Xenon Multilayer Adsorption On Silver(111) Using Surface Plasmon Resonance.

Abstract

Multilayer film growth explores the interface between the 2D world of mono-layer adsorption and the 3D realm of bulk liquid and crystal formation. The importance of explicitly characterizing such growth is confirmed by the considerable recent experimental and theoretical activities in this area. Xenon on silver has been studied extensively by LEED, UV, XPS and inelastic $\sp4 He$ beam scattering. The goal of this study is to use an unusually sensitive optical probe, Surface Plasmon Resonance Spectroscopy (SPR), to probe the regime of temperatures and film thicknesses where appreciable vapor pressure limits the above techniques. SPR follows subtle complex dielectric constant changes during multilayer film buildup. The angular shift in resonance position corresponds to adsorbed film thickness; while the intensity and width changes of the peak correlate with film roughness properties. In contrast to the complete wetting already reported at low temperatures, a combination of single, bilayer and trilayer growth steps were found. Instead of true film equilibrium, a long term underlying film instability activated by temperature was observed. Evidence for a possible roughening transition around 75 K was observed. The growth of discrete, well-formed layering is sensitively dependent on gas exposure rate and temperature. The variety of growth steps and the underlying growth instability are new film features not previously reported.