A reactive interatomic bond-order potential for bcc tungsten is presented. Special attention in t... more A reactive interatomic bond-order potential for bcc tungsten is presented. Special attention in the potential development was given for obtaining accurate formation and migration energies for point defects, making the potential useful in atomic scale simulations of point and extended defects. The potential was used to calculate binding energies and trapping distances for vacancies in vacancy clusters and the recombination radius for self-interstitial atom and monovacancy.
A comparative study on the range measurements of keV energy implants by the Time-of-Flight Elasti... more 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 'TN+ ions implanted into crystalline silicon. Range profiles of " N atoms were chosen because they can be measured accurately using a very strong and narrow resonance at Ep = 429.6 keV in the reaction " N(p,ay)'*C 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 keV energy ion range measurements.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2014
The kinetic Monte Carlo method is used to model the dynamic properties of proton diffusion in anh... more The kinetic Monte Carlo method is used to model the dynamic properties of proton diffusion in anhydrous proton conductors. The results have been discussed with reference to a two-step process called the Grotthuss mechanism. There is a widespread belief that this mechanism is responsible for fast proton mobility. We showed in detail that the relative frequency of reorientation and diffusion processes is crucial for the conductivity. Moreover, the current dependence on proton concentration has been analyzed. In order to test our microscopic model the proton transport in polymer electrolyte membranes based on benzimidazole C(7)H(6)N(2) molecules is studied.
An analytical bond-order potential for GaAs is presented, that allows one to model a wide range o... more An analytical bond-order potential for GaAs is presented, that allows one to model a wide range of properties of GaAs compound structures, as well as the pure phases of gallium and arsenide, including nonequilibrium configurations. The functional form is based on the bond-order scheme as devised by Abell-Tersoff and Brenner, while a systematic fitting scheme starting from the Pauling relation is used for determining all adjustable parameters. Reference data were taken from experiments if available, or computed by self-consistent total-energy calculations within the local density-functional theory otherwise. For fitting the parameters, only structural data of the metallic phases of gallium and arsenide as well as those of different GaAs phases were used. A number of tests on point defect properties, surface properties, and melting behavior have been performed afterward in order to validate the accuracy and transferability of the potential model, but were not part of the fitting procedure. While point defect properties and surfaces with low As content are found to be in good agreement with literature data, the description of As-rich surface reconstructions is not satisfactory. In the case of molten GaAs we find support for a structural model based on experiment that indicates a polymerized arsenic phase in the melt.
ABSTRACT We have studied effects of ion irradiation in GaN nanowires using classical molecular dy... more ABSTRACT We have studied effects of ion irradiation in GaN nanowires using classical molecular dynamics simulations. Nanowires with diameters of 3 and 4 nm were irradiated with 100 Ar ions at energies of 100 eV to 10 keV corresponding to ion fluence of about 3×10143×1014 ions/cm2. The structure of the nanowires was analyzed along with sputtering yields and mechanical properties in the form of Young’s modulus. The results show a total sputtering yield of up to 8.3 sputtered atoms per ion and preferential sputtering of nitrogen with gallium to nitrogen ratio approximately 0.7. The Young’s modulus of the nanowires was observed to decrease as a function of the irradiation dose with the largest relative effect observed for ion energies of 1 and 10 keV.
We have studied defect formation and defect distributions in silicon under low-energy ͑25-800 eV͒... more We have studied defect formation and defect distributions in silicon under low-energy ͑25-800 eV͒ selfbombardment of the 2ϫ1 terminated Si͑001͒ 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 (Ͻ400 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 and explored the energy and time dependence of the defect creation mechanisms and the sensitivity of the results to the choice of the model potential.
Atomistic simulations were used to study irradiation effects on photoluminescence (PL) decay time... more 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 (PF 4 ). 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 PF 4 projectile and five individual cascades started by one P and four F single ions (P þ 4 Â 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.
ABSTRACT We studied threshold displacement energies for creating stable Frenkel pairs in silicon ... more ABSTRACT We studied threshold displacement energies for creating stable Frenkel pairs in silicon using density functional theory molecular dynamics simulations. The average threshold energy over all lattice directions was found to be 36{+-}2{sub STAT}{+-}2{sub SYST} eV, and thresholds in the directions <100> and <111> were found to be 20{+-}2{sub SYST} eV and 12.5{+-}1.5{sub SYST} eV, respectively. Moreover, we found that in most studied lattice directions, a bond defect complex is formed with a lower threshold than a Frenkel pair. The average threshold energy for producing either a bond defect or a Frenkel pair was found to be 24{+-}1{sub STAT}{+-}2{sub SYST} eV.
