| 1. |
- Andersen, Jesper N., et al.
(författare)
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Core level binding energy shifts in interfaces between 4d and alkali metals
- 1995
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 75:C, s. 225-232
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Tidskriftsartikel (refereegranskat)abstract
- High resolution core level photoemission measurements are reported of the binding energy shifts of the 3d core level of Mo, Rh and Pd atoms in interfaces between these 4d metals and alkali metals. The core level binding energies of the interface 4d atoms are found to be almost equal to those of the clean surface atoms for Mo and Rh. For Pd a large alkali induced shift towards higher binding energy is found. The implications of these results for the information derivable from core level binding energy shifts in metallic interfaces are discussed and it is demonstrated that the present results are explained by established total energy based models for core level binding energy shifts in metallic systems.
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| 2. |
- Lundgren, Edvin
(författare)
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Alkali Metal Adsorption on Metals Studied by Hiqh Resolution Core Level Spectroscopy and Low Energy Electron Diffraction
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alkali metal adsorption on metals is studied by High Resolution Core Level Spectroscopy (HRCLS) and Low Energy Electron Diffraction (LEED). The studies can be divided into two parts: adsorption of alkali multilayers and alkali adsorption in the submonolayer regime. In the case of the adsorption of alkali multilayers, the interface region between a thin alkali film of Na,K,Rb and Cs on different single crystal surfaces has been studied by HRCLS. It is shown that the photoelectrons emitted from different alkali layers can be resolved. The layer resolved alkali core level binding energy shifts are found to depend systematically on the atomic number of the alkali and the substrate metal. The surface index of the substrate is shown to influence the layer resolved binding energy shifts. In the case of alkali adsorption on 4d-metals, measurements of the substrate core levels reveal that interpretations in terms of a simple initial state charge transfer picture do not explain the observed changes in the core level blnding energies. Values for thermo-dynamical parameters such as adhesion energies and segregation energies are extracted from the layer resloved core level binding energy shifts. Conversely, the various core level binding energy shifts measured for the different systems are estimated using thermo-dynamical models, and difficultles when using these models are discussed. For alkali films on sp-metal substrates a surprisingly regular relation is found between the alkali core level binding energy shifts and the difference in rs of the sp-metal substrate and the adsorbate. Turning to submonolayer alkali adsorption, Na,K,Rb, and Cs have been adsorbed on Al(lll) at Room Temperature (RT) and at 100 K. It is shown that alkali adsorption at RT leads to a disruption of the outermost Al layer in the Al(lll) surface. Island formation is found for Na,K, and Rb at 100 K and for Na and K at RT. In the case of Na adsorption on Al(lll) at RT, the Na and the Al atoms at the interface are found to intermix and a multilayer surface alloy is formed. It is demonstrated how such a surface alloy can be analyzed by HRCLS. The surface geometry of the Al(111)-(2x2)-Na is determined by quantitative LEED. The local geometry is shown to be different when adsorbing K and Rb on Al(lll) and Na on Al(100) at RT compared to adsorption at 100 K, even though the long range order is the same at RT and at 100 K as observed by LEED. The geometry of the Al(lll)-( v 3x v 3)R30 -Rb structure is determined by quantitative LEED for adsorption at 100 K and at RT. An on top site is found at 100 K and a substitutional site at RT adsorption. The details of the irreversible transformation between these two sites are studied with HRCLS. In addition, Na and K on Al(100) at 100 K have been investigated. It is shown that both Na and K condense into islands on the Al(100) surface.
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| 3. |
- Söderholm, S, et al.
(författare)
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A photoemission spectroscopy and X-ray absorption study of Bi(2)Sr(2)CaCu(2)O(8) single crystal with adsorbed Cs: On the origin of states affected by electron doping and evidence for spatially resolved electron doping
- 1996
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 8, s. 1307-1320
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Tidskriftsartikel (refereegranskat)abstract
- The influence of electron doping, via deposition of small amounts of Cs, on the electronic structure of has been studied by high-resolution photoelectron spectroscopy (PES) and x-ray absorption spectroscopy (XAS), utilizing synchrotron radiation. The changes in the electronic structure were monitored by PES of the valence band and of the O 1s, Bi 4f, Bi 5d, Ca 2p and Sr 3d core levels, and by XAS at the O 1s, Cu 2p and Ca 2p edges. The experimental data suggest that the loss of the Fermi edge and the loss of spectral intensity down to about 2 eV below the Fermi level, and the substantial loss of spectral intensity of the pre-edge structure in the O 1s XAS spectrum are mainly due to annihilation of states with O 2p character in the Cu - O layer. It is evident from bulk- and surface-sensitive XAS spectra that the electron doping by Cs affects the electronic structure more strongly close to the surface. This implies that the doping occurs locally and that the charge transfer between the different layers in the unit cell is not uniform. Thus it seems possible to alter the electronic properties of locally through spatially resolved electron doping. When larger amounts of Cs are deposited, a chemical reaction occurs which causes a disruption of the Bi - O layer. This deposition regime is characterized by the presence of caesium oxide and reduced (metallic) Bi.
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