NATURE OF THE INTERACTION BETWEEN ELECTRONS AND WELL-DEFINED SURFACES. III. ULTRA-HIGH VACUUM SYSTEM AND SAMPLE OUTGASSING. IV. GAS SOURCE FOR THE ULTRA-HIGH VACUUM STUDY OF ADSORPTION OF KNOWN GAS LAYERS ON CLEAR SURFACES

The obtaining and maintaining of atomically clean surfaces is a necessary basic step in the study of well characterized surfaces. The initial part of such cleaning is to incorporate the sample and necessary measuring components in an ultra-high vacuum system, capable of maintaining a pressure of 1 x 10 to the -9th power torr (1 torr 1 mm Hg) to 1 x 10 to the -10th power torr. A double pumping arrangement, using a diffusion pump and a getter pump, with appropriate vapor trapping, valves and gauges, is described; also chamber bakeout and high-frequency heating of metal com ponents. Equipment such as liquid nitrogen and oven controllers, which provide around-the-clock maintenance, is also described. Studies of the influence of known-gas layers on a clean surface necessitates an ultra-high vacuum gas manifold system. The vacuum pumping, valving, measuring equipment and gas manifold are described. Ion gauges can be calibrated absolutely against a high vacuum McLeod gauge. By this system, capable of 1 x 10 to the -9th power to 1 x 10 to the -10th power torr, partial pressures of gases of the order of 10 to the -12th power torr can be introduced into the main testing chamber.