- Email: [email protected]
Refraction effects in atom scattering from stepped surfaces
A251 Surface Science 118 (1982) 257-266 North-Holland Publishing Company
257
P H O T O E M I S S I O N S T U D I E S OF As A N D ITS R O O M - T E M P E R A T U R E OXIDATION * C.Y. SU, I. L I N D A U , P.R. SKEATH, I. H I N O and W.E. SPICER ** Electrical Engineering Department, Stanford University, Stanford, California 94305, USA Received 24 July 1981; accepted for publication 2 March 1982 The room temperature adsorption of oxygen on in situ prepared As films has been investigated with photoemission. Direct formation of a disordered As203 layer is confirmed by comparison of the photoemission spectra of the oxidized As film to those of gas phase As406 and crystalline As203. Discussion of the role of s - p hybridization in determining the electronic structure of As203 is offered based on the measured photoemission spectra.
Surface Science 118 (1982) 267-278 North-Holland Publishing Company
267
Ge(100)-ALKALI METAL SURFACE A N D INTERFACE S T A T E S L. S U R N E V and M. T I K H O V Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1040 Sofia, Bulgaria Received 19 August 1981; accepted for publication 11 December 1981 The changes of the electron loss spectrum (ELS) and the surface conductivity (Ao) caused by alkali metal (AM) adsorption on a clean Ge surface have been studied. It was found that alkali metal deposition up to moderate coverages changes the intrinsic surface state energy distribution. At higher coverages the surface states are replaced by alkali metal-Ge interface states. The ELS features associated with transitions involving alkali core levels were also discussed. The Ao changes caused by AM adsorption were explained on the basis of the ELS data.
Surface Science 118 (1982) 279-290 North-Holland Publishing Company
279
REFRACTION EFFECTS IN A T O M SCATI'ERING F R O M S T E P P E D SURFACES J. H A R R I S and A. LIEBSCH Institut fi~r Festk6rperforschung, Kernforschungsanlage Jiilich, D-5170 Ji~lich, Fed. Rep. of Germany and G. COMSA, G. MECHTERSHEIMER, B. POELSEMA and S. T O M O D A * Institut fi~r Grenzfliichenforschung und Vakuumphysik, Kernforschungsanlage Ji~lich, D-5170 Ji~lich, Fed. Rep. of Germany Received 22 December 1981 He and H 2 beams striking a Pt(997) surfce in step-down incidence give rise to a "terrace rainbow" diffraction pattern indicative of specular reflection from flat terraces. The rainbow angle, however, does not coincide with the "terrace specular" direction but shows a shift that increases
A252 with angle of incidence, much like a "refraction shift" caused by the attractive potential. A quantative analysis in these terms using the hard corrugated wall plus attractive tail (HCWT) model revealed a difference between He and H 2 beams. For He, the model was able to reproduce the experimental intensities adequately over a wide range of incident energies and angles. For H 2, however, the same was not true and we conclude that the H C W T model does not adequately represent the H 2 - m e t a l interaction. Some reasons for this difference are discussed.
Surface Science 118 (1982) 291-302 North-Holland Publishing C o m p a n y SOFT AND
SURFACE COPPER
Javier Garcia
PHONONS
291 AND
RECONSTRUCTION
-
PLATINUM
(100) FACES SANZ
Departamento de Fisica Fundamental, Universidad Nacional de Educacion a Distancia, Ciudad Universitaria, Madrid-3, Spain and Georges
ARMAND
Section d'Etudes des Interactions Gaz-Solides, Service de Physique Atomique, Centre d'Etudes Nuclbaires de Saclay, F-91191 Gif-sur-Yvette Cedex, France Received 1 July 1981; accepted for publication 21 January The surface phonon dispersion relations are calculated for the platinum and copper (100) faces using the model developed by Castiel et al. (Surface Sci. 59 (1976) 252). A relaxation of the surface force constant leads to a lowering of the phonon frequencies which can vanish for the smallest p h o n o n wavelengths (soft phonons). It is shown that this mechanism cannot yield a copper surface rearrangement but can produce a fifth order reconstruction in the case of platinum, in agreement with experimental results.
303
Surface Science 118 (1982) 303-320 North-Holland Publishing C o m p a n y
COMPARISON INTENSITIES SPECTRA Wen-Jung
FOR
OF OF
EXPERIMENTAL INELASTIC
AND
ELECTRON
THEORETICAL TUNNELING
THIOUREA*
YANG**
and H.W. WHITE
Physics Department, University of Missouri, Columbia, Missouri 65211, USA Received 9 October 1981 ; accepted for publication 17 February 1982 A comparison of experimental and calculated inelastic electron tunneling intensities for several modes of thiourea are reported. The measurements were made on a l u m i n u m - a l u m i n u m oxide-lead tunnel junctions doped with thiourea. The partial charge model of Kirtley, Scalapino and H a n s m a was used to calculate the relative intensities of each mode. The best agreement between the two sets of intensities occurred when the C = S bond was oriented perpendicular to the oxide, the structure was non-planar, and the separation between the molecule and the image plane formed by the lead electrode was about 1.6 Jk. The orientation was such that the sulfur was bonded to the aluminum oxide and the plane formed by the SCNN atoms was perpendicular to the surface.
