density evolution in formation of swift heavy ion tracks
    in insulators",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2010,
    volume = 268,
    pages = 3163,
    DOI = {10.1016/j.nimb.2010.05.079},
    myfilef =
    "Publications/final_papers/2010/Pakarinen_SHI_tracks_insulators.pdf",
    abstract = {Swift heavy ion irradiation leaves a latent ion track
    around the ion path in many materials. Here we
    report computational molecular dynamics (MD)
    simulation results on track formation in several
    insulating materials, quartz, amorphous silica
    (a-SiO2), zinc oxide and diamond, concentrating
    especially in mass transport leading to density
    variations in the track volume during the initial
    stages of track formation. These details are
    largely unobservable in experiments due to the
    picosecond timescale and very local nature, and also
    in many computational models of track
    formation. Earlier a low-density core – high-density
    shell fine structure has been observed in latent
    tracks in amorphous silica, and here we study if
    other materials than silica show similar
    behavior. The results highlight the dynamical nature
    of track formation, that includes competing effects
    of heat and mass transport, rapid quenching of the
    heated area and recrystallization.},
    project = {FAIR}
    }
  • [PDF] [DOI] H. Timko, F. Djurabekova, L. Costelle, K. Nordlund, K. Matyash, R. Schneider, A. Toerklep, G. Arnau-Izquierdo, A. Descoeudres, S. Calatroni, M. Taborelli, and W. Wuensch, “Mechanism of surface modification from the arc plasma-surface interaction in cu,” Physical review b, vol. 81, p. 184109, 2010.
    [Bibtex]
    @Article{Timk10a,
    author = "H. Timko and F. Djurabekova and L. Costelle and K. Nordlund
    and K. Matyash and R. Schneider and A. Toerklep and G. Arnau-Izquierdo and A.
    Descoeudres and S. Calatroni and M. Taborelli and W. Wuensch",
    title = "Mechanism of surface modification from the arc plasma-surface
    interaction in Cu",
    journal = " Physical Review B",
    volume = 81,
    year = 2010,
    pages = 184109,
    DOI = {10.1103/PhysRevB.81.184109},
    pdf = "http://www.acclab.helsinki.fi/~djurabek/pubs/Timko_ARCMD_PRB.pdf",
    myfile = "Publications/final_papers/2010/Timko_ARCMD_PRB.pdf",
    abstract ={Electrical sparks and arcs are plasma discharges that
    carry large currents and can strongly modify
    surfaces. This damage usually comes in the form of
    micrometer-sized craters and frozen-in liquid on the
    surface. Using a combination of experiments, plasma
    and atomistic simulation tools, we now show that the
    observed formation of deep craters and liquidlike
    features during sparking in vacuum is explained by
    the impacts of energetic ions, accelerated under the
    given conditions in the plasma sheath to
    kiloelectron volt energies, on surfaces. The flux in
    arcs is so high that in combination with
    kiloelectron volt energies it produces multiple
    overlapping heat spikes, which can lead to cratering
    even in materials such as Cu, where a single heat
    spike normally does not.},
    project = {CLIC}
    }
  • F. Djurabekova, M. Backman, O. H. Pakarinen, K. Nordlund, L. L. Araujo, and M. C. Ridgway, “Alternation of crystal structure of ge nanocrystals embedded in amorphous sio$_2$ by ion irradiation (in russian),” Uzbek journal of physics, vol. 12, p. 76 – 82, 2010.
    [Bibtex]
    @Article{Djur10c,
    author = "F. Djurabekova and M. Backman and O. H. Pakarinen and K.
    Nordlund and L. L. Araujo and M. C. Ridgway",
    title = "Alternation of crystal structure of Ge nanocrystals embedded
    in amorphous SiO$_2$ by ion irradiation (in Russian)",
    journal = "Uzbek Journal of Physics",
    year = 2010,
    volume = 12,
    pages = "76 -- 82",
    myfile = "Publications/final_papers/2010/Djurabekova_Uzb_J_Phys.pdf",
    project = {NC}
    }
  • [PDF] [DOI] F. Djurabekova, L. Malerba, R. C. Pasianot, P. Olsson, and K. Nordlund, “Kinetics versus thermodynamics in materials modelling: the case of the di-vacancy in iron,” Philosophical magazine, vol. 90, p. 2585, 2010.
    [Bibtex]
    @Article{Djur10a,
    author = "F. Djurabekova and L. Malerba and R. C. Pasianot and
    P. Olsson and K. Nordlund",
    title = "Kinetics versus thermodynamics in materials
    modelling: the case of the di-vacancy in iron",
    journal = "Philosophical Magazine",
    year = 2010,
    volume = 90,
    pages = 2585,
    doi = "10.1080/14786431003662515",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2010_Djurabekova_kinetics_2V_Fe.pdf",
    myfile =
    "Publications/final_papers/Djurabekova_kinetics_2VD_Fe_PhilMag.pdf",
    abstract = {Monte Carlo models are widely used for the study of
    microstructural and microchemical evolution of
    materials under irradiation. However, they often
    link explicitly the relevant activation energies to
    the energy difference between local equilibrium
    states. We provide a simple example (di-vacancy
    migration in iron) in which a rigorous activation
    energy calculation, by means of both empirical
    interatomic potentials and density functional theory
    methods, clearly shows that such a link is not
    granted, revealing a migration mechanism that a
    thermodynamics-linked activation energy model cannot
    predict. Such a mechanism is, however, fully
    consistent with thermodynamics. This example
    emphasizes the importance of basing Monte Carlo
    methods on models where the activation energies are
    rigorously calculated, rather than deduced from
    widespread heuristic equations.},
    project = {FF}
    }
  • [DOI] F. Djurabekova, M. Backholm, M. Backman, O. H. Pakarinen, J. Keinonen, K. Nordlund, T-R. Shan, B. D. Devine, and S. B. Sinnott, “Amorphization of $\alpha$-quartz and comparative study of defects in amorphized quartz and si nanocrystals embedded in amorphous silica,” Nuclear instruments and methods in physics research b, vol. 268, p. 3095 – 3098, 2010.
    [Bibtex]
    @Article{Djur10b,
    author = "F. Djurabekova and M. Backholm and M. Backman and
    O. H. Pakarinen and J. Keinonen and K. Nordlund and
    T-R. Shan and B. D. Devine and S. B. Sinnott",
    title = "Amorphization of $\alpha$-quartz and comparative study
    of defects in amorphized quartz and Si nanocrystals
    embedded in amorphous silica",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2010,
    volume = 268,
    pages = {3095 -- 3098},
    doi = {10.1016/j.nimb.2010.05.056},
    myfile = "Publications/final_papers/2010/Djurabekova_quartz_defects_NIMB.pdf",
    abstract = {Ion irradiation of a-quartz renders the crystal SiO2
    structure amorphous. The enormous amount of
    structural defects produced after ion irradiation
    give a chance for photoactive intrinsic defects to
    be formed. These may be responsible for the
    photoluminescence in irradiated a-quartz. On the
    other hand, the radiation defects are not stable,
    and thus, an alternative structure where the defects
    of interest can be stabilized is required. The
    stabilization of the defects can be achieved in the
    structures of amorphous silica with embedded Si
    nanocrystals (NC), thanks to the unique structure of
    the formed interface. By means of Molecular Dynamics
    (MD), we analyze defects in both amorphized a-quartz
    and Si-NC/a-SiO2 interfaces formed by 1.1, 2.4 and 4
    nm diameter NC’s. In the simulation, we employ a
    classical interatomic potential and a potential,
    which takes into consideration a charge transfer
    between Si and O atoms. We show that although the
    number of silanone bonds Si=O in irradiated quartz
    is higher, they are also found in a Si-NC/a-SiO2
    interface without the necessity of preceding
    irradiation of the sample. We also compare the
    defects in irradiation-amorphized quartz and the
    three sizes of Si-NC/a-SiO2 interfaces. Analysis of
    the charges showed that the charge state of
    coordination defects depends on the type of atoms in
    the near neighborhood.},
    project = {NC}
    }
  • [PDF] [DOI] L. Malerba, M. C. Marinica, N. Anento, C. Björkas, H. Nguyen, C. Domain, F. Djurabekova, P. Olsson, K. Nordlund, A. Serra, D. Terentyev, F. Willaime, and C. S. Becquart, “Comparison of empirical interatomic potentials for iron applied to radiation damage studies,” Journal of nuclear materials, vol. 406, p. 19 – 38, 2010.
    [Bibtex]
    @Article{Male10,
    author = "L. Malerba and M. C. Marinica and N. Anento and
    C. Björkas and H. Nguyen and C. Domain and
    F. Djurabekova and P. Olsson and K. Nordlund and
    A. Serra and D. Terentyev and F. Willaime and
    C.S. Becquart",
    title = "Comparison of empirical interatomic potentials for
    iron applied to radiation damage studies",
    journal = "Journal of Nuclear Materials",
    year = {2010},
    volume = {406},
    pages = {19 -- 38},
    DOI = {10.1016/j.jnucmat.2010.05.017},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2010_Malerba_compFe_IAP.
    pdf",
    myfile = "Publications/final_papers/2010/Malerba_compFe_IAP.pdf",
    project = {FF}
    }
  • [PDF] [DOI] A. Sakko, C. Sternemann, C. J. Sahle, H. Sternemann, O. M. Feroughi, H. Conrad, F. Djurabekova, M. Tolan, and K. Hämäläinen, “$Si/SiO_2$ interface in disproportionating a-sio studied by x-ray raman scattering,” Physical review b, vol. 81, p. 205317, 2010.
    [Bibtex]
    @Article{Sakk10,
    author = "A. Sakko and C. Sternemann and Ch. J. Sahle and
    H. Sternemann and O. M. Feroughi and H. Conrad and
    F. Djurabekova and M. Tolan and
    K. Hämäläinen",
    title = "$Si/SiO_2$ interface in disproportionating a-SiO
    studied by x-ray Raman scattering",
    journal = " Physical Review B",
    year = 2010,
    volume = 81,
    pages = 205317,
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Sakko_xray_SiObonds_PRB.pdf",
    DOI = {10.1103/PhysRevB.81.205317},
    myfile = "Publications/final_papers/Sakko_xray_SiObonds_PRB.pdf",
    abstract = {The microscopic structure of disproportionating
    amorphous silicon monoxide is studied by inelastic
    x-ray scattering at the silicon L$_{II,III}$
    edge. This material arranges into nanocrystalline
    regions of Si embedded in amorphous SiO$_2$ at proper
    annealing temperatures and in this work we
    demonstrate how the contribution of the suboxide
    interfaces between these regions can be extracted
    from the experimental data. The resulting near-edge
    spectra are analyzed in detail using a computational
    framework that combines molecular-dynamics
    simulations and density-functional theory
    calculations. The results indicate that the amount
    of silicon atoms with oxidation states between +1
    and +3 is significant and depends strongly on the
    annealing temperature. Furthermore, the presented s,
    p, and d-type local densities of states ($\l$DOS)
    demonstrate that the most significant differences
    are found in the p-type $\l$DOS.},
    project = {NC}
    }

