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Christoph Dellago - One of the best experts on this subject based on the ideXlab platform.
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cation interstitial diffusion in lead telluride and cadmium telluride studied by means of neural network potential based molecular dynamics simulations
Journal of Physics: Condensed Matter, 2021Co-Authors: Marcin Minkowski, Kerstin Hummer, Christoph DellagoAbstract:Using a recently developed approach to represent ab initio based force fields by a neural network potential, we perform molecular dynamics simulations of lead telluride and cadmium telluride crystals. In particular, we study the diffusion of a single cation interstitial in these two systems. Our simulations indicate that the Interstitials migrate via two distinct mechanisms: through hops between interstitial sites and through exchanges with lattice atoms. We extract activation energies for both of these mechanisms and show how the temperature dependence of the total diffusion coefficient deviates from Arrhenius behaviour. The accuracy of the neural network approach is estimated by comparing the results for three different independently trained potentials.
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cation interstitial diffusion in lead telluride and cadmium telluride studied by means of neural network potential based molecular dynamics simulations
arXiv: Computational Physics, 2020Co-Authors: Marcin Minkowski, Kerstin Hummer, Christoph DellagoAbstract:Using a recently developed approach to represent ab initio based force fields by a neural network potential, we perform molecular dynamics simulations of lead telluride (PbTe) and cadmium telluride (CdTe) crystals. In particular, we study the diffusion of a single cation interstitial in these two systems. Our simulations indicate that the Interstitials migrate via two distinct mechanisms: through hops between interstitial sites and through exchanges with lattice atoms. We extract activation energies for both of these mechanisms and show how the temperature dependence of the total diffusion coefficient deviates from Arrhenius behaviour. The accuracy of the neural network approach is estimated by comparing the results for three different independently trained potentials.
M F Horstemeyer - One of the best experts on this subject based on the ideXlab platform.
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probing grain boundary sink strength at the nanoscale energetics and length scales of vacancy and interstitial absorption by grain boundaries in α fe
Physical Review B, 2012Co-Authors: M A Tschopp, Fei Gao, Xin Sun, Mohammad A. Khaleel, Kiran Solanki, M F HorstemeyerAbstract:The energetics and length scales associated with the interaction between point defects (vacancies and self-interstitial atoms) and grain boundaries in bcc Fe was explored. Molecular statics simulations were used to generate a grain boundary structure database that contained {approx}170 grain boundaries with varying tilt and twist character. Then, vacancy and self-interstitial atom formation energies were calculated at all potential grain boundary sites within 15 {angstrom} of the boundary. The present results provide detailed information about the interaction energies of vacancies and self-interstitial atoms with symmetric tilt grain boundaries in iron and the length scales involved with absorption of these point defects by grain boundaries. Both low- and high-angle grain boundaries were effective sinks for point defects, with a few low-{Sigma} grain boundaries (e.g., the {Sigma}3{l_brace}112{r_brace} twin boundary) that have properties different from the rest. The formation energies depend on both the local atomic structure and the distance from the boundary center. Additionally, the effect of grain boundary energy, disorientation angle, and {Sigma} designation on the boundary sink strength was explored; the strongest correlation occurred between the grain boundary energy and the mean point defect formation energies. Based on point defect binding energies, Interstitials have {approx}80% more grain boundary sites permore » area and {approx}300% greater site strength than vacancies. Last, the absorption length scale of point defects by grain boundaries is over a full lattice unit larger for Interstitials than for vacancies (mean of 6-7 {angstrom} versus 10-11 {angstrom} for vacancies and Interstitials, respectively).« less
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probing grain boundary sink strength at the nanoscale energetics and length scales of vacancy and interstitial absorption by grain boundaries in α fe
Physical Review B, 2012Co-Authors: M A Tschopp, Fei Gao, Xin Sun, Mohammad A. Khaleel, Kiran Solanki, M F HorstemeyerAbstract:The energetics and length scales associated with the interaction between point defects (vacancies and self-interstitial atoms) and grain boundaries in bcc Fe was explored. Molecular statics simulations were used to generate a grain boundary structure database that contained $\ensuremath{\approx}$170 grain boundaries with varying tilt and twist character. Then, vacancy and self-interstitial atom formation energies were calculated at all potential grain boundary sites within 15 \AA{} of the boundary. The present results provide detailed information about the interaction energies of vacancies and self-interstitial atoms with symmetric tilt grain boundaries in iron and the length scales involved with absorption of these point defects by grain boundaries. Both low- and high-angle grain boundaries were effective sinks for point defects, with a few low-$\ensuremath{\Sigma}$ grain boundaries (e.g., the $\ensuremath{\Sigma}3$${112}$ twin boundary) that have properties different from the rest. The formation energies depend on both the local atomic structure and the distance from the boundary center. Additionally, the effect of grain boundary energy, disorientation angle, and $\ensuremath{\Sigma}$ designation on the boundary sink strength was explored; the strongest correlation occurred between the grain boundary energy and the mean point defect formation energies. Based on point defect binding energies, Interstitials have $\ensuremath{\approx}$80$%$ more grain boundary sites per area and $\ensuremath{\approx}$300$%$ greater site strength than vacancies. Last, the absorption length scale of point defects by grain boundaries is over a full lattice unit larger for Interstitials than for vacancies (mean of 6--7 \AA{} versus 10--11 \AA{} for vacancies and Interstitials, respectively).
