ELLIPSOMETRIC INVESTIGATION OF PHYSISORPTION AT LOW TEMPERATURES

The ellipsometric method measures the change in the state of polarization of a light beam upon reflection. Linear extrapolation in the macroscopic theory of homogeneous layers to the sub-monolayer region predicts that adsorbed quantities corresponding to a small fraction of a monolayer can be detected on germanium and silicon surfaces. This is shown experimentally by combined ellipsometric and volumetric measurements of the physisorption of krypton, xenon, methane, silane and nitric oxide on real surfaces at liquid nitrogen and oxygen temperatures. The results of the experiments support the assumption of a linear, or nearly linear, relationship between the ellipsometric signal δΔ and the degree of coverage. The values δΔ for monolayer coverages of the adsorbates on different adsorbents are determined by B.E.T. calculations. They are discussed in terms of molecular polarizabilities and cross-sections. © 1969.