2011

  • [DOI] P. Kluth, O. H. Pakarinen, F. Djurabekova, R. Giulian, M. C. Ridgway, A. P. Byrne, and K. Nordlund, “Nanoscale density fluctuations in swift heavy ion irradiated amorphous sio$_2$,” Journal of applied physics, vol. 110, 2011.
    [Bibtex]
    @Article{Klut11,
    author = "P. Kluth and O. H. Pakarinen and F. Djurabekova and
    R. Giulian and M. C. Ridgway and A. P. Byrne and
    K. Nordlund",
    title = "Nanoscale density fluctuations in swift heavy ion irradiated
    amorphous SiO$_2$",
    journal = "Journal of Applied Physics",
    year = 2011,
    volume = 110,
    doi = {10.1063/1.3671614},
    myfile =
    "Publications/final_papers/2011/Kluth_densityfluctuations_JAP.pdf",
    abstract = {We report on the observation of nanoscale density
    fluctuations in 2 lm thick amorphous SiO2 layers
    irradiated with 185 MeV Au ions. At high fluences,
    in excess of approximately 5x10$^{12}$ ions/cm$^2$, where
    the surface is completely covered by ion tracks,
    synchrotron small angle x-ray scattering
    measurements reveal the existence of a steady state
    of density fluctuations. In agreement with molecular
    dynamics simulations, this steady state is
    consistent with an ion track “annihilation” process,
    where high-density regions generated in the
    periphery of new tracks fill in low-density regions
    located at the center of existing tracks.},
    project = {FAIR}
    }
  • [DOI] S. A. Norris, J. Samela, C. S. Madi, M. P. Brenner, L. Bukonte, M. Backman, F. Djurabekova, K. Nordlund, and M. J. Aziz, “Md-predicted phase diagrams for pattern formation,” Nature communications, vol. 2, p. 276, 2011.
    [Bibtex]
    @Article{Norr11,
    author = {S. A. Norris and J. Samela and C. S. Madi
    and M. P. Brenner and L. Bukonte and M. Backman and
    F. Djurabekova and K. Nordlund and M. J. Aziz},
    title = {MD-Predicted Phase diagrams for Pattern Formation},
    journal = {Nature communications},
    year = 2011,
    volume = 2,
    pages = 276,
    doi = {10.1038/ncomms1280},
    myfile =
    "Publications/final_papers/2011/Norris-et-al-NCOMMS-2011-with-supplement-as-
    published.pdf",
    abstract = {Energetic particle irradiation can cause surface
    ultra-smoothening, self-organized nanoscale pattern
    formation or degradation of the structural integrity
    of nuclear reactor components. A fundamental
    understanding of the mechanisms governing the
    selection among these outcomes has been
    elusive. Here we predict the mechanism governing the
    transition from pattern formation to flatness using
    only parameter-free molecular dynamics simulations
    of single-ion impacts as input into a multiscale
    analysis, obtaining good agreement with
    experiment. Our results overturn the paradigm
    attributing these phenomena to the removal of target
    atoms via sputter erosion: the mechanism dominating
    both stability and instability is the impact-induced
    redistribution of target atoms that are not
    sputtered away, with erosive effects being
    essentially irrelevant. We discuss the potential
    implications for the formation of a mysterious
    nanoscale topography, leading to surface
    degradation, of tungsten plasma-facing fusion
    reactor walls. Consideration of impact-induced
    redistribution processes may lead to a new design
    criterion for stability under irradiation.},
    project = {ripples}
    }
  • [DOI] H. Timko, K. Matyash, R. Schneider, F. Djurabekova, K. Nordlund, A. Hansen, A. Descoeudres, J. Kovermann, A. Grudiev, W. Wuensch, S. Calatroni, and M. Taborelli, “A one-dimensional particle-in-cell model of plasma build-up in vacuum arcs,” Contributions to plasma physics, vol. 51, iss. 1, p. 5 – 21, 2011.
    [Bibtex]
    @Article{Timk11a,
    author = "H. Timko and K. Matyash and R. Schneider and
    F. Djurabekova and K. Nordlund and A. Hansen and
    A. Descoeudres and J. Kovermann and A. Grudiev and
    W. Wuensch and S. Calatroni and M. Taborelli",
    title = "A One-Dimensional Particle-in-Cell Model of Plasma Build-up
    in
    Vacuum Arcs",
    journal = "Contributions to Plasma Physics",
    volume = {51},
    number = {1},
    DOI = {10.1002/ctpp.201000504},
    year = {2011},
    pages = {5 -- 21},
    myfile = "Publications/final_papers/2011/Timko_1DPIC_CPP.pdf",
    abstract ={Understanding the mechanism of plasma build-up in vacuum
    arcs is essential in many fields of physics. A
    onedimensional particle-in-cell computer simulation
    model is presented, which models the plasma
    developing from a field emitter tip under electrical
    breakdown conditions, taking into account the
    relevant physical phenomena. As a starting point,
    only an external electric field and an initial
    enhancement factor of the tip are assumed. General
    requirements for plasma formation have been
    identified and formulated in terms of the initial
    local field and a critical neutral density. The
    dependence of plasma build-up on tip melting
    current, the evaporation rate of neutrals and
    external circuit time constant has been investigated
    for copper and simulations imply that arcing
    involves melting currents around 0.5−1 A/$\mu$m$^2$,
    evaporation of neutrals to electron field emission
    ratios in the regime 0.01 − 0.05, plasma build-up
    timescales in the order of $\sim~$ 1 − 10 ns and two
    different regimes depending on initial conditions,
    one producing an arc plasma, the other one not. Also
    the influence of the initial field enhancement
    factor and the external electric field required for
    ignition has been explored, and results are
    consistent with the experimentally measured local
    field value of $\sim~$ 10 GV/m for copper.},
    project = {CLIC}
    }
  • [PDF] [DOI] H. Timko, M. Aicheler, P. Alknes, S. Calatroni, A. Oltedal, A. Toerklep, M. Taborelli, W. Wuensch, F. Djurabekova, and K. Nordlund, “Energy dependence of processing and breakdown properties of cu and mo,” Physical review special topics – accelerators and beams, vol. 14, p. 101003, 2011.
    [Bibtex]
    @Article{Timk11b,
    author = "H. Timko and M. Aicheler and P. Alknes and
    S. Calatroni and A. Oltedal and A. Toerklep and
    M. Taborelli and W. Wuensch and F. Djurabekova and
    K. Nordlund",
    title = "Energy Dependence of Processing and Breakdown Properties
    of Cu and Mo",
    journal = "Physical Review Special Topics - Accelerators and Beams",
    year = 2011,
    volume = 14,
    pages = 101003,
    DOI = {10.1103/PhysRevSTAB.14.101003},
    myfile =
    "Publications/final_papers/2011/Timko_Energydepend_BRD_PRSTAB.pdf",
    pdf =
    {http://www.acclab.helsinki.fi/~djurabek/pubs/Timko_Energydepend_BRD_PRSTAB.pdf}
    ,
    abstract = {Obtaining basic knowledge of breakdowns is desirable in
    many fields of physics; however, often the energy
    absorbed by a breakdown is not known or can vary by
    large amounts. We have therefore investigated how
    processing and breakdown properties scale with
    available energy for two materials, Cu and Mo, in
    the energy range of about 1 mJ to 1 J. A central
    result obtained is that there appears to be an
    optimum energy for processing and thus the highest
    possible electric field a processed material can
    sustain without breaking down depends on energy
    accordingly; what this implies for radio frequency
    cavity processing is discussed as well. For Cu, both
    the local field and the field enhancement factor
    showed only a weak dependence on energy; the average
    of the local field over the entire energy range
    investigated was (9.6 $\pm$ 0.4 GV/m at
    breakdown. For Mo, the local field increased with
    increasing energy, while the field enhancement
    factor remained constant at 34$\pm$2. Finally, a
    possible explanation of the direct current (DC)
    processing mechanism—at least in the case of Mo—as
    an oxide removal process is presented.},
    project = {CLIC}
    }
  • [PDF] [DOI] S. Parviainen, F. Djurabekova, H. Timko, and K. Nordlund, “Electronic processes in molecular dynamics simulations of nanoscale metal tips under electric fields,” Computational materials science, vol. 50, iss. 7, pp. 2075-2079, 2011.
    [Bibtex]
    @article{Parv11a,
    title = "Electronic processes in molecular dynamics simulations of
    nanoscale metal tips under electric fields",
    journal = "Computational Materials Science",
    volume = 50,
    number = 7,
    pages = "2075-2079",
    year = "2011",
    issn = "0927-0256",
    doi = "DOI: 10.1016/j.commatsci.2011.02.010",
    author = "S. Parviainen and F. Djurabekova and H. Timko and
    K. Nordlund",
    keywords = "Molecular dynamics",
    keywords = "Electronic effects",
    keywords = "Resistive heating",
    keywords = "Thermal conduction",
    abstract = " Electronic effects play a crucial role in the temperature
    evolution of metal parts which have electric
    currents running through them. The increase in
    temperature due to resistive heating can cause the
    melting of metal nanoscale wires creating damage in
    electric circuits. Likewise, electric currents are
    also present in sharp features on metal surfaces
    exposed to high electric fields. The destruction of
    such tips can lead to vacuum arcs, supplying the
    neutral species to build up plasma over the
    surface. To follow the temperature evolution caused
    by electric currents in such a tip, we developed a
    new model, based on an existing molecular dynamics
    code, to include resistive heating and electronic
    thermal conduction. The results given by the new
    simulation model are in good agreement with
    analytical predictions.",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint_Parviainen_Jouleheating_CMS.pdf",
    myfile =
    "Publications/final_papers/2011/Parviainen_Jouleheating_CMS.pdf",
    project = {CLIC}
    }
  • [PDF] [DOI] S. Parviainen, F. Djurabekova, A. Pohjonen, and K. Nordlund, “Molecular dynamics simulations of nanoscale metal tips under electric fields,” Nuclear instruments and methods in physics research section b: beam interactions with materials and atoms, vol. 269, iss. 14, pp. 1748-1751, 2011.
    [Bibtex]
    @Article{Parv11b,
    title = "Molecular dynamics simulations of nanoscale metal tips under electric
    fields",
    journal = "Nuclear Instruments and Methods in Physics Research Section B: Beam
    Interactions with Materials and Atoms",
    volume = "269",
    number = "14",
    pages = "1748 - 1751",
    year = "2011",
    issn = "0168-583X",
    doi = "10.1016/j.nimb.2010.12.058",
    author = "S. Parviainen and F. Djurabekova and A. Pohjonen and K. Nordlund",
    keywords = "Molecular dynamics",
    keywords = "Field evaporation",
    keywords = "Dislocation emission",
    abstract = "Vacuum arcing is a plasma discharge over a metal surface
    under high electric fields. Plasma formation
    requires the supply of neutral atoms, which under
    high vacuum condition can only come from the surface
    itself. Nevertheless, the mechanisms by which the
    atoms are supplied are not known. In the present
    work, we propose a model for the onset of surface
    roughness and field-enhanced atom
    evaporation. Specifically, we describe a dislocation
    mechanism of tip growth from near-surface voids. We
    also simulate surface charging and resistive heating
    using a hybrid electrodynamics and molecular
    dynamics (ED&MD) code for dynamic simulations of
    electronic effects. We study the morphological
    evolution of the nanoscale protrusion under the
    electronic effects, such as the stretching of the
    tip by the stress induced by the electric field.",
    myfile =
    "Publications/final_papers/2011/Parviainen_tips_underEF_NIMB.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint_Parviainen_tips_underEF_NIMB.pdf",
    project = {CLIC}
    }
  • [PDF] [DOI] A. Pohjonen, F. Djurabekova, A. Kuronen, K. Nordlund, and S. Fitzgerald, “Dislocation nucleation from near surface void under static tensile stress on surface in cu,” Jour. appl. phys., vol. 110, p. 23509, 2011.
    [Bibtex]
    @Article{Pohj11a,
    author = "A. Pohjonen and F. Djurabekova and A. Kuronen and K. Nordlund
    and S. Fitzgerald",
    title = "Dislocation nucleation from near surface void under static
    tensile stress on surface in Cu",
    journal = "Jour. Appl. Phys.",
    year = 2011,
    volume = 110,
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2011_Pohjonen_void_noEF_JAP.pdf",
    pages = 023509,
    DOI = {10.1063/1.3606582},
    myfile = "Publications/final_papers/2011/Pohjonen_void_noEF_JAP.pdf",
    abstract = {We examine a possible mechanism for the formation of
    protrusions on a metallic surface held in a
    sufficiently high electric field in the presence of
    a near-surface void. By means of molecular dynamics
    simulations we show that the high tensile stress
    exerted on a Cu {110} surface with a near-surface
    void can promote the nucleation of dislocations on
    the void surface. These dislocations cause slip
    along {111} crystallographic planes leading to mass
    transport in the volume above the void. We find a
    linear correlation between the radius of the void
    and the maximum depth for the growth to occur.},
    project = {CLIC}
    }
  • [PDF] [DOI] F. Djurabekova, S. Parviainen, A. Pohjonen, and K. Nordlund, “Atomistic modeling of metal surfaces under electric fields: direct coupling of electric fields to a molecular dynamics algorithm,” Physical review e, vol. 83, iss. 2, p. 26704, 2011.
    [Bibtex]
    @Article{Djur11a,
    author = "F. Djurabekova and S. Parviainen and A. Pohjonen and K.
    Nordlund",
    title = "Atomistic modeling of metal surfaces under electric fields:
    Direct coupling of electric fields to a molecular dynamics algorithm",
    journal = " Physical Review E",
    year = 2011,
    volume = 83,
    number = 2,
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2011_Djurabekova_helmod.
    pdf",
    pages = 026704,
    doi = "10.1103/PhysRevE.83.026704",
    myfile = "Publications/final_papers/2011/Djurabekova_helmod_PRE.pdf",
    abstract = {The effect of electric fields on metal surfaces is fairly
    well studied, resulting in numerous analytical
    models developed to understand the mechanisms of
    ionization of surface atoms observed at very high
    electric fields, as well as the general behavior of
    a metal surface in this condition. However, the
    derivation of analytical models does not include
    explicitly the structural properties of metals,
    missing the link between the instantaneous effects
    owing to the applied field and the consequent
    response observed in the metal surface as a result
    of an extended application of an electric field. In
    the present work, we have developed a concurrent
    electrodynamic– molecular dynamic model for the
    dynamical simulation of an electric-field effect and
    subsequent modification of a metal surface in the
    framework of an atomistic molecular dynamics (MD)
    approach. The partial charge induced on the surface
    atoms by the electric field is assessed by applying
    the classical Gauss law. The electric forces acting
    on the partially charged surface atoms (Lorentz and
    Coulomb) are then introduced in theMD algorithm to
    correct the atomic motion in response to the applied
    field. The enhancement factor at sharp features on
    the surface for the electric field and the
    assessment of atomic charges are discussed. The
    results obtained by the present model compare well
    with the experimental and density-functional theory
    results.},
    project = {CLIC}
    }
  • F. Djurabekova, E. Holmstrom, S. Maksimov, and B. L. Oksengedler, “Effect of interface on the radiation stability of si and ge nanocrystals,” in Proceedings of the 2011 ion-solid interactions conference, Moscow, Russia: Moscow aviation institute publisher, 2011.
    [Bibtex]
    @InCollection{Djur11b,
    author = "F. Djurabekova and E. Holmstrom and S. Maksimov and B. L.
    Oksengedler",
    title = "Effect of interface on the radiation stability of
    Si and Ge nanocrystals",
    booktitle = "Proceedings of the 2011 Ion-Solid Interactions
    conference",
    year = 2011,
    publisher = "Moscow aviation institute publisher",
    address = "Moscow, Russia",
    filef = "Publications/final_papers/2011/",
    project = {NC}
    }
  • [PDF] M. W. Ullah, A. Kuronen, F. Djurabekova, K. Nordlund, and P. Karaseov, “Molecular dynamics simulations of damage buildup by atomic and molecular projectiles in gan,” in Proceedings of the 2011 ion-solid interactions conference, Moscow, Russia: Moscow aviation institute publisher, 2011.
    [Bibtex]
    @InCollection{Ulla11,
    author = "M. W. Ullah and A. Kuronen and F. Djurabekova and K.
    Nordlund
    and P. Karaseov",
    title = "Molecular dynamics simulations of damage buildup by
    atomic and molecular projectiles in GaN",
    booktitle = "Proceedings of the 2011 Ion-Solid Interactions
    conference",
    year = 2011,
    publisher = "Moscow aviation institute publisher",
    address = "Moscow, Russia",
    myfile = "Publications/final_papers/2011/Ullah_ISI_11.pdf",
    pdf = "http://www.acclab.helsinki.fi/~djurabek/pubs/Ullah_ISI_11.pdf",
    project = {GaN}
    }
  • [DOI] S. Hoilijoki, E. Holmström, and K. Nordlund, “Enhancement of defect production in si nanowires,” J. appl. phys., vol. 110, iss. 4, p. 43540, 2011.
    [Bibtex]
    @Article{Hoi11,
    author= "S. Hoilijoki and E. Holmström and K. Nordlund",
    title= "Enhancement of defect production in Si nanowires",
    journal= "J. Appl. Phys.",
    year= 2011,
    volume = 110,
    number = 4,
    pages = 043540,
    doi = {10.1063/1.3627234},
    file = "pub/nanowire_si_irr",
    project = {Si}
    }
  • [DOI] E. Holmström, J. Samela, and K. Nordlund, “Atomistic simulations of fracture in silica glass through hypervelocity impact,” Epl, vol. 96, p. 16005, 2011.
    [Bibtex]
    @Article{Hol10c,
    author = "E. Holmström and J. Samela and K. Nordlund",
    title = "Atomistic simulations of
    fracture in silica glass through hypervelocity impact",
    journal = "EPL",
    year = 2011,
    volume = 96,
    pages = 16005,
    doi = {10.1209/0295-5075/96/16005},
    file = "pub/sio2_fracture",
    project = {Si}
    }

