Observation of Orientational Ordering of Incommensurate Argon Monolayers on Graphite

Abstract

The relative orientation between solid argon monolayers and the basal plane of graphite single-crystal substrates has been measured as a function of mean overlayer interatomic spacing $d$ by low-energy electron diffraction for $32 \mathrm{K}\lesssim T\lesssim 52 \mathrm{K}$. For $3.82 \AA \lesssim d\lesssim 3.95 \AA$, the measured orientation varies with $d$ as quantitatively predicted by Novaco and McTague because of periodic static distortions of the argon monolayers by lateral argon-graphite forces. The relevance of these results to Villain's calculations is discussed.