MELTING OF PB NANOCRYSTALS

The size-dependent melting and surface melting of Pb nanocrystals is d emonstrated by x-ray powder diffraction in ultrahigh vacuum. Whereas s ome prior studies have measured the size-dependent melting temperature via the diffraction intensity, it is shown here that crystallite reor ientation makes the diffraction intensity an unreliable indicator of m elting. instead of the diffraction intensity, the diffraction peak sha pe reveals the size-dependent melting via changes in the crystallite s ize distribution. Measurements showed that the melting temperature var ies inversely with the crystallite size and quantitatively favors the liquid-skin melting model over the homogeneous melting model. Surface melting is demonstrated via the reversible growth of a 0.5 nm liquid s kin on 50 nm crystallites just below the size-dependent melting temper ature.