2012

  • [PDF] [DOI] A. A. Leino, O. H. Pakarinen, F. Djurabekova, and K. Nordlund, “A study on the elongation of embedded au nanoclusters in sio2 by swift heavy ion irradiation using md simulations,” Nuclear instruments and methods in physics research b, vol. 282, p. 76 – 80, 2012.
    [Bibtex]
    @Article{Lein12,
    author = {A. A. Leino and O. H. Pakarinen and F. Djurabekova
    and K. Nordlund},
    title = {A study on the elongation of embedded Au
    nanoclusters in SiO2 by swift heavy ion
    irradiation using MD simulations},
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2012,
    volume = 282,
    pages = {76 -- 80},
    DOI = {10.1016/j.nimb.2011.08.054},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2012_Leino_AuNPelongation_preliminary.pdf",
    myfile = {Publications/final_papers/Leino_AuNPelongation_NIMB.pdf},
    abstract = {We have studied the elongation of Au nanoclusters
    embedded in amorphous SiO2 using MD simulations.
    The effect of swift heavy ions (SHI) was implemented
    using instantaneous energy deposition with a radial
    profile that was obtained from the inelastic thermal
    spike model. During the first impact on the cluster,
    the clusters (d = 9–11 nm) gained about 20\% in
    length due to thermal stress within the cluster,
    which is released by a longitudinal flow of Au atoms
    to the ion track in silica. Our simulations also
    show that high temperatures at the track core lead
    to the formation of silica vapor, whose pressure may
    flatten the cluster.},
    project = {FAIR}
    }
  • [PDF] [DOI] A. S. Pohjonen, F. Djurabekova, A. Kuronen, S. G. Fitzgerald, and K. Nordlund, “Analytical model of dislocation nucleation on a near-surface void under tensile surface stress,” Philosophical magazine, vol. 92, p. 3994 – 4010, 2012.
    [Bibtex]
    @Article{Pohj12a,
    author = {A. S. Pohjonen and F. Djurabekova and A. Kuronen and
    S. G. Fitzgerald and K. Nordlund},
    title = {Analytical model of dislocation nucleation on a
    near-surface void under tensile surface stress},
    journal = {Philosophical Magazine},
    year = 2012,
    volume = 92,
    pages = {3994 -- 4010},
    doi = {10.1080/14786435.2012.700415},
    myfile =
    {Publications/final_papers/2012/Pohjonen_analyt_model_void_2012.pdf},
    pdf =
    {http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2012_Pohjonen_analyt_model_void.pdf},
    abstract = {We have analyzed in detail the mechanism leading to tip
    growth on a surface which operates via nucleation of
    dislocations on a near-surface void under tensile
    surface stress. We derived a simplified analytical
    model describing the relevant physical factors
    related to the observed linearity between the void
    radius and the maximum depth of the void for the
    growth to occur. The model is based on the direct
    numerical calculation of atomic level stresses in
    the simulated system. Based on the present model we
    can estimate this maximum depth for a void of a
    certain size under a given stress in the size range
    which is beyond the feasibility of the molecular
    dynamics simulation method.},
    project = {CLIC}
    }
  • [PDF] A. S. Pohjonen, F. Djurabekova, A. Kuronen, and S. P. Fitzgerald, “Interaction of a screw dislocation with a near-surface void under tensile surface stress,” Proceedings of “dislocations” conference, 2012.
    [Bibtex]
    @Article{Pohj12b,
    author = {A. S. Pohjonen and F. Djurabekova and A. Kuronen and
    S. P. Fitzgerald},
    title = {Interaction of a screw dislocation with a
    near-surface void under tensile surface stress},
    journal = {Proceedings of "Dislocations" conference},
    year = {2012},
    myfile =
    {Publications/final_papers/2012/Pohjonen_Dislocations_proceedings.pdf},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Pohjonen_Dislocations_proceedings.
    pdf",
    project = {CLIC}
    }
  • [DOI] A. Pohjonen, F. Djurabekova, A. Kuronen, and K. Nordlund, “Md simulations of near surface void in copper under thermal compression,” in Mrs proceedings, Warrendale, PA, USA, 2012.
    [Bibtex]
    @InProceedings{Pohj12c,
    author = {A. Pohjonen and F. Djurabekova and A. Kuronen and
    K. Nordlund},
    title = {MD simulations of near surface void in copper under
    thermal compression},
    booktitle = {MRS Proceedings},
    year = {2012},
    editor = {S. Persheyev},
    volume = {1411},
    publisher = {Cambridge University Press},
    address = {Warrendale, PA, USA},
    DOI = "10.1557/opl.2012.759",
    myfile = {Publications/final_papers/2012/Pohjonen_MRS2011.pdf},
    abstract = {Dislocation mediated mechanism of surface deformation
    due to localized stress and strain concentration
    near a void could give an explanation of field
    enhancement in conditions relevant to the design of
    rf accelerating structures of the Compact Linear
    Collider (CLIC). We have performed molecular
    dynamics simulations of a near surface void in
    copper under thermal stressing conditions. The von
    Mises strain was observed to be concentrated near
    the void surface with the maximum strain
    concentration factor of 1.9. To observe the
    activated slip-planes, we exaggerated the
    compressive stress to the extent that the
    dislocations were nucleated on the void surface at
    sites where von Mises strain was largest. Void depth
    and size were found to affect the dislocation
    nucleation. The nucleation was easier for larger
    voids and for voids which were closer to the
    surface.},
    project = {CLIC}
    }
  • [DOI] M. W. Ullah, A. Kuronen, K. Nordlund, F. Djurabekova, P. Karaseov, and A. I. Titov, “Atomistic simulation of damage production by atomic and molecular irradiation in gan,” Journal of applied physics, vol. 112, p. 43517, 2012.
    [Bibtex]
    @Article{Ulla12,
    author = {M. W. Ullah and A. Kuronen and K. Nordlund and
    F. Djurabekova and P. Karaseov and A. I. Titov},
    title = {Atomistic simulation of damage production by atomic
    and molecular irradiation in GaN},
    journal = {Journal of Applied Physics},
    year = 2012,
    volume = 112,
    pages = 043517,
    doi = {10.1063/1.4747917},
    myfile =
    "Publications/final_papers/2012/Ullah_singlecascade_GaN_JAP.pdf",
    abstract = {We have studied defect production during single ato mic
    and molecular ion irradiation having an energy of
    50eV/amu in GaN by molecular dynamics
    simulations. Enhanced defect recombination is found
    in GaN, in accordance with experimental
    data. Instantaneous damage shows non-linearity with
    different molecular pro jectile and increasing
    molecular mass. Number of instantaneous defects
    produced by the PF$_4$ molecule close to target
    surface is four times higher than that for PF$_2$
    molecule and three times higher than that calculated
    as a sum of the damage produced by one P and four F
    ion irradiation (P + 4xF). We explain this
    non-linearity by energy spike due to molecular
    effects. On the contrary, final damage created by
    PF$_4$ and PF$_2$ shows a linear pattern when the
    sample cools down. Total numbers of defects produced
    by Ag and PF$_4$ having similar atomic masses are
    comparab le. However, defect-depth distributions
    produced by these species are quite differ ent, also
    indicating molecular effect.},
    project = {GaN}
    }
  • [PDF] [DOI] A. Debelle, M. Backman, L. Thomé, W. J. Weber, M. Toulemonde, S. Mylonas, A. Boulle, O. H. Pakarinen, N. Juslin, F. Djurabekova, K. Nordlund, and F. Garrido, “Combined experimental and computational study of the recrystallization process induced by electronic interactions of swift heavy ions with silicon carbide crystals,” Physical review b, vol. 86, p. 100102(R), 2012.
    [Bibtex]
    @Article{Debe12,
    author = {A. Debelle and M. Backman and L. Thom{\'e} and
    W. J. Weber and M. Toulemonde and
    S. Mylonas and A. Boulle and O. H. Pakarinen and
    N. Juslin and F. Djurabekova and K. Nordlund and
    F. Garrido},
    title = {Combined experimental and computational study of the
    recrystallization process induced by electronic
    interactions of swift heavy ions with silicon
    carbide crystals},
    journal = {Physical Review B},
    year = 2012,
    volume = 86,
    DOI = {10.1103/PhysRevB.86.100102},
    pages = {100102(R)},
    myfile = "Publications/final_papers/2012/Debelle_healing_SiC_RC.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Debelle_healing_SiC_RC.pdf",
    abstract = {The healing effect of intense electronic energy
    deposition arising during swift heavy ion (SHI)
    irradiation is demonstrated in the case of 3C-SiC
    damaged by nuclear energy deposition. Experimental
    (ion channeling experiments) and computational
    (molecular dynamics simulations) studies provide
    consistent indications of disorder decrease after
    SHI irradiation. Furthermore, both methods establish
    that SHI-induced recrystallization takes place at
    amorphous-crystalline interfaces. The recovery
    process is unambiguously accounted for by the
    thermal spike phenomenon.},
    project = {FAIR}
    }
  • [PDF] [DOI] K. Nordlund and F. Djurabekova, “Defect model for the dependence of breakdown rate on external electric fields,” Physical review special topics -accelerators and beams, vol. 15, iss. 7, p. 71002, 2012.
    [Bibtex]
    @Article{Nord12,
    author = "K. Nordlund and F. Djurabekova",
    title = "Defect model for the dependence of breakdown rate on
    external electric fields",
    journal = "Physical Review Special Topics -Accelerators and Beams",
    year = 2012,
    volume = 15,
    number = 7,
    pages = 071002,
    DOI = {10.1103/PhysRevSTAB.15.071002},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    Nordlund_BRD_dislocationmodel_PRSTAB.pdf",
    myfile =
    "Publications/final_papers/2012/Nordlund_BRD_dislocationmodel_PRSTAB.pdf",
    abstract = {We develop an analytical model for the vacuum electric
    breakdown rate dependence on an external electric
    field, observed in test components for the compact
    linear collider concept. The model is based on a
    thermodynamic consideration of the effect of an
    external electric field on the formation enthalpy of
    defects. Although strictly speaking only valid for
    electric fields, the model also reproduces very well
    the breakdown rate of a wide range of
    radio-frequency breakdown experimental data.We
    further show that the fitting parameter in the model
    can be interpreted to be the relaxation volume of
    dislocation loops in materials. The values obtained
    for the volume are consistent with dislocation loops
    with radii of a few tens of nanometers.},
    project = {CLIC}
    }
  • [PDF] [DOI] F. Djurabekova, J. Samela, H. Timko, K. Nordlund, S. Calatroni, M. Taborelli, and W. Wuensch, “Crater formation by single ions, cluster ions and ion ‘showers’,” Nuclear instruments and methods in physics research b, vol. 272, p. 26704, 2012.
    [Bibtex]
    @Article{Djur12a,
    author = "F. Djurabekova and J. Samela and H. Timko and
    K. Nordlund and S. Calatroni and M. Taborelli and
    W. Wuensch",
    title = "Crater formation by single ions, cluster ions and
    ion 'showers' ",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2012,
    volume = 272,
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2012_Djurabekova_showers.
    pdf",
    pages = {374 -- 376},
    myfile = "Publications/final_papers/2012/Djurabekova_showers.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2012_Djurabekova_showers.
    pdf",
    pages = 026704,
    doi = {10.1016/j.nimb.2011.01.104},
    abstract = {The various craters formed by giant objects, macroscopic
    collisions and nanoscale impacts exhibit an
    intriguing resemblance in shapes. At the same time,
    the arc plasma built up in the presence of
    sufficiently high electric fields at close look
    causes very similar damage on the surfaces. Although
    the plasma–wall interaction is far from a single
    heavy ion impact over dense metal surfaces or the
    one of a cluster ion, the craters seen on metal
    surfaces after a plasma discharge make it possible
    to link this event to the known mechanisms of the
    crater formations. During the plasma discharge in a
    high electric field the surface is subject to high
    fluxes ($\sim~10^{25}$ cm$^{−2}$ s$^{−1}$) of ions
    with roughly equal energies typically of the order
    of a few keV. To simulate such a process it is
    possible to use a cloud of ions of the same
    energy. In the present work we follow the effect of
    such a flux of ions impinging the surface in the
    “shower” manner, to find the transition between the
    different mechanisms of crater formation. We also
    introduce the “shower”-like regime of ion
    bombardment (underdense cloud of ions) as a
    subsequent regime between the single ion impact (a
    rare “shower”) and cluster ions (densely packed
    cloud).},
    project = {CLIC}
    }
  • [PDF] [DOI] M. Backman, F. Djurabekova, O. H. Pakarinen, K. Nordlund, Y. Zhang, M. Toulemonde, and W. J. Weber, “Cooperative effect of electronic and nuclear stopping on ion irradiation damage in silica,” Journal of physics d: applied physics, vol. 45, p. 505305, 2012.
    [Bibtex]
    @Article{Back12a,
    author = {M. Backman and F. Djurabekova and
    O. H. Pakarinen and K. Nordlund and
    Y. Zhang and M. Toulemonde and W. J. Weber},
    title = {Cooperative effect of electronic and nuclear stopping
    on ion irradiation damage in silica},
    journal = "Journal of Physics D: Applied Physics",
    year = 2012,
    volume = 45,
    pages = 505305,
    DOI = {10.1088/0022-3727/45/50/505305},
    myfile = "Publications/final_papers/2012/Backman_Au_SiO2_synergy.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2012_Backman_Au_SiO2_synergy.pdf",
    abstract = { Radiation damage by ions is conventionally believed to
    be produced either by displacement cascades or
    electronic energy deposition acting
    separately. There is, however, a range of ion
    energies where both processes are significant and
    can contribute to irradiation damage. The
    combination of two computational methods, namely
    binary collision approximation and molecular
    dynamics, the latter with input from the inelastic
    thermal spike model, makes it possible to examine
    the simultaneous contribution of both energy
    deposition mechanisms on the structural damage in
    the irradiated structure. We study the effect in
    amorphous SiO2 irradiated by Au ions with energies
    ranging between 0.6 and 76.5MeV. We find that in the
    intermediate energy regime, the local heating due to
    electronic excitations gives a significant
    contribution to the displacement cascade damage.},
    project = {FAIR}
    }

