INELASTIC ENERGY-LOSS IN LOW-ENERGY NE+ SCATTERING FROM A SI SURFACE

We report a study on single scattering of 500-1950-eV Ne+ ions from a Si surface. Our results show a sharp increase in the inelastic energy loss suffered by backscattered Ne+ for the distance of closest approac h R(min)less than or equal to 0.59 Angstrom. A detailed data analysis which considers both the continuous interactions with the target valen ce electrons and the discrete inelasticity Q(o) in the binary Ne-Si co llisions reveals a constant Q(o) = 45+/-4 eV for R(min)less than or eq ual to 0.47 Angstrom. This is attributed to the simultaneous excitatio n of two electrons from the neutralized Ne to the 2p(4)(D-1)3s(2) auto ionization state. A small doubly charged Ne2+ single-scattering peak h as also been observed for R(min)less than or equal to 0.59 Angstrom, I n this case, the inelasticity of 86+/-5 eV in the binary collisions is ascribed to the two-electron excitation of surviving Ne+ to Ne2+ 2p( 3)3s. These assignments are: consistent with all previously reported e xperimental results of autoionization electron emission, and the charg e fraction, intensity, and energy spectral line shape of backscattered singly and doubly charged ions, for Ne+ and Ne-o impact on Si. Al, Mg , and Na surfaces. Our results indicate that in low-energy collisions the excited electrons can be located in bound atomic outer shells with out being transferred to the conduction band of the solid. The similar threshold internuclear distances for the excitation of Ne 2p electron s for both Ne+-Si and Ne-o-Si indicate that transitions occur at simil ar crossings of the promoted 4f sigma molecular orbital (correlated to Ne 2p) with high-lying empty orbitals. [S1050-2947(98)05801-6].