Lattice parameter and orientation of xenon on graphite at low pressures

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×{}10^-81.8×{}10^-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 ±{}0.1%, and the misorientation {θ} to ±{}0.1^∘{} accuracy. The misfit in the incommensurate phase is parametrized as m=B(T-T₀{)}^{{β}}, with β=0.80±0.03 and B and{T}₀$ as functions of ${log}₁₀(p). A tricritical point (I-C monolayer, bilayer) is observed at p=2.0±0.5×{10}^{{{-}}6}$ Torr, T=62.5±{}1 K. The small misorientation (0{≤}{θ}0.4^∘{}) is a well-defined function of m in the monolayer phase, with an aligned-rotated transition at m=1.5±{}0.5%. These features are compared with other experiments and with theoretical predictions.