Complete list of scientific publications
Note: the rest of this page is no longer maintained. The link above has an up-to-date list of all of my publications and links to copies of many of them.
Nanotube pages, with additional preprints
This is a collection of abstracts and preprints of some of my scientific refereed publications (a complete list of publications is found here ).
Note that the material in all publications are copyright either to some publishing company, to the authors, or both. you are not allowed to republish any part of this material in any context without permission. For more legalese, see the end of this page.
I have tried to put here some sort of postscript and PDF version of as many publications as possible; if one is missing, and you can not find the paper in your library, feel free to mail me and ask for a reprint of it. All the full-text files are preprints, and hence differ from the final published version in the layout and possibly slightly in the text. The scientific content is the same in all cases.
Of course, the papers not yet published may still be subject to changes. Furthermore, the layout in the papers here is probably not identical to that in the published paper.
Nucl. Instr. Meth. Phys. Res. B 84 (1994) 105-
Nucl. Instr. Meth. Phys. Res. B 88 (1994) 382-
Phys. Rev. C 50 (1994) 682-
Physica Scripta T54 (1994) 34-
Comp. Mat. Sci. 3 (1995) 448
Nucl. Instr. Meth. Phys. Res B. 115 (1995) 528 (conference paper at ICACS-16).
Phys. Rev. B 52, 15170 (1995)
K. Nordlund: Molecular dynamics simulations of atomic collisions for ion irradiation experiments.
Acta Polytechnica Scandinavica, Applied Physics Series No. 202, Helsinki 1995, 72 pp. Published by the Finnish Academy of Technology, ISBN 951-666-465-2. ISSN 0355-2721.
Available in a separate html document
Nucl. Instr. Meth. Phys. Res. B 111 (1996) 1
Postscript copy of publication, 340 kB, 7 figures, 2 tables.
Phys. Rev. Lett. 77 (1996) 699.
Scanning probe microscopy experiments show
that ion irradiation of (1000) graphite
results in the formation of isolated
defects comprising of a few tens of atoms.
We use molecular dynamics simulations and
density-functional theory
calculations to study the formation probabilities of
these defects.
We identify different defect structures which correspond to
experimentally observed hillocks on graphite surfaces.
We find that the predominant source of defects are
vacancies and interlayer interstitials, and identify
a three-atom carbon ring defect on the graphite surface.
COSIRES '96 conference paper, Rad. Eff. & Def. in Sol. 142 (1996) 450.
A comparative study on the range measurements of keV-energy implants
by the Time-of-Flight Elastic Recoil Detection Analysis (TOF-ERDA)
and conventionally used nuclear resonance reaction methods has been
performed for 20 -- 100-keV 15N+ ions implanted into
crystalline silicon. Range profiles of 15 N atoms were chosen
because they can be measured accurately using a very strong and
narrow resonance at E_p = 429.6 keV in the reaction
15N(p, \alpha \gamma)12C
which provides a challenging
test for other methods. The measured range profiles were simulated
by molecular dynamics calculations where the interatomic N-Si pair
potential is deduced from first principles calculations. The
electronic stopping power for 20 -- 100 keV nitrogen ions in silicon
is deduced from the comparison of the measured and simulated range
profiles. The results are discussed in the framework of the
applicability of the TOF-ERDA technique for range measurements of
keV-energy ions.
Nucl. Instr. Meth. Phys. Res. B 119 (1996) 533
The effect of collision cascades on
pre-existing point defects in crystalline
materials was studied
by simulating 5 keV collision cascades in gold, copper, aluminum,
platinum and silicon.
The results indicate that collision cascades do not significantly
affect interstitials or vacancies outside the liquid core
of the cascade, although
in the FCC metals, the heating of the crystal due to the cascade
causes some thermal migration of the interstitials.
Within the liquid cascade core, both interstitials and vacancies move
towards the center of the molten region when it resolidifies
and recombine or cluster there.
At elevated temperatures, random jumps of
interstitials during the thermal spike phase can cause
significant additional trapping of interstitials in
the liquid.
In contrast to the annealing effects of pre-existing damage in the FCC metals,
in silicon the amount of new damage created by a cascade is
roughly independent of the number of initial point defects.
The difference is attributed to the nature of the bonding in the
materials.
Phys. Rev. B. 56 (1997) 2421
The repulsive part of the interatomic potential affects the outcome of
computer simulations of many irradiation processes of practical interest,
like sputtering and ion irradiation range distributions. The accuracy of
repulsive potentials is studied by comparing potentials calculated using
commonly available density-functional theory and Hartree-Fock methods
to highly accurate fully numerical Hartree-Fock and
Hartree-Fock-Slater calculations.
We find that density-functional-theory calculations utilizing
numerical basis sets and
Hartree-Fock calculations using decontracted standard
basis sets provide repulsive potentials which are significantly
improved compared to the standard
universal ZBL potential. The accuracy of the calculated
potentials is almost totally governed by the quality of the one-particle basis
set. The use of reliable
repulsive potentials open up new avenues for analysis of
ion irradiation experiments.
Nucl. Instr. Meth. Phys. Res. B 132 (1997) 45
Ion beam mixing was investigated in crystalline and amorphous
Si using molecular dynamics simulations. The magnitude of mixing was
found to be larger in amorphous Si by a factor of about two. The
difference is attributed to local relaxation mechanisms occurring
during the cooling down phase of the cascade. Comparison of mixing between
Si and Al shows that short range structural order also has a significant
influence on mixing.
Appl. Phys. Lett. 70 (1997) 3103
Diffuse X-ray scattering is a useful method for studying
defects in silicon and metals. Although the traditional
approaches of analyzing experimental diffuse X-ray scattering
data have given much information about the size of defects and defect
clusters, they are not very well suited for determining the
atomic configuration. We present a fully atomistic
computational method to calculate the diffuse X-ray scattering
line profile of an arbitrary atomic configuration,
and compare line profiles of point defects and Frenkel
pair configurations with experiment.
MRS Spring meeting paper, to be published in Mat. Res. Soc. Symp. Proc. (1997)
We study the mechanisms of damage production during ion irradiation
using molecular dynamics simulations of 400 eV - 10 keV collision cascades in
four different materials. The materials Al, Si, Cu and Ge are contrasted
to each other with respect to the mass, melting temperature
and crystal structure. The results show that the crystal structure
clearly has the strongest effect on the nature of the damage
produced, and elucidate how the open crystal structure affects
the nature of defects produced in silicon.
MRS Spring meeting paper, to be published in Mat. Res. Soc. Symp. Proc. (1997)
Molecular dynamics computer simulations were employed to study
damage production mechanisms at solid surfaces during bombardment
with keV ions. Three separate mechanisms are identified: ballistic damage,
viscous flow, and microexplosions. Ballistic damage is created by the direct
knock-on of atoms onto the surface as described within the binary collision
approximation. Viscous flow refers to local melting and convective mass flow
onto the surface, and microexplosions occur when the high pressures
developed in cascades lead to rupturing of the nearby surface. The
relative importance of each mechanism depends on several parameters:
atomic mass, melting temperature, atomic density, structure and atomic
bonding of the target, and the mass and energy of the projectile.
