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.
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.
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.
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.
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.
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.
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.
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.
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