Fei Gao - One of the best experts on this subject based on the ideXlab platform.
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self healing mechanism of irradiation defects in nickel graphene nanocomposite an energetic and kinetic perspective
Journal of Alloys and Compounds, 2018Co-Authors: Hai Huang, Fei Gao, Xiaobin Tang, Feida Chen, Qing Peng, Xiangyu SunAbstract:Abstract The self-healing mechanism of radiation-induced defects in nickel–graphene nanocomposite is investigated by atomistic simulations. Compared with pure nickel, nickel–graphene nanocomposite has less defects remained in the bulk region after collision cascades, illustrating self-healing performance. Nickel–graphene interfaces (NGIs) serve as sinks for radiation-induced defects and preferentially trap Interstitials over vacancies. Energetic and kinetic calculations reveal that the defect formation energy and diffusion barrier are reduced in the vicinity of NGIs, and the reduction are pronounced for Interstitials. When NGIs are loaded with Interstitials, their segregation ability on radiation-induced defects improves significantly, and the radiation-induced defects near the NGIs diffuse more easily. Especially, the vacancies (or Interstitials) near the NGIs tend to annihilate (or aggregate) with the Interstitials trapped at the NGIs, which only happens at the interstitial-loaded side of NGIs. Therefore, nickel–graphene nanocomposite exhibits excellent radiation tolerance and shows promise as a structural material for advanced nuclear reactors due to its NGIs with the energetic and kinetic driving forces acting on radiation-induced defects.
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probing grain boundary sink strength at the nanoscale energetics and length scales of vacancy and interstitial absorption by grain boundaries in α fe
Physical Review B, 2012Co-Authors: M A Tschopp, Fei Gao, Xin Sun, Mohammad A. Khaleel, Kiran Solanki, M F HorstemeyerAbstract:The energetics and length scales associated with the interaction between point defects (vacancies and self-interstitial atoms) and grain boundaries in bcc Fe was explored. Molecular statics simulations were used to generate a grain boundary structure database that contained {approx}170 grain boundaries with varying tilt and twist character. Then, vacancy and self-interstitial atom formation energies were calculated at all potential grain boundary sites within 15 {angstrom} of the boundary. The present results provide detailed information about the interaction energies of vacancies and self-interstitial atoms with symmetric tilt grain boundaries in iron and the length scales involved with absorption of these point defects by grain boundaries. Both low- and high-angle grain boundaries were effective sinks for point defects, with a few low-{Sigma} grain boundaries (e.g., the {Sigma}3{l_brace}112{r_brace} twin boundary) that have properties different from the rest. The formation energies depend on both the local atomic structure and the distance from the boundary center. Additionally, the effect of grain boundary energy, disorientation angle, and {Sigma} designation on the boundary sink strength was explored; the strongest correlation occurred between the grain boundary energy and the mean point defect formation energies. Based on point defect binding energies, Interstitials have {approx}80% more grain boundary sites permore » area and {approx}300% greater site strength than vacancies. Last, the absorption length scale of point defects by grain boundaries is over a full lattice unit larger for Interstitials than for vacancies (mean of 6-7 {angstrom} versus 10-11 {angstrom} for vacancies and Interstitials, respectively).« less
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probing grain boundary sink strength at the nanoscale energetics and length scales of vacancy and interstitial absorption by grain boundaries in α fe