The simulations were performed for Pt, Au, Cu, Ni and Ge targets.
Cascades in the interior of the targets were also examined to
provide a comparison for the surface events. In addition several
events of 4.5 keV Ne and Xe bombardment of Pt(111) were simulated
for comparison with experimental studies of these same bombardments
using scanning tunneling microscopy.
Phil. Mag. A 79 (1999) 795
We use molecular dynamics simulations and {\it ab initio} calculations to
study the structures and formation probabilities of
isolated surface defects produced
by ion irradiation of (1000) graphite.
We improve the conventionally used Tersoff potential
[J. Tersoff, Phys. Rev. Lett. {\bf 61}, 2879 (1988)] to
realistically describe interlayer forces in graphite and
high-energy processes in carbon.
We identify three defect structures which correspond to
experimentally observed hillocks on graphite surfaces,
and examine their formation at different implantation energies.
Postscript copy of publication, 3 figures, 1 table, 1.25 Mb.
Hillock formation on ion-irradiated graphite surfaces
Preprint of publication, 2.2 Mb, 5 pages, 3 figures.
PDF Preprint of publication, 2.2 Mb, 5 pages, 3 figures.
Comparison of TOF-ERDA and nuclear resonance reaction techniques
for range profile measurements of keV-energy implants
Postscript copy of publication, 396 kb, 9 pages, 9 figures.
PDF copy of publication, 396 kb, 9 pages, 9 figures.
Point defect movement and annealing in collision cascades
Preprint of publication, 1.6 Mb, 12 pages, 16 figures, 1 table.
PDF Preprint of publication, 1.6 Mb, 12 pages, 16 figures, 1 table.
Repulsive interatomic potentials calculated
using Hartree-Fock and density-functional theory methods
Preprint of publication, 0.3 Mb, 8 pages, 3 figures.
PDF Preprint of publication, 0.3 Mb, 8 pages, 3 figures.
Atomic displacement processes in irradiated amorphous and crystalline silicon
Preprint of publication, 0.13 Mb, 3 pages, 3 figures, 2 tables.
PDF Preprint of publication, 0.13 Mb, 3 pages, 3 figures, 2 tables.
Fully atomistic analysis of diffuse X-ray scattering spectra of silicon
defects
Preprint of publication, 0.2 Mb, 6 pages, 3 figures.
PDF Preprint of publication, 0.2 Mb, 6 pages, 3 figures.
Effect of atomic bonding on defect production in
collision cascades.
Preprint of publication, 0.5 Mb, 7 pages, 2 figures, 1 table
PDF Preprint of publication, 0.5 Mb, 7 pages, 2 figures, 1 table
Molecular dynamics investigations of surface damage
produced by keV self-bombardment of solids
Preprint of publication not available
Ion beam mixing was investigated in crystalline and amorphous semiconductors and metals using molecular dynamics simulations. The magnitude of mixing in an amorphous element compared to its crystalline counterpart was found to be larger by a factor of two or more. Mixing in semiconductors was found to be significantly larger than in an FCC metal of corresponding mass and atomic density. The difference in mixing between amorphous and crystalline materials is attributed to local relaxation mechanisms occurring during the cooling down phase of the cascade. Comparison of mixing in semiconductors and metals shows that short range structural order also has a significant influence on mixing. The mixing results in FCC metals indicate that the role of the electron-phonon coupling in the evolution of collision cascades may be less significant than previously thought.
J. Appl. Phys. 83 (1998) 1238
Preprint of publication; 1.0 Mb, 16 figures, 3 tables
PDF Preprint of publication; 1.0 Mb, 16 figures, 3 tables
Molecular dynamics simulations of Large-Angle-Tilt Implanted Drain technology are shown. Calculation results are shown of ion range variation as a function of implant angle over the entire spectrum of possible implant angles. Through this calculation, it is possible to determine the optimal angles for large tilt angle implants. The simulator also allows for the definition of amorphous layers over a crystalline substrate. Results of these calculations accurately predict effects such as paradoxical profile broadening.
Proceedings of the 1997 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD), p. 245
Preprint of publication; 3.0 Mb, 5 figures.
PDF Preprint of publication; 3.0 Mb, 5 figures.
A comparative molecular dynamics simulation study of collision cascades in two elemental semiconductors and five FCC metals is performed to elucidate how different materials characteristics affect primary defect production during ion irradiation. By using simulations of full 400 eV -- 10 keV collision cascades and contrasting the results on different materials to each other, we probe the effect of the mass, melting temperature, material strength and crystal structure on the modification of the material due to the cascade. The results show that the crystal structure has a strong effect on most aspects of damage production, while other material characteristics are of lesser overall importance. In all materials studied, isolated point defects produced by the cascade are predominantly interstitials. In semiconductors, amorphous clusters are produced in the cascade core, whereas in metals most of the crystal regenerates leaving only small vacancy-rich clusters. Large interstitial clusters found in a few events in the heavy metals were observed to form by the isolation of a high-density liquid zone during the recrystallization phase of a cascade.
Phys. Rev. B 57 (1998) 7556.
Preprint of publication; 2.3 Mb, 9 figures, 4 tables.
PDF Preprint of publication; 2.3 Mb, 9 figures, 4 tables.
Auxiliary material: Animations of cascade development
Molecular dynamics (MD) computer simulations of 20 - 30 keV self-ion bombardment of W were performed and compared to past Field Ion Microscopy (FIM) studies [M. I. Current et al., Phil. Mag A 47, 407 (1983)]. The simulations show that the unusually high defect production efficiencies obtained by FIM is a consequence of a surface effect, which greatly enhances defect production compared to that in the crystal interior. Comparison of clustering of vacancies and the formation of interstitial atoms found in the FIM experiments and MD simulations shows overall good agreement.
Phys. Rev. B (brief reports) 57 (1998) 13965.
Preprint of publication; 0.7 Mb, 3 figures, 1 table.
Equilibrium concentrations of self-interstitial atoms and divacancies
have been determined in Cu by molecular dynamics computer simulations
using embedded atom potentials. Near the melting temperature these
concentrations are both $\sim 10^{-6}$. Owing to the higher mobility of
the interstitial atoms, however, they contribute more to diffusion.
In perfect, or pulse-heated crystals, spontaneous Frenkel pair
production results in even higher interstitial concentrations.
Phys. Rev. Lett. 80 (1998) 4201
Electron-phonon coupling in energetic collision cascades
is believed to
greatly enhance the cooling rate of heat spikes in many metals.
Previous studies have not been able to conclusively
determine the magnitude of the coupling, however.
