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Andreas Wucher - One of the best experts on this subject based on the ideXlab platform.
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Formation of excited Ag atoms in sputtering of silver
2020Co-Authors: Z. Šroubek, Andreas Wucher, Filip Sroubek, J A YarmoffAbstract:A model is presented for the formation of excited Ag* (4d 9 5s 2 ) atoms during sputtering of Ag metal by energetic Ar ϩ ions. The essential part of the formation process is the slow diffusion of 4d holes in the Collision Cascade from the sites of violent Ag-Ag Collisions to the emitted Ag atoms. A computer simulation of Ag Cascades and of the 4d-hole transport allows us to quantify the model and to describe all characteristic features of the available experimental data, in particular the fact that the sputtered Ag* atoms exhibit a narrower kinetic energy distribution than those ejected in the electronic ground state
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influence of the polar angle of incidence on electronic substrate excitations in kev self bombardment of solid silver
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2011Co-Authors: S Hanke, A Duvenbeck, B Weidtmann, Andreas WucherAbstract:Abstract We present a computer simulation study on the influence of the polar angle of incidence on electronic substrate excitations in the self-sputtering of silver. For the bombardment of a silver target with 5-keV Ag atoms, we employ a standard molecular dynamics code to follow the microscopic particle dynamics within the atomic Collision Cascade following the primary particle impact. The transfer of kinetic energy of Cascade atoms into the electronic subsystem of the metal is treated in terms of the Lindhard model of electronic stopping and an electron promotion model describing the generation of hot electrons in close binary Collisions. The transport of excitation energy away from the spot of generation is treated in a diffusive manner. The calculations yield a time- and space-dependent excitation energy density E ( r → , t ) that can be converted into an electron temperature profile T e ( r → , t ) . The results of our calculations show an angle-dependent duration of the initial electron temperature peak at the surface which coincides with the time the projectile needs to cross the first layer of the model crystal.
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influence of the polar angle of incidence on secondary ion formation in self sputtering of silver
Surface and Interface Analysis, 2011Co-Authors: B Weidtmann, S Hanke, A Duvenbeck, Andreas WucherAbstract:The influence of the projectile impact angle on secondary ion formation was studied using a computer simulation model applied to the bombardment of an amorphous silver crystal by 5-keV Ag atoms. The model employs a molecular dynamics (MD) scheme for the description of particle dynamics within the atomic Collision Cascade. The electronic degree of freedom is treated within the framework of a free electron gas model incorporating kinetic excitation by electronic friction and electron promotion. Transport of the excitation energy away from the spot of generation is treated by a diffusive approach. In combination with a rate equation model for electronic charge transfer an individual ionization probability a + is assigned to each sputtered particle. The results reveal that the average ionization probability of sputtered atoms increases upon the transition from normal to oblique incidence. The dependence of α + on the emission velocity of ejected atoms is traced back to the temporal structure of the excitation profile induced after projectile impact.
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low energy electronic excitation in atomic Collision Cascades a nonlinear transport model
Physical Review B, 2005Co-Authors: A Duvenbeck, Andreas WucherAbstract:A computer simulation model is presented which allows one to incorporate low-energy electronic excitation into the molecular dynamics computer simulation of atomic Collision Cascades in metals. The model treats the electronic energy losses experienced by all moving atoms as a source term for electronic excitation energy, which is assumed to spread around the original point of excitation with a diffusivity D. In order to acknowledge i the large temperature gradients and ii the local lattice disorder within the Cascade volume, the electronic heat diffusivity is allowed to vary as a function of space and time, thus leading to a strongly nonlinear diffusion of electronic excitation energy. The corresponding diffusion equation is developed and numerically solved for an exemplary Collision Cascade initiated by the impact of a 5 keV silver atom onto an Ag111 surface. It is shown that electron surface temperatures of several thousand kelvin can be reached at times after the impact at which most emission of surface particles occurs. This excitation may therefore influence the ionization or excitation of such sputtered species.
