Reflectance of semitransparent platinum films on various substrates in the vacuum ultraviolet.

The reflectance of semitransparent Pt films deposited on various substrates at close to room temperature was measured at lambda = 584 A and lambda = 736 A and in the wavelength region 1000-2000 A and was compared with that of opaque films of Pt. All Pt films were prepared by high-vacuum evaporation with an electron gun and deposited on the substrates most frequently used in spectrographs: glass and fused quartz of which most mirrors are made, evaporated Al and Au in which diffraction gratings are ruled, and semitransparent Cr on glass used to increase the adherence of Pt films. At lambda = 584 A and 736 A thin semitransparent films of t = 100-200 A showed higher reflectance than opaque ones for all substrates with the exception of Au. At wavelengths longer than 1000 A, thin Pt films showed an increase in reflectance over that of opaque Pt, if deposited on glass, but had extremely low reflectance values when deposited on Al. Calculations made to explain the experimentally determined reflectance behavior of thin Pt films on the various substrates are discussed.