By directly comparing ion beam mixing experiments and molecular dynamics
simulations of collision cascades in Ni, Pd and Pt, metals in which
the coupling is
believed to be most important, we show that the influence of
electron-phonon coupling on mixing can be no more than about
30 %, roughly an order of magnitude less than the most
widely used models predict.
Phys. Rev. B. (Rapid comm.) 57 (1998) 13965
We have studied defect formation and defect distributions in silicon under
low-energy (25 -- 800 eV)
self-bombardment of the $2\times1$ terminated Si (001) surface.
We applied the classical molecular dynamics technique and collected
statistically significant averages to be able to detect defect
production trends
in the energy dependence.
The number of defects created in
implantations was found to be a superlinear function
of energy at low energies ($\le$ 200 eV), and larger than the defect
production in the bulk up to about 1 keV.
We have also examined the depth dependence of close-to-surface
damage, explored the energy and time dependence of the
defect creation mechanisms and the sensitivity of the results to the
choice of the model potential.
Phys. Rev. B 58 (1998) 9907
We examine how channeling effects affect ion implantation depth
profiles in silicon and whether channeling can be beneficial for
achieving a sharp end-of-range in the profile.
Accurate modeling of channeling requires a molecular dynamics program with a
realistic electronic stopping model.
We have implemented the local electronic stopping model originally proposed
by Cai et al. and the Firsov model to describe energy
loss in inelastic collisions between recoiling ions and target atoms.
Simulations of 0.25 - 15 keV B and As ions in the <100>, <110>, <111> and
off-channel directions in silicon show that channeling effects become
unimportant at keV energies in the <100> and <111> directions, whereas
in the <110> channel they persist down to the very lowest
energies.
Implantation into the <100> channel gives optimal sharpness
of the profiles down to implantation depths of roughly 400 Å,
indicating that no tilt is necessary for the very shallow
implants needed in next-generation semiconductors.
Nordic semiconductor conference paper.
Physica Scripta T79 (1998) 272-274.
Diffuse X-ray scattering (DXS) at glancing incidence is a potentially
powerful means for elucidating damage structures in irradiated solids.
Fundamental to the analysis of diffuse X-ray scattering data is a knowledge
of the atomic displacement field around defects, which for implantation
damage in crystals like Si has been difficult to obtain using analytical
solutions of elastic continuum theory. We present a method for predicting
the diffuse scattering pattern by calculating the displacement field around
a defect using fully atomistic simulations and performing discrete sums for
the scattering intensity.
We apply the method to analyze experimental DXS results of defects
produced by 4.5 keV He and 20 keV Ga irradiations of
Si at temperatures of 100~-~300~K.
The results show that the self-interstitial in ion-irradiated Si becomes
mobile around 150 K, and that amorphization of silicon by light and
medium-heavy projectiles occurs homogeneously through the buildup
of interstitial clusters, and not within single cascade events.
EMRS-98 conference paper.
Nucl. Instr. Meth. Phys. Res. B 147 (1999) 399
We study ion beam mixing of metallic bilayer interfaces using
classical molecular dynamics simulations of 5 keV collision
cascades in the vicinity of Co/Cu and Ni/Cu (111) interfaces.
We find that the
production of vacancies and interface roughening is asymmetrical.
On average, more Cu is introduced into the Co or Ni parts than vice versa,
and more vacancies are produced in the Cu, indicative of an inverse
Kirkendall effect in collision cascades. The effect is explained by
the difference in melting points leading to different
recrystallization rates of the two materials.
Phys. Rev. B 59 (1999) 20.
We review some recent simulation results on mechanisms of
damage production close to a surface during ion irradiation.
The simulation work encompasses studies of several metals
and semiconductors at irradiation energies ranging from
a few tens of eV:s to 50 keV. The results show that in dense metals
the presence of a surface can dramatically enhance the damage production up to
energies of at least 50 keV. The added damage is mostly in
the form of vacancy clusters, which can extend quite deep,
~ 10 nm, in the sample. In semiconductors, by contrast, the
surface in general has little effect on the
damage production in bulk.
IBMM-98 conference paper.
Nucl. Instr. Meth. Phys. Res. B 148 (1999) 74.
We have studied the ion-beam - surface interactions with the
classical molecular dynamics simulation method. The properties
of the GaAs (001) surface predicted by the potential model were
investigated. The structure and amount of defects created on the
GaAs (001) and Ge (001) surfaces 50 eV Ga and Ge ions, respectively,
were investigated and compared. The defect creation for the GaAs
system was found to differe considerably from that of the Ge system.
Since Ga, As and Ge have similar masses this illustrates the importance
of chemical effects on damage production in low-energy ion irradiation.
COSIRES '98 conference paper,
Nucl. Instr. Meth. Phys. Res. B. 153 (1999) 209
We have studied atomic mixing in silicon by the classical molecular dynamics
method, and directly compared the simulated data to experimental
measurements. The relative importance of ballistic collisions and
heat spike to the
mixing is considered. We obtain a
fairly good agreement between experiments and
simulations. The heat spike contribution to the total
mixing seems to be much lower than that of ballistic collisions.
COSIRES '98 conference paper, Nucl. Instr. Meth. Phys. Res. B. 153 (1999) 378-382
Using molecular dynamics simulations of collision cascades,
we examine point defect and defect cluster formation
mechanisms in metals and semiconductors.
In metals we find that the primary mechanism causing separation of
interstitials and vacancies is the pushing of vacancies toward
the cascade center during the cooling phase of the cascade.
We further describe how the isolation of a part of
the liquid formed in the cascade can lead to the formation
of interstitial clusters in metals.
By comparing ballistically similar pairs
of metals and semiconductors like Al and Si and Cu and Ge,
we deduce how the cascade behaviour
depend on the nature of interatomic bonding and crystal structure.
We also find that close to sharp interfaces
of metals with different melting points the ``vacancy push''
mechanism can lead to most vacancies being pushed to
one of the materials, and an asymmetry in the impurity
introduction over the interface owing to an inverse Kirkendall effect.
Spain metals irradiation workshop paper,
J. Nucl. Mater. 276 (2000) 194.
One of the central outstanding questions in radiation damage is
how stacking fault tetrahedra (SFT's) can be formed below the vacancy
migration temperature.
Using molecular dynamics simulations of energetic collision
cascades we now describe how a stacking fault tetrahedron
can be created directly in a collision cascade.
We also show that while the number of
SFT's is small at low temperatures, at elevated temperatures the
number will increase by rearrangement of complex
damage clusters into SFT's, in good agreement with experiments.
Appl. Phys. Lett. 74 (1999) 2720
Metal nanoparticles can display a unique behavior when deposited
on substrates with a significantly lower surface energy .
