Electron emission from aluminum and copper under molecular-hydrogen-ion bombardment

The secondary electron yields from polycrystalline aluminum and copper under ${\mathrm{H}}^{+}$-, $\mathrm{H}_2^{}{}_{}{}^{+}$-, and $\mathrm{H}_3^{}{}_{}{}^{+}$-ion bombardment are compared as a function of ion velocity. The ratios obtained by dividing the yields for $\mathrm{H}_2^{}{}_{}{}^{+}$ and $\mathrm{H}_3^{}{}_{}{}^{+}$ ions with the yield for protons increase with ion velocity. The rate of increase is higher for aluminum targets than for copper targets. The experimental results are explained by considering the charge states of the molecular constituents during penetration of the first few atomic layers important for the electron emission process. Both effects caused by close single-particle collisions and distant plasma collisions are considered.