Using evaporation conditions adjusted for the deposition of true silicon monoxide, a series of films ranging in thickness from 0.03 to 10 microns was prepared on fused quartz, glass, rock salt, and highly reflecting aluminum surfaces. The optical constants of the films were computed in the wavelength region from 0.24 to 14 microns from reflectance, transmittance, and thickness measurements. Silicon monoxide films exhibit strong absorption in the ultraviolet which extends into the visible, and an infrared absorption maximum at 10 microns which differs significantly from the position of the absorption maximum of fused quartz. In the wavelength region from 0.40 to 0.70 micron, the refractive index of SiO decreases with increasing wavelength from 2.15 to 1.95. Strongly oxidized films show less ultraviolet absorption, lower indexes of refraction, and a shift of the infrared absorption band to shorter wavelength. Decomposition of SiO to Si+ SiO2 results in increased ultraviolet absorption and higher refractive indexes. In the region of the 10-micron absorption a silicon monoxide protective layer of 0.125 micron in thickness has no appreciable effect on the reflectance of a highly reflecting metallic surface, but decreases the transmittance of a rock salt plate by 30 percent.
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