Mass-dependent effects of channel electron multipliers in residual gas analyzers

Abstract

Residual gas analyzers (RGA’s) are increasingly being used to obtain quantitative information about vacuum processes. The gain for an ion [electron multiplier (EM) output current divided by the Faraday cup (FC) output current] determined by experiment for a combination FC/EM sensor was not constant for increasing mass. The gain for ions of different masses was also found to be dependent on the chemical nature of the ion, reflecting the conversion efficiency of incident ions to secondary electrons [U. Fehn, Int. J. Mass Spectrom. Ion Phys. 15, 391 (1974); 21, 1 (1976)]. Allowance for these effects makes quantitative RGA measurements in the EM mode of the sensor more reliable. Methods for determining a correction factor are discussed.