SPECTROSCOPIC ELLIPSOMETRY ON XENON MONOLAYERS ADSORBED ON GOLD-FILMS

Thin polycrystalline gold films of 50-70 nm thickness are deposited under UHV conditions on glass substrates. After an annealing treatment at 423 K the films exhibit a very smooth surface. The dielectric constants measured in situ by means of an automatic ellipsometer (wavelength range 400 - 920 nm) show good agreement with data published for bulk gold samples. The xenon adsorption is studied at 77 K. The main result is that the change in the ellipsometrical parameter DELTA occurs stepwise at distinct gas pressure values. Up to three steps with decreasing step heights were detected in the DELTA versus pressure curves. A qualitative description on the basis of Fresnel's formulae for a simple three-layer model leads to epsilon(Xe) = 2.2. A better agreement is achieved when the dielectric constant epsilon(Xe) is reduced from 2.25 to 2.15 and then to 2.10 while describing the adsorption properties of the first, second and third xenon monolayer, respectively. Obviously a successive layer-by-layer growth is dominant in the initial stages of xenon adsorption. At higher pressures, condensation of xenon takes place at the gold surface.