Ejection of electrons from molybdenum and tungsten by kilo-electron-volt potassium ions

The experimental coefficient of ion-electron emission for K⁺ in the 0.6-6-keV energy range incident on pure Mo has been found to be in excellent qualitative and numerical agreement with the calculation by Parilis and Kishinevski. Sharp thresholds were measured at, respectively, 0.59 and 0.64 × 10⁷ cm/sec for Mo and W. Evidence involving the distribution in energy of electrons ejected at angles near the target normal showed that incident-beam particles embedded in the target fundamentally affect the nature of the ejection process. This contamination factor is basically the cause of the discrepancy between the new and previous data. In particular, the linear intercept for Mo differs by 50% from Brunn\'ee's value. Pulse measurement techniques were used and pure Mo surfaces were prepared by subliming away contaminated metal layers at 2000 °K. The electron emission for K⁺ on Mo was found to be augmented by monolayer coverage of pure Mo by N₂ at low energies but was reduced slightly at incident energies above 3 keV. This observation is discussed in terms of the surface-barrier effect on escaping electrons.