Showing papers by "Robert S Averback published in 1994"
TL;DR: Molecular dynamics computer simulations of Au bombardment of Au substrates were performed to elucidate the influence of surfaces on defect production, and the nature of nonlinear sputtering is discussed.
Abstract: Molecular dynamics computer simulations of 10 and 20 keV Au bombardment of Au substrates were performed to elucidate the influence of surfaces on defect production. Nearly all of the damage was due to local melting and viscous flow of hot liquid onto the surface. For the 10 keV event, 554 atoms flowed to the surface, and this led to the formation of a dislocation network that extended \ensuremath{\approxeq}6 nm below the surface. Only three interstitial atoms, and no isolated vacancies or small vacancy clusters were produced. Loop punching and the nature of nonlinear sputtering are also discussed.
197 citations
TL;DR: In this paper, the fundamental theory underlying these processes is presented, including primary recoil spectra, spatial distributions of damage energy, defect production, and ion beam mixing, and selected results of computer simulation are presented to elucidate the discussion and to introduce the latest developments in this field.
123 citations
TL;DR: In this paper, a model for defect production near the surface of an ion-irradiated solid is developed based on the concept of local melting, and the results of the model are compared to results from molecular dynamics simulations and to experimental observations.
Abstract: A model for defect production near the surface of an ion‐irradiated solid is developed based on the concept of local melting. The model shows that, as heat diffuses radially outward from the track of an ion, a cylinder of melt is created, and owing to the large volume change on melting, pressure is developed in the liquid. Unlike displacement cascades in the interior of the crystal, the pressure is relieved by the viscous flow of liquid through the surface. The results of the model are compared to results from molecular dynamics simulations and to experimental observations.
48 citations
02 May 1994-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the interaction of low-energy particles and clusters with metal surfaces has been investigated using molecular dynamics computer simulations, and a new mechanism for producing damage at surfaces was revealed in simulations of 10 and 20 keV Au bombardment of Au surfaces.
Abstract: The interaction of low-energy particles and clusters with metal surfaces has been investigated using molecular dynamics computer simulations. For the particle interactions, a new mechanism for producing damage at surfaces was revealed in simulations of 10 and 20 keV Au bombardment of Au surfaces. Macroscopic modeling of this phenomenon illustrates the important parameters. For the cluster interactions, many different clusters and substrates were employed: the energies were varied from less than one eV (soft landings) to over 3 keV; the size of the clusters was varied from 87 to 1000, the angle of incidence was varied from near glancing to near normal, and both solid and liquid clusters were examined. Embedded atom method potentials were employed to represent the different metals and alloys. A broad range of behavior was observed in the simulations: splatting of the cluster over the surface, the formation of globs, the penetration of the clusters deep into the substrate. General rules are suggested for predicting which type of behavior prevails.
41 citations
TL;DR: In this article, the lattice parameter of the AlAs was investigated by measurements of the X-ray diffraction using x-ray radiometric diffraction and high-resolution and conventional transmission electron microscopy.
Abstract: Radiation‐induced damage and strain in AlAs were investigated by measurements of the lattice parameter using x‐ray diffraction. Irradiations employed MeV C, Ar, and Au ion beams at 25 or 80 K. The out‐of‐plane lattice parameter increased with fluence at low doses, saturated, and then decreased to nearly its original value. The in‐plane lattice parameter did not change, throughout. These results were independent of the irradiation particle when scaled by damage energy. Selected samples were examined by high‐resolution and conventional transmission electron microscopy. Recovery of the lattice parameter during subsequent thermal annealing was also investigated.
20 citations
TL;DR: In this paper, the interaction of small energetic clusters of metal atoms with surfaces has been investigated by molecular dynamics computer simulations, and a mechanism map for cluster-solid interactions is developed.
Abstract: The interaction of small energetic clusters of metal atoms with surfaces has been investigated by molecular dynamics computer simulations. A wide variety of cluster-solid combinations have been studied so that the effects of the energy, size, and angle of incidence of the cluster, and the relative elastic properties of the cluster and substrate could be elucidated. ‘Soft landings’ were also investigated. From these studies, a mechanism map for cluster-solid interactions is developed. The results have particular importance for cluster beam deposition of thin films. The simulations are fully dynamical and 3-dimensional; they employ embedded-atom method potentials, which have been modified for interactions at close separations. A scheme for reducing the CPU time that is required for these and other simulations of radiation effects is described.
16 citations
TL;DR: In this paper, thermal and radiation-enhanced diffusion of Ni and Pd impurity tracers were investigated on a metal having the L12 structure, specifically Cu3Au, for the first time.
Abstract: Direct measurements of thermal and radiation-enhanced diffusion were performed above and below the ordering temperature on a metal having the L12 structure, specifically Cu3Au, for the first time. Ni and Pd impurity tracers were employed to simulate the diffusion of Cu and Au respectively. Apparent activation enthalpies were obtained for these two tracers above and below the ordering temperature. Both diffusion coefficients were found to decrease significantly on ordering, by factors of two and four for thermal and radiation-enhanced diffusion respectively. The results indicate that the contribution of interstitial atoms to the radiation-enhanced diffusion of Ni and Pd may be negligible.