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computer simulation of low energy electronic excitations in atomic Collision Cascades
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2004Co-Authors: A Duvenbeck, Z. Šroubek, Filip Sroubek, Andreas WucherAbstract:We present a computer simulation of low-energy electronic excitations that are created in atomic Collision Cascades initiated by the impact of energetic particles onto a solid surface. In order to render a chemically inert system, the selfbombardment of a silver (1 1 1) surface with Ag atoms is simulated. In the model, the atomic motion following the particle impact is described by a classical molecular dynamics approach. The transfer of kinetic into electronic excitation energy is described in terms of a friction-like electronic energy loss experienced by every moving atom in the solid, thus leading to a space and time dependent density of electron–hole pair excitation energy generated in the course of the Collision Cascade. This energy is assumed to spread around the point of original excitation with a diffusion coefficient D and to equipartition in the Ag sp band according to a Fermi distribution characterized by an electronic temperature Teðr; tÞ. It is shown that for reasonable values of D the electronic energy deposited at the surface can be substantial, thus leading to transient electronic surface temperatures reaching several thousands of Kelvin which, for instance, can influence the ionization probabilities of sputtered atoms. � 2004 Published by Elsevier B.V.
S O Kucheyev - One of the best experts on this subject based on the ideXlab platform.
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deterministic role of Collision Cascade density in radiation defect dynamics in si
Physical Review Letters, 2018Co-Authors: J B Wallace, L Bayu B Aji, Lin Shao, S O KucheyevAbstract:The formation of stable radiation damage in solids often proceeds via complex dynamic annealing (DA) processes, involving point defect migration and interaction. The dependence of DA on irradiation conditions remains poorly understood even for Si. Here, we use a pulsed ion beam method to study defect interaction dynamics in Si bombarded in the temperature range from ∼-30 °C to 210 °C with ions in a wide range of masses, from Ne to Xe, creating Collision Cascades with different densities. We demonstrate that the complexity of the influence of irradiation conditions on defect dynamics can be reduced to a deterministic effect of a single parameter, the average Cascade density, calculated by taking into account the fractal nature of Collision Cascades. For each ion species, the DA rate exhibits two well-defined Arrhenius regions where different DA mechanisms dominate. These two regions intersect at a critical temperature, which depends linearly on the Cascade density. The low-temperature DA regime is characterized by an activation energy of ∼0.1 eV, independent of the Cascade density. The high-temperature regime, however, exhibits a change in the dominant DA process for Cascade densities above ∼0.04 at.%, evidenced by an increase in the activation energy. These results clearly demonstrate a crucial role of the Collision Cascade density and can be used to predict radiation defect dynamics in Si.
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effects of Collision Cascade density on radiation defect dynamics in 3c sic
Scientific Reports, 2017Co-Authors: L Bayu B Aji, J B Wallace, S O KucheyevAbstract:Effects of the Collision Cascade density on radiation damage in SiC remain poorly understood. Here, we study damage buildup and defect interaction dynamics in 3C-SiC bombarded at 100 °C with either continuous or pulsed beams of 500 keV Ne, Ar, Kr, or Xe ions. We find that bombardment with heavier ions, which create denser Collision Cascades, results in a decrease in the dynamic annealing efficiency and an increase in both the amorphization cross-section constant and the time constant of dynamic annealing. The Cascade density behavior of these parameters is non-linear and appears to be uncorrelated. These results demonstrate clearly (and quantitatively) an important role of the Collision Cascade density in dynamic radiation defect processes in 3C-SiC.
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molecular effect in semiconductors under heavy ion bombardment quantitative approach based on the concept of nonlinear displacement spikes
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2002Co-Authors: A I Titov, V S Belyakov, S O KucheyevAbstract:Abstract A model is developed which is able to describe depth profiles of the efficiency of the molecular effect in damage accumulation in semiconductors under heavy atomic and molecular ion bombardment. In the model, it is assumed that completely disordered zones form due to a catastrophic collapse of the crystalline lattice into an amorphous state when the disorder level within a Collision Cascade exceeds some critical value fc. Rather low values of fc are obtained for this spontaneous crystalline–amorphous transition within dense Collision Cascades produced in Si by heavy ions. Physical mechanisms responsible for such low values of fc are discussed.
