Sputtering of metals at ion-electron irradiation

It has been found that, in contrast to the commonly accepted opinion, simultaneous irradiation by $15$-keV Ar$^+$ ions and $2.5$-keV electrons at temperatures above $0.5T_m$ ($T_m$ is the melting temperature) induces much larger sputtering of metallic copper, nickel, and steel than irradiation only by Ar$^+$ ions. The effect increases with the temperature. At $T= 0.7T_m$, the sputtering coefficients in the case of ion-electron irradiation are more than twice as large as the sputtering coefficients in the case of irradiation by Ar$^+$ ions. The experiments on the sublimation of copper show that the sublimation rate in the case of the heating of a sample by an electron beam is higher than that in the case of heating in an electric vacuum oven. The revealed effects are explained by the electron-induced excitation of adatoms (atoms stuck over the surface, which appear owing to ion bombardment). Excited adatoms have a smaller binding energy with the surface and are sputtered more easily.