Surface morphology of laser-superheated Pb(111) and Pb(100)

Abstract

The surface step density on the vicinal Pb(111) and the surface vacancy density on Pb(100) after laser superheating and melting are investigated using reflection high-energy electron diffraction. With \ensuremath{\sim}100-ps laser pulses, Pb(111) surface superheating does not significantly change the density of the steps and step-edge roughness. However, after laser surface melting, the average terrace width and the string length at the step edge become as large as those at room temperature. The average terrace width at 573 K changes from 38\ifmmode\pm\else\textpm\fi{}15 to 64\ifmmode\pm\else\textpm\fi{}19 \AA{} after laser surface melting, while the average string length at the step edge changes from 90\ifmmode\pm\else\textpm\fi{}14 to 250\ifmmode\pm\else\textpm\fi{}38 \AA{}. For Pb(100), the surface vacancy density remains unchanged when the surface is superheated without melting. However, when the laser fluence is high enough to cause surface melting, the surface vacancy density increases. This increase in vacancy density is attributed to fast diffusion of atoms in the liquid film formed on Pb(100) during laser melting.