Using contact resistance to measure adsorption of gases on metals

The contact resistance between electrodes of molybdenum and tungsten is used to investigate the adsorption of nitrogen and oxygen. It is found that, on clean metals, the initial period of fast adsorption gives rise to a surface resistivity of about 4 × 10⁻¹⁰ ohm-cm², corresponding to a layer of the order of 1.6 Angstroms thick on each surface. To remove, within a minute or so, the layers resulting from adsorption beyond this initial period, temperatures near 1700°K are required for all four metal-gas combinations. Some of the oxygen adsorbed at a pressure of a few torr* at room temperature can be removed by lowering the pressure, but such an effect was not observed for nitrogen. Nitrogen or oxygen adsorbed during the initial period of fast adsorption on clean molybdenum or tungsten at a temperature of 100°K is not removed in times of the order of one hour by lowering the pressure, in disagreement with some results in the literature. The rate of migration of adsorbed oxygen into and out of the region between closed contacts is found to be much lower than that reported in an earlier experiment of the same type.