Surface tension enhancement of TRIM sputtering yields for liquid metal targets

A critical part of all models of physical sputtering is the magnitude of th e attractive interaction of a surface atom with the bulk, the surface bindi ng energy, which is often equated to the heat of sublimation, independent o f temperature and regardless of the state of aggregation of the target. Spu ttering occurs when target particles which are accelerated by atomic collis ions caused by an incident energetic projectile, reach the surface with eno ugh energy to overcome the surface binding energy. This surface binding ene rgy influences sputtering in two ways: (1) it acts as a barrier which must be overcome by the escaping atoms and so affects the sputtering yield, and (2) its directional properties influence the directions taken by the ejecte d target atoms. Lower surface binding energies increase the sputtering yiel d, while higher surface binding energies reduce the sputtering yield. The t hermodynamics of liquid surfaces is used to determine the temperature depen dence of surface tension and thus the binding energy of atoms in the liquid surface. Liquid lithium and gallium have surface tensions that follow the same universal function of T/T-c observed for most simple atomic liquids. T he decrease of surface binding energy with increasing target temperature is calculated, and the TRIM code is then used to determine the resulting incr ease in sputtering yield with temperature as functions of the incident angl e for these targets under bombardment by low energy deuteron projectiles, ( C) 2001 Published by Elsevier Science B.V.