ELLIPSOMETRY IN SUB-MONOLAYER REGION

Gas adsorption (physisorption and chemisorption) in the monolayer range on silicon and germanium surfaces was studied by means of ellipsometry and the results were compared with volumetric adsorption measurements on powders. Using these data together with literature values of atomic polarizabilities and Van der Waals diameters, good agreement was found between observed and calculated values of the ellipsometric effect. A review is given of the theories concerning ellipsometry, especially in the sub-monolayer region. In the chemisorption experiments an anomalous change was observed in one of the ellipsometrically determined angles (ψ). This is explained by assuming that the clean silicon or germanium crystal has a very thin (10 Å) optically absorbing surface layer, which becomes less absorbing due to the chemisorption process. Comparison of the ellipsometric results of chemisorption experiments on Si (111) and Si (100) surfaces showed that several gases adsorb twice as much on Si (100), whereas other gases adsorb in the same amounts on both surface planes. © 1969.