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Angle-resolved photoemission from Cu(001)c(2 × 2)-Br
A84 Surface Science 167 (1986) 401-416 North-Holland, Amsterdam
401
A LEED, AES AND XPS STUDY OF SINGLE CRYSTAL Nbjlr SURFACES S. S I N H A R O Y ,
A.l. BRAGINSKI
a n d J. T A L V A C C H I O
*
Westinghouse R&D Center. 1310 Beulah Road, Pittsburgh, Pennsvh'ania 15235, USA and E. W A L K E R
D~partement de Pt~vsique de la MatiOre (-ondensg,e, Uni~ersit~ de Gen&'e. Genet'a, Swit~erhmd Received 23 July 1985: accepted for publication 30 October 1985
Single crystal Nb~lr crystals were grown by pulling from levitated melt and subsequent zone refining. Polished (100), (111) and (110) surfaces ,aere prepared to study epitaxial growth of high-critical-temperature superconductors crystallizing in the A15 structure, and especially Nb~Gc. The effects of a variety of surface cleaning treatments, and of the surface oxidation have been examined by LEED. RHEED, AES and XPS. The main findings of this study are: (1) Thc ion-heat-treatment (I HT) at temperatures above 700°C is necessary to produce clean, ordered A15 Nb~lr single crystal surfaces. (2) ('lcan (100) and (1 l l ) surfaces exhibit (1 x 1) unreconstructed pattern. The (110) clean surface exhibits a (1 × 2) recons'truction. (3) Reconstructions induced by surface oxidation are caused by niobium suboxide a n d / o r oxide formation. (4) Recons{ructions induced by surface oxidation are accompanied by atomic segregation such that underneath a niobium-enriched surface an lr-enrichcd layer is present. ( 5 ) T h e ( l l l ) N b ~ l r surface is the most stuble, since it resists reconstruction up to over 20 alq; oxygen. (6)The (100)Nb~Ir surface exhibits the strongest tendency for suboxide and lower oxide formation. The atomic segregation is most pronounced on this surface, the passivation (equilibrium) Nb-oxidc thickness is only 2 / 3 of that on (111) and (110) surfaces. (7) No change in surface reconstructions occurs between the room temperaturc and 500 to 5500( '.
Surface Science 167 (1986) 417 426 North-Holland, Amsterdam
417
ANGLE-RESOLVED P H O T O E M I S S I O N FROM Cu((~l)e(2 x 2)-Br K.K. K L E I N H E R B E R S , H.-G. ZIMMER and A. GOLDMANN Laboratorium ff~r FestkOrperpl~vsik der Uni~,ersitikt-GH-Duisburg. D-4100 Duisburg 1, Fed. Rep. of Germany Received 20 September 1985: accepted for publication 8 November 1985 The dissociative adsorption of bromine on Cu(001) at room temperature has been studied by angle-resolved photoemission. Our results supplement an earlier study of this system by Richardson and Sass [Surface Sci. 103 (1981) 496]. Four adsorbate-derived bands can be identified at the center of the surface Brillouin zone and their dispersion E ( k . ) along FX and FM, their respective mirror symmetry and their orbital character are determined. In addition, angle-resolved electron energy-loss spectra have been obtained. Our results are consistent with a simple adsorbate overlayer geometry, and exhibit a close analogy to the Cu(001)c(2 x 2)-C1 system.
401
A LEED, AES AND XPS STUDY OF SINGLE CRYSTAL Nbjlr SURFACES S. S I N H A R O Y ,
A.l. BRAGINSKI
a n d J. T A L V A C C H I O
*
Westinghouse R&D Center. 1310 Beulah Road, Pittsburgh, Pennsvh'ania 15235, USA and E. W A L K E R
D~partement de Pt~vsique de la MatiOre (-ondensg,e, Uni~ersit~ de Gen&'e. Genet'a, Swit~erhmd Received 23 July 1985: accepted for publication 30 October 1985
Single crystal Nb~lr crystals were grown by pulling from levitated melt and subsequent zone refining. Polished (100), (111) and (110) surfaces ,aere prepared to study epitaxial growth of high-critical-temperature superconductors crystallizing in the A15 structure, and especially Nb~Gc. The effects of a variety of surface cleaning treatments, and of the surface oxidation have been examined by LEED. RHEED, AES and XPS. The main findings of this study are: (1) Thc ion-heat-treatment (I HT) at temperatures above 700°C is necessary to produce clean, ordered A15 Nb~lr single crystal surfaces. (2) ('lcan (100) and (1 l l ) surfaces exhibit (1 x 1) unreconstructed pattern. The (110) clean surface exhibits a (1 × 2) recons'truction. (3) Reconstructions induced by surface oxidation are caused by niobium suboxide a n d / o r oxide formation. (4) Recons{ructions induced by surface oxidation are accompanied by atomic segregation such that underneath a niobium-enriched surface an lr-enrichcd layer is present. ( 5 ) T h e ( l l l ) N b ~ l r surface is the most stuble, since it resists reconstruction up to over 20 alq; oxygen. (6)The (100)Nb~Ir surface exhibits the strongest tendency for suboxide and lower oxide formation. The atomic segregation is most pronounced on this surface, the passivation (equilibrium) Nb-oxidc thickness is only 2 / 3 of that on (111) and (110) surfaces. (7) No change in surface reconstructions occurs between the room temperaturc and 500 to 5500( '.
Surface Science 167 (1986) 417 426 North-Holland, Amsterdam
417
ANGLE-RESOLVED P H O T O E M I S S I O N FROM Cu((~l)e(2 x 2)-Br K.K. K L E I N H E R B E R S , H.-G. ZIMMER and A. GOLDMANN Laboratorium ff~r FestkOrperpl~vsik der Uni~,ersitikt-GH-Duisburg. D-4100 Duisburg 1, Fed. Rep. of Germany Received 20 September 1985: accepted for publication 8 November 1985 The dissociative adsorption of bromine on Cu(001) at room temperature has been studied by angle-resolved photoemission. Our results supplement an earlier study of this system by Richardson and Sass [Surface Sci. 103 (1981) 496]. Four adsorbate-derived bands can be identified at the center of the surface Brillouin zone and their dispersion E ( k . ) along FX and FM, their respective mirror symmetry and their orbital character are determined. In addition, angle-resolved electron energy-loss spectra have been obtained. Our results are consistent with a simple adsorbate overlayer geometry, and exhibit a close analogy to the Cu(001)c(2 x 2)-C1 system.