Doctor of Philosophy (PhD)
Physics and Astronomy
The purpose of this dissertation is to investigate the nanoscale hardness of gallium arsenide thin films and the elastic-plastic behavior of gallium arsenide under an indenter. These investigations were carried out using molecular dynamics (MD) simulations. The simulations are based on interatomic potentials that accurately reproduce many properties of bulk GaAs. The MD simulations performed required scalable and efficient algorithms for implementation on large parallel computers. Nanoindentation simulations were performed using an ideal indenter that was held rigid during the simulation. To reduce the transient effects due to loading, the traversal of the indenter was interrupted periodically to allow the substrate to relax. Load-displacement curves were calculated and Vickers hardness and Young’s modulus were computed from the curves. The damage caused by the indenter was characterized in three ways. The material deposited on the surface was compared to bulk amorphous GaAs and found to be structually similar, indicating that the material underwent solid-state amorphization under the indenter. Analysis of energetic atoms beneath the surface suggested the presence of dislocation loops. A centrosymmetry method was applied to characterize these defects. It was found that the method used did not perform adequately in the presence of amorphized material. Pressure distributions were calculated and atomic configurations were plotted to determine if subsurface microcracking due to the indentation was present. No indication of microcracking or pore formation was found. Adhesion between the tip and substrate was also studied. The effect of the tip-surface attraction was studied for a modified Vickers indenter with a small flat surface instead of an atomically sharp tip. For indentations less than the yield point in GaAs, the bond formation between the tip and the surface led to nonelastic deformation of the surface layer, while the layers undeneath the surface behaved in a purely elastic fashion. Through a series of small indenter traversals, the yield point of GaAs was determined to be 0.6 µN.
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Neal, Jr., Francis Brent, "Molecular dynamics simulations of adhesion and nanoidentation of gallium arsenide" (2002). LSU Doctoral Dissertations. 3210.