12 citations
TL;DR: Thomas et al. as discussed by the authors proposed a new explanation for the creation of vacancy clusters based on viscous flow of liquid metal through the irradiated surface, which can now predict much of what these authors reported in 1969.
3 citations
TL;DR: In the early 1970s, Balluffi and co-workers synthesized artificial twist boundaries of gold and employed them in seminal studies of grain boundary structure as mentioned in this paper, showing that synthesis of special materials structures continues to provide a productive pathway to the investigation of materials properties.
3 citations
TL;DR: In this paper, the authors investigated the effect of the details of the energy deposition along individual ion trajectories in self-ion irradiations of Au, Cu, and Pt in the range of 5-20 keV and found that significantly more damage is produced and more atomic mixing takes place relative to corresponding recoil events in the crystal interior.
Abstract: MD simulations have been employed to investigate damage processes during keV bombardment of metal targets. For self-ion irradiations of Au, Cu, and Pt in the range of 5-20 keV, we have found that both the amount and the character of the damage created in the surface depends sensitively on the details of the energy deposition along individual ion trajectories. In all of these cases, significantly more damage is produced and more atomic mixing takes place relative to corresponding recoil events in the crystal interior. In some cases, enormous craters are formed in an explosive event, while in others a convective flow of atoms to the surface leaves dislocations behind. The results of these simulations will be summarized and their significance for damage studies of ion irradiated materials, discussed.
3 citations
TL;DR: In this paper, marker spreading following 2.0 MeV Kr+ irradiation at 25 to 1300°C have been performed on MgO samples containing O18, Ca and Zn buried tracer atoms.
Abstract: Measurements of marker spreading following 2.0 MeV Kr+ irradiation at 25 to 1300°C have been performed on MgO samples containing O18, Ca and Zn buried tracer atoms. Ion beam mixing at room temperature on both sublattices was approximately 2.0 to 3.0 A5/eV. From 600 to 1000°C, the apparent activation enthalpy for diffusion on the anion sublattice (O18) was 0.35 eV and the diffusion coefficient was linear in the irradiation flux. From 1150 to 1300°C the measured activation enthalpy was 4.1 eV and the diffusion coefficient was proportional to the square root of flux. The measured activation enthalpy on the cation sublattice was roughly 0.30 eV up to 700°C for both Ca or Zn doped samples. Measurable extrinsic thermal diffusion from vacancies present for trivalent impurity charge compensation occurred above this temperature, complicating the analysis at higher temperatures. The observed kinetics in the lower temperature range are most likely controlled by interstitial loop formation. In the higher temperature range, vacancy traps with a binding energy of approximately 2 eV could account for the high activation enthalpy.
TL;DR: In this article, the lattice parameters of Al.5Ga.5As were measured using x-ray diffraction and the results showed that the out-of-plane lattice parameter increased monotonically with dose to large strains until the layer amorpnized.
Abstract: Radiation-induced damage and strain in AlxGai-xAs (x=5 to 1) were investigated by measurements of the lattice parameter using x-ray diffraction. Irradiations employed MeV C, Ar and Au ion beams with a substrate temperature of 80 K. For samples with high Al content, the out-of-plane lattice parameter increased with fluence at low doses, saturated, and then decreased to nearly its original value. The in-plane lattice parameter did not change, throughout. These results were independent of the irradiation particle when scaled by damage energy. For the Al.5Ga.5As samples, however, the out-of-plane lattice parameter increased monotonically with dose to large strains until the layer amorpnized. Selected samples were examined by high resolution and conventional transmission electron microscopy (TEM). Channeling Rutherford backscattering spectrometry (CRBS) was also employed to monitor the buildup of damage in many samples. Recovery of the lattice parameter during subsequent thermal annealing was also investigated.
TL;DR: In this article, the ion beam mixing behavior of InGaAs/GaAs strained layer superlattice structures grown by metalorganic chemical vapor deposition was studied using secondary ion mass spectroscopy and Rutherford backscattering channeling.
Abstract: The ion beam mixing behavior of InGaAs/GaAs strained layer superlattice structures grown by metalorganic chemical vapor deposition was studied using secondary ion mass spectroscopy and Rutherford backscattering channeling. The fluence dependence of intermixing by MeV Kr+ irradiation has been investigated. Significant intermixing occurs for fluences much lower than for similar intermixing in other superlattice systems (i.e. ALAs/GaAs). The intermixing exhibits no temperature dependence for fluences of 2 x 1015 to 5 x 1015 cm−2 which sharply contrasts with the behavior of the AlAs/GaAs superlattice system which shows a strong temperature dependence, including a miscibility gap, in the temperature range 523 to 973K. Samples irradiated at 573K retain a high degree of crystallinity when compared to lower temperature irradiations indicating that the InGaAs/GaAs superlattice can be disordered and still retain crystallinity.