Preliminary Study of the Apparatus for Electron Stimulated Desorption of Rare Gas Solids

Abstract

An electron stimulated desorption (ESD) experimental system consisting of a ultrahigh vacuum chamber, micro channel plate, electron gun, quadrupole mass spectrometer, liquid helium and liquid nitrogen cryostat, and a gas supply tube etc., was set up and evaluated in order to investigate desorption particles at the surface of rare gas solids (RGS). Ar was deposited on the copper sample for 200 seconds at a pressure of 6.3 x 10–4 Pa. Ion currents from the RGS during bombardment at various electron gun energies were measured. These increased proportionally with filament currents between 1.5 A and 1.75 A. With the electron gun turned on, the dominant residual species in the vacuum chamber were H2O, H2, C, O, N2, Ar, and CO2, as measured using a quadrupole mass spectrometer (QMS). The H2O partial pressure was almost 50 % of the total pressure, and that of the other gas species were lower than 20 %. Before starting the experiments, the ultimate base pressure of the ultrahigh vacuum chamber reached 10–8 Pa.