Co nanoparticles in the 10 nm size regime burrow into clean Cu(100)
and Ag(100) substrates when deposited at 600 K and also assume
the substrate orientation. Deposition at room temperature
fails to show either burrowing or reorientation. Crucial in
understanding these results are the capillary forces and surface
tension associated with a nanoparticle: they must be high
enough to drive atoms away from underneath the cluster.
Phys. Rev. Lett. 83 (1999) 1163.
Ion irradiation is a common technique of materials processing, as well as being relevant to the
radiation damage incurred in nuclear reactors. Early models of the effects of
ion irradiation typically
assumed that particles undergo two-body elastic collisions, like billiard balls colliding in three
dimensions. Later descriptions invoked such phenomena as localization of kinetic energy,
thermalization and localized melting. In all these descriptions, the displacement of atoms is chaotic
in that slight variations in the ion's trajectory produce completely different, unpredictable sets of
atomic displacements. Here we report molecular-dynamics simulations of high-energy
self-bombardment of copper and nickel, in which we see collective displacements of atoms. The
high pressures developed in collision cascades centred well below the surface can cause a coherent
displacement of thousands of atoms, over tens of atomic planes, in a shear-induced slip motion
towards the surface. The mechanism leads to a significant increase in damage production near the
surface, characterized by well-ordered islands of adsorbed atoms. Our findings suggest an
explanation for some features of radiation damage, as well as for differences between ion and
neutron irradiation.
Nature 398, 49 - 51 (1999) © Macmillan Publishers Ltd.
For an accurate prediction of penetration depths of energetic
ions in materials, especially in crystal channels, a
realistic electronic stopping model is needed. Usually simulation codes
employing the binary collision approximation are used and the
electronic stopping is
calculated from either a spherically symmetric or uniform charge distribution.
By using molecular
dynamics and calculating the electronic stopping from a 3D
charge distribution without using any free parameters, we obtain
accurate range distributions on a realistic physical basis.
Our electronic stopping model is based on the
Brandt--Kitagawa (BK) [W. Brandt and M. Kitagawa, Phys. Rev. B
25 5631(1982)] theory,
in which the electronic stopping of a heavy ion is
the electronic stopping of a
proton scaled by the square of the effective charge. We first test the
model for hydrogen, to determine whether or not a basis
exists for the
scaling hypothesis, and then for other ions. The results are compared
with experimental range
profiles and show good agreement, much better than that achieved by using
standard (nonlocal) electronic stopping models. Our model has a sound
physical basis, no free parameters and can be used for all
ion-target--combinations.
Phys. Rev. B 62 (2000) 3109.
Although ion beam mixing has been studied intensively over the
last 20 years, many questions about the fundamental mechanisms
involved during mixing remain unresolved.
We review here recent simulation and experimental work
which provides answers to some of the lingering questions
about mixing in elemental materials.
The results make clear the specific role which thermodynamic material
properties, the nature of atomic bonding and electron-phonon
coupling can have on ion beam mixing.
Agreement obtained by direct comparison of simulated and
experimental mixing coefficients gives confidence in our
results, indicating that the experimental
mixing values in heavy metals can be understood predominantly on the
basis of atomic motion in liquid-like zones, and that the role of the
electron-phonon coupling on ion beam mixing is much smaller than previously
thought.
ICACS-18 conference paper, Nucl. Instr. Meth. Phys. Res. B 164-165 (2000) 441
Variable-temperature scanning tunneling microscopy is used to characterize surface defects created by 4.5 keV He ion bombardment of Si(001) at 80-294 K; surface defects are created directly by ion bombardment and by diffusion of bulk defects to the surface. The heights and areal densities of adatoms, dimers, and
adatom clusters at 80 and 130 K are approximately independent of temperature and in reasonable agreement with molecular dynamics calculations of adatom
production. At 180 K, the areal density of these surface features is enhanced by a factor of ~3. This experimental result is explained by the migration and surface
trapping of bulk interstitials formed within ~2 nm of the surface.
Phys. Rev. Lett. 83 (1999) p. 4788-4791
The erosion of carbon by intensive hydrogen bombardment has been recently
shown to decrease sharply at very high fluxes
(~ 1019 ions/cm2s). This effect can not be explained by standard
sputtering or erosion models, yet understanding it is central for
selection of fusion reactor divertor materials,
and formulation of sputtering models for high-flux conditions.
Using molecular dynamics computer simulations we now show that the
effect is due to the buildup of a high hydrogen content
at the surface, leading to a shielding of carbon atoms
by the hydrogen.
Phys. Rev. B (Rapid commun.) 60 (1999) 14005.
Since extrinsic stacking faults can form during post-implantation
annealing of Si, understanding their properties is important for
reliable control of semiconductor manufacturing processes.
We demonstrate how grazing-incidence X-ray scattering methods
can be used as a non-destructive means for detecting extrinsic stacking
faults in Si. Atomistic analysis of diffuse intensity streaks is
used to determine the size of the faults, the
minimum size at which the streak pattern in the scattering will be
visible, and the magnitude of atomic displacements in the center
of the stacking fault.
Appl. Phys. Lett. 76 (2000) 846
Diffuse X-ray scattering is a powerful means to study the
structure of defects in crystalline solids. The
traditional analysis of diffuse X-ray scattering experiments
relies on analytical and numerical methods which are not
well suited for studying complicated defect configurations.
We present here an atomistic simulation method by which
the diffuse X-ray scattering can be calculated for an arbitrary
finite-sized defect in any material where reliable interatomic
force models exist. We present results of the method for point
defects, defect clusters and dislocations in semiconductors and
metals, and show that surface effects on diffuse scattering,
which might be important for the investigation of shallow
implantation damage, will be negligible in most practical cases.
We also compare the results with
X-ray experiments on defects in semiconductors to demonstrate
how the method can be used to understand complex damage configurations.
J. Appl. Phys. 88 (2000) 2278-.
By using classical molecular dynamics
technique we have simulated the effects of 5 keV Xe atoms impinging
on the strained Ge(100)2x1 surface. We found that large adatom
islands are formed on top of the amorphous zones created by the
cascades. We also found that lattice atoms around the molten zone move
radially inwards and thus cause strain relief in the sample.
ICACS-18 conference paper,
Nucl. Instr. Meth. Phys. Res. B 164-165 (2000) 482
We use molecular dynamics
computer simulations to study the damage production by collision
cascades at Si/Ge and AlAs/GaAs and InAs/GaAs interfaces.
For the arsenide systems we find that present interatomic
potentials have troubles in describing even the basic elastic
and melting properties.
We report parameter refinements which give a significantly
better description of these properties.
Our results for collision cascades at strained semiconductor
interfaces show a strong asymmetry in the distribution of
vacancies and impurities produced at the interface.
The effect is explained as a strain-induced effect
analogous to the classical Kirkendall effect.
We also show that although the chemical composition
of compound semiconductors does not strongly affect the overall
evolution of collision cascades, the composition
may in some cases have a significant effect on
the final distribution of defects.