2013

  • [DOI] M. Backman, M. Toulemonde, O. H. Pakarinen, N. Juslin, F. Djurabekova, K. Nordlund, A. Debelle, and W. J. Weber, “Molecular dynamics simulations of swift heavy ion induced defect recovery in sic,” Computational materials science, vol. 67, p. 261 – 265, 2013.
    [Bibtex]
    @Article{Back13a,
    author = {Backman, M. and Toulemonde, M. and Pakarinen,
    O. H. and Juslin, N. and Djurabekova, F. and
    Nordlund, K. and Debelle, A. and Weber, W. J.},
    title = {Molecular dynamics simulations of swift heavy ion
    induced defect recovery in SiC},
    Journal = {Computational Materials Science},
    year = 2013,
    volume = 67,
    pages = {261 -- 265},
    DOI = {10.1016/j.commatsci.2012.09.010},
    myfile = {Publications/final_papers/2013/Backman_SiC_CMS.pdf},
    abstract = {Swift heavy ions induce a high density of electronic
    excitations that can cause the formation of
    amorphous ion tracks in insulators. No ion tracks
    have been observed in the semiconductor SiC, but
    recent experimental work suggests that irradiation
    damaged SiC can undergo defect recovery under swift
    heavy ion irradiation. It is believed that local
    heating of the lattice due to the electronic energy
    deposition can anneal, and thereby recover, some of
    the disordered structure. We simulate the local
    heating due to the ions by the inelastic thermal
    spike model and perform molecular dynamics
    simulations of different model damage states to
    study the defect recovery on an atomistic level. We
    find significant recovery of point defects and a
    disordered layer, as well as recrystallization at
    the amorphous-to-crystalline interface of an
    amorphous layer. The simulation results support the
    swift heavy ion annealing hypothesis.},
    project = {FAIR}
    }
  • [DOI] M. Backman, F. Djurabekova, O. H. Pakarinen, K. Nordlund, and W. J. Weber, “Atomistic simulations of mev ion irradiation of silica,” Nuclear instruments and methods in physics research b, vol. 303, p. 129, 2013.
    [Bibtex]
    @Article{Back13b,
    author = {M. Backman and F. Djurabekova and O. H. Pakarinen
    and K. Nordlund and W. J. Weber},
    title = "Atomistic simulations of MeV ion irradiation of silica",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2013,
    doi = "10.1016/j.nimb.2012.10.020",
    volume = 303,
    pages = 129,
    myfile = "Publications/final_papers/2013/Backman_MeVirr_SiO2_NIMB.pdf",
    abstract = {We used molecular dynamics simulations to study 2.3 MeV
    Au ion irradiation of silica. In this energy regime,
    the energy loss of the ion is divided almost equally
    between electronic and nuclear energy loss. The
    inelastic thermal spike model was used to model the
    electron–phonon interactions due to the high
    electronic energy loss. Binary collision
    approximation calculations provided input for the
    recoil energies due to MeV ions. We performed
    simulations of the damage due to the separate damage
    mechanisms as well as together, and found that the
    inelastic thermal spike is needed to accurately
    simulate the irradiation damage from MeV ions.},
    project = {FAIR}
    }
  • [DOI] M. W. Ullah, A. Kuronen, K. Nordlund, F. Djurabekova, P. A. Karaseov, K. V. Karabeshkin, and A. I. Titov, “Effects of defect clustering on optical properties of gan by single and molecular ion irradiation,” Journal of applied physics, vol. 114, p. 183511, 2013.
    [Bibtex]
    @Article{Ulla13a,
    author = {M. W. Ullah and A. Kuronen and K. Nordlund and
    F. Djurabekova and P. A. Karaseov and
    K. V. Karabeshkin and A. I. Titov},
    title = {Effects of defect clustering on optical properties
    of GaN by single and molecular ion irradiation},
    journal = {Journal of Applied Physics},
    year = {2013},
    volume = {114},
    pages = {183511},
    DOI = {10.1063/1.4829904},
    myfile = {Publications/final_papers/Ullah_GaN_molecular_ion.pdf},
    abstract = {The effects of irradiation by F, P, and PF4 on optical
    properties of GaN were studied experimentally and by
    atomistic simulations. Additionally, the effect of
    Ag was studied by simulation. The irradiation energy
    was 0.6 keV/amu for all projectiles. The measured
    photoluminescence (PL) decay time was found to be
    decreasing faster when irradiation was done by
    molecular ion compared to light ion irradiation. The
    PL decay time change is connected with the types of
    defect produced by different projectiles. Simulation
    results show that the light ions mainly produce
    isolated point defects while molecular and heavy
    ions produce clusters of point defects. The total
    amount of defects produced by the PF4 projectile was
    found to be very close to the sum of all defects
    produced in five individual cascades started by one
    P and four F single ions. This and the similar depth
    profiles of damage produced by molecular and light
    ion irradiations suggest that the defect clusters
    are one of the important reasons for fast PL
    decay. Moreover, the simulations of irradiation by
    Ag ions, whose mass is close to the mass of the PF4
    molecule, showed that the produced defects are
    clustering in even bigger conglomerates compared to
    PF4 case. The latter has a tendency to split in the
    pre-surface region, reducing on average the density
    of the collision cascade.},
    project = {GaN}
    }
  • [DOI] L. Thomé, A. Debelle, F. Garrido, S. Mylonasa, B. Décamps, C. Bachelet, G. Sattonnay, S. Moll, S. Pellegrino, S. Miro, P. Trocellier, Y. Serruys, G. Velisa, C. Grygiel, I. Monnet, M. Toulemonde, P. Simon, J. Jagielski, I. Jozwik-Biala, L. Nowicki, M. Behar, W. J. Weber, Y. Zhang, M. Backman, K. Nordlund, and F. Djurabekova, “Radiation effects in nuclear materials: role of nuclear and electronic energy losses and their synergy,” Nuclear instruments and methods in physics research b, vol. 307, p. 43 – 48, 2013.
    [Bibtex]
    @Article{Thom13,
    author = {L. Thom{\'e} and A. Debelle and F. Garrido and
    S. Mylonasa and B. D{\'e}camps and C. Bachelet and
    G. Sattonnay and S. Moll and S. Pellegrino and
    S. Miro and P. Trocellier and Y. Serruys and
    G. Velisa and C. Grygiel and I. Monnet and
    M. Toulemonde and P. Simon and J. Jagielski and
    I. Jozwik-Biala and L. Nowicki and M. Behar and
    W.J. Weber and Y. Zhang and M. Backman and
    K. Nordlund and F. Djurabekova},
    title = {Radiation effects in nuclear materials: Role of
    nuclear and electronic energy losses and their
    synergy},
    journal = {Nuclear Instruments and Methods in Physics Research B},
    year = 2013,
    DOI = {10.1016/j.nimb.2012.11.077},
    volume = 307,
    pages = {43 -- 48},
    myfile = {Publications/final_papers/2013/Thome_synergy_NIMB.pdf},
    abstract = {Ceramic oxides and carbides are promising matrices for
    the immobilization and/or transmutation of nuclear
    wastes, cladding materials for gas-cooled fission
    reactors and structural components for fusion
    reactors. For these applications there is a need of
    fundamental data concerning the behavior of nuclear
    ceramics upon irradiation. This article is focused
    on the presentation of a few remarkable examples
    regarding ion-beam modifications of nuclear ceramics
    with an emphasis on the mechanisms leading to damage
    creation and phase transformations. Results obtained
    by combining advanced techniques (Rutherford
    backscattering spectrometry and channeling, X-ray
    diffraction, transmission electron microscopy, Raman
    spectroscopy) concern irradiations in a broad energy
    range (from keV to GeV) with the aim of exploring
    both nuclear collision (Sn) and electronic
    excitation (Se) regimes. Finally, the daunting
    challenge of the demonstration of the existence of
    synergistic effects between Sn and Se is tackled by
    discussing the healing due to intense electronic
    energy deposition (SHIBIEC) and by reporting results
    recently obtained in dual-beam irradiation (DBI)
    experiments.},
    project = {FAIR}
    }
  • [PDF] [DOI] M. C. Ridgway, T. Bierschenk, R. Giulian, B. Afra, M. D. Rodriguez, L. L. Araujo, A. P. Byrne, N. Kirby, O. H. Pakarinen, F. Djurabekova, K. Nordlund, M. Schleberger, O. Osmani, N. Medvedev, B. Rethfeld, W. Wesch, and P. Kluth, “Track and bowtie-shaped void formation-beam processed amorphous ge,” Physical review letters, vol. 110, p. 245502, 2013.
    [Bibtex]
    @Article{Ridg13,
    author = {M.C. Ridgway and T. Bierschenk and R. Giulian and
    B. Afra and M.D. Rodriguez and L.L. Araujo
    and A. P. Byrne and N. Kirby and O. H. Pakarinen and
    F. Djurabekova and K. Nordlund and M. Schleberger
    and O. Osmani and N. Medvedev and B. Rethfeld and
    W. Wesch and P. Kluth},
    title = {Track and bowtie-shaped void formation-beam
    processed amorphous Ge},
    journal = "Physical Review Letters",
    year = 2013,
    volume = 110,
    pages = 245502,
    DOI = {10.1103/PhysRevLett.110.245502},
    myfile = "Publications/final_papers/2013/Ridgway_Ge_bowtie_PRL.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2013_Ridgway_Ge_bowtie.
    pdf",
    abstract = { Ion tracks formed in amorphous Ge by swift heavy-ion
    irradiation have been identified with experiment and
    modeling to yield unambiguous evidence of tracks in
    an amorphous semiconductor. Their underdense core
    and overdense shell result from quenched-in radially
    outward material flow. Following a solid-to-liquid
    phase transformation, the volume contraction
    necessary to accommodate the high-density molten
    phase produces voids, potentially the precursors to
    porosity, along the ion direction. Their bow-tie
    shape, reproduced by simulation, results from
    radially inward resolidification.},
    project = {FAIR}
    }
  • [PDF] [DOI] A. S. Pohjonen, S. Parviainen, T. Muranaka, and F. Djurabekova, “Dislocation nucleation on a near surface void leading to surface protrusion growth under an external electric field,” Journal of applied physics, vol. 114, p. 33519, 2013.
    [Bibtex]
    @Article{Pohj13,
    author = "A. S. Pohjonen and S. Parviainen and T. Muranaka and F.
    Djurabekova",
    title = {Dislocation nucleation on a near surface void leading to
    surface protrusion growth under an external electric field},
    journal = {Journal of Applied Physics},
    year = 2013,
    volume = 114,
    pages = 033519,
    doi={10.1063/1.4815938},
    myfile = {Publications/final_papers/2013/Pohjonen_EF_void.pdf},
    abstract = {The stress exerted on a conducting material surface by
    an external electric field can cause plastic
    deformation if the stress is concentrated somewhere
    in the material. Such concentration can occur due to
    the presence of a near surface void. The plastic
    deformation can lead to growth of a protrusion on
    the surface. To investigate the conditions where
    such a mechanism can operate, we employ concurrent
    electrodynamics-molecular dynamics simulations,
    analyze the distribution of stress near the void by
    using both the molecular dynamics and finite element
    method, and compare the result to the analytical
    expression for a void located deep in the bulk. By
    applying an electric field of exaggerated strength
    we are able to simulate the plastic deformation
    process within the timespan allowed by molecular
    dynamics simulations. In reality, longer timespans
    would allow for the initiation of the proposed
    mechanism at electric field strengths much lower
    than the values assumed for the simulations in the
    present work.},
    pdf =
    {http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2013_Pohjonen_EF_void.pdf}
    ,
    project = {CLIC}
    }
  • [DOI] L. Bukonte, F. Djurabekova, J. Samela, K. Nordlund, S. Norris, and M. Aziz, “Molecular dynamics and binary collision approximation simulations for atom displacement analysis,” Nuclear instruments and methods in physics research b, vol. 297, p. 23 – 28, 2013.
    [Bibtex]
    @Article{Buko13,
    author = "L. Bukonte and F. Djurabekova and J. Samela and K. Nordlund
    and S. Norris and M. Aziz",
    title = "Molecular dynamics and binary collision approximation
    simulations for atom displacement analysis",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2013,
    volume = 297,
    pages = {23 -- 28},
    DOI = {10.1016/j.nimb.2012.12.014},
    myfile = {Publications/final_papers/2013/Bukonte_MD_BCA_ripples.pdf},
    abstract = {Molecular dynamics (MD) and binary collision
    approximation (BCA) computer simulations are
    employed to study surface damage by single ion
    impacts. The predictions of BCA and MD simulations
    of displacement cascades in amorphous and
    crystalline silicon and BCC tungsten by 1 keV Arþ
    ion bombardment are compared. Single ion impacts are
    studied at angles of 50$^o$, 60$^o$ and 80$^o$ from normal
    incidence. Four parameters for BCA simulations have
    been optimized to obtain the best agreement of the
    results with MD. For the conditions reported here,
    BCA agrees with MD simulation results at
    displacements larger than 5$\AA$ for amorphous Si,
    whereas at small displacements a difference between
    BCA and MD arises due to a material flow component
    observed in MD simulations but absent from a regular
    BCA approach due to the algorithm limitations. MD
    and BCA simulation results for crystalline W are
    found to be in a good agreement even at small
    displacements, while in crystalline Si there is some
    difference due to displacements in amorphous
    pockets.},
    project = {ripples}
    }
  • [PDF] [DOI] F. Djurabekova, A. Ruzibaev, E. Holström, S. Parviainen, and M. O. Hakala, “Local changes of work function near rough features on cu surfaces operated under high external electric field,” Journal of applied physics, vol. 114, p. 243302, 2013.
    [Bibtex]
    @Article{Djur13b,
    author = {F. Djurabekova and A. Ruzibaev and E. Holstr\"om and
    S. Parviainen and M. O. Hakala},
    title = {Local changes of work function near rough features
    on Cu surfaces operated under high external electric
    field},
    journal = {Journal of Applied Physics},
    year = 2013,
    volume = {114},
    pages = {243302},
    DOI = {10.1063/1.4856875},
    pdf =
    {http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2013_Djurabekova_Cu_WF.pdf
    },
    myfile = {Publications/final_papers/2013/Djurabekova_Cu_WF.pdf},
    abstract = {Metal surfaces operated under high electric fields
    produce sparks even if they are held in ultra high
    vacuum. In spite of extensive research on the topic
    of vacuum arcs, the mystery of vacuum arc origin
    still remains unresolved. The indications that the
    sparking rates depend on the material motivate the
    research on surface response to extremely high
    external electric fields. In this work by means of
    density-functional theory calculations we analyze
    the redistribution of electron density on {100} Cu
    surfaces due to self-adatoms and in presence of high
    electric fields from -1V/nm up to -2V/nm (-1 to
    -2 GV/m, respectively). We also calculate the
    partial charge induced by the external field on a
    single adatom and a cluster of two adatoms in order
    to obtain reliable information on charge
    redistribution on surface atoms, which can serve as
    a benchmarking quantity for the assessment of the
    electric field effects on metal surfaces by means of
    molecular dynamics simulations. Furthermore, we
    investigate the modifications of work function
    around rough surface features, such as step edges
    and self-adatoms.},
    project = {CLIC}
    }
  • [DOI] F. Djurabekova, K. B. Ashurov, S. E. Maksimov, N. N. Turaeva, and B. L. Oksengendler, “Fundamental processes of radiation modification of semiconductor nanostructures,” Physica status solidi c, vol. 10, iss. 4, p. 685 – 688, 2013.
    [Bibtex]
    @Article{Djur13c,
    author = {F. Djurabekova and K. B. Ashurov and S. E. Maksimov
    and N. N. Turaeva and B. L. Oksengendler},
    title = {Fundamental processes of radiation modification of
    semiconductor nanostructures},
    journal = "Physica Status Solidi C",
    year = 2013,
    volume = 10,
    number = 4,
    pages = {685 -- 688},
    DOI = {10.1002/pssc.201200751},
    myfile =
    {Publications/final_papers/2013/Djurabekova_Oksengendler_RadModSemicondustors.
    pdf},
    abstract = {The amount of studies performed in the field of
    microscopic models of radiation nanophysics is
    rather limited and, with the exception of carbon
    nanostructures, they are non-systematic. The purpose
    of the present work is to initiate a systematic
    approach to build the theoretical models of
    radiation nanophysics with the account for
    fundamental properties of nano-objects. We choose at
    this stage to consider two basic phenomena (Frenkel
    pair formation and amorphization) modified by only
    one nanoproperty, i.e. the presence of an
    interface. We develop a mathematical framework to
    describe the modification on the nanoscale. From the
    general expression for the modified radiation
    phenomena, we find that any radiation effect can be
    modified at least by 48 ways. This predicts a very
    rich future of radiation nanophysics both in the
    fundamental and applied aspects.},
    project = {NC}
    }
  • [DOI] B. Afra, M. D. Rodriguez, C. Trautmann, O. H. Pakarinen, F. Djurabekova, K.Nordlund, T. Bierschenk, R. Giulian, M. C. Ridgway, G. Rizza, N. Kirby, M. Toulemonde, and P. Kluth, “Saxs investigations of the morphology of swift heavy ion tracks in $\alpha$-quartz,” Journal of physics: condensed matter, vol. 25, p. 455006, 2013.
    [Bibtex]
    @Article{Afra13,
    author = {B. Afra and M. D. Rodriguez and C. Trautmann and
    O. H. Pakarinen and F. Djurabekova and K.Nordlund
    and T. Bierschenk and R. Giulian and M. C. Ridgway
    and G. Rizza and N. Kirby and M. Toulemonde and
    P. Kluth},
    title = {SAXS investigations of the morphology of swift heavy
    ion tracks in $\alpha$-quartz},
    journal = "Journal of Physics: Condensed matter",
    year = 2013,
    volume = 25,
    pages = 0455006,
    doi = {10.1088/0953-8984/25/4/045006},
    myfile = {Publications/final_papers/Afra_SAXS_track_quartz.pdf},
    abstract = {The morphology of swift heavy ion tracks in crystalline
    $\alpha$-quartz was investigated using small angle x-ray
    scattering (SAXS), molecular dynamics (MD)
    simulations and transmission electron
    microscopy. Tracks were generated by irradiation
    with heavy ions with energies between 27 MeV and 2.2
    GeV. The analysis of the SAXS data indicates a
    density change of the tracks of $\sim$2$\pm$1\%
    compared to the surrounding quartz matrix for all
    irradiation conditions. The track radii only show a
    weak dependence on the electronic energy loss at
    values above 17 keV nm$^{-1}$, in contrast to values
    previously reported from Rutherford backscattering
    spectrometry measurements and expectations from the
    inelastic thermal spike model. The MD simulations
    are in good agreement at low energy losses, yet
    predict larger radii than SAXS at high ion
    energies. The observed discrepancies are discussed
    with respect to the formation of a defective halo
    around an amorphous track core, the existence of
    high stresses and/or the possible presence of a
    boiling phase in quartz predicted by the inelastic
    thermal spike model.},
    project = {FAIR}
    }
  • [PDF] [DOI] K. A. Avchaciov, Y. Ritter, F. Djurabekova, K. Nordlund, and K. Albe, “Controlled softening of cu64 zr36 metallic glass by ion irradiation,” Applied physics letters, vol. 102, p. 181910, 2013.
    [Bibtex]
    @Article{Avch13a,
    author = "K. A. Avchaciov and Y. Ritter and F. Djurabekova and
    K. Nordlund and K. Albe",
    title = "Controlled softening of Cu64 Zr36
    metallic
    glass by ion irradiation",
    journal = {Applied Physics Letters},
    year = 2013,
    volume = 102,
    pages = 181910,
    DOI = {10.1063/1.4804630},
    myfile = {Publications/final_papers/Avchaciov_CuZr_softening_APL.pdf},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2013_Avchaciov_CuZr_softening.pdf",
    abstract = {We study the effect of irradiation with 5–20 keV recoils
    on the topological and chemical short-range order of
    Cu64Zr36 metallic glass using molecular dynamics
    simulations. We show that within the cascade region,
    the structural backbone of stiff Cu-centered
    icosahedral units is destroyed, leading to locally
    softened areas. Under mechanical load, the formation
    of shear transformation zones is thus promoted in
    the damaged area. Our results suggest that
    irradiation is a means to introduce nucleation sites
    for multiple shear bands and thus prevents
    catastrophic failure due to the presence of a single
    critical shear band.},
    project = {MG}
    }
  • [PDF] [DOI] T. Bierschenk, R. Giulian, B. Afra, M. D. Rodriguez, D. Schauries, S. Mudie, O. H. Pakarinen, F. Djurabekova, K. Nordlund, O. Osmani, N. Medvedev, B. Rethfeld, M. C. Ridgway, and P. Kluth, “Latent ion tracks in amorphous silicon,” Physical review b, vol. 88, p. 174111, 2013.
    [Bibtex]
    @Article{Bier13,
    author = {T. Bierschenk and R. Giulian and B. Afra and
    M.D. Rodriguez and D. Schauries and S. Mudie and
    O.H. Pakarinen and F. Djurabekova and K. Nordlund
    and O. Osmani and N. Medvedev and B. Rethfeld and
    M.C. Ridgway and P. Kluth},
    title = "Latent ion tracks in amorphous silicon",
    journal = "Physical Review B",
    year = 2013,
    volume = 88,
    pages = 174111,
    DOI = {10.1103/PhysRevB.88.174111},
    abstract = { We present experimental evidence for the formation of
    ion tracks in amorphous Si induced by swift
    heavy-ion irradiation. An underlying core-shell
    structure consistent with remnants of a high-density
    liquid structure was revealed by small-angle x-ray
    scattering and molecular dynamics simulations. Ion
    track dimensions differ for as-implanted and relaxed
    Si as attributed to different microstructures and
    melting temperatures. The identification and
    characterization of ion tracks in amorphous Si
    yields new insight into mechanisms of damage
    formation due to swift heavy-ion irradiation in
    amorphous semiconductors.},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2013_Bierschenk_Si_track.
    pdf",
    myfile = {Publications/final_papers/2013/Bierschenk_Si_track.pdf},
    project = {FAIR}
    }
  • [PDF] F. Djurabekova, M. Backman, O. H. Pakarinen, A. A. Leino, and K.Nordlund, “Processing of insulators with and without nanoparticles by swift heavy ions,” in Proceedings of the 2013 ion-solid interactions conference, Moscow, Russia: Moscow aviation institute publisher, 2013, p. 51 – 55.
    [Bibtex]
    @InCollection{Djur13a,
    author = {F. Djurabekova and M. Backman and O. H. Pakarinen
    and A. A. Leino and K.Nordlund},
    title = {Processing of insulators with and without
    nanoparticles by swift heavy ions},
    booktitle = {Proceedings of the 2013 Ion-Solid Interactions
    conference},
    pages = {51 -- 55},
    publisher = {Moscow aviation institute publisher},
    year = 2013,
    address = "Moscow, Russia",
    myfile = {Publications/final_papers/2013/Djurabekova_ISI_2013.pdf},
    pdf = {http://www.acclab.helsinki.fi/~djurabek/pubs/Djurabekova_ISI_2013.pdf},
    project = {FAIR}
    }
  • F. Djurabekova, A. Ruzibaev, E. Holmström, S. Parviainen, and M. Hakala, “Local changes of work function near rough features on cu surfaces operated under high external electric field,” Journal of applied physics, vol. 114, iss. 24, p. 243302, 2013.
    [Bibtex]
    @article{djurabekova2013local,
    title={Local changes of work function near rough features on Cu surfaces operated under high external electric field},
    author={Djurabekova, Flyura and Ruzibaev, Avaz and Holmstr{\"o}m, Eero and Parviainen, Stefan and Hakala, Mikko},
    journal={Journal of Applied Physics},
    volume={114},
    number={24},
    pages={243302},
    year={2013},
    publisher={AIP Publishing},
    project = {CLIC}
    }

