A New Monitor of Gas-Surface Interactions
03 October 1988
Adsorption and desorption of molecules on compensated semiconductor crystals causes dramatic changes in their electrical resistance due to band bending and can be used for very sensitive detection of gas-surface interactions. Likewise, the diffraction of He beams, in particular the specular intensity, is strongly affected by smallest amounts of adsorbed molecules (10 sup -3 of a monolayer). We have investigated the influence of NO sub 2 adsorption and desorption on high resistivity GaAs (110) by simultaneously recording the resistance and the He specular intensity during various exposure cycles. Upon adsorption the resistance and the He intensity decreased in a correlated manner, whereas upon desorption they differ in a manner indicative of a chemical reaction. We will discuss our experiments using these ultra sensitive techniques, in combination with thermal desorption mass spectrometry and other surface chemically sensitive probes, to provide a new measure of low coverage chemical dynamics.