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A mass spectrometer study is made of the residual gases in several types of vacuum evaporators ranging from oil-diffusion-pumped, conventional systems to an oil-free, ultra-high-vacuum chamber. Partial pressures of water vapor, hydrogen, carbon monoxide, carbon dioxide, nitrogen, oxygen, argon and hydrocarbon vapors varied appreciably in the evaporators studied. The performance of a conventional system was improved by using special low-vapor-pressure gasket materials to minimize hydrocarbon contamination, a liquid-nitrogen trap to reduce water vapor, titanium gettering for oxygen and nickel-iron gettering for hydrogen. For thin-film deposition, the importance of thoroughly outgassing the source materials is pointed out.
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