ESCA Study of Xenon Adsorbed on the Tungsten (111) Plane

Abstract

X-ray photoelectron spectroscopy (ESCA) is a powerful technique for the study of the bonding of adsorbed molecules to surfaces. We have employed an ultrahigh vacuum ESCA spectrometer to study the adsorption of Xe on a W(111) single crystal disk at ∼100 K. The photoelectron spectrum of Xe is compared with flash desorption measurements of Xe surface coverage and desorption energy. The ESCA measurement has a limiting sensitivity of ∼0.05 monolayer of Xe, and involves digital summation of multiple scans. As Xe coverage increases in the range 0.05\\leqslantθXe\\leqslant1.0 the Xe (3d5/2) level is shifted monotonically upward in binding energy by 0.5 ± 0.1 eV, relative to the Fermi level of W(111). Part of this shift may be due to preferential Xe adsorption on extraneous sites other than W(111), the remainder being related to weak interactional effects between Xe molecules on W(111). Above θXe\\cong0.2 the desorption energy of Xe is constant on this W(111) crystal, in agreement with previous work where a constant desorption energy of 9.3 kcal.mole-1 was measured. The work function decreases by 1.0 ± 0.1 eV upon adsorption of Xe to monolayer coverage at ∼100 K.