Comput. Mater. Sci. (2000) 18 (2000) 283.
While the physical sputtering of atoms caused by
keV and MeV ions has been studied extensively both
by MD simulation and experiments, the mechanisms
leading to atom and molecule erosion
at energies $\sim 1 - 100$~eV are not very
well understood.
We now describe how
low-energy hydrogen ions can cause erosion of carbon atoms and
hydrocarbon molecules by entering the region of a carbon-carbon
chemical bond and hence breaking it, a process
we call ``swift chemical sputtering''.
In the particular case of hydrogen bombardment of
carbon-based materials, we further show that this can lead to
erosion yields far exceeding those expected for a
physical sputtering process.
COSIRES 2000 conference paper, Nucl. Instr. Meth. Phys. Res. B 180 (2001) 77.
Energetic ions are known to be able to erode atoms from a solid
even when a collisional mechanism can not transfer enough kinetic
energy from the impinging ions to substrate atoms to overcome
the surface binding energy.
We now describe how low-energy ions can cause erosion of atoms and molecules
by colliding with and breaking chemical bonds between the
atoms. In the particular case of hydrogen bombardment of
amorphous carbon networks, we further show that this can lead to
erosion yields far exceeding those expected for a collisional process alone.
Europhys. Lett. 52 (2000) 504.
The properties of self-interstitial defects in ion-irradiated Si were
investigated using in situ grazing
incidence diffuse x-ray scattering. Comparison of defect structures produced
by 4.5 keV He ions
with those produced by MeV electrons reveals that the migration of
interstitials below 10 K is
induced by electron excitation. Annealing studies showed, moreover, that the
thermal migration of
interstitials occurs between 80 K and 170 K, while vacancies become mobile
at higher temperatures.
Phys. Rev. B 64 (2002) 235207
Ion bombardment of carbon materials is known to cause
erosion with energies far below the threshold energy of physical
sputtering, as well as at temperatures below the threshold of thermal
desorption. Generally regarded as chemical sputtering, this effect and
factors contributing to it, are not well understood.
We use classical molecular dynamics simulations, capable of
realistically describing bond formation and breaking, to study
amorphous hydrogenated carbon surfaces under low-energy hydrogen bombardment.
We present a swift chemical sputtering mechanism which can explain
the experimentally observed characteristics of erosion by low-energy
ion irradiation.
We also show how the difference in the surface hydrogen concentration
and carbon coordination fractions at various temperatures affect
the carbon sputtering yield.
Phys. Rev. B. 63 (2001) 195415
Predicting range profiles of low-energy (0.1 - 10 keV/amu)
ions implanted in materials is a long-standing
problem of considerable theoretical and practical interest.
We combine here the best available method for treating
the nuclear slowing down, namely a molecular dynamics
range calculation method, with a method based on
density-functional-theory to calculate electronic slowing down for
each ion-target atom pair separately. Calculation of
range profiles of technologically important dopants in Si
shows that the method is of comparable accuracy to
previous methods for B, P and As implantation of Si, and clearly
more accurate for Al implantation of Si.
Phys. Rev. B. 63 (2001) 134113
It has long been clear that vacancies are usually the most abundant defect
in equilibrium in most dense, close-packed metals.
However, some important effects, such as the observed deviation of
the diffusion coefficient from pure Arrhenius behaviour, can not
be explained by invoking only a single vacancy.
The most common explanation to the deviations is that also divacancies,
and possibly even trivacancies, play a significant role. However,
some evidence also indicate that interstitials could play
a significant role. In this article, we review some
recent work and our computer simulation results on this issue.
Both the reviewed work and simulations point in the direction
that the interstitial could be of major importance close
to the melting temperature and during rapid heating.
The results also strongly support the Granato model of
liquids and solids.
Defect and Diffusion in Metals - Annual Retrospective 2000
( invited review paper )
Preprint of publication not available, but see the PRL
on the same topic.
Defect formation in compound semiconductors such as GaAs under
ion irradiation is not as well understood as in
of Si and Ge. We show here how a combination of ion range
calculations and molecular dynamics computer simulations
can be used to predict the atomic-level
damage structures produced by MeV ions. The results show
that the majority of damage produced in GaAs both by
low-energy self-recoils and 6 MeV He ions is in clusters,
and that a clear majority of the isolated defects are interstitials.
Implications of the results to
suggested applications are also discussed.
J. Appl. Phys. 90 (2000) 1710.
Recent experiments on irradiated carbon nanotubes evidence that ion
bombardment gives rise to their amorphization and dramatic
dimensional changes. Using an empirical potential along with
molecular dynamics,
we study structure and formation probabilities of atomic-scale
defects produced by low-dose irradiation of nanotubes with Ar ions.
For this, we simulate impact events over a wide energy range of
incident ions. We show that the maximum damage production occurs
for a bombarding ion energy of about 600 eV, and that the most
common defects produced at all energies are vacancies, which at low
temperatures are metastable but long-lived defects. Employing the
tight-binding Green's function technique, we also calculate STM
images of irradiated nanotubes. We demonstrate that
irradiation-induced defects may be detected by STM and that
isolated vacancies may look like bright spots in
atomically-resolved STM images of irradiated nanotubes.
Phys. Rev. B. 63 (2001) 245405
It has recently become clear that electron irradiation
can recrystallise amorphous zones in semiconductors
even at very low temperatures, and even when
the electron beam energy is so low that it
can not induce atomic displacements by ballistic collisions.
We study the mechanism of this effect
using classical molecular dynamics augmented with
models describing the breaking of covalent bonds induced
by electronic excitations.
We show that the bond-breaking allows geometric rearrangement
at the crystal-amorphous interface which can induce recrystallisation
in silicon without any thermal activation.
Phys. Rev. B 64 (2001) 125313
We are studying ion irradiation induced
amorphization in Si, Ge and GaAs using molecular
dynamics simulations.
Although high-energy recoils produce defects and amorphous
pockets, we show that low-energy recoils (about 5 - 10 eV)
can lead to a significant component of athermal recrystallization
of pre-existing damage. For typical experimental
irradiation conditions this recrystallization is, however, not sufficient
to fully recrystallize larger amorphous
pockets, which grow and induce full amorphization.
We also examine the coordination and topological defect
structures in Si, Ge and GaAs observed in the simulations, and find that
these structures can explain some experimentally
observed features found in amorphous semiconductors. For irradiated
amorphous GaAs, we suggest that long (about 2.8 Å) and weak Ga-Ga bonds,
also present in pure Ga, are produced during irradiation.
