Resistance of sputtered platinum films; aging in vacuo and in various gases.—The rapid decrease of resistance which occurs if a film is kept in vacuo after sputtering, is doubtless due to coalescence or agglomeration of the particles making up the film. In air, oxygen and hydrogen, however, this aging practically stops, probably because the adsorption of gas around the particles prevents further coalescence until the gas is removed by reëvacuation or by chemical means. This adsorption theory was tested in various ways and was found in accord with all the facts. Nitrogen and carbon dioxide are only slightly adsorbed. The effect of heating is to accelerate and further the aging process but with prolonged heating the resistance reaches a minimum and then increases indefinitely. Temperature coefficients of resistance to 200° C. were measured for films previously aged at a higher temperature and were found to depend, like the resistance itself, more on the physical condition, as determined by heat treatment, than on the thickness of the film. The highest coefficient measured was 0.002 which is about 4/7 of that of platinum in bulk. Very thin films have negative coefficients.

Activation of platinum by sputtering.—Both the sputtered film and the cathode used in sputtering cause hydrogen and oxygen to combine at room temperature so rapidly that the film and the cathode may become very hot.

DOI:https://doi.org/10.1103/PhysRev.18.221