2014

  • [PDF] [DOI] K. Nordlund and F. Djurabekova, “Multiscale modelling of irradiation in nanostructures,” Journal of computational electronics, vol. 13, p. 122 – 141, 2014.
    [Bibtex]
    @Article{Nord14,
    author = {K. Nordlund and F. Djurabekova },
    title = {Multiscale modelling of irradiation in nanostructures},
    journal = {Journal of Computational Electronics},
    year = {2014},
    volume = {13},
    pages = {122 -- 141},
    DOI = {10.1007/s10825-013-0542-z},
    myfile =
    "Publications/final_papers/2014/preprint_review_Nordlund_MMMofNC.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint_review_Nordlund_MMMofNC.
    pdf",
    project = {NC}
    }
  • [PDF] [DOI] A. A. Leino, F. Djurabekova, and K. Nordlund, “Radiation effects in nanoclusters embedded in solids,” European physical journal b, vol. 87, iss. 10, 2014.
    [Bibtex]
    @Article{Lein14c,
    author = "A. A. Leino and F. Djurabekova and K. Nordlund ",
    title = "Radiation effects in nanoclusters embedded in solids",
    journal = "European Physical Journal B",
    year = 2014,
    volume = 87,
    number = 10,
    eid = 242,
    doi = {10.1140/epjb/e2014-50359-x},
    myfile =
    "Publications/final_papers/2014/preprint_review_Leino_RadiationeffectsinNC.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint_review_Leino_RadiationeffectsinNC.pdf",
    project = {FAIR}
    }
  • [DOI] K. A. Avchaciov, Y. Ritter, F. Djurabekova, K. Nordlund, and K. Albe, “Effect of ion irradiation on structural properties of cu64 zr36 metallic glass,” Nuclear instruments and methods in physics research section b: beam interactions with materials and atoms, 2014.
    [Bibtex]
    @Article{Avch14,
    author = "K. A. Avchaciov and Y. Ritter and F. Djurabekova and K.
    Nordlund and K. Albe",
    title = "Effect of ion irradiation on structural properties of
    Cu64 Zr36 metallic glass",
    journal = "Nuclear Instruments and Methods in Physics Research Section
    B:
    Beam Interactions with Materials and Atoms",
    year = 2014,
    DOI = {10.1016/j.nimb.2014.06.036},
    note = {also available online at \url
    {http://dx.doi.org/10.1016/j.nimb.2014.06.036}},
    myfile = {Publications/final_papers/Avchaciov_CuZr_rods_NIMB.pdf},
    abstract = {By means of molecular dynamics simulations, we study the
    low energy ion irradiation effect on the short-range
    order (SRO) of metallic glass structures. Breaking
    the topological SRO in a controlled manner may lead
    to desirable modifications of deformation behavior
    of glass structures. These changes in SRO were also
    found to be stable during the thermal annealing at
    temperatures below the glass transition temperature
    (Tg). The tensile deformation simulations
    performed for the Cu–Zr glass nanorods show that
    irradiated nanorods become softer compared to the
    pristine ones, changing the yielding mechanism –
    from a slip via formation of a single shear band to
    formation of a broad necking region.},
    project = {MG}
    }
  • [DOI] A. Debelle, M. Backman, L. Thome, K. Nordlund, F. Djurabekova, W. J. Weber, I. Monnet, O. H. Pakarinen, F. Garrido, and F. Paumier, “Swift heavy ion induced recrystallization in cubic silicon carbide: new insights from designed experiments and md simulations,” Nuclear instruments and methods in physics research b, vol. 326, p. 326 – 331, 2014.
    [Bibtex]
    @Article{Debe14,
    author = "A. Debelle and M. Backman and L. Thome and K. Nordlund and
    F.
    Djurabekova and W. J. Weber and I. Monnet and O. H. Pakarinen and F. Garrido
    and
    F. Paumier",
    title = "Swift heavy ion induced recrystallization in cubic silicon
    carbide: new insights from designed experiments and MD simulations",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2014,
    DOI = {10.1016/j.nimb.2013.10.080},
    volume = {326},
    pages = {326 -- 331},
    myfile = {Publications/final_papers/2014/Debelle_SHI_SiC_NIMB.pdf},
    abstract = {3C-SiC single crystals have been initially irradiated in
    the nuclear energy loss regime with 100 keV Fe ions
    to fluences ranging from 4x10$^{13}$ to 4x10$^{14}$
    cm$^{-2}$ (i.e. 0.07–0.7 dpa). RBS/C measurements
    indicate that SiC rapidly becomes amorphous (at
    0.4 dpa). Two damaged SiC crystals exhibiting a
    different defective structure have been subsequently
    irradiated in the electronic energy loss regime with
    870 MeV swift heavy (Pb) ions (SHIs) up to a fluence
    of 4x10$^{13}$ cm$^{-2}$. Initially fully amorphous SiC
    layers showed a decrease in size after SHI
    irradiation with a recrystallization occurring at
    the amorphous–crystalline interface. On the
    contrary, partially amorphous crystals for which
    onset of amorphization just initiated at the damage
    peak recovered over the entire damage
    thickness. Variation of amorphous thickness or
    disorder level has been monitored as a function of
    Pb ion fluence, which allowed deriving
    recrystallization kinetics. Data have been fitted
    with the direct-impact model and recrystallization
    cross-sections and threshold values for recovery
    have been determined for both types of initially
    defective structures. Differences are qualitatively
    discussed in terms of nature and density of
    irradiation defects. All experimental trends have
    been successfully reproduced by molecular dynamics
    simulations that mimicked thermal spikes induced by
    SHIs.},
    project = {FAIR}
    }
  • [PDF] [DOI] F. Granberg, D. Terentyev, K. O. E. Henriksson, F. Djurabekova, and K. Nordlund, “Interaction of dislocations with carbides in bcc fe studied by molecular dynamics,” Fusion science and technology, vol. 66, p. 283 – 288, 2014.
    [Bibtex]
    @Article{Gran14a,
    author = {F. Granberg and D. Terentyev and K. O. E. Henriksson
    and F. Djurabekova and K. Nordlund},
    title = {Interaction of dislocations with carbides in BCC Fe
    studied by molecular dynamics},
    journal = {Fusion Science and Technology},
    year = 2014,
    volume = 66,
    pages = {283 -- 288},
    DOI = {10.13182/FST13-728},
    myfile =
    {Publications/final_papers/2014/preprint_Granberg_dislocatons.pdf},
    pdf =
    {http://www.acclab.helsinki.fi/~djurabek/pubs/preprint_Granberg_dislocations.pdf
    },
    abstract = {Iron carbide (Fe3C), also known as cementite, is present
    in many steels, and may due to radiation be
    destroyed into nanosized precipitates. We examine
    the interaction of edge dislocations with nanosized
    cementite precipitates in Fe by molecular dynamics.
    The simulations are carried out with a Tersoff-like
    bond order interatomic potential by Henriksson et
    al. for Fe-C-Cr systems. Comparing the results
    obtained with this potential for a defect free Fe
    system with results from previously used potentials,
    we find that the potential by Henriksson et
    al. gives significantly higher values for the
    critical stress, at least at low temperatures. The
    results show that edge dislocations can penetrate
    cementite precipitates of sizes 1 nm and 2 nm even
    at a temperature of 1 K, although the stresses
    needed for this are high. On the other hand, a 4 nm
    precipitate is impenetrable for edge dislocations at
    low temperatures (< 100 K) on our simulation
    timescale.},
    project = {FF}
    }
  • [PDF] [DOI] F. Granberg, S. Parviainen, F. Djurabekova, and K. Nordlund, "Investigation of the thermal stability of cu nanowires using atomistic simulations," Journal of applied physics, vol. 115, p. 213518, 2014.
    [Bibtex]
    @Article{Gran14b,
    author = {F. Granberg and S. Parviainen and F. Djurabekova and
    K. Nordlund},
    title = {Investigation of the thermal stability of Cu
    nanowires using atomistic simulations},
    journal = {Journal of Applied Physics},
    year = 2014,
    volume = 115,
    pages = 213518,
    myfile =
    "Publications/final_papers/2014/preprint_Granberg_NW_melting.pdf",
    DOI = {10.1063/1.4876743},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint_Granberg_CuNW_melting.
    pdf",
    myfile = {Publications/final_papers/2014/Granberg_CuNW_melting.pdf},
    abstract = {We present a method for determining the melting point of
    copper nanowires based on classical molecular
    dynamics simulations and use it to investigate the
    dependence of the melting point on wire
    diameter. The melting point is determined as the
    temperature at which there is a significant change
    in the fraction of liquid atoms in the wire,
    according to atomic bond angle analysis. The results
    for the wires with diameters in the range 1.5nm to
    20nm show that the melting point is inversely
    proportional to the diameter while the
    cross-sectional shape of the wire does not have a
    significant impact. Comparison of results obtained
    using different potentials show that while the
    absolute values of the melting points may differ
    substantially, the melting point depression is
    similar for all potentials. The obtained results are
    consistent with predictions based on the semi-
    empirical liquid drop model.},
    project = {CLIC}
    }
  • [PDF] [DOI] S. Parviainen and F. Djurabekova, "Molecular dynamics simulations of ion irradiation of a surface under an electric field," Nuclear instruments and methods in physics research section b: beam interactions with materials and atoms, vol. 339, iss. 15, p. 63 – 66, 2014.
    [Bibtex]
    @article{Parv14a,
    author = {Parviainen, S. and Djurabekova, F.},
    doi = {10.1016/j.nimb.2014.03.009},
    issn = {0168583X},
    journal = {Nuclear Instruments and Methods in Physics Research
    Section B: Beam Interactions with Materials and
    Atoms},
    keywords = {electric\_field, irradiation, molecular\_dynamics,
    sputtering, sputtering\_yield},
    month = mar,
    title = {Molecular dynamics simulations of ion irradiation of a
    surface under an electric field},
    number = {15},
    volume = 339,
    year = {2014},
    pages = {63 -- 66},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint_sput_underEF.pdf",
    myfile = "Publications/final_papers/2014/Parviainen_sput_underEF.pdf",
    abstract = {The presence of high electric fields may affect
    significantly the process of sputtering of metal
    surfaces by energetic ions, especially in the
    vicinity of rough surface features. The effect can
    be significant if the energy of ions is fairly
    low. Moreover, the nanosized rough surface features
    – invisible to a naked eye, both intrinsic ones due
    to technological processing of surfaces and those
    forming because of sputtering – may affect the
    topology of surface erosion under ion
    bombardment. In this work we study by means of
    concurrent electrodynamics–molecular dynamics the
    sputtering yield of Cuþ ions hitting a flat Cu
    surface or a nanosized Cu protrusion as a function
    of both ion energy and electric field strength. The
    results show that the sputtering yield is
    significantly enhanced in the presence of an
    electric field in both cases.},
    project = {CLIC}
    }
  • [PDF] [DOI] V. Zadin, A. Pohjonen, A. Aabloo, K. Nordlund, and F. Djurabekova, "Electrostatic-elastoplastic simulations of copper surface under high electric fields," Physical review st accel. beams, vol. 17, 2014.
    [Bibtex]
    @Article{Zadi14a,
    author = {V. Zadin and A. Pohjonen and A. Aabloo and K. Nordlund and F.
    Djurabekova},
    title = {Electrostatic-elastoplastic simulations of copper surface
    under high electric fields},
    journal = { Physical Review ST Accel. Beams},
    year = {2014},
    myfile = {Publications/final_papers/2014/Zadin_FEM_matproperties_PRST.pdf},
    OPTkey = {},
    volume = {17},
    OPTpages = {103501},
    DOI = {http://dx.doi.org/10.1103/PhysRevSTAB.17.103501},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/Zadin_FEM_matproperties_PRST.pdf",
    abstract = {Maximizing the performance of modern linear
    accelerators working with high gradient
    electromagnetic fields depends to a large extent on
    ability to control breakdown rates near metal
    surfaces in the accelerating structures. Nanoscale
    voids, presumably forming in the surface layers of
    metals during the technological processing, can be
    responsible for the onset of the growth of a surface
    protrusion. We use finite element simulations to
    study the evolution of annealed copper, single
    crystal copper and stainless steel surfaces that
    contain a void under high electric fields. We use a
    fully coupled electrostatic-elastoplastic model in
    the steady state. Gradually increasing the value of
    an external electric field, we analyze the
    relationship of surface failure and depth of the
    void for the chosen materials with different
    elastoplastic properties. According to our results,
    the stainless steel and single crystal copper
    surfaces demonstrate the formation of well-defined
    protrusions, when the external electric field
    reaches a certain critical value. Among the three
    materials, annealed copper surface starts yielding
    at the lowest electric fields due to the lowest
    Young’s modulus and yield stress. However, it
    produces the smallest protrusions due to a
    significant strain hardening characteristic for this
    material.},
    project = {CLIC}
    }
  • [DOI] B. E. Umirzakov, D. A. Tashmukhamedova, M. K. Ruzibaeva, F. G. Djurabekova, and S. B. Danaev, "Investigation of change of the composition and structure of the caf2/si films surface at the low-energy bombardment," Nuclear instruments and methods in physics research b, vol. 326, p. 322 – 325, 2014.
    [Bibtex]
    @Article{Umir14a,
    author = { B. E. Umirzakov and D. A. Tashmukhamedova and M. K.
    Ruzibaeva
    and F. G. Djurabekova and S.B. Danaev},
    title = {Investigation of change of the composition and structure of
    the CaF2/Si films surface at the low-energy bombardment},
    journal = {Nuclear Instruments and Methods in Physics Research B},
    year = {2014},
    volume = {326},
    pages = {322 -- 325},
    DOI = {10.1016/j.nimb.2013.10.094},
    note = {also available at \url
    {http://dx.doi.org/10.1016/j.nimb.2013.10.094}},
    myfile = {Publications/final_papers/2014/Umirzakov_CaF2_REI_NIMB.pdf},
    mynote = "{REI 2013 conference paper}",
    abstract = {The influence of the bombardment by the Ar+, Ba+ and Na+
    ions and the subsequent annealing on composition and
    electron structure of a surface of the CaF2/Si (111)
    films is studied. The energy band diagram of the
    epitaxial nanofilm systems of the Ca–CaF2–Si type is
    constructed. Optimum regimes of ion implantation and
    annealing for the production of three-componental
    nanodimensional structures of the Ca_{1−X}Ме_XF_2 type
    are determined and parameters of their energy bands
    are estimated.},
    project = {CLIC}
    }
  • [PDF] [DOI] A. A. Leino, O. H. Pakarinen, F. Djurabekova, K. Nordlund, P. Kluth, and M. C. Ridgway, "Swift heavy ion shape transformation of au nanocrystals mediated by molten material flow and recrystallization," Materials research letters, vol. 2, iss. 1, p. 37 – 42, 2014.
    [Bibtex]
    @Article{Lein14a,
    author = "A. A. Leino and O. H. Pakarinen and F. Djurabekova
    and K. Nordlund and P. Kluth and M. C. Ridgway",
    title = "Swift Heavy Ion Shape Transformation of Au Nanocrystals
    Mediated by Molten Material Flow and Recrystallization",
    journal = "Materials Research Letters",
    year = 2014,
    volume = 2,
    number = 1,
    pages = {37 -- 42},
    DOI = {10.1080/21663831.2013.856816},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2014_Leino_elongationofAuNP.pdf",
    myfile = {Publications/final_papers/2014/Leino_elongationofAuNP.pdf},
    abstract = {Swift heavy ion (SHI) irradiation of amorphous SiO2 that
    contains metal nanocrystals can be used to transform
    the shape of the particles into peculiar asymmetric
    ones not easily achievable by other means. Using a
    molecular dynamics simulation framework augmented to
    include the electronic excitations of the SHIs, we
    predict that the reshaping of spherical particles
    into nanorods occurs continuously during consecutive
    ion impacts by a dynamic crystal–liquid–crystal
    phase transition of metal particle with the flow of
    liquid phase into an underdense track core in
    silica. The simulated nanocrystals are shown to have
    a saturation width that agrees with experiments.},
    project = {FAIR}
    }
  • [PDF] [DOI] A. A. Leino, S. L. Daraszewicz, O. Pakarinen, F. Djurabekova, K. Nordlund, B. Afra, and P. Kluth, "Structural analysis of simulated swift heavy ion tracks in quartz," Nuclear instruments and methods in physics research b, vol. 326, p. 289 – 292, 2014.
    [Bibtex]
    @Article{Lein14b,
    author = "Aleksi A. Leino and Szymon L. Daraszewicz and Olli
    H. Pakarinen and Flyura Djurabekova and Kai Nordlund and Boshra Afra
    and Patrick Kluth",
    title = "Structural analysis of simulated swift heavy ion
    tracks in quartz",
    journal = "Nuclear Instruments and Methods in Physics Research B",
    year = 2014,
    volume = 326,
    pages = {289 -- 292},
    mynote = "{REI 2013 conference paper}",
    myfile = "Publications/final/2014/Leino_2TMD_quartz_NIMB.pdf",
    DOI = {10.1016/j.nimb.2013.10.075},
    abstract = {Swift heavy ions (SHI), of specific kinetic energies in
    the excess of 1 MeV/u, can create cylindrical
    regions of structural transformation in SiO2
    targets, also known as SHI tracks. Recent
    measurements of the track cross-sections in
    αα-quartz show significant and consistent
    discrepancies across different experimental
    techniques used. In particular, the track radii
    obtained from channelling experiments based on the
    Rutherford Backscattering Spectrometry (RBS-c)
    method increase monotonically with the electronic
    stopping power, whereas the track radii obtained
    from the Small Angle X-ray scattering (SAXS)
    saturate past a certain stopping power threshold. We
    perform a systematic study of the structure of the
    αα-quartz tracks obtained from the molecular
    dynamics (MD) simulations incorporating a
    time-dependent energy deposition based on the
    inelastic thermal spike model, which allows us to
    discuss the possible origins of these experimental
    discrepancies.},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2014_Leino_2TMD_quartz_NIMB.pdf",
    project = {FAIR}
    }
  • [DOI] M. W. Ullah, A. Kuronen, K. Nordlund, F. Djurabekova, A. I. Titov, and P. Karaseov, "Defect clustering in irradiation of gan by single and molecular ions," Vacuum, vol. 105, p. 88 – 90, 2014.
    [Bibtex]
    @Article{Ulla14a,
    author = "M. W. Ullah and A. Kuronen and K. Nordlund and
    F. Djurabekova and A. I. Titov and P. Karaseov",
    title = "Defect clustering in irradiation of GaN by single
    and molecular ions",
    journal = {Vacuum},
    year = {2014},
    volume = {105},
    pages = {88 -- 90},
    DOI = {10.1016/j.vacuum.2013.12.015},
    myfile = "Publications/final_papers/2014/Ullah_defectclustersGaN_Vacuum.pdf",
    abstract = {Atomistic simulations were used to study irradiation
    effects on photoluminescence (PL) decay time of
    GaN. Irradiations were done by single (F, P) and
    molecular ions (PF4). Equal energy per mass (0.6
    keV/ amu) was used for all projectiles. Irradiation
    by the molecular ion shows faster PL decay time in
    comparison with the single ion. The simulation
    results show that single ions produce isolated point
    defects, whereas molecular ions produce big clusters
    of points defects. The total amount of defects
    produced by a PF4 projectile and five individual
    cascades started by one P and four F single ions (P
    + 4 x F) were very close and their defect depth
    profile follows the same pattern. These findings
    suggest that defect clusters are one of the
    important reasons for fast PL decay.},
    project = {GaN}
    }
  • [DOI] M. W. Ullah, A. Kuronen, A. Stukowski, F. Djurabekova, and K. Nordlund, "Atomistic simulation of er irradiation induced defects in gan nanowires," Journal of applied physics, vol. 116, 2014.
    [Bibtex]
    @Article{Ulla14b,
    author = "M. W. Ullah and A. Kuronen and A. Stukowski and F.
    Djurabekova and K. Nordlund",
    title = "Atomistic simulation of Er irradiation induced defects in
    GaN nanowires",
    journal = "Journal of Applied Physics",
    volume = 116,
    year = 2014,
    note = {also available at \url{http://dx.doi.org/10.1063/1.4896787}},
    DOI = {10.1063/1.4896787},
    ownhref =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2014_Ullah_GaN_NW.pdf",
    myfile = "Publications/final_papers/2014/Ullah_GaN_NW.pdf",
    abstract = {Classical molecular dynamics simulation was used to
    irradiate a GaN nanowire with rear-earth erbium
    (Er). Ten cumulative irradiations were done using an ion
    energy of 37.5 keV on a 10^{10} nm^2 surface area
    which corresponds to a fluence of 10^{13}cm^{-2}. We
    studied the location and types of defects produced
    in the irradiation. Er implantation leads to a net
    positive (expansion) strain in the nanowire and
    especially at the top region a clear expansion has
    been observed in the lateral and axial
    directions. The lattice expansion is due to the
    hydrostatic strain imposed by a large number of
    radiation induced defects at the top of the NW. Due
    to the large surface-to-volume ratio, most of the
    defects were concentrated at the surface region,
    which suggests that the experimentally observed
    yellow luminescence (YL) in ion implanted GaN NWs
    arises from surface defects. We observed big
    clusters of point defects and vacancy clusters which
    are correlated with stable lattice strain and the YL
    band, respectively.},
    project = {GaN}
    }
  • F. Granberg, S. Parviainen, F. Djurabekova, and K. Nordlund, "Investigation of the thermal stability of cu nanowires using atomistic simulations," Journal of applied physics, vol. 115, iss. 21, p. 213518, 2014.
    [Bibtex]
    @article{granberg2014investigation,
    title={Investigation of the thermal stability of Cu nanowires using atomistic simulations},
    author={Granberg, F and Parviainen, S and Djurabekova, F and Nordlund, K},
    journal={Journal of Applied Physics},
    volume={115},
    number={21},
    pages={213518},
    year={2014},
    publisher={AIP Publishing},
    project = {CLIC}
    }

