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Ab initio calculations of the electronic structure and effective magnetic moment of Nb4
A440 782
ANGLE R E S O L V E D P H O T O E M I S S I O N STATES IN W(II0)
Surface Science 189/190 (1987) 782-787 North-Holland, A m s t e r d a m
S T U D Y OF S U R F A C E C O R E
Y. JUGNET, N.S. PRAKASH, Tran Minh DUC lnstitut de Physique Nud6aire de Lyon, Universit6 Claude Bernard Lyon l, 43 Boulevard du 11 noc,embre 1918, 69622 Villeurbanne Cedex, France
H.C. POON, G. GRENET and J.B. PENDRY The Bla~kett Laboratory, Imperial College, London SW7 2BZ, UK Received 30 March 1987; accepted for publication 15 April 1987 Azimuthal and polar distributions of photoelectrons from W ( l l 0 ) , with the contributions of surface and bulk core states resolved, are measured. Strong modulations in intensity of both contributions are observed and ascribed to photoelectron diffraction final state effects. Dynamical calculation within a LEED formalism of their relative contributions is also presented and compared with experimental measurements. Such analysis is expected to be applicable to reconstructed surfaces with measurable surface core level shifts.
788
Surface Science 189/190 (1987) 788-794 North-Holland, A m s t e r d a m
AB INITIO C A L C U L A T I O N S OF T H E E L E C T R O N I C S T R U C T U R E A N D EFFECTIVE M A G N E T I C M O M E N T OF Nb 4
Tornas WAHNSTROM and Arne ROSEN Department of Physi(u', Chalmers UniversiO' of Technology and Univer~iO" of Gi~tehorg, S-412 96 GOteborg, Sweden Received 13 April 1987; accepted for publication 6 May 1987 The electronic structure of Nb4 clusters has been calculated within the spin-polarized local density approximation using the LCAO method. The calculations were performed for a pyramidal and a planar structure with equal bond lengths extending from the value in the bulk to the value for the dimer. The position and symmetry of the H O M O and L U M O levels depend strongly on the bond length in the pyramidal as well as the planar structure. All clusters are diamagnetic except for the planar structure with a bond length longer than 4.85 au for which a net spin polarization is obtained.
Surface Science 189/190 (1987) 795 800 North-Holland, Amsterdam
A N G L E - R E S O L V E D I N V E R S E P H O T O E M I S S I O N OF GaP(II0) T. RIESTERER, P. PERFETTI *, M. T S C H U D Y and B. REIHL IBM Research Division, Zurich Research Laboratoo,, 8803 Riischlikon, Switzerland Received 7 April 1987; accepted for publication 30 April 1987
795
A441 We have measured angle-resolved inverse-photoemission spectra of GaP(110) along the FX and F X ' symmetry direction. An unoccupied surface-state band near the bottom of the conduction band exhibits a downward dispersion along FX and appears to be quite flat along FX'. Its minimum energy is found at X to be Ev+0.9 eV. Combining this value with angle-resolved ultraviolet-photoemission results, we find a direct surface-state band gap of 3.4 eV, while optical data show a first surface-sensitive transition around 2.8 eV.
Surface Science 189/190 (1987) 801-822 North-Holland, Amsterdam THE IMPACT
OF SURFACE
SCIENCE
801 ON TECHNOLOGY
D. B R I G G S lCl PLC, International Materials Centre, P. 0. Box 90, Wilton, Cleveland TS6 8JE. UK Received 13 April 1987; accepted for publication 15 May 1987 The inter-relationships between surface science and technology are complex. After reviewing the extent to which surface analytical instrumentation is now used in various technological fields this paper looks at the role of surface science, in the wider sense, in three areas: metallurgy, heterogeneous catalysis and polymer technology. In metallurgy there has been an impressive unification of the effect of residual elements on several types of intergranular failure through a combination of theoretical developments underpinned by grain boundary analysis using high resolution AES. Complex heterogeneous catalysts of empirical origin have been intensively investigated using many surface techniques in order to elucidate the active structural units, their dependence on preparative route and their mechanisms of deactivation and regeneration. Studies of Co-Mo-S/AI203 HDS catalysts are illustrative. The fundamentals of catalysis, especially by metals, are also being systematically revealed by single crystal studies. In polymer technology the fundamentals of adhesion and adhesion promotion have been investigated by XPS whilst SIMS now allows the role of polymer additives on surface behaviour to be explored. Clearly, between them, these three areas provide a representative cross-section of both materials and technologies.
Surface Science 189/190 (1987) 823-831 North-Holland, Amsterdam EFFICIENT TITANIUM
823
SPECTRAL SENSITISATION OF POLYCRYSTALLINE DIOXIDE PHOTOELECTRODES
N. V L A C H O P O U L O S ,
P, L I S K A , A . J . M c E V O Y
a n d M. G R A T Z E L
lnstitut de Chirnie Physique, Ecole Polytechnique Fdd~rale de Lausanne, 1015 Lausanne, Switzerland Received 30 March 1987; accepted for publication 16 April 1987 Stable oxide semiconductor photoelectrodes for photoelectrochemical cells have a very low response to solar light due to their wide band gaps. Their sensitivity to visible light may be enhanced by chemisorbed charge-transfer dyes. Bis and tris (2,2'bipyridyl-4,4'dicarboxylate) ruthenium, zinc tetra (4-carboxyphenyl) porphyrin and ferrocyanide anion sensitised titanium dioxide photoelectrodes are described with high quantum yield under visible irradiation, due to derivatisation of a noval structured semiconductor surface.
