Changes in the rf conductivity of discontinuous molybdenum films exposed to oxygen

The frequency-dependent electrical resistance of discontinuous (i.e., ultrathin, <100-Å thick) metal films can be interpreted in terms of a simple equivalent circuit with frequency independent parameters whose values can be obtained by a computer analysis of the film resistance as a function of frequency in the megahertz range. The equivalent circuit is composed of a resistance Rb, associated with conduction in the film grains, and a resistance Rg in parallel with a capacitance Cg, associated with conduction across intergranular gaps. By observing changes in these quantities for evaporated Mo films exposed to O2 in situ, it has been possible to differentiate between the effects of this gas on the bulk conductivity in the grains from its effects on intergranular conductivity. Upon exposure to O2 at 10−7 to 10−4 Torr and room temperature (∼22°C), Mo films showed a more rapid increase in Rb than Rg during initial stages of chemisorption and oxidation, and vice versa as oxidation proceeded, showing that the changes in conductivity of these films produced by the interaction with gas molecules depends upon the location of the molecules within the film.