We have analyzed in detail the mechanism leading to tip growth on a surface which operates via nu... more 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.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
We have studied the ion beam -surface interactions with the classical molecular dynamics simulati... more 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 under 50 eV Ga and Ge ions, respectively, were investigated and compared. The defect creation for the GaAs system was found to di er considerably from that of the Ge system. Since Ga, As, and Ge have similar masses this illustrates the importance of chemical e ects on damage production in low-energy ion irradiation.
We have simulated using molecular dynamics the thermal stability and crystallization kinetics of ... more We have simulated using molecular dynamics the thermal stability and crystallization kinetics of nanometre-sized clusters of amorphous Si embedded in crystalline Si, which are of interest for phase-change memory devices. We have calculated the interfacial and bulk excess energies of the amorphous clusters, and studied their crystallization kinetics at 700-1500 K. At temperatures below (above) 1150 K the activation energy is 0.73 ± 0.04 eV (1.52 ± 0.07 eV), indicating a change of mechanism at 1150 K. We predict the stability of much larger amorphous clusters by extrapolating our simulation data using an analytic model.
The radiation spectra of 111In, 113In, and 114mIn are calculated with the Monte Carlo computer pr... more The radiation spectra of 111In, 113In, and 114mIn are calculated with the Monte Carlo computer program IMRDEC. The relaxation probabilities are taken from the EADL file of the Lawrence Livermore National Laboratory. Because this file does not include data for some N and O transitions, these were additionally determined by applying the Kassis rule. Two schemes are applied to calculate the transition energies: 1) a simple (Z + 1)/Z scheme, and 2) accurate calculation solving the relativistic Dirac equations. It is shown that using the extended set of relaxation probabilities leads to generation of many additional low-energy Auger and CK electrons if the (Z + 1)/Z rule is applied. On the other hand, the emissions of almost all these electrons are rejected if their energies are calculated solving the Dirac equations taking into consideration realistic electron vacancies.
We study in detail self-assembled (In,Ga)As quantum dots grown on GaP substrate from the structur... more We study in detail self-assembled (In,Ga)As quantum dots grown on GaP substrate from the structural, theoretical and optical points of view. Single quantum dot morphology is first determined at the atomic level using plane-view scanning tunnelling microscopy. Unusual C 2 symmetry properties with high index {136} facets are demonstrated for small quantum dots, whereas a C 2 to C 2v symmetry transition is observed, with the appearance of low index {111} facets when the quantum dot ripens. This is interpreted as a consequence of the competition between strain and surface energy during quantum dot formation. Electronic properties are then simulated using both k·p and tight-binding models. The indium content and geometry of the quantum dots are found to have a strong influence on the transition type (direct-indirect).
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1996
We present an efficient molecular dynamics method for calculating ion ranges and deposited energi... more We present an efficient molecular dynamics method for calculating ion ranges and deposited energies in the recoil energy region 100 eV to 100 keV. The method overcomes some of the drawbacks of the binary collision approximation methods conventionally used to calculate ion ranges. We describe principles by which one can simulate implantation into polycrystalline materials, and study the effect of the crystal structure on the ion range. Application of the simulation method to practical cases is demonstrated by analyzing experimental range results of 50 keV silicon self-ion-implantation measured at our laboratory.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1996
A comparative study on the range measurements of keV energy implants by the Time-of-Flight Elasti... more 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 'TN+ ions implanted into crystalline silicon. Range profiles of "N atoms were chosen because they can be measured accurately using a very strong and narrow resonance at Ep = 429.6 keV in the reaction "N(p,ay)'*C 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 keV energy ion range measurements.