Physical Review B, 2012Co-Authors: M A Tschopp, Fei Gao, Xin Sun, Mohammad A. Khaleel, Kiran Solanki, M F HorstemeyerAbstract:The energetics and length scales associated with the interaction between point defects (vacancies and self-interstitial atoms) and grain boundaries in bcc Fe was explored. Molecular statics simulations were used to generate a grain boundary structure database that contained $\ensuremath{\approx}$170 grain boundaries with varying tilt and twist character. Then, vacancy and self-interstitial atom formation energies were calculated at all potential grain boundary sites within 15 \AA{} of the boundary. The present results provide detailed information about the interaction energies of vacancies and self-interstitial atoms with symmetric tilt grain boundaries in iron and the length scales involved with absorption of these point defects by grain boundaries. Both low- and high-angle grain boundaries were effective sinks for point defects, with a few low-$\ensuremath{\Sigma}$ grain boundaries (e.g., the $\ensuremath{\Sigma}3$${112}$ twin boundary) that have properties different from the rest. The formation energies depend on both the local atomic structure and the distance from the boundary center. Additionally, the effect of grain boundary energy, disorientation angle, and $\ensuremath{\Sigma}$ designation on the boundary sink strength was explored; the strongest correlation occurred between the grain boundary energy and the mean point defect formation energies. Based on point defect binding energies, Interstitials have $\ensuremath{\approx}$80$%$ more grain boundary sites per area and $\ensuremath{\approx}$300$%$ greater site strength than vacancies. Last, the absorption length scale of point defects by grain boundaries is over a full lattice unit larger for Interstitials than for vacancies (mean of 6--7 \AA{} versus 10--11 \AA{} for vacancies and Interstitials, respectively).
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interaction of helium atoms with edge dislocations in α fe
Journal of Nuclear Materials, 2006Co-Authors: Howard L Heinisch, Fei Gao, Richard J KurtzAbstract:Abstract Formation energies, binding energies, and migration energies of interstitial He atoms in and near the core of an a/2〈1 1 1〉{1 1 0} edge dislocation in α-Fe are determined in atomistic simulations using conjugate gradient relaxation and the Dimer method for determining saddle point energies. Results are compared as a function of the proximity of the He to the dislocation core and the excess interstitial volume in regions around the dislocation. Interstitial He atoms have negative binding energy on the compression side of the dislocation and strong positive binding energy on the tension side. Even at low temperatures, interstitial He atoms in the vicinity of the dislocation easily migrate to the dislocation core, where they form crowdion Interstitials oriented along the close-packed slip direction, with binding energies in excess of 2 eV. Crowdion interstitial He atoms diffuse along the dislocation core, transverse to the crowdion direction, with a migration energy of 0.4–0.5 eV.
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wannier orbitals and bonding properties of interstitial and antisite defects in gan
Applied Physics Letters, 2004Co-Authors: Fei Gao, Eric J Bylaska, Anter Elazab, William J WeberAbstract:Intrinsic interstitial and antisite defects in GaN have been studied using density functional theory (DFT), and their configurations, electronic structures, and bonding properties have been characterized using the Wannier function. All N interstitial configurations eventually transform into N–N split Interstitials, between which two π orbitals exist. The relaxation of a Ga antisite defect also leads to the formation of a N–N split configuration; however, its local Wannier orbitals are remarkably different from the N–N split interstitial. The different local Wannier orbitals around Ga interstitial configurations demonstrate that Ga Interstitials are critical defects in GaN. The most striking feature is that Ga–Ga⟨112¯0⟩ split Interstitials can bridge the gap between nonbonded Ga atoms, thereby leading to a chain of four metallic-like-bonded Ga atoms along the ⟨112¯0⟩ direction in GaN, which may exhibit quantum properties.
Oleg Pankratov - One of the best experts on this subject based on the ideXlab platform.