2015

  • S. Parviainen, F. Djurabekova, S. Fitzgerald, A. Ruzibaev, and K. Nordlund, "Atomistic simulations of field assisted evaporation in atom probe tomography," Journal of physics d: applied physics, vol. 49, iss. 4, p. 45302, 2015.
    [Bibtex]
    @article{parviainen2015atomistic,
    title={Atomistic simulations of field assisted evaporation in atom probe
    tomography},
    author={Parviainen, S and Djurabekova, F and Fitzgerald, SP and Ruzibaev, A
    and Nordlund, K},
    journal={Journal of Physics D: Applied Physics},
    volume={49},
    number={4},
    pages={045302},
    year={2015},
    publisher={IOP Publishing},
    abstract={Atom probe tomography (APT) is an extremely powerful technique for
    determining the three-dimensional structure and chemical composition of a given
    sample. Although it is designed to provide images of material structure with
    atomic scale resolution, reconstruction artifacts, well-known to be present in
    reconstructed images, reduce their accuracy. No existing simulation technique
    has been able to describe the origin of these artifacts. Here we develop a
    simulation technique which allows for atomistic simulations of the atom emission
    process in the presence of high electric fields in APT experiments. Our code
    combines hybrid concurrent electrodynamics—molecular dynamics and a Monte Carlo
    approach. We use this technique to demonstrate the atom-level origin of
    artifacts in APT image reconstructions on examples of inclusions and voids in
    investigated samples. The results show that even small variations in the surface
    topology give rise to distortions in the local electric field, limiting the
    accuracy
    of conventional APT reconstruction algorithms.},
    project = {CLIC}
    }
  • [PDF] I. Profatilova, S. Calatroni, A. Korsback, T. Muranaka, and W. Wuensch, "DC Breakdown Experiments with Iridium Cathode," CERN, Geneva, CERN-ACC-2015-0061, 2015.
    [Bibtex]
    @techreport{Profatilova15,
    author = "Profatilova, I. and Calatroni, S. and Korsback, A. and
    Muranaka, T. and Wuensch, W.",
    title = "{DC Breakdown Experiments with Iridium Cathode}",
    institution = "CERN",
    address = "Geneva",
    number = "CERN-ACC-2015-0061",
    month = "Jun",
    year = "2015",
    reportNumber = "CERN-ACC-2015-0061",
    url = "https://cds.cern.ch/record/2027807",
    pdf = {https://cds.cern.ch/record/2027807/files/CERN-ACC-2015-0061.pdf},
    abstract={Electrical breakdown occurring in rf accelerating structures is one
    of
    the major disruptions of the accelerated beam in CLIC. At CERN, as complements
    to rf facilities, DC-spark systems have been used to study breakdown properties
    of many candidate materials for making rf components. In this note,
    measurements
    of conditioning speed, breakdown field and field enhancement factor of iridium
    are presented comparing with previously tested materials. The average breakdown
    field after conditioning reached 238 MV/m, which places iridium next to copper.
    By comparison with results and properties of other metals, the low breakdown
    field of iridium could be explained by its face-centred-cubic crystal
    structure.},
    project = {CLIC}
    }
  • [PDF] K. A. Avchaciov, W. Ren, F. Djurabekova, K. Nordlund, I. Sveklo, and A. Maziewski, "Modification of pt/co/pt film properties by ion irradiation," Phys. rev. b, 2015.
    [Bibtex]
    @Article{Avch15,
    author = {K. A. Avchaciov and W. Ren and F. Djurabekova and K.
    Nordlund and I. Sveklo and A. Maziewski},
    title = {Modification of Pt/Co/Pt film properties by ion
    irradiation},
    journal = {Phys. Rev. B},
    year = {2015},
    OPTkey = {},
    OPTvolume = {},
    OPTnumber = {},
    OPTpages = {},
    OPTmonth = {},
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2015_Avchaciov_ptco.pdf",
    project={NC},
    note = {accepted for publication}
    }
  • [DOI] A. D. A. . F. K. Eimre S. Parviainen and V. Zadin, "Application of the general thermal field (gtf) model to simulate the behaviour of nanoscale cu field emitters," Journal of applied physics, vol. 118, iss. 3, 2015.
    [Bibtex]
    @Article{Eimre2015Application,
    author = {K. Eimre, S. Parviainen, A. Abloo, F. Djurabekova and V.
    Zadin},
    title = {Application of the general thermal field (GTF) model to
    simulate the behaviour of nanoscale Cu field emitters},
    journal = {Journal of Applied Physics},
    number = "3",
    url =
    "http://scitation.aip.org/content/aip/journal/jap/118/3/10.1063/1.4926490",
    volume = "118",
    year = {2015},
    doi = "10.1063/1.4926490",
    abstract = {Strong field electron emission from a nanoscale tip can cause the
    temperature rise at the tip apex due to Joule heating. This becomes
    particularly
    important when the current value grows rapidly as in the pre-breakdown (the
    electrostatic discharge) condition which may occur near metal surfaces
    operating
    under high electric fields. The high temperatures introduce uncertainties in
    calculations of the current values when using the Fowler-Nordheim equation
    only,
    since the thermionic component in such condition cannot be neglected.
    In this paper we analyze the field electron emission currents as the function
    of
    applied electric field, given by both the conventional Fowler-Nordheim field
    emission and the recently developed generalized thermal field emission
    formalisms. We also compare the results in two limits: discrete (atomistic
    simulations) and continuum (finite element calculations). The discrepancies of
    both implementations and their effect on final results are discussed.
    In both approaches the electric field, electron emission currents and Joule
    heating processes are simulated concurrently and self-consistently. We show
    that
    the conventional Fowler-Nordheim equation results in significant
    underestimation
    of electron emission currents. We also show that Fowler-Nordheim plots used to
    estimate the field enhancement factor may lead to significant overestimation of
    this parameter especially in the range of relatively low electric fields.},
    project = {CLIC}
    }
  • [PDF] [DOI] M. C. Ridgway, F. Djurabekova, and K. Nordlund, "Ion-solid interactions at the extremes of electronic energy loss," Current opinion in solid state & materials science, vol. 19, p. 29 – 38, 2015.
    [Bibtex]
    @Article{Ridg14a,
    author = "M. C. Ridgway and F. Djurabekova and K. Nordlund",
    title = "Ion-solid interactions at the extremes of electronic
    energy loss",
    journal = "Current opinion in Solid State \& Materials Science",
    year = 2015,
    volume = 19,
    pages = {29 -- 38},
    DOI = {10.1016/j.cossms.2014.10.001},
    myfile =
    "Publications/final_papers/2014/Ridgway_review_COSSMS-D-14-00084R1.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint_review_Ridgway_COSSMS-D-
    14-00084R1.pdf",
    project = {FAIR}
    }
  • S. B. Danaev, F. G. Djurabekova, D. A. Tashmukhamedova, and B. E. Umirzakov, "Formation of nanodimensional structures on the surface of gaas and si by means of ion implantation," Physica status solidi c, vol. 12, p. 89 – 93, 2015.
    [Bibtex]
    @Article{Umir14b,
    author = { S. B. Danaev and F. G. Djurabekova and D. A.
    Tashmukhamedova and B. E. Umirzakov},
    title = {Formation of nanodimensional structures on the
    surface of GaAs and Si by means of ion implantation},
    journal = {Physica Status Solidi C},
    year = {2015},
    volume = {12},
    pages = {89 -- 93},
    note = {also available at
    \url{http://dx.doi.org/10.1002/pssc.201400156}},
    mynote = {EMRS 2014 conference paper},
    myfile =
    {Publications/final_papers/2014/preprint_pssc2914_Umizakov_CoSi.pdf and
    Publications/final_papers/2015/Umirzakov_pssc_2015.pdf},
    ownhref =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2014_Umizakov_CoSi_pssc.
    pdf",
    abstract = {We obtained the two- and three-component nanostructures
    by means of ion implantation of low-energy Co and Ba
    ions in the surface layers of Si and GaAs in
    combination with the post-implantation annealing.
    We show that flat shaped nanocrystals (nanoislands)
    of two- and three-component composition, Co-Si and
    Ga- Ba-As, start forming at the ion fluences Φ=
    (6÷8)x1014 cm-2. After the laser annealing and short
    time electron heating we observed the formation of
    CoSi2 and Ga0.4Ba0.6As nanocrystals. Our results
    show that the size effects are clearly seen in
    electronic properties (opening of the band gap) when
    the lateral size of nanocrystals is less than 15 –
    30 nm, or in case of solid nanofilms, similar effect
    is observed at the thickness less than 3 – 4 nm.},
    project = {CLIC}
    }
  • [PDF] [DOI] V. Zadin, A. V. Krasheninnikov, F. Djurabekova, and K. Nordlund, "Simulations of electromechanical shape transformations of au nanoparticles," Physica status solidi b, vol. 252, iss. 1, pp. 144-148, 2015.
    [Bibtex]
    @Article{Zadi14b,
    author = {V. Zadin and A. V. Krasheninnikov and F. Djurabekova and K.
    Nordlund},
    title = {Simulations of electromechanical shape transformations of Au
    nanoparticles},
    journal = {Physica Status Solidi B},
    year = {2015},
    doi = "10.1002/pssb.201400140",
    issn = "1521-3951",
    number = "1",
    pages = "144-148",
    url = "http://dx.doi.org/10.1002/pssb.201400140",
    volume = "252",
    pdf =
    {http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2014_Zadin_FEM_AuNP_W.pdf}
    ,
    myfile = {Publications/final_papers/2014/preprint2014_Zadin_FEM_AuNP_W.pdf},
    mynote = {EMRS 2014 conference paper},
    note = "and back cover",
    project = {NC}
    }
  • [DOI] S. Vigonski, F. Djurabekova, M. Veske, A. Aabloo, and V. Zadin, "Molecular dynamics simulations of near-surface fe precipitates in cu under high electric fields," Mod. sim. in mat. sci. and eng., vol. 23, iss. 2, p. 25009, 2015.
    [Bibtex]
    @Article{Vigo14a,
    author = "S. Vigonski and F. Djurabekova and M. Veske and A. Aabloo and
    V. Zadin",
    title = "Molecular dynamics simulations of near-surface Fe
    precipitates
    in Cu under high electric fields",
    journal = "Mod. Sim. in Mat. Sci. and Eng.",
    year = 2015,
    url = "http://stacks.iop.org/0965-0393/23/i=2/a=025009",
    volume = "23",
    number = "2",
    pages = "025009",
    doi = "10.1088/0965-0393/23/2/025009",
    abstract = {High electric fields in particle accelerators cause vacuum
    breakdowns in the accelerating structures. The breakdowns are thought to be
    initiated by the modification of material surface geometry under high electric
    fields. These modifications in the shape of surface protrusions enhance the
    electric field locally due to the increased surface curvature. We simulate,
    using molecular dynamics, the behaviour of Cu containing a near-surface Fe
    precipitate under a high electric field. We find that the presence of a
    precipitate under the surface can cause nucleation of dislocations in the
    material, leading to appearance of atomic steps on the surface. Steps resulting
    from several precipitates in close proximity can also form protruding plateaus.
    Under very high external fields, in some cases we observed the formation of
    voids above or below the precipitate, providing additional dislocation
    nucleation sites.},
    project = {CLIC}
    }
  • [PDF] [DOI] J. Zhao, C. Cassidy, P. Grammatikopoulos, V. Singh, K. Aranishi, M. Sowwan, K. Nordlund, and F. Djurabekova, "Crystallization of silicon nanoclusters with inert gas temperature control," Physical review b, vol. 91, p. 35419, 2015.
    [Bibtex]
    @Article{Zhao14a,
    author = "J. Zhao and C. Cassidy and P. Grammatikopoulos and V. Singh
    and K. Aranishi and M. Sowwan and K. Nordlund and F. Djurabekova",
    title = "Crystallization of Silicon Nanoclusters with Inert
    Gas Temperature Control",
    journal = " Physical Review B",
    year = 2015,
    volume = 91,
    pages = 035419,
    DOI = {10.1103/PhysRevB.91.035419},
    myfile =
    "Publications/final_papers/2014/preprint2014_Zhao_SiNC_crystallization.pdf",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/
    preprint2014_Zhao_SiNC_crystallization.pdf",
    project = {NC}
    }
  • [DOI] C. M. Müller, S. Parviainen, F. Djurabekova, K. Nordlund, and R. Spolenak, "The as-deposited structure of co-sputtered cu–ta alloys, studied by x-ray diffraction and molecular dynamics simulations," Acta materialia, vol. 82, pp. 51-63, 2015.
    [Bibtex]
    @article{Mull15,
    title = {The as-deposited structure of co-sputtered Cu–Ta alloys, studied by
    X-ray diffraction and molecular dynamics simulations },
    journal = {Acta Materialia},
    volume = {82},
    number = {0},
    pages = {51 - 63},
    year = {2015},
    issn = {1359-6454},
    doi = {http://dx.doi.org/10.1016/j.actamat.2014.08.066},
    author = {C. M. Müller and S. Parviainen and F. Djurabekova and K.
    Nordlund and R. Spolenak},
    myfile = {Publications/final_papers/2015/Muller_CuTa_APT.pdf},
    keywords = {Sputter deposition},
    keywords = {Immiscible materials},
    keywords = {Thin films},
    keywords = {Molecular dynamics },
    abstract = {In this study a direct comparison between
    lattice spacings predicted by molecular dynamics
    (MD) simulations and values measured from sputtered
    Cu–Ta films by X-ray diffraction (XRD) is
    reported. The study spans the entire composition
    range between pure Cu and pure Ta and takes into
    account all the phases documented for the Cu–Ta
    system in the literature (i.e. α-Cu, α-Ta, β-Ta as
    well as X-ray amorphous structures). For both the
    experiments and the {MD} simulations the results
    are compared to the literature and discrepancies are
    critically discussed. A direct comparison between
    simulation and experiments shows that the {MD}
    simulations reproduce the interatomic distances
    observed in the experiments accurately over most of
    the composition range, with the exception of alloys
    with 15–30at.\% Ta content where the {MD}
    simulations show spontaneous amorphization whereas
    the experiments suggest that Ta-rich particles are
    formed in face-centered cubic solid-solution
    phase. },
    project = {CLIC}
    }
  • [PDF] [DOI] S. Vigonski, M. Veske, A. Aabloo, F. Djurabekova, and V. Zadin, "Verification of a multiscale surface stress model near voids in copper under the load induced by external high electric field," Applied mathematics and computation, 2015.
    [Bibtex]
    @article{Vigo15b,
    title = {Verification of a multiscale surface stress model near voids
    in
    copper under the load induced by external high electric field},
    url =
    {http://www.sciencedirect.com/science/article/pii/S0096300315001344},
    doi = {10.1016/j.amc.2015.01.102},
    abstract = {In the current study we use a model of surface stress for
    finite element method calculations to complement existing bulk stress models.
    The resulting combined model improves the accuracy of stress calculations near
    nanoscale imperfections in the material. We verify the results by simulating
    differently-shaped voids in single crystal copper both with FEM and with
    molecular dynamics, and compare the resulting stress distributions. The
    compared
    results agree well within small uncertainties, indicating that the implemented
    surface stress model is able to capture all the major features of the stress
    distributions in the material. Discrepancies occur near surfaces, where the
    crystal faces were not defined explicitly in the model. The fast and accurate
    FEM calculations can be used to estimate the stress concentration of specific
    extended defects, such as voids, while studying the dislocation-mediated
    mechanisms near these defects in the presence of external stresses by atomistic
    techniques.},
    journal = {Applied Mathematics and Computation},
    author = {Vigonski, Simon and Veske, Mihkel and Aabloo, Alvo and
    Djurabekova, Flyura and Zadin, Vahur},
    keywords = {Finite element simulations, Molecular dynamics simulations,
    Multiscale simulations, Surface stress model, Void under copper surface},
    pdf =
    {http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2014_Vigonsky_surfstress.
    pdf},
    year = 2015,
    project = {CLIC}
    }
  • [PDF] [DOI] H. Timko, K. {Ness Sjobak}, L. Mether, S. Calatroni, F. Djurabekova, K. Matyash, K. Nordlund, R. Schneider, and W. Wuensch, "From Field Emission to Vacuum Arc Ignition: A New Tool for Simulating Copper Vacuum Arcs," Contributions to plasma physics, vol. 55, iss. 4, p. 299–314, 2015.
    [Bibtex]
    @Article{Timk14,
    abstract = "Understanding plasma initiation in vacuum arc discharges
    can
    help to bridge the gap between nano-scale triggering phenomena and the
    macroscopic surface damage caused by vacuum arcs. We present a new
    twodimensional particle-in-cell tool to simulate plasma initiation in
    direct-current (DC) copper vacuum arc discharges starting from a single, strong
    field emitter at the cathode. Our simulations describe in detail how a
    sub-micron field emission site can evolve to a macroscopic vacuum arc
    discharge,
    and provide a possible explanation for why and how cathode spots can spread on
    the cathode surface. Furthermore, the model provides us with a prediction for
    the current and voltage characteristics, as well as for properties of the
    plasma
    like densities, fluxes and electric potentials in a simple DC discharge case,
    which are in agreement with the known experimental values.",
    author = "Timko, H. and {Ness Sjobak}, K. and Mether, L. and Calatroni,
    S. and Djurabekova, F. and Matyash, K. and Nordlund, K. and Schneider, R. and
    Wuensch, W.",
    doi = "10.1002/ctpp.201400069",
    issn = "1521-3986",
    journal = "Contributions to Plasma Physics",
    keywords = "Vacuum arcs; cathode plasma; PIC simulations",
    number = "4",
    pages = "299–314",
    publisher = "WILEY-VCH Verlag",
    title = "{From Field Emission to Vacuum Arc Ignition: A New Tool for
    Simulating Copper Vacuum Arcs}",
    url = "http://dx.doi.org/10.1002/ctpp.201400069",
    volume = "55",
    year = "2015",
    pdf =
    "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2014_2D_ArcPIC.pdf",
    project = {CLIC}
    }
  • [PDF] A. Leino, S. Daraszewicz, O. Pakarinen, K. Nordlund, and F. Djurabekova, "Atomistic two-temperature modelling of ion track formation in silicon dioxide," Epl (europhysics letters), vol. 110, iss. 1, p. 16004, 2015.
    [Bibtex]
    @article{leino2015atomistic,
    title={Atomistic two-temperature modelling of ion track formation in silicon dioxide},
    author={Leino, AA and Daraszewicz, SL and Pakarinen, OH and Nordlund, K and Djurabekova, F},
    journal={EPL (Europhysics Letters)},
    volume={110},
    number={1},
    pages={16004},
    year={2015},
    publisher={IOP Publishing},
    pdf = "http://www.acclab.helsinki.fi/~djurabek/pubs/preprint2014_Leino_TTMD.pdf",
    project = {FAIR},
    abstract = {We study swift heavy ion track formation in α-quartz
    using the two-temperature molecular dynamics (2T-MD)
    model realised as a concurrent multiscale scheme. We
    compare the simulated track radii to the existing
    SAXS and RBS-c experimental data sets. The 2T-MD
    model provides an explanation to the origin of the
    track radii saturation at high electronic stopping
    power. Furthermore, we study the track structure and
    show that the crystallographic defects formed in the
    matrix after a swift heavy ion impact outside the
    region of density fluctuations can explain the
    conflicting track radii produced by the two
    experimental techniques.}
    }
  • M. Bohra, P. Grammatikopoulos, R. Rivas, V. Singh, J. Zhao, J. Bobo, A. Kuronen, F. Djurabekova, K. Nordlund, and M. Sowwan, "Surface segregation in chromium-doped nicr alloy nanoparticles and its effect on their magnetic behavior," Chemistry of materials, vol. 27, p. 3216 – 3225, 2015.
    [Bibtex]
    @Article{Bohr14,
    author = "M. Bohra and P. Grammatikopoulos and R. Rivas and
    V. Singh and J. Zhao and J. Bobo and A. Kuronen and F. Djurabekova,
    and K. Nordlund and M. Sowwan",
    title = " Surface Segregation in Chromium-Doped NiCr Alloy
    Nanoparticles and Its Effect on Their Magnetic Behavior",
    journal = "Chemistry of Materials",
    year = 2015,
    volume = {27},
    pages = {3216 -- 3225},
    project={NC},
    myfile = "do not have it yet"
    }