Single walled carbon nanotubes as all-carbon molecules of tubular form exemplify modern nanometre... more Single walled carbon nanotubes as all-carbon molecules of tubular form exemplify modern nanometre scale material structures, where the number of atoms range from less than a million up to few millions. Such system are quite ideal for computational studies like Molecular Dynamics simulations because the studies can be done at the realistic limit, rendering them in a way predictive. This point of view we try to explore through simulations of novel ring-like carbon nanotubes, observed experimentally. Whether these structures are toroidal or coiled is under debate. To this question we seek insight by studying the structure, the minimum energy configuration, and the thermal stability of large toroidal nanotubes of (n, n)-and (n, 0)-helicity using large scale Molecular Dynamics simulations based on the interaction potential by Brenner. The system sizes of the studied tori range one and half orders of magnitude, in diameter from about 22 nm up to 700 nm, where the latter corresponds to the sizes of experimentally observed ring-like structures. Our simulations indicate that the toroidal form influences strongly the structure of the tubes for small tori while for the larger tori the structural changes are extremely small. We also find that there exists a critical tube radius dependent buckling radius at which the torus buckles. This was also found to be helicity dependent.
Collision cascades in crystalline silicon due to impinging 10eV - 1keV Si atoms are simulated usi... more Collision cascades in crystalline silicon due to impinging 10eV - 1keV Si atoms are simulated using molecular dynamics methods. The simulations are carried out for 30-100 events to obtain representative statistics for production of different types of vacancies. The results are used to examine the dependence of vacancy production on the interatomic Si-Si potential between the colliding atoms. The dependence of the number of vacancies was found to be sensitive to the form of the potential well but not to the repulsive potential. The results suggest that within the heavily damaged volume of the collision cascade an interatomic potential with somewhat narrower well than that of the commonly used Stillinger-Weber potential should be used to simulate the vacancy production in silicon.
The effects of a patterned substrate on island nucleation are investigated using kinetic Monte Ca... more The effects of a patterned substrate on island nucleation are investigated using kinetic Monte Carlo simulations. Two different models are formulated by incorporating an inhomogeneous energy surface into the basic solid-on-solid model of epitaxial growth to describe surface diffusion and consequent island nucleation on a patterned substrate. These models are related to two examples of real systems in which preferential nucleation at specific sites is encountered. Growth on a patterned substrate produces quite uniformly sized islands, which are are found to order into regular arrays displaying the periodicity of the underlying substrate. Confinement due to the patterned substrate is observed to be strongly dependent on the growth conditions. We demonstrate that there exists an optimal set of growth conditions determined by the length scale of the substrate pattern. In addition, the influence of the patterned substrate on the process of Ostwald ripening is discussed.
A reactive interatomic bond-order potential for bcc tungsten is presented. Special attention in t... more A reactive interatomic bond-order potential for bcc tungsten is presented. Special attention in the potential development was given for obtaining accurate formation and migration energies for point defects, making the potential useful in atomic scale simulations of point and extended defects. The potential was used to calculate binding energies and trapping distances for vacancies in vacancy clusters and the recombination radius for self-interstitial atom and monovacancy.
A comparative study on the range measurements of keV energy implants by the Time-of-Flight Elasti... more 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 'TN+ ions implanted into crystalline silicon. Range profiles of " N atoms were chosen because they can be measured accurately using a very strong and narrow resonance at Ep = 429.6 keV in the reaction " N(p,ay)'*C 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 keV energy ion range measurements.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2014
The kinetic Monte Carlo method is used to model the dynamic properties of proton diffusion in anh... more The kinetic Monte Carlo method is used to model the dynamic properties of proton diffusion in anhydrous proton conductors. The results have been discussed with reference to a two-step process called the Grotthuss mechanism. There is a widespread belief that this mechanism is responsible for fast proton mobility. We showed in detail that the relative frequency of reorientation and diffusion processes is crucial for the conductivity. Moreover, the current dependence on proton concentration has been analyzed. In order to test our microscopic model the proton transport in polymer electrolyte membranes based on benzimidazole C(7)H(6)N(2) molecules is studied.
An analytical bond-order potential for GaAs is presented, that allows one to model a wide range o... more An analytical bond-order potential for GaAs is presented, that allows one to model a wide range of properties of GaAs compound structures, as well as the pure phases of gallium and arsenide, including nonequilibrium configurations. The functional form is based on the bond-order scheme as devised by Abell-Tersoff and Brenner, while a systematic fitting scheme starting from the Pauling relation is used for determining all adjustable parameters. Reference data were taken from experiments if available, or computed by self-consistent total-energy calculations within the local density-functional theory otherwise. For fitting the parameters, only structural data of the metallic phases of gallium and arsenide as well as those of different GaAs phases were used. A number of tests on point defect properties, surface properties, and melting behavior have been performed afterward in order to validate the accuracy and transferability of the potential model, but were not part of the fitting procedure. While point defect properties and surfaces with low As content are found to be in good agreement with literature data, the description of As-rich surface reconstructions is not satisfactory. In the case of molten GaAs we find support for a structural model based on experiment that indicates a polymerized arsenic phase in the melt.