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Different roles of carbon and silicon Interstitials in the interstitial-mediated boron diffusion in SiC
Physical Review B, 2004Co-Authors: Michel Bockstedte, Alexander Mattausch, Oleg PankratovAbstract:The interstitial and vacancy mediated boron diffusion in silicon carbide is investigated with an ab initio method. The boron Interstitials in $p$-type and $n$-type materials are found to be far more mobile than the boron-vacancy complexes. A kick-out mechanism and an interstitialcy mechanism govern the diffusion in $p$-type/intrinsic and $n$-type material, respectively. A comparison of activation energies demonstrates that the equilibrium diffusion is dominated by the positive hexagonal interstitial for typical experimental conditions. The activation energy and the charge state is in agreement with experimental findings. The analysis of the kick-out reaction demonstrates that silicon and carbon Interstitials have different effects on boron acceptors on the silicon and carbon sublattice (${\mathrm{B}}_{\mathrm{Si}}$ and ${\mathrm{B}}_{\mathrm{C}}$). While silicon Interstitials mediate the diffusion of both acceptors, carbon Interstitials are only relevant for ${\mathrm{B}}_{\mathrm{C}}$. A larger kick-in barrier into silicon sites is found than into carbon sites. This implies a dominant formation of ${\mathrm{B}}_{\mathrm{C}}$ in the extended diffusion tails of boron profiles. The stable boron complexes with carbon or boron Interstitials are found that potentially reduce the boron diffusion. This and the characteristics of the kick-out mechanism facilitate an explanation of recent co-implantation experiments.
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Ab initio study of the annealing of vacancies and Interstitials in cubic SiC: Vacancy-interstitial recombination and aggregation of carbon Interstitials
Physical Review B, 2004Co-Authors: Michel Bockstedte, Alexander Mattausch, Oleg PankratovAbstract:The annealing kinetics of mobile intrinsic defects in cubic SiC is investigated by an ab initio method based on density-functional theory. The interstitial-vacancy recombination, the diffusion of vacancies, and Interstitials to defect sinks ~e.g., surfaces or dislocations! as well as the formation of interstitial clusters are considered. The calculated migration and reaction barriers suggest a hierarchical ordering of competing annealing mechanisms. The higher mobility of carbon and silicon Interstitials as compared to the vacancies drives the annealing mechanisms at lower temperatures including the vacancy-interstitial recombination and the formation of interstitial carbon clusters. These clusters act as a source of carbon interstials at elevated temperatures. In p-type material the transformation of the silicon vacancy into the more stable vacancy-antisite complex constitutes an annealing mechanism which is activated before the vacancy migration. Recent annealing studies of vacancyrelated centers in irradiated 3C-SiC and 4H-SiC and semi-insulating 4H-SiC are interpreted in terms of the proposed hierarchy of annealing mechanisms.
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ab initio study of the migration of intrinsic defects in 3 c sic
Physical Review B, 2003Co-Authors: Michel Bockstedte, Alexander Mattausch, Oleg PankratovAbstract:The diffusion of intrinsic defects in $3C\ensuremath{-}\mathrm{SiC}$ is studied using an ab initio method based on density functional theory. The vacancies are shown to migrate on their own sublattice. The carbon split-Interstitials and the two relevant silicon Interstitials, namely the tetrahedrally carbon-coordinated interstitial and the $〈110〉$-oriented split interstitial, are found to be by far more mobile than the vacancies. The metastability of the silicon vacancy, which transforms into a vacancy-antisite complex in p-type and compensated material, kinetically suppresses its contribution to diffusion processes. The role of Interstitials and vacancies in the self-diffusion is analyzed. Consequences for the dopant diffusion are qualitatively discussed. Our analysis emphasizes the relevance of mechanisms based on silicon and carbon Interstitials.
J M Poate - One of the best experts on this subject based on the ideXlab platform.
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physical mechanisms of transient enhanced dopant diffusion in ion implanted silicon
Journal of Applied Physics, 1997Co-Authors: P A Stolk, H.-j. Gossmann, C. S. Rafferty, H. S. Luftman, D J Eaglesham, D C Jacobson, J M Poate, G H Gilmer, M Jaraiz, T E HaynesAbstract:Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during annealing which arises from the excess Interstitials generated by the implant. In order to study the mechanisms of TED, transmission electron microscopy measurements of implantation damage were combined with B diffusion experiments using doping marker structures grown by molecular-beam epitaxy (MBE). Damage from nonamorphizing Si implants at doses ranging from 5×1012 to 1×1014/cm2 evolves into a distribution of {311} interstitial agglomerates during the initial annealing stages at 670–815 °C. The excess interstitial concentration contained in these defects roughly equals the implanted ion dose, an observation that is corroborated by atomistic Monte Carlo simulations of implantation and annealing processes. The injection of Interstitials from the damage region involves the dissolution of {311} defects during Ostwald ripening with an activation energy of 3.8±0.2 eV. The excess Interstitials drive substitutional B into electric...
