Heekeun Shin

Structural and thermal properties of Xe on the Pb(111) surface studied by low-energy electron diffraction

The growth, structures and thermodynamics of Xe adsorbed on Pb(111) were studied with low-energy electron diffraction (LEED). Measurements of equilibrium adsorption isobars indicate layer-by-layer growth for at least two layers in the temperature range 60–90 K, and an isosteric heat of adsorption of 191 ± 10 meV for the first Xe layer and 158 ± 20 meV for the second Xe layer. The monolayer has an incommensurate hexagonal structure with a lattice parameter similar to that found in bulk Xe, and its thermal expansion coefficient was measured to be 9 ± 1 × 10−4 K−1. The average overlayer–substrate spacing was determined from a constant-momentum-transfer analysis of the LEED intensities to be 3.95 ± 0.10 A. Vibrational information was obtained from measuring the decay of the diffraction intensities as a function of temperature. The perpendicular root mean square displacement of the Xe atoms at 50 K is 0.12 ± 0.01 A, giving an effective Debye temperature for adsorbed Xe of 37 ± 2 K. The corresponding vibrational energy for the perpendicular mode of Xe is 3.2 ± 0.3 meV.