SURFACE STOPPING

Detailed, materials-specific stopping calculations for ultrathin films exhibit a scaling with layer number N which would be expected for asy mptotic N but not small N's: a bulk contribution plus a term linear in 1/N fit the calculations extremely well. We derive this scaling for a jellium model with a general spatially varying density profile. The m odel gives the magnitude of the 1/N term correctly as well as the scal ing with kinetic energy of that contribution to the stopping. We also show that the loss to surface excitations is larger than the 1/N term for upsilon greater than or equal to 0.7 (atomic units) and calculate the projectile velocity dependence of the apparent position of the sur face plane. [S1050-2947(97)05410-3].