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The formation of the gadolinium-Si(111)7 × 7 interface: Reactivity at room temperature
A504 Surface Science 222 (1989) 131-143 North-Holland, Amsterdam
132
T H E FORMATION OF T H E G A D O L I N I U M - S i ( I I I ) 7 REACTIVITY AT ROOM TEMPERATURE W.A. HENLE,
× 7 INTERFACE:
F.P. NETZER
Institut fl:tr Physikalische Chemie, Universit~it Innsbruck, A-6020 lnnsbruck, Austria R. CIMINO
Fritz.Haber-lnstitut der Max-Planck.Gesellschaft, Faradayweg 4-6, D-IO00 Berlin 33, Germany and W. BRAUN
BESSY GmbH, Lentzeallee 100, D-2000 Berlin 33, Germany Received 12 April 1989; accepted for publication 13 June 1989 The room temperature formation of the G d - S i ( l l l ) 7 × 7 interface has been investigated, as a function of Gd coverage, with photoelectron spectroscopy of the valence and core levels using synchrotron radiation, Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). The data indicate interfacial reaction onset at - 0.8 /k Od coverage as confirmed by careful analysis of the Si2p core level spectra. An intermixed monolayer stage is proposed and corroborated by photoemission and LEED results. Complete scrambling of the Si(211) surface sets in beyond the monolayer stage, and a reacted interface, approximately 20 :k thick, is formed. The Od layer is metallic for Od depositions > 25 /~. The photoemission spectra reveal shifts to lower binding energy with increasing Od coverage for the reacted Si 2p components arid the Od 4f levels. The detailed inspection of the Od4f behaviour at very low coverages suggests the absence of metal clustering in the initial chemisorption regime. The Si L23W Auger lineshapes, the valence band signature and the Si2p core level spectra indicate a well-defined silicide-type interracial reaction product. The reactivity of Od on Si(121) is high, consistent with thermodynamical considerations.
244
Surface Science 222 (2989) 244-159 North-Holland, Amsterdam
OXYGEN ADSORP~ON ON Ta(II0)-SUPPORTED Pd FILMS WITH PHOTOEMISSION M.W. RUCKMAN, L.Q. J I A N G * a n d M y r o n S T R O N G I N
STUDIED
Brookhaven National Laboratory, Upton, N Y 11073, USA Received 26 October 1988; accepted for publication 22 May 1989 Oxygen chemisorption on Ta(ll0)-supported palladium films, five monolayers or less in thickness, is studied using photoemission and work function measurements. Palladium monolayers have valence band photoemission spectra which differ significantly when compared to subsequent layers or published results for Pd(122) (i.e. photocmission intensity 0 - 2 eV below E r is smaller). The photcemission work function change ( - 0 . 7 eV) for the Ta(ll0)-supported Pd monolayer when compared to P d ( l l l ) suggests there is charge transfer from Pd to the Ta substrate. Oxygen absorption increases the work function and the work function increase is largest for the Pd monolayer but becomes smaller with increasing Pd coverage. Oxygen adsorption on Ta(ll0) produces a strong valence band photocmission feature which peaks near 5.8 eV binding energy. Oxygen interaction with the Pd monolayer produces two valence band features near 4 and 7.8 eV binding energy. A feature at 5.8 eV is seen after the adsorption of 2 or more langmuirs of oxygen. The modification of the Ta4f corelevel and valence band spectra during oxidation of the Pd-Ta bilayer suggests that oxygen enters the Ta substrate and suggests that the absorption of 2 or more langmuirs of oxygen causes the Pd monolayer to cluster permitting direct oxidation of the substrate.
132
T H E FORMATION OF T H E G A D O L I N I U M - S i ( I I I ) 7 REACTIVITY AT ROOM TEMPERATURE W.A. HENLE,
× 7 INTERFACE:
F.P. NETZER
Institut fl:tr Physikalische Chemie, Universit~it Innsbruck, A-6020 lnnsbruck, Austria R. CIMINO
Fritz.Haber-lnstitut der Max-Planck.Gesellschaft, Faradayweg 4-6, D-IO00 Berlin 33, Germany and W. BRAUN
BESSY GmbH, Lentzeallee 100, D-2000 Berlin 33, Germany Received 12 April 1989; accepted for publication 13 June 1989 The room temperature formation of the G d - S i ( l l l ) 7 × 7 interface has been investigated, as a function of Gd coverage, with photoelectron spectroscopy of the valence and core levels using synchrotron radiation, Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). The data indicate interfacial reaction onset at - 0.8 /k Od coverage as confirmed by careful analysis of the Si2p core level spectra. An intermixed monolayer stage is proposed and corroborated by photoemission and LEED results. Complete scrambling of the Si(211) surface sets in beyond the monolayer stage, and a reacted interface, approximately 20 :k thick, is formed. The Od layer is metallic for Od depositions > 25 /~. The photoemission spectra reveal shifts to lower binding energy with increasing Od coverage for the reacted Si 2p components arid the Od 4f levels. The detailed inspection of the Od4f behaviour at very low coverages suggests the absence of metal clustering in the initial chemisorption regime. The Si L23W Auger lineshapes, the valence band signature and the Si2p core level spectra indicate a well-defined silicide-type interracial reaction product. The reactivity of Od on Si(121) is high, consistent with thermodynamical considerations.
244
Surface Science 222 (2989) 244-159 North-Holland, Amsterdam
OXYGEN ADSORP~ON ON Ta(II0)-SUPPORTED Pd FILMS WITH PHOTOEMISSION M.W. RUCKMAN, L.Q. J I A N G * a n d M y r o n S T R O N G I N
STUDIED
Brookhaven National Laboratory, Upton, N Y 11073, USA Received 26 October 1988; accepted for publication 22 May 1989 Oxygen chemisorption on Ta(ll0)-supported palladium films, five monolayers or less in thickness, is studied using photoemission and work function measurements. Palladium monolayers have valence band photoemission spectra which differ significantly when compared to subsequent layers or published results for Pd(122) (i.e. photocmission intensity 0 - 2 eV below E r is smaller). The photcemission work function change ( - 0 . 7 eV) for the Ta(ll0)-supported Pd monolayer when compared to P d ( l l l ) suggests there is charge transfer from Pd to the Ta substrate. Oxygen absorption increases the work function and the work function increase is largest for the Pd monolayer but becomes smaller with increasing Pd coverage. Oxygen adsorption on Ta(ll0) produces a strong valence band photocmission feature which peaks near 5.8 eV binding energy. Oxygen interaction with the Pd monolayer produces two valence band features near 4 and 7.8 eV binding energy. A feature at 5.8 eV is seen after the adsorption of 2 or more langmuirs of oxygen. The modification of the Ta4f corelevel and valence band spectra during oxidation of the Pd-Ta bilayer suggests that oxygen enters the Ta substrate and suggests that the absorption of 2 or more langmuirs of oxygen causes the Pd monolayer to cluster permitting direct oxidation of the substrate.