2016

  • [PDF] A. Kyritsakis and F. Djurabekova, "A general computational method for electron emission and thermal effects in field emitting nanotips," Arxiv preprint arxiv:1609.02364, 2016.
    [Bibtex]
    @article{kyritsakis2016general,
    title={A general computational method for electron emission and thermal effects in field emitting nanotips},
    author={Kyritsakis, A and Djurabekova, F},
    journal={arXiv preprint arXiv:1609.02364},
    year={2016},
    url = {http://arxiv.org/abs/1609.02364},
    pdf = {http://arxiv.org/pdf/1609.02364v1.pdf},
    project={CLIC},
    abstract={Electron emission from nanometric size emitters becomes of increasing interest
    due to its involvement to sharp electron sources, vacuum breakdown phenomena and
    various other vacuum nanoelectronics applications. The most commonly used
    theoretical tools for the calculation of electron emission are still nowadays
    the Fowler-Nordheim and the Richardson-Laue-Dushman equations although it has
    been shown since the 1990s that they are inadequate for nanometrically sharp
    emitters or in the intermediate thermal-field regime. In this paper we develop a
    computational method for the calculation of emission currents and Nottingham
    heat, which automatically distinguishes among different emission regimes, and
    implements the appropriate calculation method for each. Our method covers all
    electron emission regimes (thermal, field and intermediate), aiming to maximize
    the calculation accuracy while minimizing the computational time. As an example,
    we implemented it in atomistic simulations of the thermal evolution of Cu
    nanotips under strong electric fields and found that the predicted behavior of
    such nanotips by the developed technique differs significantly from estimations
    obtained based on the Fowler-Nordheim equation. Finally, we show that our tool
    can be also successfully applied in the analysis of experimental data.}
    }
  • [PDF] T. CLIC, M. Boland, U. Felzmann, P. Giansiracusa, T. Lucas, R. Rassool, C. Balazs, T. Charles, K. Afanaciev, I. Emeliantchik, and others, "Updated baseline for a staged compact linear collider," Arxiv preprint arxiv:1608.07537, 2016.
    [Bibtex]
    @article{clic2016updated,
    title={Updated baseline for a staged Compact Linear Collider},
    author={CLIC, The and Boland, MJ and Felzmann, U and Giansiracusa, PJ and Lucas, TG and Rassool, RP and Balazs, C and Charles, TK and Afanaciev, K and Emeliantchik, I and others},
    journal={arXiv preprint arXiv:1608.07537},
    year={2016},
    url={https://arxiv.org/abs/1601.00407},
    pdf={https://arxiv.org/pdf/1608.07537.pdf},
    project={CLIC}
    }
  • [PDF] M. Veske, S. Parviainen, V. Zadin, A. Aabloo, and F. Djurabekova, "Electrodynamics—molecular dynamics simulations of the stability of cu nanotips under high electric field," Journal of physics d: applied physics, vol. 49, iss. 21, p. 215301, 2016.
    [Bibtex]
    @article{veske2016electrodynamics,
    title={Electrodynamics—molecular dynamics simulations of the stability of Cu nanotips under high electric field},
    author={Veske, Mihkel and Parviainen, Stefan and Zadin, Vahur and Aabloo, Alvo and Djurabekova, Flyura},
    journal={Journal of Physics D: Applied Physics},
    volume={49},
    number={21},
    pages={215301},
    year={2016},
    publisher={IOP Publishing},
    eprint = {1601.00407},
    primaryClass = "cond-mat.mtrl-sci",
    url = {https://arxiv.org/abs/1601.00407},
    pdf={https://arxiv.org/pdf/1601.00407v2.pdf},
    project={CLIC},
    abstract={The shape memory effect and pseudoelasticity in Cu nanowires is one possible
    pair of mechanisms that prevents high aspect ratio nanosized field electron emitters to
    be stable at room temperature and permits their growth under high electric field. By utilizing
    hybrid electrodynamics molecular dynamics simulations we show that a global electric field of
    1 GV/m or more significantly increases the stability and critical temperature of spontaneous
    reorientation of nanosized <100> Cu field emitters. We also show that in the studied tips the
    stabilizing effect of an external applied electric field is an order of magnitude greater than
    the destabilization caused by the field emission current. We detect the critical temperature of
    spontaneous reorientation using the tool that spots the changes in crystal structure. The method
    is compatible with techniques that consider the change in potential energy, has a wider range of
    applicability and allows pinpointing different stages in the reorientation processes.}
    }
  • [PDF] V. Jansson, E. Baibuz, and F. Djurabekova, "Long-term stability of Cu surface nanotips," Nanotechnology, vol. 27, iss. 26, p. 265708, 2016.
    [Bibtex]
    @article{jansson2016long,
    author={V Jansson and E Baibuz and F Djurabekova},
    title={{Long-term stability of Cu surface nanotips}},
    journal={Nanotechnology},
    volume={27},
    number={26},
    pages={265708},
    archivePrefix = "arXiv",
    eprint = {1508.06870},
    primaryClass = "cond-mat.mtrl-sci",
    url = {http://arxiv.org/abs/1508.06870},
    pdf = {https://arxiv.org/pdf/1508.06870.pdf},
    year={2016},
    project = {CLIC},
    abstract={Sharp nanoscale tips on metal surfaces of electrodes enhance locally applied electric
    fields. Strongly enhanced electric fields trigger electron field emission and atom evaporation
    from the apexes of the nanotips. Combined together, these processes may explain electric
    discharges in form of small local arcs observed near metal surfaces in the presence of electric
    fields even in ultra high vacuum conditions. In the present work we investigate the stability of
    nanoscale tips by means of computer simulations of surface diffusion processes on copper, the
    main material of high voltage electronics.
    We study the stability and life-time of thin copper (Cu) surface nanotips at different temperatures
    in terms of diffusion processes. For this purpose, we have developed a surface Kinetic Monte Carlo
    model where the jump processes are described by tabulated precalculated energy barriers. We show that
    tall surface features with high aspect ratios can be fairly stable at room temperature. However, the
    stability was found to depend strongly on the temperature: 13 nm nanotips with the major axes in the
    <110> crystallographic directions were found to flatten down to half of the original height in less
    than 100 ns at temperatures close to the melting point, whereas no significant change in the height
    of these nanotips was observed after 10 µs at room temperature. Moreover, the nanotips built up along
    the <110> crystallographic directions were found significantly more stable than those oriented in the
    <100> or <111> crystallographic directions.
    The proposed Kinetic Monte Carlo model has been found well suited for simulating atomic surfaces
    processes and was validated against Molecular Dynamic simulation results via the comparison of the
    flattening times obtained by both methods. We also note that the Kinetic Monte Carlo simulations were
    two orders of magnitude computationally faster than the corresponding Molecular Dynamics calculations.}
    }
  • A. Xydou, S. Parviainen, M. Aicheler, and F. Djurabekova, "Thermal stability of interface voids in cu grain boundaries with molecular dynamic simulations," Journal of physics d: applied physics, vol. 49, iss. 35, p. 355303, 2016.
    [Bibtex]
    @article{xydou2016thermal,
    title={Thermal stability of interface voids in Cu grain boundaries with molecular dynamic simulations},
    author={Xydou, A and Parviainen, S and Aicheler, M and Djurabekova, F},
    journal={Journal of Physics D: Applied Physics},
    volume={49},
    number={35},
    pages={355303},
    year={2016},
    publisher={IOP Publishing},
    project = {CLIC}
    }
  • [PDF] J. Zhao, E. Baibuz, J. Vernieres, P. Grammatikopoulos, V. Jansson, M. Nagel, S. Steinhauer, M. Sowwan, A. Kuronen, K. Nordlund, and others, "Formation mechanism of fe nanocubes by magnetron sputtering inert gas condensation," Acs nano, 2016.
    [Bibtex]
    @article{zhao2016formation,
    title={Formation Mechanism of Fe Nanocubes by Magnetron Sputtering Inert Gas Condensation},
    author={Zhao, Junlei and Baibuz, Ekaterina and Vernieres, Jerome and Grammatikopoulos, Panagiotis and Jansson, Ville and Nagel, Morten and Steinhauer, Stephan and Sowwan, Mukhles and Kuronen, Antti and Nordlund, Kai and others},
    journal={ACS nano},
    year={2016},
    publisher={ACS Publications},
    pdf = {http://www.acclab.helsinki.fi/~djurabek/pubs/preprint_Fe_nanocubes_ACSNano.pdf},
    project = {NC},
    url = {http://pubs.acs.org/doi/abs/10.1021/acsnano.6b01024},
    abstract = {In this work, we study the formation mechanisms of iron nanoparticles
    (Fe NPs) grown by magnetron sputtering inert gas condensation and emphasize the
    decisive kinetics effects that give rise specifically to cubic morphologies. Our
    experimental results, as well as computer simulations carried out by two different methods,
    indicate that the cubic shape of Fe NPs is explained by basic differences in the kinetic
    growth modes of {100} and {110} surfaces rather than surface formation energetics. Both
    our experimental and theoretical investigations show that the final shape is defined by
    the combination of the condensation temperature and the rate of atomic deposition onto
    the growing nanocluster. We, thus, construct a comprehensive deposition rate-temperature
    diagram of Fe NP shapes and develop an analytical model that predicts the temporal evolution
    of these properties. Combining the shape diagram and the analytical model, morphological
    control of Fe NPs during formation is feasible; as such, our method proposes a roadmap for
    experimentalists to engineer NPs of desired shapes for targeted applications.}
    }
  • E. Holmstrom, B. Haberl, O. H. Pakarinen, K. Nordlund, F. Djurabekova, R. Arenal, J. S. Williams, J. E. Bradby, T. C. Petersen, and A. Liu, "Diversity in short-to-intermediate range order in pure forms of amorphous silicon generated by a variety of experimental and modeling techniques," Journal of non-crystalline solids, vol. 438, 2016.
    [Bibtex]
    @article{holmstrom2016diversity,
    title={Diversity in short-to-intermediate range order in pure forms of amorphous silicon generated by a variety of experimental and modeling techniques},
    author={Holmstrom, Eero and Haberl, Bianca and Pakarinen, Olli H and Nordlund, Kai and Djurabekova, Flyura and Arenal, Raul and Williams, James S and Bradby, Jodie E and Petersen, Timothy C and Liu, Amelia},
    journal={Journal of Non-Crystalline Solids},
    volume={438},
    year={2016},
    publisher={Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source},
    project = {Si}
    }

