SURFACE ELECTRON-EMISSION INDUCED BY ION-BOMBARDMENT - METHODS OF OBSERVATION

The energy spectra of Ne+ ions reflected from the cold (100) nickel surface covered by an adsorbed layer of Ar and the energy spectra of secondary electrons emitted under ion bombardment were measured simultaneously. The dependences of the single-scattering nickel peak and ion-induced electron yield on the incidence angle were compared. It was found that in the range of incidence angles when the violent collisions are impossible due to shadowing of the substrate atoms by the adsorbed layer (the scattering angle was fixed at theta(s) = 150-degrees) secondary electrons are emitted and their energy spectrum shows some structure. This structure disappears when violent collisions with substrate atoms become possible. It is assumed that the additional structure of the energy spectrum is connected with weak surface collisions and creation of (Ne+ + Ni) quasimolecules. The decay of the inner-shell excited states of such quasimolecules can lead to escape of the electrons in the direction theta(e) = 90-degrees. In the case of violent collisions the production of electrons increases, but they leave the quasimolecules mainly in the directions theta(e) > 90-degrees and cannot be detected (the detection angle of electrons was fixed at theta(e) = 90-degrees).