ABSTRACT We have studied effects of ion irradiation in GaN nanowires using classical molecular dy... more ABSTRACT We have studied effects of ion irradiation in GaN nanowires using classical molecular dynamics simulations. Nanowires with diameters of 3 and 4 nm were irradiated with 100 Ar ions at energies of 100 eV to 10 keV corresponding to ion fluence of about 3×10143×1014 ions/cm2. The structure of the nanowires was analyzed along with sputtering yields and mechanical properties in the form of Young’s modulus. The results show a total sputtering yield of up to 8.3 sputtered atoms per ion and preferential sputtering of nitrogen with gallium to nitrogen ratio approximately 0.7. The Young’s modulus of the nanowires was observed to decrease as a function of the irradiation dose with the largest relative effect observed for ion energies of 1 and 10 keV.
We have studied defect formation and defect distributions in silicon under low-energy ͑25-800 eV͒... more We have studied defect formation and defect distributions in silicon under low-energy ͑25-800 eV͒ selfbombardment of the 2ϫ1 terminated Si͑001͒ 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 (Ͻ400 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 and explored the energy and time dependence of the defect creation mechanisms and the sensitivity of the results to the choice of the model potential.
Atomistic simulations were used to study irradiation effects on photoluminescence (PL) decay time... more 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 (PF 4 ). 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 PF 4 projectile and five individual cascades started by one P and four F single ions (P þ 4 Â 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.
ABSTRACT We studied threshold displacement energies for creating stable Frenkel pairs in silicon ... more ABSTRACT We studied threshold displacement energies for creating stable Frenkel pairs in silicon using density functional theory molecular dynamics simulations. The average threshold energy over all lattice directions was found to be 36{+-}2{sub STAT}{+-}2{sub SYST} eV, and thresholds in the directions <100> and <111> were found to be 20{+-}2{sub SYST} eV and 12.5{+-}1.5{sub SYST} eV, respectively. Moreover, we found that in most studied lattice directions, a bond defect complex is formed with a lower threshold than a Frenkel pair. The average threshold energy for producing either a bond defect or a Frenkel pair was found to be 24{+-}1{sub STAT}{+-}2{sub SYST} eV.
We have analyzed in detail the mechanism leading to tip growth on a surface which operates via nu... more 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.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
We have studied the ion beam -surface interactions with the classical molecular dynamics simulati... more 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 under 50 eV Ga and Ge ions, respectively, were investigated and compared. The defect creation for the GaAs system was found to di er considerably from that of the Ge system. Since Ga, As, and Ge have similar masses this illustrates the importance of chemical e ects on damage production in low-energy ion irradiation.
We have simulated using molecular dynamics the thermal stability and crystallization kinetics of ... more We have simulated using molecular dynamics the thermal stability and crystallization kinetics of nanometre-sized clusters of amorphous Si embedded in crystalline Si, which are of interest for phase-change memory devices. We have calculated the interfacial and bulk excess energies of the amorphous clusters, and studied their crystallization kinetics at 700-1500 K. At temperatures below (above) 1150 K the activation energy is 0.73 ± 0.04 eV (1.52 ± 0.07 eV), indicating a change of mechanism at 1150 K. We predict the stability of much larger amorphous clusters by extrapolating our simulation data using an analytic model.
The radiation spectra of 111In, 113In, and 114mIn are calculated with the Monte Carlo computer pr... more The radiation spectra of 111In, 113In, and 114mIn are calculated with the Monte Carlo computer program IMRDEC. The relaxation probabilities are taken from the EADL file of the Lawrence Livermore National Laboratory. Because this file does not include data for some N and O transitions, these were additionally determined by applying the Kassis rule. Two schemes are applied to calculate the transition energies: 1) a simple (Z + 1)/Z scheme, and 2) accurate calculation solving the relativistic Dirac equations. It is shown that using the extended set of relaxation probabilities leads to generation of many additional low-energy Auger and CK electrons if the (Z + 1)/Z rule is applied. On the other hand, the emissions of almost all these electrons are rejected if their energies are calculated solving the Dirac equations taking into consideration realistic electron vacancies.