257
P H O T O E M I S S I O N S T U D I E S OF As A N D ITS R O O M - T E M P E R A T U R E OXIDATION * C.Y. SU, I. L I N D A U , P.R. SKEATH, I. H I N O and W.E. SPICER ** Electrical Engineering Department, Stanford University, Stanford, California 94305, USA Received 24 July 1981; accepted for publication 2 March 1982 The room temperature adsorption of oxygen on in situ prepared As films has been investigated with photoemission. Direct formation of a disordered As203 layer is confirmed by comparison of the photoemission spectra of the oxidized As film to those of gas phase As406 and crystalline As203. Discussion of the role of s - p hybridization in determining the electronic structure of As203 is offered based on the measured photoemission spectra.
Surface Science 118 (1982) 267-278 North-Holland Publishing Company
267
Ge(100)-ALKALI METAL SURFACE A N D INTERFACE S T A T E S L. S U R N E V and M. T I K H O V Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1040 Sofia, Bulgaria Received 19 August 1981; accepted for publication 11 December 1981 The changes of the electron loss spectrum (ELS) and the surface conductivity (Ao) caused by alkali metal (AM) adsorption on a clean Ge surface have been studied. It was found that alkali metal deposition up to moderate coverages changes the intrinsic surface state energy distribution. At higher coverages the surface states are replaced by alkali metal-Ge interface states. The ELS features associated with transitions involving alkali core levels were also discussed. The Ao changes caused by AM adsorption were explained on the basis of the ELS data.
Surface Science 118 (1982) 279-290 North-Holland Publishing Company
279
REFRACTION EFFECTS IN A T O M SCATI'ERING F R O M S T E P P E D SURFACES J. H A R R I S and A. LIEBSCH Institut fi~r Festk6rperforschung, Kernforschungsanlage Jiilich, D-5170 Ji~lich, Fed. Rep. of Germany and G. COMSA, G. MECHTERSHEIMER, B. POELSEMA and S. T O M O D A * Institut fi~r Grenzfliichenforschung und Vakuumphysik, Kernforschungsanlage Ji~lich, D-5170 Ji~lich, Fed. Rep. of Germany Received 22 December 1981 He and H 2 beams striking a Pt(997) surfce in step-down incidence give rise to a "terrace rainbow" diffraction pattern indicative of specular reflection from flat terraces. The rainbow angle, however, does not coincide with the "terrace specular" direction but shows a shift that increases
A252 with angle of incidence, much like a "refraction shift" caused by the attractive potential. A quantative analysis in these terms using the hard corrugated wall plus attractive tail (HCWT) model revealed a difference between He and H 2 beams. For He, the model was able to reproduce the experimental intensities adequately over a wide range of incident energies and angles. For H 2, however, the same was not true and we conclude that the H C W T model does not adequately represent the H 2 - m e t a l interaction. Some reasons for this difference are discussed.
Surface Science 118 (1982) 291-302 North-Holland Publishing C o m p a n y SOFT AND
SURFACE COPPER
Javier Garcia
PHONONS
291 AND
RECONSTRUCTION
-
PLATINUM
(100) FACES SANZ
Departamento de Fisica Fundamental, Universidad Nacional de Educacion a Distancia, Ciudad Universitaria, Madrid-3, Spain and Georges
ARMAND
Section d'Etudes des Interactions Gaz-Solides, Service de Physique Atomique, Centre d'Etudes Nuclbaires de Saclay, F-91191 Gif-sur-Yvette Cedex, France Received 1 July 1981; accepted for publication 21 January The surface phonon dispersion relations are calculated for the platinum and copper (100) faces using the model developed by Castiel et al. (Surface Sci. 59 (1976) 252). A relaxation of the surface force constant leads to a lowering of the phonon frequencies which can vanish for the smallest p h o n o n wavelengths (soft phonons). It is shown that this mechanism cannot yield a copper surface rearrangement but can produce a fifth order reconstruction in the case of platinum, in agreement with experimental results.
303
Surface Science 118 (1982) 303-320 North-Holland Publishing C o m p a n y
COMPARISON INTENSITIES SPECTRA Wen-Jung
FOR
OF OF
EXPERIMENTAL INELASTIC
AND
ELECTRON
THEORETICAL TUNNELING
THIOUREA*
YANG**
and H.W. WHITE
Physics Department, University of Missouri, Columbia, Missouri 65211, USA Received 9 October 1981 ; accepted for publication 17 February 1982 A comparison of experimental and calculated inelastic electron tunneling intensities for several modes of thiourea are reported. The measurements were made on a l u m i n u m - a l u m i n u m oxide-lead tunnel junctions doped with thiourea. The partial charge model of Kirtley, Scalapino and H a n s m a was used to calculate the relative intensities of each mode. The best agreement between the two sets of intensities occurred when the C = S bond was oriented perpendicular to the oxide, the structure was non-planar, and the separation between the molecule and the image plane formed by the lead electrode was about 1.6 Jk. The orientation was such that the sulfur was bonded to the aluminum oxide and the plane formed by the SCNN atoms was perpendicular to the surface.