Ion beam enhanced grain growth in thin films

A research program has been established to study ion beam enhanced grain growth (IBEGG). Ion beam enhanced grain growth has been studied experimentally in Ge, Au and Si films. IBEGG has been characterized by varying the ion dose, ion energy, ion flux, ion species, temperature, and thin film deposition onrditions. The effect of these parameters on grain size and microstructure has Leen analyzed both qualitatively and quantitatively using transmission electron microscopy (TEM). A transition state model has been developed to describe the motion of grain boundaries during ion bombardment. The model has three criteria, which are based on experimental observations and simple assumptions: first, only elastic collisions at or very near grain boundaries contribute to enhanced grain growth; second, heating of the film by inelastic collisions has a negligible effect on grain growth; and third, ion bombardment does not influence the driving force for grain boundary migration. The model accounts for the dependence of IBEGG on the experimental parameters cited above. An atomistic picture of the jump rate at grain boundaries during IBEGG is presented. Monte-Carlo simulation of ion range and defect production was performed using the TRIM code and a modified Kinchin Pease formula. The calculated defect yield per incident ion was found to be directly related to enhanced grain growth, and was used to estimate the number of atomic jumps at the grain boundary per defect generated at the boundary for a given driving force. The IBEGG and thermal growth rates are related to their respective point defect populations. .I,