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effect of ion species on the accumulation of ion beam damage in gan
Physical Review B, 2001Co-Authors: S O Kucheyev, J S Williams, C Jagadish, G Li, A I TitovAbstract:Wurtzite GaN epilayers bombarded with a wide range of ion species (10 keV H-1, 40 keV C-12, 50 keV O-16, 600 keV Si-28, 130 keV Cu-63, 200 keV Ag-107, 300 keV Au-197, and 500 keV Bi-209) are studied by a combination of Rutherford backscattering/channeling (RBS/C) spectrometry and cross-sectional transmission electron microscopy. Results show that strong dynamic annealing processes lead to a complex dependence of the damage-buildup behavior in GaN on ion species. For room-temperature bombardment with different ion species, bulk disorder, as measured by RBS/C, saturates at some level that is below the random level, and amorphization proceeds layer-by-layer from the GaN surface with increasing ion dose. The saturation level of bulk disorder depends on implant conditions and is much higher for light-ion bombardment than for the heavy-ion irradiation regime. In the case of light ions, when ion doses needed to observe significant lattice disorder in GaN are large (greater than or similar to 10(16) cm(-2)), chemical effects of implanted species dominate. Such implanted atoms appear to stabilize an amorphous phase in GaN and/or to act as effective traps for ion-beam-generated mobile point defects and enhance damage buildup. In particular, the presence of a large conce ntration of carbon in GaN strongly enhances the accumulation of implantation-produced disorder. For heavier ions, where chemical effects of implanted species seem to be negligible, an increase in the density of Collision Cascades strongly increases the level of implantation-produced lattice disorder in the bulk as well as the rate of layer-by-layer amorphization proceeding from the surface. Such an increase in stable damage and the rate of planar amorphization is attributed to (i) an increase in the defect clustering efficiency with increasing density of ion-beam-generated defects and/or (ii) a superlinear dependence of ion-beam-generated defects, which survive Cascade quenching, on the density of Collision Cascades. Physical mechanisms responsible for such a superlinear dependence of ion-beam-generated defects on Collision Cascade density are considered. Mechanisms of surface and bulk amorphization in GaN are also discussed.
A Duvenbeck - One of the best experts on this subject based on the ideXlab platform.
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influence of the polar angle of incidence on electronic substrate excitations in kev self bombardment of solid silver
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2011Co-Authors: S Hanke, A Duvenbeck, B Weidtmann, Andreas WucherAbstract:Abstract We present a computer simulation study on the influence of the polar angle of incidence on electronic substrate excitations in the self-sputtering of silver. For the bombardment of a silver target with 5-keV Ag atoms, we employ a standard molecular dynamics code to follow the microscopic particle dynamics within the atomic Collision Cascade following the primary particle impact. The transfer of kinetic energy of Cascade atoms into the electronic subsystem of the metal is treated in terms of the Lindhard model of electronic stopping and an electron promotion model describing the generation of hot electrons in close binary Collisions. The transport of excitation energy away from the spot of generation is treated in a diffusive manner. The calculations yield a time- and space-dependent excitation energy density E ( r → , t ) that can be converted into an electron temperature profile T e ( r → , t ) . The results of our calculations show an angle-dependent duration of the initial electron temperature peak at the surface which coincides with the time the projectile needs to cross the first layer of the model crystal.
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influence of the polar angle of incidence on secondary ion formation in self sputtering of silver
Surface and Interface Analysis, 2011Co-Authors: B Weidtmann, S Hanke, A Duvenbeck, Andreas WucherAbstract:The influence of the projectile impact angle on secondary ion formation was studied using a computer simulation model applied to the bombardment of an amorphous silver crystal by 5-keV Ag atoms. The model employs a molecular dynamics (MD) scheme for the description of particle dynamics within the atomic Collision Cascade. The electronic degree of freedom is treated within the framework of a free electron gas model incorporating kinetic excitation by electronic friction and electron promotion. Transport of the excitation energy away from the spot of generation is treated by a diffusive approach. In combination with a rate equation model for electronic charge transfer an individual ionization probability a + is assigned to each sputtered particle. The results reveal that the average ionization probability of sputtered atoms increases upon the transition from normal to oblique incidence. The dependence of α + on the emission velocity of ejected atoms is traced back to the temporal structure of the excitation profile induced after projectile impact.
