Complex study of surface and bulk defects was performed by field ion and scanning tunnel microscopy. Specimens were irradiated by 20-to 50-keV He+, Ar+, and Bi+ ions at room temperature. The irradiation fluences were between 1018 and 1020 ion m−2. Calculated parameters of depletion zones and atomic displacement cascades were compared with theoretical estimates. It was shown that controlled ion bombardment of material surface is an effective tool for fabricating field-emission cathodes for vacuum microelectronics.