Phys. Rev. B 65 (2002) 165329
Using classical molecular-dynamics simulations we examine the formation of craters during 0.4-100-keV Xe bombardment of Au. Our simulation results, and comparison with experiments
and simulations of other groups, are used to examine to what extent analytical models can be used to predict the size and properties of craters. We do not obtain a fully predictive analytical
model (with no fitting parameters) for the cratering probability, because of the difficulty in predicting the probability of cascades splitting into subcascades, and the relation of the heat spike
lifetime and energy density. We do, however, demonstrate that the dependence of the crater size on the incident ion energy can be well understood qualitatively in terms of the lifetime of the
heat spike and the cohesive energy of the material. We also show that a simple energy density criterion cannot be used to predict cratering in a wide ion energy range because of the
important role of the heat spike lifetime in high-energy cascades. The cohesive energy dependence differs from that obtained for macroscopic cratering (observed, e.g., in astrophysics)
because of the crucial role of melting in the development of heat spikes.
Phys. Rev. B, 64, 235426 (2001)
Using empirical-potential and tight-binding models, we study the
structure and stability of atomic-scale irradiation-induced defects
on walls of carbon nanotubes. Since atomic vacancies are the most
prolific but metastable defects which appear under low-dose, low
temperature ion irradiation, we model the temporal evolution of
single vacancies and vacancy-related defects (which isolated
vacancies can turn into) and calculate their lifetimes at various
temperatures. We further simulate scanning-tunneling microscopy
(STM) images of irradiated nanotubes with the defects, employing
for this the tight-binding Green's function technique. Our
simulations demonstrate that the defects live long enough at low
temperatures to be detected by STM and that different defects
manifest themselves in STM images in different ways, all of which
makes it possible to detect and distinguish the defects
experimentally.
J. Vac. Sci. Techn. 20 (2001) 728.
311 defects are extended, rod-like defects which play a
central role in the processing of Si during integrated circuit
manufacturing. Diffuse x-ray scattering techniques provide a non-destructive
means to detect defects in solids. However, to date there
has been no knowledge of what the x-ray scattering pattern
from 311 defects looks like.
Using a recently introduced fully atomistic modeling
scheme, I calculate the diffuse x-ray scattering patterns from
311 defects. The results demonstrate how
311 defects can be detected, how the main varieties of
311 defect can be distinguished, and how both the defect
width and length can be derived from the scattering.
J. Appl. Phys. 91 (2002) 2978
Molecular dynamics has been successful in predicting range profiles
for ions implanted into crystalline materials in the dose regime where
it can be approximated that changes in the sample structure do not
affect the profiles. Many experimental distributions are, however,
strongly dose-dependent due to the amorphization of the crystalline
material. This has so far been taken into account only in some
binary-collision-approximation calculations with a damage build-up
model that depends on the probability for the amorphization to occur
at a certain depth. We present here a fast molecular dynamics model
for predicting range profiles of ions in crystalline Si. The model
includes cumulative damage build-up, where the amorphization states
are taken from molecular dynamics simulations of cascade damage. The
method can be used to predict profiles for any material. We used
silicon because of the large amount of experimental data available. No
free parameters were used. Comparison of results to a wide range of
experiments show very good agreement.
Nucl. Instr. Meth. Phys. Res. B. 195 (2002) 269-280
Ion irradiation of individual carbon nanotubes deposited on
substrates may be used for making metallic nanowires and
studying effects of disorder on the electronic transport in low-dimensional
systems. In order to understand the basic physical mechanisms of
radiation damage production in supported nanotubes, we employ
molecular dynamics and simulate ion impacts on nanotubes lying on
different substrates, such as platinum and graphite. We show that
the defect production depends on the type of
the substrate and the damage is higher for metallic heavy-atom
substrates than for light-atom substrates, since
in the former case sputtered metal atoms and backscattered recoils
produce extra damage in the nanotube. We further study the behavior
of defects upon high-temperature annealing and demonstrate
that, although ions may
severely damage nanotubes in a local region, the nanotube carbon
network has a unique ability to heal such a strong localized damage
due to defect migration and dangling bond saturation. We
also show that after annealing the residual damage in nanotubes
is independent of the substrate type. We predict pinning of
nanotubes to substrates through nanotube-substrate bonds which
appear near irradiation-induced defects.
Phys. Rev. B 65 (2002) 164523.
Employing both quantum-mechanical and empirical force models, we
use molecular dynamics simulations to obtain
sticking cross-sections for CH3 radical chemisorption on
unsaturated sites on carbon surfaces. Effects of
the local atomic neighbourhood on the chemisorption were examined in
order to compare the results with experiments. Our results show that
the chemisorption of a CH3 radical onto a dangling bond is highly
affected by the neighbourhood of the unsaturated carbon atom sites.
Notably, sticking cross sections of totally bare dangling bond sites
at the surface and sites partly shielded by neighbouring methyl groups
were observed to differ by two orders of magnitude, (15.3 ± 1.7)
Å2 and (0.2 ± 0.1) Å2, respectively.
J. Appl. Phys. 93, 1826 (2003)
Doping is a widely used method to enhance the properties of
materials. Despite the recently increased understanding of the
mechanisms of chemical erosion by low-energy hydrogen ions, the effect of
doping on these types of processes is still not well understood. We
study the erosion of Si-doped (0 -- 30 at.\%) carbon under 20 eV
deuterium irradiation using molecular dynamics simulations.
We show that the chemical sputtering of carbon decreases with
increasing Si concentration. The reasons for the reduced sputtering
yield lie in the longer Si--C interaction lengths and efficient
dynamic rebonding of hydrocarbon species.
J. Appl. Phys. 92 (2002) 2216
Molecular dynamics has proven to be succesful in calculating range
profiles for low energy (keV) ions implanted into crystalline
materials. However, for high fluences the structure of the material
changes during the impl antation process. The crystalline material
becomes amorphized, which changes the range profiles. This damage
build-up process has usually been taken into account with
probabilities for changing the crystal structure during the
simulation, and typically only BCA methods have been used. We present
a fast MD method that simulates the damage build-up process in
silicon, without bringing any free parameters to the simulation. Dama
ge accumulation during the implantation is simulated by changing the
material structure in front of path of the incoming ion. The
amorphization l evel at each depth is proportional to the nuclear
deposited energy in that depth region. The amorphization states are
obtained from MD simulations of cascade dam age. Silicon was used as a
target material because of the large amount of experimental data
available. Comparison with the simulations show a go od agreement for
a wide range of experiments.
Nucl. Instr. Meth. Phys. Res. B 202 (2003) 132.
Using classical molecular dynamics method we have studied the burrowing mechanis
m of Co nanoclusters on a Cu substrate. We found that
there are primarily two different mechanisms for the burrowing, depending on the
configuration of the cluster after thermal deposition. Deposited
clusters with an epitaxial configuration will burrow through vacancy migration a
long the Co-Cu interface, and non-aligned clusters
burrow through disordered motion of atoms. The re-alignment of the non-aligned c
lusters was found to be due to a collective rotational
movement of the whole cluster during the burrowing process. We discuss these res
ults and perform a comparison with experimental
and previously simulated results.