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low energy electronic excitation in atomic Collision Cascades a nonlinear transport model
Physical Review B, 2005Co-Authors: A Duvenbeck, Andreas WucherAbstract:A computer simulation model is presented which allows one to incorporate low-energy electronic excitation into the molecular dynamics computer simulation of atomic Collision Cascades in metals. The model treats the electronic energy losses experienced by all moving atoms as a source term for electronic excitation energy, which is assumed to spread around the original point of excitation with a diffusivity D. In order to acknowledge i the large temperature gradients and ii the local lattice disorder within the Cascade volume, the electronic heat diffusivity is allowed to vary as a function of space and time, thus leading to a strongly nonlinear diffusion of electronic excitation energy. The corresponding diffusion equation is developed and numerically solved for an exemplary Collision Cascade initiated by the impact of a 5 keV silver atom onto an Ag111 surface. It is shown that electron surface temperatures of several thousand kelvin can be reached at times after the impact at which most emission of surface particles occurs. This excitation may therefore influence the ionization or excitation of such sputtered species.
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computer simulation of low energy electronic excitations in atomic Collision Cascades
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2004Co-Authors: A Duvenbeck, Z. Šroubek, Filip Sroubek, Andreas WucherAbstract:We present a computer simulation of low-energy electronic excitations that are created in atomic Collision Cascades initiated by the impact of energetic particles onto a solid surface. In order to render a chemically inert system, the selfbombardment of a silver (1 1 1) surface with Ag atoms is simulated. In the model, the atomic motion following the particle impact is described by a classical molecular dynamics approach. The transfer of kinetic into electronic excitation energy is described in terms of a friction-like electronic energy loss experienced by every moving atom in the solid, thus leading to a space and time dependent density of electron–hole pair excitation energy generated in the course of the Collision Cascade. This energy is assumed to spread around the point of original excitation with a diffusion coefficient D and to equipartition in the Ag sp band according to a Fermi distribution characterized by an electronic temperature Teðr; tÞ. It is shown that for reasonable values of D the electronic energy deposited at the surface can be substantial, thus leading to transient electronic surface temperatures reaching several thousands of Kelvin which, for instance, can influence the ionization probabilities of sputtered atoms. � 2004 Published by Elsevier B.V.
K Nordlund - One of the best experts on this subject based on the ideXlab platform.
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computational study of crystal defects formation in mo by machine learned molecular dynamics simulations
arXiv: Materials Science, 2020Co-Authors: F J Dominguezgutierrez, K Nordlund, J Byggmastar, Flyura Djurabekova, U Von ToussaintAbstract:In this work, we study the damage in crystalline molybdenum material samples due to neutron bombardment in a primary knock-on atom range of 0.5-10 keV at room temperature. We perform machine learned molecular dynamics (MD) simulations with a previously developed interatomic potential based on the Gaussian Approximation Potential (GAP) framework. We utilize a recently developed software workflow for fingerprinting and visualizing defects in damage crystal structures to analyze the damaged Mo samples by computing the formation of point defects during and after a Collision Cascade. As a benchmark, we report results for the total number of Frenkel pairs (a self-interstitial atom and a single vacancy) formed and atom displacement as a function of the PKA energy. A comparison to results obtained by using an Embedded Atom Method (EAM) potential is presented to discuss the advantages and limits of the machine learned MD simulations. The formation of Frenkel pairs follows a sublinear scaling law related to the PKA energy with $E^{0.54}_\mathrm{PKA}$ to the GAP MD results and $E^{0.667}_\mathrm{PKA}$ for the EAM simulations. Although the average number total defects is similar for both methods, we notice that MD potentials model different atomic geometries for the complex point defects, where the formation of crowdions is more favorable for the GAP potential. Finally, ion beam mixing results for GAP MD simulations are reported and discussed.
