Electron- and photon-stimulated modification of GaAs(110), Si(100), and Si(111)

Scanning tunneling microscopy results show that irradiation with electrons of primary energies of 90--2000 eV created single-layer deep vacancies on GaAs(110), Si(100), and Si(111). The removal yield was linear with dose during the initial stages of surface modification, but it increased as the surface damage increased. The cross section varied with primary electron energy, increasing from 4.4×10^-20cm² at 100 eV to 1.8×10^-19cm² at 2000 eV for GaAs(110) and from 1×10^-20cm² at 90 eV to 5×10^-20cm² at 2000 eV for Si(111)-7×7. The mechanisms responsible for atom displacement and desorption involve excitations in the surface region achieved by the cascade of inelastically scattered electrons. Processes involving long-lived localized states facilitate the coupling to the nuclear motion needed for atom displacement, with details that reflect surface reconstructions, surface states, and defect levels. Once surface defects have been created by electron irradiation of GaAs(110), they can be expanded by irradiation with photons of energy 2.3 eV. Photon irradiation involves site-selective desorption, and this allows patterning and atomic layer removal.