SURFACE MELTING ON SMALL PARTICLES

Surface melting on small particles was detected using x-ray diffractio n from Pb crystallites of 50 nm diam in ultrahigh vacuum. Since the me lting temperature depends on particle size, it can be difficult to dis tinguish between the melting and surface melting. A sharp crystallite size distribution is obtained by melting the smaller particles while a liquid skin forms on the remaining crystallites. When the sample is c ooled slightly, the liquid particles remain liquid while the liquid sk in on the crystallites solidifies. In situ x-ray diffraction reveals t hat the liquid skin thickness changes reversibly. (C) 1997 American In stitute of Physics.