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subCascade formation and defect cluster size scaling in high energy Collision events in metals
EPL, 2016Co-Authors: A De Backer, A E Sand, K Nordlund, Laurence Luneville, David Simeone, S L DudarevAbstract:Please note that terms and conditions apply. You may also be interested in: High-energy Collision Cascades in tungsten: Dislocation loops structure and clustering scaling laws A. E. Sand, S. L. Dudarev and K. Nordlund Cascade morphology transition in bcc metals Wahyu Setyawan, Aaron P Selby, Niklas Juslin et al. Simulation of defects in fusion plasma first wall materials Troev T, Nankov N and Yoshiie T Primary damage in tungsten using the binary Collision approximation, molecular dynamic simulations and the density functional theory A De Backer, A Sand, C J Ortiz et al. Electronic excitations in atomistic models of radiation damage C P Race, D R Mason, M W Finnis et al. Electronic effects in high-energy radiation damage in tungsten E Zarkadoula, D M Duffy, K Nordlund et al. Variability in atomic Collision Cascade distributions
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direct observation of size scaling and elastic interaction between nano scale defects in Collision Cascades
EPL, 2015Co-Authors: A E Sand, K Nordlund, S L Dudarev, D R Mason, M A Kirk, S G RobertsAbstract:Using in situ transmission electron microscopy, we have directly observed nano-scale defects formed in ultra-high–purity tungsten by low-dose high-energy self-ion irradiation at 30 K. At cryogenic temperature lattice defects have reduced mobility, so these microscope observations offer a window on the initial, primary damage caused by individual Collision Cascade events. Electron microscope images provide direct evidence for a power-law size distribution of nano-scale defects formed in high-energy Cascades, with an upper size limit independent of the incident ion energy, as predicted by Sand et al. (EPL, 103 (2013) 46003). Furthermore, the analysis of pair distribution functions of defects observed in the micrographs shows significant intra-Cascade spatial correlations consistent with strong elastic interaction between the defects.
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direct observation of size scaling and elastic interaction between nano scale defects in Collision Cascades
arXiv: Materials Science, 2015Co-Authors: A E Sand, K Nordlund, S L Dudarev, D R Mason, M A Kirk, S G RobertsAbstract:Using in-situ transmission electron microscopy, we have directly observed nano-scale defects formed in ultra-high purity tungsten by low-dose high energy self-ion irradiation at 30K. At cryogenic temperature lattice defects have reduced mobility, so these microscope observations offer a window on the initial, primary damage caused by individual Collision Cascade events. Electron microscope images provide direct evidence for a power-law size distribution of nano-scale defects formed in high-energy Cascades, with an upper size limit independent of the incident ion energy, as predicted by Sand et al. [Eur. Phys. Lett., 103:46003, (2013)]. Furthermore, the analysis of pair distribution functions of defects observed in the micrographs shows significant intra-Cascade spatial correlations consistent with strong elastic interaction between the defects.
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influence of the picosecond defect distribution on damage accumulation in irradiated α fe
Physical Review B, 2012Co-Authors: K Nordlund, C Bjorkas, M J CaturlaAbstract:The importance of the defect distribution produced in the first few picoseconds of a Collision Cascade on long-term damage evolution is studied with molecular dynamics and kinetic Monte Carlo (KMC) methods. Three different interatomic potentials are used to obtain the primary damage produced by energetic recoils in α-Fe. Contrary to previous results, a dependence of cluster-size distribution with recoil energy is obtained. Moreover, large variations in this distribution are observed depending on the interatomic potential. Using the results for 50 keV Collision Cascades, damage accumulation is modeled with KMC. The accumulation rate of damage visible under transmission electron microscopy predicted by KMC depends significantly on the database used for Cascade damage and, therefore, on the interatomic potential. Based on these results, we show that the comparison of cluster-size distributions with experiments can be used to test the reliability of interatomic potentials.
