Surface diffusion of xenon on Pt(111)

• Published in: The Journal of chemical physics 1993-06, Vol.98 (11), p.9115-9125
• Main Authors: MEIXNER, D. L, GEORGE, S. M
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Mechanical and acoustical properties; adhesion; Metals. Metallurgy; Physics; Solid surfaces and solid-solid interfaces; Solid-fluid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.464419

The surface diffusion of xenon on the Pt(111) surface was investigated using laser induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The surface diffusion coefficient at 80 K decreased dramatically from D=8×10−7 cm2/s at θ=0.05θs to approximately D=2×10−8 cm2/s at θ=θs, where θs denotes the saturation coverage at 85 K, corresponding to a commensurate monolayer coverage of 5.0×1014 xenon atoms/cm2. This coverage dependence was consistent with attractive interactions between the adsorbed xenon atoms and the existence of two-dimensional condensed phases of xenon on Pt(111). The kinetic parameters for surface diffusion at θ=θs were Edif=1.3±0.1 kcal/mol and D0=1.1×10−4±0.2 cm2/s. The magnitude of Edif at θ=θs represented the combined effect of the intrinsic corrugation of the adsorbate–surface potential and attractive interactions between the adsorbed xenon atoms. LITD experiments at θ=0.25 θs revealed diffusion kinetic parameters of Edif=1.2±0.2 kcal/mol and D0=3.4×10−4±0.5 cm2/s. The constant Edif at low and high coverage was attributed to the ‘‘breakaway’’ of xenon atoms from the edges of condensed phase xenon islands. The coverage dependence of the surface diffusion coefficient for Xe/Pt(111) was explained by a multiple site diffusion mechanism, where collisions with xenon islands limit diffusional motion. Thermal desorption kinetics for xenon on Pt(111) were determined using TPD experiments. Using the variation of heating rates method, the desorption parameters were Edes=6.6±0.2 kcal/mol and νdes=1.3×1013±0.4 s−1, in good agreement with previous studies. The xenon TPD peak shifted to higher temperature versus initial coverage at a fixed heating rate, providing further evidence for attractive interactions between the adsorbed xenon atoms.