Premelting and postmelting in clusters.
Caloric curves for sodium clusters with N=139 and 147 atoms show a fine structure near the solid-to-liquid transition. Neither of the two sizes exhibit surface melting. For N=139, diffusion of the surface vacancies is observed, which is not possible in the closed-shell N=147 cluster. A few kelvin above the peak in the heat capacity, N=139 is completely liquid. This is not the case for N=147. Here the inner 13 atoms remain nearly fixed up to several tens of kelvin above the melting temperature of the outer two layers. A simple physical reason is suggested for this unexpected behavior.
Hock
Christian
C
Fakultät für Physik, Universität Freiburg, H. Herderstrasse 3, 79104 Freiburg, Germany.
Bartels
Christof
C
Strassburg
Samuel
S
Schmidt
Martin
M
Haberland
Hellmut
H
von Issendorff
Bernd
B
Aguado
Andrés
A