Lattice parameter and orientation of xenon on graphite at low pressures.

Abstract

A study of xenon adsorbed on (0001) graphite has been performed using transmission high-energy electron diffraction (THEED). The single crystal diffraction patterns have been obtained at a range of pressures 1.8\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$1.8\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ Torr and temperatures 50T80 K, which covers the incommensurate monolayer, commensurate monolayer, and bilayer phases. The lattice-parameter misfit, m, has been measured to \ifmmode\pm\else\textpm\fi{}0.1%, and the misorientation \ensuremath{\theta} to \ifmmode\pm\else\textpm\fi{}0.1\ifmmode^\circ\else\textdegree\fi{} accuracy. The misfit in the incommensurate phase is parametrized as m=B(T-${T}_{0}$${)}^{\ensuremath{\beta}}$, with \ensuremath{\beta}=0.80\ifmmode\pm\else\textpm\fi{}0.03 and B and ${T}_{0}$ as functions of ${\mathrm{log}}_{10}$(p). A tricritical point (I-C monolayer, bilayer) is observed at p=2.0\ifmmode\pm\else\textpm\fi{}0.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$ Torr, T=62.5\ifmmode\pm\else\textpm\fi{}1 K. The small misorientation (0\ensuremath{\le}\ensuremath{\theta}0.4\ifmmode^\circ\else\textdegree\fi{}) is a well-defined function of m in the monolayer phase, with an aligned-rotated transition at m=1.5\ifmmode\pm\else\textpm\fi{}0.5%. These features are compared with other experiments and with theoretical predictions.