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Two-channel surface ion neutralization
A636 Surface Science 224 (1989) 543 558 North-Holland, Amsterdam
543
T W O - C H A N N E L SURFACE ION N E U T R A L I Z A T I O N K.W.
SULSTON
*, A . T . A M O S
Department oj Mathematics, University of Nottingham, Nottm,~ham NG7 2RD, UK and S.G. DAVISON
Departments of Applied Mathematics and Physics, L.;nit~ersitv of Waterloo, Waterloo, Ontario. ('anada N2L 3G1 Received 25 May 1989: accepted for publication 27 July 1989
A previously described many-el.:ctron treatment of charge transfer in surface-ion scattering is extended to the case where there are two neutralization channels. Experiments have shown that in some cases an ion can be neutralized either as a ground-state or as an excited-state atom; a specific example is Li + ions scattered from cesiated tungsten. This system is investigated and the relative proportions of the various products are calculated as functions of ion kinetic energy and surface work function. Additionally, the effect of ion neutralization on the excitation spectrum of the solid is examined.
Surface Science 224 (1989) 559 569 North-Holland, Amsterdam
559
S U R F A C E E N R I C H M E N T OF Li ON LiF SINGLE CRYSTAL AFTER CLEAVING OR U N D E R ELECTRON B O M B A R D M E N T P. W U R Z
* and C.H.
BECKER
Molecular Physics Laboratoo', SRI International, Menlo Park. CA 94025, USA Received 23 February 1989; accepted for publication 1 September 1989 The build-up of an excess metal layer on the surface of LiF(100), after cleaving or due to electron irradiation, is examined by monitoring the neutral atom and molecule emission during sputter depth profiling. At room temperature the Li enrichment on the surface saturates at an electron fluence of 2.5 × 1015 e l e c t r o n s / e r a 2 at 500 eV energy. In addition, lesser enrichment of the crystal surface by Li after cleavage without electron irradiation was observed, which also reappears after removal by moderate sputtering by a 3 keV ion beam. Enrichment is attributed to the difference in the formation energies of cation and anion vacancies, The time constants for the build up of the metal layer at room temperature for the unirradlated but cleaved crystal and the cleaved crystal exposed to the saturation dose of electrons are 2 and 40 rain, respectively.
543
T W O - C H A N N E L SURFACE ION N E U T R A L I Z A T I O N K.W.
SULSTON
*, A . T . A M O S
Department oj Mathematics, University of Nottingham, Nottm,~ham NG7 2RD, UK and S.G. DAVISON
Departments of Applied Mathematics and Physics, L.;nit~ersitv of Waterloo, Waterloo, Ontario. ('anada N2L 3G1 Received 25 May 1989: accepted for publication 27 July 1989
A previously described many-el.:ctron treatment of charge transfer in surface-ion scattering is extended to the case where there are two neutralization channels. Experiments have shown that in some cases an ion can be neutralized either as a ground-state or as an excited-state atom; a specific example is Li + ions scattered from cesiated tungsten. This system is investigated and the relative proportions of the various products are calculated as functions of ion kinetic energy and surface work function. Additionally, the effect of ion neutralization on the excitation spectrum of the solid is examined.
Surface Science 224 (1989) 559 569 North-Holland, Amsterdam
559
S U R F A C E E N R I C H M E N T OF Li ON LiF SINGLE CRYSTAL AFTER CLEAVING OR U N D E R ELECTRON B O M B A R D M E N T P. W U R Z
* and C.H.
BECKER
Molecular Physics Laboratoo', SRI International, Menlo Park. CA 94025, USA Received 23 February 1989; accepted for publication 1 September 1989 The build-up of an excess metal layer on the surface of LiF(100), after cleaving or due to electron irradiation, is examined by monitoring the neutral atom and molecule emission during sputter depth profiling. At room temperature the Li enrichment on the surface saturates at an electron fluence of 2.5 × 1015 e l e c t r o n s / e r a 2 at 500 eV energy. In addition, lesser enrichment of the crystal surface by Li after cleavage without electron irradiation was observed, which also reappears after removal by moderate sputtering by a 3 keV ion beam. Enrichment is attributed to the difference in the formation energies of cation and anion vacancies, The time constants for the build up of the metal layer at room temperature for the unirradlated but cleaved crystal and the cleaved crystal exposed to the saturation dose of electrons are 2 and 40 rain, respectively.