Phys. Rev. B 67 (2002) 075415
Recent experiments have shown that when gold atom clusters
bombard copper with an energy of 10 keV/atom,
the mean range of the gold atoms is independent
of the cluster size, but the straggling (broadening) of the depth
distribution is an increasing function of the cluster size. The same
set of experiments did not show this effect when the target was amorphous Si.
Using molecular dynamics computer simulations we have studied this effect
by simulating Au cluster bombardment of Cu and Si with energies
1 -- 10 keV/atom. We
found that in Cu, the mean range is not fully independent of the
cluster size, but the dependence on cluster size is so weak it is
hard to observe experimentally. On the other hand, we
found a strong enhancement of the straggling in Cu, but not Si,
in agreement with the experiments. By following the time
dependence of the straggling we show that this is due to the massive
heat spike effects which are present in Cu but not Si.
Phys. Rev. B 68 (2003) 035419
Recent experiments on ion irradiation of heavy metals such as
gold and silver have shown that very unusual surface configurations
can be produced by the irradiation. Typically, the surface
damage has the shape of a crater, similar to those
produced by meteorite impacts. The crater shapes are, however,
often highly asymmetric and can show extended
adatom ridges extending far from the crater well.
Using molecular dynamics simulations we show how such
exotic atom arrangements are produced. We describe
atomic bridges over a crater and
illustrate a slingshot-like effect which can propel
atom clusters far from an impact position to
produce isolated adatom islands.
Nucl. Instr. Meth. Phys. Res. B 206, 189 (2003).
An analytical bond-order potential for GaN is presented that describes a
wide range of structural
properties of GaN as well as bonding and structure of the pure constituents.
For the systematic fit of the potential parameters reference data are taken
from total energy calculations within the
density functional theory if not available from experiments.
Although long-range interactions are not explicitly included in the potential,
the present model provides a good fit to different structural geometries
including defects and high pressure phases of GaN.
Journal of Physics: Condensed Matter 15 (2003) 5649.
Non-molecular solid nitrogen, metastable
even at zero pressure and low temperature, was recently
manufactured by Eremets et al. [Nature 411 (2001) 173]
and investigated with respect to its pressure stability.
In this study we present analytical potential molecular dynamics simulations
that allow reproducing all the stages of the experiment.
The bonding structure and energetics of the N polymeric state
obtained from the dynamical simulations are verified to be
reasonable using a plane wave {\it ab initio} method.
We predict that the metastable low-pressure phase has
predominantly 3-folded bonded atoms in a disordered configuration.
The energy accumulated in the metastable phase is
about 1 eV/atom.
Europhysics Letters 65 (2004) 400
Recent experiments have shown that when gold atom clusters
bombard copper with an energy of 10 keV/atom,
the mean range of the gold atoms is independent
of the cluster size, but the straggling (broadening) of the depth
distribution is an increasing function of the cluster size. The same
set of experiments did not show this effect when the target was amorphous Si.
Using molecular dynamics computer simulations we have studied this effect
by simulating Au cluster bombardment of Cu and Si with energies
1 -- 10 keV/atom. We
found that in Cu, the mean range is not fully independent of the
cluster size, but the dependence on cluster size is so weak it is
hard to observe experimentally. On the other hand, we
found a strong enhancement of the straggling in Cu, but not Si,
in agreement with the experiments. By following the time
dependence of the straggling we show that this is due to the massive
heat spike effects which are present in Cu but not Si.
Phys. Rev. B 68, 035419 (2003).
We have used molecular dynamics methods to study the accumulation of damage d
uring ion beam irradiation of GaN. First we
analyzed individual recoils between 200 eV and 10 keV. We found that the spatial
average of the threshold displacement
energy was high and much less damage was produced in GaN than in Si, Ge or GaAs
cascades.
Most of the damage was in isolated point defects or small clusters, which enhanc
es the damage recombination probability.
Ion beam amorphization was simulated by starting successive 400 eV or 5 keV reco
ils
in initially perfect crystal. The development of volume, energy and ring statist
ics,
as well as segregation of compounds was followed through the process. The simul
ations show that the amorphization
begins with single defects and formation of long weak Ga-Ga bonds in the distort
ed lattice. We also observe that nitrogen
gas is produced during prolonged irradiation, in agreement
with experimental observations.
We recognize two reasons for the high amorphization dose of GaN, the
high threshold displacement energy (about a factor of 5) and in-cascade recombin
ation (about a factor of 1-2).
Phys. Rev. B 68, 184104 (2003)
Using molecular dynamics simulations combined with kinetic Monte Carlo methods w
e have studied the evolution of copper nanoclusters on a copper (100) surface.
We have developed a method for relaxing the clusters into a suitable configurati
on for input into the kinetic Monte Carlo method using molecular dynamics.
Using kinetic Monte Carlo methods we have simulated the evolution of clusters wi
th sizes of 22 -- 2045 atoms at temperatures of 220 -- 1020 K.
We found that the Cu clusters on the surface will be reduced to one monolayer if
given enough time to relax, and that this process shows an Arrhenius behaviour.
In this article we present the relaxation method we developed and our observatio
ns for the evolution of the clusters.
Journal of Physics: Condensed Matter (2004), accepted for publication
Using molecular dynamics simulations and the Embedded Atom Method (EAM)
potential we have investigated the sputtered atom clusters produced by
15 keV xenon impacts on silver and 20 keV xenon impacts on gold.
Ejected clusters were simulated for long times, up to 0.01 - 1 microseconds,
in order to investigate the fragmentation of nascent clusters.
The size distributions of nascent and final clusters were calculated
and fitted to an inverse power law, resulting in exponents close to 2 and 3,
depending on the range of the cluster sizes used. These values are in
agreement with other simulations and experiments.
The results show that clusters are subject to a dramatic breakup, which
makes the size of the largest sputtered cluster go down by a factor of 2-4.
Despite this, the exponent in the power law does not change very much
from the size distribution of nascent to that of final clusters.
Considering the uncertainties, the exponent of the final size
distribution is 1.0-1.7 times the exponent of the nascent size distribution.
Physical Review B, accepted for publication
We employ a theoretical model to calculate mechanical
characteristics of macroscopic mats and fibers of single-walled
carbon nanotubes. We further investigate irradiation-induced
covalent bonds between nanotubes and their effects on
the tensile strength of nanotube mats and fibers.
We show that the stiffness and strength of the mats can be
increased at least by an order of magnitude,
and thus small-dose irradiation with energetic particles is
a promising tool for making macroscopic nanotube materials with
excellent mechanical characteristics.
Physical Review Letters 93, 215503 (2004)
A reactive interatomic potential based on an analytic bond-order scheme is devel
oped for the ternary system W-C-H. The
model combines Brenner's hydrocarbon potential with parameter sets for W-W, W-C
and W-H interactions and is adjusted
to materials properties of reference structures with different local atomic coor
dinations including tungsten carbide, W-H molecules
as well as H dissolved in bulk W.
