Ultrahigh vacuum: A survey

Somewhat over a decade ago, certain problems in the physics laboratory led to a major step forward in vacuum technology. These problems were in the fields of atomic collision processes and surface physics, in which it was impossible to obtain either high gas purity or atomically clean surfaces with the experimental techniques available. For example, at a pressure of ${10}^{\text{−7}}\hspace{0.17em}\mathrm{Torr}$ (1 Torr is $\mathrm{approximately}\text{\hspace{0.17em}=\hspace{0.17em}1\hspace{0.17em}}\mathrm{mm}\hspace{0.17em}\mathrm{Hg}$ ) of molecular gas, a surface which had been previously cleaned would adsorb a complete monolayer of gas in a matter of seconds. The combined efforts of a number of physicists resulted in a new set of tools which made it possible to achieve and measure pressure two or three orders of magnitude lower than was previously possible: that is, pressures down to ${10}^{\text{−10}}$ or somewhat lower. Among them were Nottingham of MIT and groups at three major laboratories: Apker at General Electric, Lander and Becker at Bell Telephone Laboratories, and several of us at Westinghouse Research Laboratories.