ANGLE R E S O L V E D P H O T O E M I S S I O N STATES IN W(II0)
Surface Science 189/190 (1987) 782-787 North-Holland, A m s t e r d a m
S T U D Y OF S U R F A C E C O R E
Y. JUGNET, N.S. PRAKASH, Tran Minh DUC lnstitut de Physique Nud6aire de Lyon, Universit6 Claude Bernard Lyon l, 43 Boulevard du 11 noc,embre 1918, 69622 Villeurbanne Cedex, France
H.C. POON, G. GRENET and J.B. PENDRY The Bla~kett Laboratory, Imperial College, London SW7 2BZ, UK Received 30 March 1987; accepted for publication 15 April 1987 Azimuthal and polar distributions of photoelectrons from W ( l l 0 ) , with the contributions of surface and bulk core states resolved, are measured. Strong modulations in intensity of both contributions are observed and ascribed to photoelectron diffraction final state effects. Dynamical calculation within a LEED formalism of their relative contributions is also presented and compared with experimental measurements. Such analysis is expected to be applicable to reconstructed surfaces with measurable surface core level shifts.
788
Surface Science 189/190 (1987) 788-794 North-Holland, A m s t e r d a m
AB INITIO C A L C U L A T I O N S OF T H E E L E C T R O N I C S T R U C T U R E A N D EFFECTIVE M A G N E T I C M O M E N T OF Nb 4
Tornas WAHNSTROM and Arne ROSEN Department of Physi(u', Chalmers UniversiO' of Technology and Univer~iO" of Gi~tehorg, S-412 96 GOteborg, Sweden Received 13 April 1987; accepted for publication 6 May 1987 The electronic structure of Nb4 clusters has been calculated within the spin-polarized local density approximation using the LCAO method. The calculations were performed for a pyramidal and a planar structure with equal bond lengths extending from the value in the bulk to the value for the dimer. The position and symmetry of the H O M O and L U M O levels depend strongly on the bond length in the pyramidal as well as the planar structure. All clusters are diamagnetic except for the planar structure with a bond length longer than 4.85 au for which a net spin polarization is obtained.
Surface Science 189/190 (1987) 795 800 North-Holland, Amsterdam
A N G L E - R E S O L V E D I N V E R S E P H O T O E M I S S I O N OF GaP(II0) T. RIESTERER, P. PERFETTI *, M. T S C H U D Y and B. REIHL IBM Research Division, Zurich Research Laboratoo,, 8803 Riischlikon, Switzerland Received 7 April 1987; accepted for publication 30 April 1987
795
A441 We have measured angle-resolved inverse-photoemission spectra of GaP(110) along the FX and F X ' symmetry direction. An unoccupied surface-state band near the bottom of the conduction band exhibits a downward dispersion along FX and appears to be quite flat along FX'. Its minimum energy is found at X to be Ev+0.9 eV. Combining this value with angle-resolved ultraviolet-photoemission results, we find a direct surface-state band gap of 3.4 eV, while optical data show a first surface-sensitive transition around 2.8 eV.
Surface Science 189/190 (1987) 801-822 North-Holland, Amsterdam THE IMPACT
OF SURFACE
SCIENCE
801 ON TECHNOLOGY
D. B R I G G S lCl PLC, International Materials Centre, P. 0. Box 90, Wilton, Cleveland TS6 8JE. UK Received 13 April 1987; accepted for publication 15 May 1987 The inter-relationships between surface science and technology are complex. After reviewing the extent to which surface analytical instrumentation is now used in various technological fields this paper looks at the role of surface science, in the wider sense, in three areas: metallurgy, heterogeneous catalysis and polymer technology. In metallurgy there has been an impressive unification of the effect of residual elements on several types of intergranular failure through a combination of theoretical developments underpinned by grain boundary analysis using high resolution AES. Complex heterogeneous catalysts of empirical origin have been intensively investigated using many surface techniques in order to elucidate the active structural units, their dependence on preparative route and their mechanisms of deactivation and regeneration. Studies of Co-Mo-S/AI203 HDS catalysts are illustrative. The fundamentals of catalysis, especially by metals, are also being systematically revealed by single crystal studies. In polymer technology the fundamentals of adhesion and adhesion promotion have been investigated by XPS whilst SIMS now allows the role of polymer additives on surface behaviour to be explored. Clearly, between them, these three areas provide a representative cross-section of both materials and technologies.
Surface Science 189/190 (1987) 823-831 North-Holland, Amsterdam EFFICIENT TITANIUM
823
SPECTRAL SENSITISATION OF POLYCRYSTALLINE DIOXIDE PHOTOELECTRODES
N. V L A C H O P O U L O S ,
P, L I S K A , A . J . M c E V O Y
a n d M. G R A T Z E L
lnstitut de Chirnie Physique, Ecole Polytechnique Fdd~rale de Lausanne, 1015 Lausanne, Switzerland Received 30 March 1987; accepted for publication 16 April 1987 Stable oxide semiconductor photoelectrodes for photoelectrochemical cells have a very low response to solar light due to their wide band gaps. Their sensitivity to visible light may be enhanced by chemisorbed charge-transfer dyes. Bis and tris (2,2'bipyridyl-4,4'dicarboxylate) ruthenium, zinc tetra (4-carboxyphenyl) porphyrin and ferrocyanide anion sensitised titanium dioxide photoelectrodes are described with high quantum yield under visible irradiation, due to derivatisation of a noval structured semiconductor surface.