W Bolse - One of the best experts on this subject based on the ideXlab platform.
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ion beam erosion of graphite surfaces studied by stm ripples self affine roughening and near surface damage accumulation
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2000Co-Authors: S Habenicht, K P Lieb, W Bolse, U Geyer, Fabrizio Roccaforte, Carsten RonningAbstract:Abstract The surface topography of (0 0 0 1) highly oriented pyrolytic graphite eroded by Xenon ions at an incidence tilted relative to the surface normal was measured as function of the tilt angle θ and the ion energy E and fluence Φ by means of scanning tunneling microscopy (STM). Up to about 1018 ions/cm2, the formation of periodic ripple structures was observed. The switching of the wave pattern from parallel to perpendicular orientation relative to the ion beam projection, as predicted for increasing tilt angle θ, was confirmed. Moreover, the wavelength was found to scale with the range and longitudinal straggling width of the Collision Cascade. This fact allows a direct determination of the mean lateral size of the Collision Cascade. The dependence of the measured wavelength on the three parameters θ, E and Φ is reproduced by the theory of sputter erosion by Bradley and Harper. The high-fluence regime can be described by the Kardar–Parisi–Zhang theory (KPZ).
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mechanisms of ion beam induced atomic mixing in solids
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1998Co-Authors: W BolseAbstract:Abstract In the present paper, selected typical studies on the ion-beam mixing of bi- and multi-layer systems are reviewed. It is shown that by proper variation of the materials (atomic number, chemical affinity between top and bottom layer) and of the irradiation conditions (ion species, energy, fluence, target temperature), significant conclusions can be drawn concerning the relevant mixing mechanisms. It is found that low temperature ion-beam mixing of light systems ( Z ≤18) is of pure ballistic character, without any influence of chemical driving forces. For higher atomic numbers and low or medium mass ions, mixing occurs by chemically biased diffusion in spatially separated local thermal-spikes. For very heavy ions mixing effects, which are non-linear with respect to the deposited energy density, point to the formation of coherent global spikes along the ion path by the overlapping of local spikes. Very heavy ions might also be able to initiate thermal-spikes in otherwise ballistic systems ( Z ≤18) at their end of range (end-of-range spikes) by a high density of subCascades. Chemically guided motion of residual defects from the Collision Cascade seems to play a role for ion beam induced mixing only at elevated temperatures.
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irradiation effects in ag fe bilayers ion beam mixing recrystallization and surface roughening
Physical Review B, 1996Co-Authors: A Crespososa, Peter Schaaf, K P Lieb, W Bolse, Matthias Gimbel, U Geyer, C ToselloAbstract:Ag/Fe bilayers deposited onto ${\mathrm{SiO}}_{2}$/Si substrates were irradiated at 20, 77, and 300 K with 300--750 keV Ar and Xe ions in order to study the ion-beam-induced mixing and phase formation in this thermally immiscible system. A combination of Rutherford backscattering spectroscopy (RBS), channeling, conversion electron M\"ossbauer spectroscopy (CEMS), and scanning tunneling microscopy (STM) was used to analyze the atomic transport at the interface and the resulting microstructure and morphology changes of the samples. In the CEMS measurements, a 13 nm thin $^{57}\mathrm{Fe}$ marker layer at the Ag/Fe interface was introduced in order to enhance the sensitivity to alterations of the interfacial composition. From the small amount of Ag atoms found to be dissolved in Fe and from the sharpness of the element profiles at the interface, we derived a very small mixing efficiency, which is significantly smaller than the prediction of the ballistic model. Since ballistic mixing is expected in any case, we argue that demixing and phase separation occur in the relaxation stage or thermal spike phase of the Collision Cascade, as a consequence of the positive heat of mixing. On the other hand, ion irradiation induces a large surface roughening of the Ag top layer as proven by STM. This effect is obviously due to recrystallization of Ag, which results in grain growth and texture formation along the direction of the impinging ion, as demonstrated by RBS/channeling measurements. \textcopyright{} 1996 The American Physical Society.