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.