Auger Ejection of Electrons from Molybdenum by Noble Gas Ions

Experimental investigation of electron ejection from atomically clean molybdenum by singly-and doubly-charged ions of the noble gases is reported. The basic measurements of electron yield and energy distribution of ejected electrons have been made for ions of kinetic energy in the range 10 to 1000 ev. Measurements are made at bombarding electron energies in the ion source below the threshold for formation of metastable ions. The electron ejection for molybdenum, as previously found for tungsten, has characteristics appropriate to ejection in Auger-type processes of neutralization and de-excitation at the metal surface. Values of 0.300, 0.254, 0.122, 0.069, and 0.022 were obtained for the electron yield for 10 ev ${\mathrm{He}}^{+}$, ${\mathrm{Ne}}^{+}$, ${\mathrm{A}}^{+}$, ${\mathrm{Kr}}^{+}$, and ${\mathrm{Xe}}^{+}$ ions, respectively. Extensive comparison of the present results with the work of others is possible. Comparison of the results for molybdenum and tungsten shows the differences to be largely attributable to the effect of work function change on the probability of escape of internally excited electrons from the metal. The ${\mathrm{Ne}}^{+}$ ion shows the anomalies characteristic of the resonance neutralization and Auger de-excitation of a fraction of the ions at higher ion energies as was found for tungsten. Careful measurements have been made of yield and energy distributions of electrons ejected by doubly-charged ions. The processes by which a doubly-charged ion is de-excited and neutralized at a clean metal surface have been investigated in detail.