The potential has been tested in various scenarios, like surface, defect, and me
lting properties, none of which were considered in the fitting.
The intended area of application is simulations of hydrogen and hydrocarbon inte
ractions
with tungsten, that have a crucial role in fusion reactor plasma-walls.
Furthermore, this study shows that the angular dependent bond-order scheme can b
e extended to second-nearest neighbour interactions,
which are relevant in bcc metals. Moreover, it provides a possibly general route
for modeling metal carbides.
Journal of Applied Physics, accepted for publication (2005)
We have developed a two-band model of Fe-Cr, fitted to properties of
the ferro-magnetic alloy. Fitting many-body functionals to the
calculated mixing enthalpy of the alloy and the mixed interstitial
binding energy in iron, our potential reproduces changes in sign of
the formation energy as function of Cr concentration. When applied in
Kinetic Monte Carlo simulations, the potential correctly predicts
decomposition of initially random Fe-Cr alloys into the $\alpha$-prime
phase as function of Cr concentration.
Physical Review B 72 (2005) 214119.
Recent work has shown that
atom motion in liquids is not completely
homogeneous, but that stringlike cooperative motion
can be used to explain several properties
of liquids. We now show that with increasing concentration
the properties of interstitial atoms in crystalline materials
smoothly approach
and eventually completely match the properties
of the string atoms in liquids.
In terms of the interstitialcy theory of liquids
and solids, the strings are direct manifestations of
interstitials.
Europhys. Lett. 71 (2005) 625.
Numerous
experiments have shown that low-energy H ions and neutrals can erode
amorphous carbon at ion energies of 1-10 eV, where physical sputtering
is impossible, but at erosion rates which are clearly higher than
those caused by thermal ions. In this paper we will first review our
computer simulation work providing an atom-level mechanism for how
this erosion occurs, and then present some
new results for H and He bombardment of tungsten carbide and amorphous
hydrogenated silicon, which indicate the mechanism can be of
importance in a wide range of covalently bonded materials.
We also discuss how the presented mechanism relates to previously
described abstraction and etching mechanisms.
Pure and Applied Chemistry 78 (2005) 1203-1212
We study the initial state of irradiation damage in WC, an alloy with
a large mass difference between the constituents, using molecular
dynamics computer simulations. We find that a vast majority of the
resulting isolated defects are carbon. Moreover, an in-cascade defect
recombination effect even more pronounced than that known previously
to occur in metals is observed. Both effects are shown to be related
to the high formation energy of W defects.
Phys. Rev. B (Rapid comm.) 74 (2006) 140103
Using large-scale atomistic simulations, we show that the macroscopic
cratering behavior emerges for projectile impacts on Au at projectile sizes
between 1,000--10,0000 Au atoms at impact velocities comparable to typical
meteoroid velocities. In this size regime, we detect the compression of
material in Au nanoparticle impacts similar to that observed for hypervelocity
macroscopic impacts. The simulated crater volumes agree with the values
calculated using the macroscopic crater size scaling law, in spite of a
downwards extrapolation over more than fifteen orders of magnitude in terms of
the impactor volume. The result demonstrate that atomistic simulations can be
used as a tool to understand the strength properties of materials in cases
where only continuum models have been possible before.
Phys. Rev. Lett. 101 (2008) 027601, and cover of issue 2.
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The role of self-interstitial atoms on the high temperature
properties of metals
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Role of electron-phonon coupling on collision cascade development
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Effect of Surface on Defect Creation by Self-ion Bombardment of Si
(001)
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Channeling in Manufacturing Sharp Junctions: a Molecular
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Glancing Incidence Diffuse X-ray Scattering Studies of Implantation
Damage in Si
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Inverse Kirkendall mixing in collision cascades
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Recoils, flows and explosions: surface damage mechanisms in metals
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Defect creation by low-energy ion bombardment on GaAs (001) and
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Heat spike and ballistic phase contribution to mixing in Si
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Collision cascades in metals and semiconductors:
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Burrowing of Co nanoparticles on clean Cu and Ag surfaces
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Coherent displacement of atoms during ion irradiation
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Electronic stopping of Silicon from a 3D Charge Distribution
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Heat spike effects on ion beam mixing
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Surface Defects and Bulk Defect Migration Produced by Ion Bombardment of Si(001)
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Suppression of carbon erosion by hydrogen shielding
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Diffuse X-ray streaks from stacking faults in Si
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Atomistic simulation of diffuse X-ray scattering from
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Strain effects in Ge surface cascades
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Strain-induced Kirkendall mixing at semiconductor interfaces
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Sputtering of hydrocarbons by ion-induced breaking of chemical bonds
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Bond-breaking mechanism of sputtering
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Properties of intrinsic point defects in irradiated Si
Swift chemical sputtering of amorphous hydrogenated carbon
Electronic stopping calculated using explicit phase shift factors
Self-interstitial atoms at high temperatures in dense metals
Defect clustering during ion irradiation of GaAs:
insight from molecular dynamics simulations
Formation of ion irradiation-induced atomic-scale defects on walls
of carbon nanotubes
Mechanism of electron-irradiation induced recrystallisation in Si
Amorphization mechanism and defect
structures in ion beam amorphized Si, Ge and GaAs
Cratering-energy regimes: From linear collision cascades to heat spikes to macroscopic impacts
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Stability of irradiation-induced point defects on walls of carbon
nanotubes
Diffuse x-ray scattering from 311 defects in Si
Effects of damage build-up in range profiles in crystalline Si; molecular dynamics simulations
Production of defects in supported carbon nanotubes under ion irradiation
Molecular dynamics simulations of CH3 sticking on carbon surfaces
Reduced chemical sputtering of carbon by silicon doping
Molecular dynamics simulation method for calculating fluence-dependent
range profiles
Mechanism of Co nanocluster burrowing on (100) Cu surface
Heat spike effect on the straggling of cluster implants
Atomic fingers, bridges and slingshots: formation of exotic
surface structures during ion irradiation of heavy metals
Modelling of compound semiconductors: Analytical bond-order potential for gallium, nitrogen and gallium nitride
Structure and stability of non-molecular nitrogen at
ambient pressure.
Heat spike effect on the straggling of cluster implants
A molecular dynamics study of damage accumulation in GaN during ion beam irradiation
Evolution of Cu nanoclusters on Cu(100)
Fragmentation of clusters sputtered from silver and gold
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Carbon nanotube mats and fibers with irradiation-improved mechanical
characteristics: a theoretical model
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Analytical interatomic potential
for modeling non-equilibrium processes in the W--C--H system
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Two-band model of alpha-prime phase formation in Fe-Cr.
Strings and interstitials in liquids, glasses and crystals
Swift chemical sputtering of covalently bonded materials
Major elemental assymetry and recombination effects in irradiated WC
Atomistic simulation of the transition from
atomistic to macroscopic cratering
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