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Quantum theory of charge exchange scattering of atoms at solid surfaces
A15 Surface Science 165 .(1986) 477-487 North-Holland, Amsterdam QUANTUM ATOMS
THEORY
477
OF CHARGE EXCHANGE
SCATFERING
OF
AT SOLID SURFACES
Shigeru SHINDO
Department of Physics, Tokyo Gakugei University, Koganei, Tokyo 184, Japan and Ryoichi KAWAI
Department of Physics, Waseda University, Ohkubo 3-4-1 Shinjuku, Tokyo 160, Japan Received 8 July 1985; accepted for publication 4 September 1985 Numerical calculations of charge exchange scattering are done on the basis of the semiclassical Anderson-Newns hamiltonian. The validity of the various approximation theories is examined in the limit of the semiclassical theory. Moreover the quantum theory of charge exchange scattering of atoms is developed. It is shown that the quantum theory gives a charge exchange probability comparable to that from the semiclassical theory.
488
Surface Science 165 (1986) 488-506 North-Holland, Amsterdam
SULFUR ADSORPTION CHEMISORPTION *
O N Ni(100) A N D I T S E F F E C T O N C O
I. T D S , A E S a n d w o r k f u n c t i o n r e s u l t s E.L. H A R D E G R E E ,
Pin H O and J.M. W H I T E
Department of Chemist~, University of Texax, Austin, Texas 78712, USA Received 8 April 1985; accepted for publication 19 August 1985 The adsorption of H2S on Ni(100) at 300 K was investigated. Adsorption is dissociative and proceeds via a mobile precursor, with sulfur strongly chemisorbed and hydrogen desorbing both during the dose and upon subsequent heating. Chemisorbed sulfur causes an increase in surface work function due to charge transfer of about 0.04e from nickel to sulfur. The adsorption of CO at 95 K was studied on the sulfur-predosed surface using AES, TDS and work function change measurements. Evidence is presented for steric and relatively short-range ( = 4 ,~) electronic effects of S on CO. One sulfur blocks two high-temperature (f12) CO sites by steric (site-blocking) effects. In the presence of sulfur, CO redistributes into several lower-temperature desorption states, some of which exist on regions of bare Ni, and some within sulfur domains. At a sulfur coverage of 0.40 ML, a new CO state at 140 K was observed which, unlike the other CO states, caused a slight decrease in the surface work function. The behavior of this state is explained in terms of reduced back-donation from the metal due to close association of the CO with sulfur. Several proposed modes for sulfur's action are evaluated on the basis of the data. These include steric effects, a through-space electrostatic potential, and a through-metal electronic effect involving density of state changes.
THEORY
477
OF CHARGE EXCHANGE
SCATFERING
OF
AT SOLID SURFACES
Shigeru SHINDO
Department of Physics, Tokyo Gakugei University, Koganei, Tokyo 184, Japan and Ryoichi KAWAI
Department of Physics, Waseda University, Ohkubo 3-4-1 Shinjuku, Tokyo 160, Japan Received 8 July 1985; accepted for publication 4 September 1985 Numerical calculations of charge exchange scattering are done on the basis of the semiclassical Anderson-Newns hamiltonian. The validity of the various approximation theories is examined in the limit of the semiclassical theory. Moreover the quantum theory of charge exchange scattering of atoms is developed. It is shown that the quantum theory gives a charge exchange probability comparable to that from the semiclassical theory.
488
Surface Science 165 (1986) 488-506 North-Holland, Amsterdam
SULFUR ADSORPTION CHEMISORPTION *
O N Ni(100) A N D I T S E F F E C T O N C O
I. T D S , A E S a n d w o r k f u n c t i o n r e s u l t s E.L. H A R D E G R E E ,
Pin H O and J.M. W H I T E
Department of Chemist~, University of Texax, Austin, Texas 78712, USA Received 8 April 1985; accepted for publication 19 August 1985 The adsorption of H2S on Ni(100) at 300 K was investigated. Adsorption is dissociative and proceeds via a mobile precursor, with sulfur strongly chemisorbed and hydrogen desorbing both during the dose and upon subsequent heating. Chemisorbed sulfur causes an increase in surface work function due to charge transfer of about 0.04e from nickel to sulfur. The adsorption of CO at 95 K was studied on the sulfur-predosed surface using AES, TDS and work function change measurements. Evidence is presented for steric and relatively short-range ( = 4 ,~) electronic effects of S on CO. One sulfur blocks two high-temperature (f12) CO sites by steric (site-blocking) effects. In the presence of sulfur, CO redistributes into several lower-temperature desorption states, some of which exist on regions of bare Ni, and some within sulfur domains. At a sulfur coverage of 0.40 ML, a new CO state at 140 K was observed which, unlike the other CO states, caused a slight decrease in the surface work function. The behavior of this state is explained in terms of reduced back-donation from the metal due to close association of the CO with sulfur. Several proposed modes for sulfur's action are evaluated on the basis of the data. These include steric effects, a through-space electrostatic potential, and a through-metal electronic effect involving density of state changes.