Electron-Impact Desorption of Ions from Polycrystalline Tungsten

Abstract

A cylindrical magnetic spectrometer has been constructed to study the electron-impact desorption of ions and neutrals from solid surfaces. The instrument has high-energy resolution and sensitivity and allows the determination of the charge-to-mass ratio of the emitted ions. The apparatus has been applied to the study of polycrystalline tungsten with ${\mathrm{O}}_2$, CO, C${\mathrm{O}}_2$, ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, and ${\mathrm{H}}_2$O adsorbed. The ions which have been observed are ${\mathrm{O}}^{+}$ from ${\mathrm{O}}_2$/W, CO/W, and C${\mathrm{O}}_2$/W; C${\mathrm{O}}^{+}$ from CO/W; and ${\mathrm{H}}^{+}$ from ${\mathrm{H}}_2$/W and ${\mathrm{H}}_2$O/W. The ion energy distributions, ionic and total desorption cross sections, threshold energies, and other experimental results are presented and discussed.