Changes of some optical constants of thin metallic films due to exposure to gases
Sherman, John Wise
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The reflectivity, transmissivity, and absorptivity of freshly evaporated silver and copper films were measured in vacuo and then in the presence of several gases. These measurements were performed, using the photoelectric method, with two photomultiplier tubes (931-A and 1P21), and were made at an angle of incidence of zero degrees for two different wavelengths (4047 A and 4358 A). The gases used were air, argon, nitrogen and oxygen. The use of oxygen required several changes in the evaporating system in order that the diffusion pump oil would not oxidize too rapidly and cause an explosion. Air was found to increase the transmissivity in two steps, first an initial change, and second a gradual change. The reflectivity decreased in two similar changes. Nitrogen and oxygen revealed to a greater or lesser extent the same changes as were observed for air. Argon produced only a gradual change in both reflectivity and transmissivity. The initial change in oxygen was attributed to oxidation, and the initial change in nitrogen attributed to chemisorption. The gradual change in all gases was due to physical adsorption. The possibility that chemisorption might have caused the initial change in oxygen was pointed out, but this experiment did not allow a definite choice to be made.
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