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Abstract

This chapter provides a reliable guide to ultrahigh-vacuum techniques. The chapter discusses the production of ultrahigh vacuum. There are a number of pumps or pump combinations which may be used to reach the ultrahigh-vacuum range. The choice of a roughing pump to reduce the pressure from atmospheric to about 10-2 Torr requires some discussion. The two chief alternatives are the rotary oil-sealed mechanical pump and the cryosorption pump utilizing a molecular sieve cooled by liquid nitrogen. The chapter discusses the different methods of gas purification. Chemical and atomic interactions in the gas phase have cross sections as large as those for near-resonant excitation transfer (∼l013 to 10-16 cm2) and electron spin exchange (1014 to 1015 cm2), whereas the processes of interest are often many orders of magnitude smaller in effective cross section. This range often leads to requirements of ultrapure gases (here 1 ppm or less) at least as regards “active” impurities. This level of purity may be maintained by initial careful outgassing of the system, or by continuous purification. The process of physical adsorption provides convenient methods of purification at moderate to high pressures. Adsorption is often limited to a monolayer of adsorbate, but this amounts to a considerable amount of gas even for smooth surfaces.