Auger Electron Emission from Clean Mo Bombarded by Positive Ions. II. Effect of Angle of Incidence

Values are reported for the number of electrons ejected from a polycrystalline molybdenum target bombarded by mass-selected beams of the positive ions, ${\mathrm{He}}^{+}$, ${\mathrm{Ne}}^{+}$, ${\mathrm{Ar}}^{+}$, ${\mathrm{N}}_2^{+}$, ${\mathrm{N}}^{+}$, ${\mathrm{H}}_2^{+}$, and N${\mathrm{O}}^{+}$. Measurements were made over the range of ion kinetic energies from 30-400 eV. Experiments were conducted in an ultrahigh vacuum system with particular attention paid to producing an atomically clean and smooth target surface. The variation of the electron yield ${\gamma }_i$ (electrons/ion) with angle of incidence of the ion beam was studied. It was found that the yield varied smoothly over the range of angle of incidence from 0 to 60°, although the sense of the variation (i.e., increase or decrease) was different for different ions. The dependence of ${\gamma }_i$ on angle of incidence is discussed in terms of the existing models of kinetic and potential (or Auger) electron emission. The experimental data at low ion kinetic energies is quantitatively explained by assuming that all the ions are Auger-neutralized before reaching the surface. At the high ion kinetic energies, it appears that some non-Auger processes are occurring in which the ion produces secondary electrons within the metal lattice. The variation of the electron yield with angle of incidence for ${\mathrm{He}}^{+}$ bombarding a heavily contaminated tungsten surface is also reported and compared with Oliphant's early results.