Physisorbed Rare-Gas Monolayers: Evidence for Domain-Wall Tilting

Abstract

We have studied the structure of Xe adsorbed on a highly oriented pyrolytic graphite surface in the submonolayer regime using scanning tunneling microscopy (STM) at $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5\mathrm{K}$. The Xe adlayer forms hexagonal domains in a honeycomblike superstructure. We observe domain walls tilted by roughly 12\ifmmode^\circ\else\textdegree\fi{} with respect to the atomic rows of the Xe layer, which explains the previously found rotation of the diffraction pattern of about 0.5\ifmmode^\circ\else\textdegree\fi{} relative to the ideal $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ layer. The STM signal exhibits a voltage-dependent contrast between Xe domains and domain walls, which can be understood by the different adsorption sites and the band structure of the Xe adlayer.