PUMPING OF HELIUM AND HYDROGEN BY SPUTTER-ION PUMPS .2. HYDROGEN PUMPING

The pumping of helium by various forms of sputter-ion pumps (i.e., SIP s) is given in part I [K. M. Welch, D. J. Pate, and R. J. Todd, J. Vac . Sci. Technol. A 11, 1607 (1993)]. The pumping of hydrogen in diode a nd triode SIPs is herein discussed. The type of cathode material used in these pumps is shown to have a significant impact on the effectiven ess with which hydrogen is pumped. Examples of this include data for p umps with aluminum, titanium, and titanium-alloy cathodes. Diode pumps with aluminum cathodes are shown to be no more effective in the pumpi ng of hydrogen than in the pumping of helium. The use of titanium anod es and titanium shielding of a pump body is also shown to impact measu rably the speed of a pump at very low pressures. This stems from the f act that hydrogen is X 10(6) more soluble in titanium than in stainles s steel. Hydrogen becomes resident in the anodes because of fast neutr al burial. Ions and fast neutrals of hydrogen are also buried in the w alls of pump bodies. Outgassing of this hydrogen from the anodes and p ump bodies results in a gradual increase in pump base pressure and con sequential decrease in hydrogen pump speed at very low base pressures.