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interactions of ion implantation induced Interstitials with boron at high concentrations in silicon
Applied Physics Letters, 1996Co-Authors: T E Haynes, H.-j. Gossmann, P A Stolk, D J Eaglesham, D C Jacobson, J M PoateAbstract:Ion implantation of Si (60 keV, 1×1014/cm2) has been used to introduce excess Interstitials into silicon predoped with high background concentrations of B, which were varied between 1×1018 and 1×1019/cm3. Following post‐implantation annealing at 740 °C for 15 min to allow agglomeration of the available Interstitials into elongated {311} defects, the density of the agglomerated Interstitials was determined by plan‐view transmission electron microscopy observation of the defects. We report a significant reduction in the fraction of excess Interstitials trapped in {311} defects as a function of boron concentration, up to nearly complete disappearance of the {311} defects at boron concentrations of 1×1019/cm3. The reduction of the excess interstitial concentration is interpreted in terms of boron‐interstitial clustering, and implications for transient‐enhanced diffusion of B at high concentrations are discussed.
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carbon incorporation in silicon for suppressing interstitial enhanced boron diffusion
Applied Physics Letters, 1995Co-Authors: P A Stolk, H.-j. Gossmann, D J Eaglesham, J M PoateAbstract:The effect of substitutional C on interstitial‐enhanced B diffusion in Si has been investigated. Substitutional C was incorporated into B doped Si superlattices using molecular‐beam‐epitaxial growth under a background of acetylene gas. Excess Si self‐Interstitials were generated by near‐surface 5×1013/cm2, 40 keV Si implants and diffused at 790 °C. The interstitial‐enhanced diffusion of the B marker layers is fully suppressed for C concentrations of 2×1019/cm3, thus demonstrating that substitutional C acts as a trap for Interstitials in crystalline Si. Uniform C incorporation of 5×1018/cm2 significantly reduces the transient enhanced diffusion of a typical B junction implant without perturbing its electrical activity.
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trap limited interstitial diffusion and enhanced boron clustering in silicon
Applied Physics Letters, 1995Co-Authors: P A Stolk, H.-j. Gossmann, D J Eaglesham, D C Jacobson, J M Poate, H. S. LuftmanAbstract:Boron doped superlattices have been used to detect the diffusion of self‐Interstitials in Si. Interstitials were generated in the near‐surface region by 40 keV Si implantation followed by diffusion at 670–790 °C. The interstitial diffusion profile at 670 °C is stationary for t≤1 h, demonstrating that the penetration depth of Interstitials is limited by trapping. The concentration of traps is estimated to be ∼1017/cm3. For sufficiently long annealing times, Interstitials diffuse beyond the trapping length with an effective trap‐limited diffusivity ranging from ∼6×10−15 cm2/s at 670 °C to ∼1×10−12 cm2/s at 790 °C. The high interstitial supersaturation adjacent to the implant damage drives substitutional B into metastable clusters at concentrations below the B solid solubility limit.
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implantation and transient b diffusion in si the source of the Interstitials
Applied Physics Letters, 1994Co-Authors: D J Eaglesham, H.-j. Gossmann, P A Stolk, J M PoateAbstract:Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during initial annealing, due to Si Interstitials being emitted from the region of the implant damage. The structural source of these Interstitials has not previously been identified. Quantitative transmission electron microscopy measurements of extended defects are used to demonstrate that TED is caused by the emission of Interstitials from specific defects. The defects are rodlike defects running along 〈110〉 directions, which consist of Interstitials precipitating on {311} planes as a single monolayer of hexagonal Si. We correlate the evaporation of {311} defects during annealing at 670 and 815 °C with the length of the diffusion transient, and demonstrate a link between the number of Interstitials emitted by the defects, and the flux of Interstitials driving TED. Thus not only are {311} defects contributing to the interstitial flux, but the contribution attributable to {311} defect evaporation is sufficient to explain the whole ...
