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Interaction of helium with a metal surface
A455 338 INTERACTION
Surface Science 123 (1982) 338-354 North-Holland Publishing Company OF HELIUM
WITH
A METAL
SURFACE
I. Determination of density profile of Cu(llO) via analysis of diffraction intensities A. LIEBSCH
a n d J. H A R R I S
lnstitut fi~r FestklJrperforschung, Kernforschungsanlage Ji~lich, D- 5170 JiJlich, Fed. Rep. of Germany and B. S A L A N O N
a n d J. L A P U J O U L A D E
Centre d'Etudes Nucleaires de Saclay, Service de Physique des Atomes et des Surfaces, F-91191 Gif - sur - Yvette Cedex, France Received 2 August 1982 Using the simple asymptotic expression derived previously from a microscopic theory of the interaction of helium with a metal surface, it is shown that a quantitative fit of selective adsorption resonance energies and diffraction data for He-Cu(110) can be obtained. A detailed analysis is given for spectra taken over a wide range of incident angles (20 ° to 77 °) and energies (21 to 124 meV). The corrugation amplitude perpendicular to the rows of atoms is an exponential function of the distance from the surface and has the values 0.10a 0 and 0.17a o at the classical turning points for He particles with energies 10 and 150 meV. The determination of the repulsive potential from the data yields the electronic density profile outside the Cu(110) surface. As expected for itinerant electrons, this density is much smoother than the sum of overlapped atom densities.
Surface Science 123 (1982) 355-368 North-Holland Publishing Company INTERACTION
OF HELIUM
355 WITH
A METAL
SURFACE
II. Coupled channels method and effect of out-of-plane scattering for Cu(llO) A. LIEBSCH
a n d J. H A R R I S
lnstitut fiat Festlci~rperforschung, Kernforschungsanlage Ji~lich, D-5170 Ji~lich, Fed. Rep. of Germany Received 2 August 1982 A coupled channels method for helium scattering from surfaces is presented. The method applies to arbitrary potentials and can easily be generalized to include internal excitations in the case of molecule scattering. The procedure is based on that of Barnes et al. but is improved to avoid numerical instabilities arising from evanescent channels. As an application, helium diffraction from Cu(ll0) is treated using a three-dimensional potential. In general, the corrugation of such surfaces along the rows of surface atoms influences the in-plane intensities for scattering perpendicular to the rows in a non-trivial way. For the incidence conditions considered in the previous paper, however, the effect is small and amounts merely to a scaling down of the intensity of all in-plane beams by a constant factor.
Surface Science 123 (1982) 338-354 North-Holland Publishing Company OF HELIUM
WITH
A METAL
SURFACE
I. Determination of density profile of Cu(llO) via analysis of diffraction intensities A. LIEBSCH
a n d J. H A R R I S
lnstitut fi~r FestklJrperforschung, Kernforschungsanlage Ji~lich, D- 5170 JiJlich, Fed. Rep. of Germany and B. S A L A N O N
a n d J. L A P U J O U L A D E
Centre d'Etudes Nucleaires de Saclay, Service de Physique des Atomes et des Surfaces, F-91191 Gif - sur - Yvette Cedex, France Received 2 August 1982 Using the simple asymptotic expression derived previously from a microscopic theory of the interaction of helium with a metal surface, it is shown that a quantitative fit of selective adsorption resonance energies and diffraction data for He-Cu(110) can be obtained. A detailed analysis is given for spectra taken over a wide range of incident angles (20 ° to 77 °) and energies (21 to 124 meV). The corrugation amplitude perpendicular to the rows of atoms is an exponential function of the distance from the surface and has the values 0.10a 0 and 0.17a o at the classical turning points for He particles with energies 10 and 150 meV. The determination of the repulsive potential from the data yields the electronic density profile outside the Cu(110) surface. As expected for itinerant electrons, this density is much smoother than the sum of overlapped atom densities.
Surface Science 123 (1982) 355-368 North-Holland Publishing Company INTERACTION
OF HELIUM
355 WITH
A METAL
SURFACE
II. Coupled channels method and effect of out-of-plane scattering for Cu(llO) A. LIEBSCH
a n d J. H A R R I S
lnstitut fiat Festlci~rperforschung, Kernforschungsanlage Ji~lich, D-5170 Ji~lich, Fed. Rep. of Germany Received 2 August 1982 A coupled channels method for helium scattering from surfaces is presented. The method applies to arbitrary potentials and can easily be generalized to include internal excitations in the case of molecule scattering. The procedure is based on that of Barnes et al. but is improved to avoid numerical instabilities arising from evanescent channels. As an application, helium diffraction from Cu(ll0) is treated using a three-dimensional potential. In general, the corrugation of such surfaces along the rows of surface atoms influences the in-plane intensities for scattering perpendicular to the rows in a non-trivial way. For the incidence conditions considered in the previous paper, however, the effect is small and amounts merely to a scaling down of the intensity of all in-plane beams by a constant factor.