2017

  • [DOI] V. Jansson, E. Baibuz, A. Kyritsakis, and F. Djurabekova, "Adatom diffusion in high electric fields," in 2017 30th international vacuum nanoelectronics conference (ivnc), 2017, p. 40–41.
    [Bibtex]
    @InProceedings{jansson2017adatom,
    author = {V Jansson and E Baibuz and A Kyritsakis and F Djurabekova},
    title = {Adatom diffusion in high electric fields},
    booktitle = {2017 30th International Vacuum Nanoelectronics Conference (IVNC)},
    pages = {40--41},
    year = {2017},
    editor = {Christoph Langer and Robert Lawrowski},
    organization = {IEEE},
    isbn = {978-1-5090-3973-9},
    archivePrefix = "arXiv",
    primaryClass = "cond-mat.mtrl-sci",
    eprint = {1608.07537},
    url={https://arxiv.org/abs/1709.04694},
    doi={https://doi.org/10.1109/IVNC.2017.8051541},
    project={CLIC},
    abstract={Strong electric fields are known to create biased adatom migration on metallic
    surfaces. We present a Kinetic Monte Carlo model that can simulate adatom
    migration on a tungsten (W) surface in electric fields. We validate our model by
    using it to calculate the drift velocity of the adatom at different fields and
    temperature and comparing the results with experimental data from the
    literature. We obtain excellent agreement.}
    }
  • [DOI] A. Kyritsakis, M. Veske, F. Djurabekova, and V. Zadin, "Nanotip evaporation under high electric fiele," in 2017 30th international vacuum nanoelectronics conference (ivnc), 2017, p. 38–39.
    [Bibtex]
    @InProceedings{kyritsakis2017nanotip,
    author = {A. Kyritsakis and M. Veske and F. Djurabekova and V. Zadin},
    title = {{Nanotip evaporation under high electric fiele}},
    pages = {38--39},
    booktitle = {2017 30th International Vacuum Nanoelectronics Conference (IVNC)},
    year = {2017},
    editor = {Christoph Langer and Robert Lawrowski},
    organization = {IEEE},
    isbn = {978-1-5090-3973-9},
    doi={10.1109/IVNC.2017.8051540},
    project={CLIC},
    abstract={Vacuum arcing (also known as breakdown), is a major limiting factor in various
    applications such as particle accelerators, fusion reactors etc. Although it is
    well-established that vacuum arcs appear after intense Field electron Emission
    (FE), the physical mechanism that leads from FE to the ignition of plasma is not
    yet understood. A common hypothesis is that intense FE leads to excessive
    heating of the cathode, which causes its deformation, and eventually material
    evaporation and plasma formation. However, this process has never been observed
    experimentally or fully understood theoretically. Here we present atomistic
    simulations of this process that give an insight to it and provide possible
    mechanisms that can explain the initiation of plasma. Our simulations take into
    account various physical processes, namely field-induced stresses, electron
    emission with finite-size and space-charge effects, Nottingham and Joule
    heating. We find that under certain conditions the cathode apex melts and the
    field-induced stress deforms it to become longer and sharper. This initiates a
    positive feedback process that leads to extremely high local temperatures, and
    causes evaporation of material. This mechanism might give a plausible
    explanation to the initiation of plasma.}
    }

2018

  • [DOI] E. Baibuz, S. Vigonski, J. Lahtinen, J. Zhao, V. Jansson, V. Zadin, and F. Djurabekova, "Migration barriers for surface diffusion on a rigid lattice: challenges and solutions," Computational materials science, vol. 146, p. 287–302, 2018.
    [Bibtex]
    @article{baibuz2018migration,
    title={Migration barriers for surface diffusion on a rigid lattice: challenges and solutions},
    author={Baibuz, Ekaterina and Vigonski, Simon and Lahtinen, Jyri and Zhao, Junlei and Jansson, Ville and Zadin, Vahur and Djurabekova, Flyura},
    journal={Computational Materials Science},
    volume={146},
    issue={C},
    pages={287--302},
    url={https://doi.org/10.1016/j.commatsci.2017.12.054},
    doi={https://doi.org/10.1016/j.commatsci.2017.12.054},
    year={2018},
    project={CLIC},
    abstract={Atomistic rigid lattice Kinetic Monte Carlo is an efficient method for
    simulating nano-objects and surfaces at timescales much longer than those
    accessible by molecular dynamics. A laborious part of constructing any Kinetic
    Monte Carlo model is, however, to calculate all migration barriers that are
    needed to give the probabilities for any atom jump event to occur in the
    simulations. One of the common methods of barrier calculations is Nudged Elastic
    Band. The number of barriers needed to fully describe simulated systems is
    typically between hundreds of thousands and millions. Calculations of such a
    large number of barriers of various processes is far from trivial. In this
    paper, we will discuss the challenges arising during barriers calculations on a
    surface and present a systematic and reliable tethering force approach to
    construct a rigid lattice barrier parameterization of face-centred and
    body-centred cubic metal lattices. We have produced several different barrier
    sets for Cu and for Fe that can be used for KMC simulations of processes on
    arbitrarily rough surfaces. The sets are published as Data in Brief articles and
    available for the use.}
    }
  • [DOI] V. Zadin, M. Veske, S. Vigonski, V. Jansson, J. Muszinsky, S. Parviainen, A. Aabloo, and F. Djurabekova, "Simulations of surface stress effects in nanoscale single crystals," Modelling and simulation in materials science and engineering, vol. 26, iss. 73, p. 35006, 2018.
    [Bibtex]
    @article{zadin2018simulations,
    title={Simulations of surface stress effects in nanoscale single crystals},
    author={Zadin, V and Veske, M and Vigonski, S and Jansson, V and Muszinsky, J and Parviainen, S and Aabloo, A and Djurabekova, F},
    journal={Modelling and Simulation in Materials Science and Engineering},
    volume={26},
    number={73},
    pages={035006},
    url={https://arxiv.org/abs/1708.05189},
    doi={https://doi.org/10.1088/1361-651X/aaa928},
    year={2018},
    project={CLIC},
    abstract={Onset of vacuum arcing near a metal surface is often associated with nanoscale
    asperities, which may dynamically appear due to different processes ongoing in
    the surface and subsurface layers in the presence of high electric fields.
    Thermally activated processes, as well as plastic deformation caused by tensile
    stress due to an applied electric field, are usually not accessible by atomistic
    simulations because of the long time needed for these processes to occur. On the
    other hand, finite element methods, able to describe the process of plastic
    deformations in materials at realistic stresses, do not include surface
    properties. The latter are particularly important for the problems where the
    surface plays crucial role in the studied process, as for instance, in the case
    of plastic deformations at a nanovoid. In the current study by means of
    molecular dynamics (MD) and finite element simulations we analyse the stress
    distribution in single crystal copper containing a nanovoid buried deep under
    the surface. We have developed a methodology to incorporate the surface effects
    into the solid mechanics framework by utilizing elastic properties of crystals,
    pre-calculated using MD simulations. The method leads to computationally
    efficient stress calculations and can be easily implemented in commercially
    available finite element software, making it an attractive analysis tool.}
    }
  • [DOI] E. Baibuz, S. Vigonski, J. Lahtinen, J. Zhao, V. Jansson, V. Zadin, and F. Djurabekova, "Data sets of migration barriers for atomistic Kinetic Monte Carlo simulations of Cu self-diffusion via first nearest neighbour atomic jumps," Data in brief, vol. 17, p. 739–743, 2018.
    [Bibtex]
    @article{baibuz2018data,
    author={Ekaterina Baibuz and Simon Vigonski and Jyri Lahtinen and Junlei Zhao and Ville Jansson and Vahur Zadin and Flyura Djurabekova},
    title={{Data sets of migration barriers for atomistic Kinetic Monte Carlo simulations of Cu self-diffusion via first nearest neighbour atomic jumps}},
    journal={Data in Brief},
    volume={17},
    pages={739--743},
    url = {https://doi.org/10.1016/j.dib.2018.01.066},
    doi = {https://doi.org/10.1016/j.dib.2018.01.066},
    year={2018},
    project={CLIC},
    abstract={Atomistic rigid lattice Kinetic Monte Carlo (KMC) is an efficient method for
    simulating nano-objects and surfaces at timescales much longer than those
    accessible by molecular dynamics. A laborious and non-trivial part of
    constructing any KMC model is, however, to calculate all migration barriers that
    are needed to give the probabilities for any atom jump event to occur in the
    simulations. We have calculated three data sets of migration barriers for Cu
    self-diffusion with two different methods. The data sets were specifically
    calculated for rigid lattice KMC simulations of copper self-diffusion on
    arbitrarily rough surfaces, but can be used for KMC simulations of bulk
    diffusion as well.}
    }
  • [DOI] S. Vigonski, V. Jansson, S. Vlassov, B. Polyakov, E. Baibuz, S. Oras, A. Aabloo, F. Djurabekova, and V. Zadin, "Au nanowire junction breakup through surface atom diffusion," Nanotechnology, vol. 29, iss. 1, p. 15704, 2018.
    [Bibtex]
    @article{vigonski2018au,
    author={Simon Vigonski and Ville Jansson and Sergei Vlassov and Boris Polyakov and Ekaterina Baibuz and Sven Oras and Alvo Aabloo and Flyura Djurabekova and Vahur Zadin},
    title={{Au nanowire junction breakup through surface atom diffusion}},
    journal={Nanotechnology},
    volume={29},
    number={1},
    pages={015704},
    archivePrefix = "arXiv",
    eprint = {1709.09104},
    primaryClass = "cond-mat.mtrl-sci",
    url = {http://arxiv.org/abs/1709.09104},
    doi = {https://doi.org/10.1088/1361-6528/aa9a1b},
    year={2018},
    project={CLIC},
    abstract={Metallic nanowires are known to break into shorter fragments due to the Rayleigh
    instability mechanism. This process is strongly accelerated at elevated
    temperatures and can completely hinder the functioning of nanowire-based devices
    like e.g. transparent conductive and flexible coatings. At the same time,
    arranged gold nanodots have important applications in electrochemical sensors.
    In this paper we perform a series of annealing experiments of gold and silver
    nanowires and nanowire junctions at fixed temperatures 473, 673, 873 and 973 K
    (200 °C, 400 °C, 600 °C and 700 °C) during a time period of 10 min. We show that
    nanowires are especially prone to fragmentation around junctions and crossing
    points even at comparatively low temperatures. The fragmentation process is
    highly temperature dependent and the junction region breaks up at a lower
    temperature than a single nanowire. We develop a gold parametrization for
    kinetic Monte Carlo simulations and demonstrate the surface diffusion origin of
    the nanowire junction fragmentation. We show that nanowire fragmentation starts
    at the junctions with high reliability and propose that aligning nanowires in a
    regular grid could be used as a technique for fabricating arrays of nanodots.}
    }
  • [DOI] T. Metspalu, V. Jansson, V. Zadin, K. Avchaciov, K. Nordlund, A. Aabloo, and F. Djurabekova, "Cu self-sputtering MD simulations for 0.1–5 keV ions at elevated temperatures," Nuclear instruments and methods in physics research section b: beam interactions with materials and atoms, vol. 415, iss. {Supplement C}, p. 31–40, 2018.
    [Bibtex]
    @article{metspalu2018cu,
    title = {{Cu self-sputtering MD simulations for 0.1--5 keV ions at elevated temperatures}},
    journal = {Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms},
    volume = {415},
    number = {{Supplement C}},
    pages = {31--40},
    year = {2018},
    issn = {0168-583X},
    doi = {https://doi.org/10.1016/j.nimb.2017.11.001},
    url = {https://arxiv.org/abs/1708.03173},
    archivePrefix = {arXiv},
    primaryClass = {cond-mat.mtrl-sci},
    eprint = {1708.03173},
    author = {Tarvo Metspalu and Ville Jansson and Vahur Zadin and Konstantin Avchaciov and Kai Nordlund and Alvo Aabloo and Flyura Djurabekova},
    project={CLIC},
    abstract={Self-sputtering of copper under high electric fields is considered to contribute
    to plasma buildup during a vacuum breakdown event frequently observed near metal
    surfaces, even in ultra high vacuum condition in different electric devices. In
    this study, by means of molecular dynamics simulations, we analyze the effect of
    surface temperature and morphology on the yield of self-sputtering of copper
    with ion energies of 0.1–5 keV. We analyze all three low-index surfaces of Cu,
    {1 0 0}, {1 1 0} and {1 1 1}, held at different temperatures, 300 K, 500 K and
    1200 K. The surface roughness relief is studied by either varying the angle of
    incidence on flat surfaces, or by using arbitrary roughened surfaces, which
    result in a more natural distribution of surface relief variations. Our
    simulations provide detailed characterization of copper self-sputtering with
    respect to different material temperatures, crystallographic orientations,
    surface roughness, energies, and angles of ion incidence.}
    }