Surface Ionization of Some Rare Earths on Tungsten

The surface ionization of Gd, Er, and Yb atomic beams on a clean (112) tungsten surface has been studied in an ultrahigh-vacuum mass spectrometer. For the first time, the absolute ionization efficiencies have been determined as a function of surface temperature. The degree of ionization $\alpha$ was found to follow the general form of the Saha-Langmuir equation $A$ $\alpha =A{e}^{-\frac{E}{\mathrm{kT}}}$. The magnitudes of $A$ and $E$, however, are not consistent with the predicted values. Values of $A$ and $E$ are summarized below: