Origin and excitation mechanism of electron-stimulated desorption ofH+from Nb(110) and O-contaminated Nb(100) and Ta(110) surfaces

Electron-stimulated desorption of ${\mathrm{H}}^{+}$ from a pure H adsorbate on a foil-recrystallized Nb(110) surface and from a mixture of ${\mathrm{H}}_2$ and ${\mathrm{H}}_2$O on O-contaminated Nb(100) and Ta(110) surfaces is studied as a function of electron-impact energy and ion energy. In the former case, it is found that the desorption of ${\mathrm{H}}^{+}$ has a low but detectable yield and is proceeded most likely via the excitation of the bonding (valence) electron. In the latter case, two distinguishable types of ${\mathrm{H}}^{+}$ ions are observed. Their desorption is shown to proceed via the creation of the highest-lying metal and the O $2s$ core holes, respectively, indicating two different origins of ${\mathrm{H}}^{+}$, namely, an OH or hydroxyl species and single H atoms bonded to the metals.