Adsorption on clean germanium surfaces

Abstract

The adsorption of various gases on clean germanium surfaces has been investigated. At room temperature and for ( p p 8 ) ≲ 5 × 10 −3 , the gases found to be adsorbed were H 2O, CH 3OH, (CH 3) 2O, CH 3COOH, (CH 3) 2CHCH 2NH 2, C 5H 5N, and p-dioxan, while H 2, N 2, CO, CO 2, CH 4, C 2H 4, CCl 4, CHCl 3, (C 2H 5) 2O, C 6H 6 and C 6H 5Cl were found not to be adsorbed within the limits of our experimental error. For those gases that were adsorbed, the adsorption was extremely rapid, and the extent of take-up was equivalent to about a monolayer coverage. The various classes of adsorbent-adsorbate binding forces have been examined with a view to identifying the type of binding force predominant in the adsorption. For H 2O, CH 3OH, (CH 3) 2O in its enolic modification, CH 3COOH, and (CH 3) 3CNH 2, electrostatic interaction between the permanent charge distributions of the adsorbent and the adsorbate was found to account for adsorption; the nature of the binding for these systems can be described as a form of “hydrogen bond”. The adsorption of pyridine and p-dioxan cannot readily be explained on the basis of a simple classical electrostatic interaction picture. The non-adsorption of the gases listed above is shown to be expected if only classical electrostatic interaction is considered. However, it is not suggested that this electrostatic criterion is by itself the only criterion for non-adsorption.