We study in detail self-assembled (In,Ga)As quantum dots grown on GaP substrate from the structur... more We study in detail self-assembled (In,Ga)As quantum dots grown on GaP substrate from the structural, theoretical and optical points of view. Single quantum dot morphology is first determined at the atomic level using plane-view scanning tunnelling microscopy. Unusual C 2 symmetry properties with high index {136} facets are demonstrated for small quantum dots, whereas a C 2 to C 2v symmetry transition is observed, with the appearance of low index {111} facets when the quantum dot ripens. This is interpreted as a consequence of the competition between strain and surface energy during quantum dot formation. Electronic properties are then simulated using both k·p and tight-binding models. The indium content and geometry of the quantum dots are found to have a strong influence on the transition type (direct-indirect).
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1996
We present an efficient molecular dynamics method for calculating ion ranges and deposited energi... more We present an efficient molecular dynamics method for calculating ion ranges and deposited energies in the recoil energy region 100 eV to 100 keV. The method overcomes some of the drawbacks of the binary collision approximation methods conventionally used to calculate ion ranges. We describe principles by which one can simulate implantation into polycrystalline materials, and study the effect of the crystal structure on the ion range. Application of the simulation method to practical cases is demonstrated by analyzing experimental range results of 50 keV silicon self-ion-implantation measured at our laboratory.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1996
A comparative study on the range measurements of keV energy implants by the Time-of-Flight Elasti... more 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 'TN+ ions implanted into crystalline silicon. Range profiles of "N atoms were chosen because they can be measured accurately using a very strong and narrow resonance at Ep = 429.6 keV in the reaction "N(p,ay)'*C 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 keV energy ion range measurements.
Single walled carbon nanotubes as all-carbon molecules of tubular form exemplify modern nanometre... more Single walled carbon nanotubes as all-carbon molecules of tubular form exemplify modern nanometre scale material structures, where the number of atoms range from less than a million up to few millions. Such system are quite ideal for computational studies like Molecular Dynamics simulations because the studies can be done at the realistic limit, rendering them in a way predictive. This point of view we try to explore through simulations of novel ring-like carbon nanotubes, observed experimentally. Whether these structures are toroidal or coiled is under debate. To this question we seek insight by studying the structure, the minimum energy configuration, and the thermal stability of large toroidal nanotubes of (n, n)-and (n, 0)-helicity using large scale Molecular Dynamics simulations based on the interaction potential by Brenner. The system sizes of the studied tori range one and half orders of magnitude, in diameter from about 22 nm up to 700 nm, where the latter corresponds to the sizes of experimentally observed ring-like structures. Our simulations indicate that the toroidal form influences strongly the structure of the tubes for small tori while for the larger tori the structural changes are extremely small. We also find that there exists a critical tube radius dependent buckling radius at which the torus buckles. This was also found to be helicity dependent.
Collision cascades in crystalline silicon due to impinging 10eV - 1keV Si atoms are simulated usi... more Collision cascades in crystalline silicon due to impinging 10eV - 1keV Si atoms are simulated using molecular dynamics methods. The simulations are carried out for 30-100 events to obtain representative statistics for production of different types of vacancies. The results are used to examine the dependence of vacancy production on the interatomic Si-Si potential between the colliding atoms. The dependence of the number of vacancies was found to be sensitive to the form of the potential well but not to the repulsive potential. The results suggest that within the heavily damaged volume of the collision cascade an interatomic potential with somewhat narrower well than that of the commonly used Stillinger-Weber potential should be used to simulate the vacancy production in silicon.
The effects of a patterned substrate on island nucleation are investigated using kinetic Monte Ca... more The effects of a patterned substrate on island nucleation are investigated using kinetic Monte Carlo simulations. Two different models are formulated by incorporating an inhomogeneous energy surface into the basic solid-on-solid model of epitaxial growth to describe surface diffusion and consequent island nucleation on a patterned substrate. These models are related to two examples of real systems in which preferential nucleation at specific sites is encountered. Growth on a patterned substrate produces quite uniformly sized islands, which are are found to order into regular arrays displaying the periodicity of the underlying substrate. Confinement due to the patterned substrate is observed to be strongly dependent on the growth conditions. We demonstrate that there exists an optimal set of growth conditions determined by the length scale of the substrate pattern. In addition, the influence of the patterned substrate on the process of Ostwald ripening is discussed.
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Papers by Antti Kuronen