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| 2. |
- Lindgren, S.Å., et al.
(författare)
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Surface state energy shifts by molecular adsorption : CO on clean and Na covered Cu(111)
- 1982
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 117:1-3, s. 426-433
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Tidskriftsartikel (refereegranskat)abstract
- Angle resolved photoelectron energy spectra recorded in the near UV show that the surface state 0.4 eV below EF of Cu(111) shifts to higher energy upon CO adsorption. The surface band related emission intensity is reduced by the adsorption at a rate suggesting that each adsorbed molecule wipes out the surface state over an area corresponding to seven surface layer Cu atoms. The surface state energy shift is not as closely related to the adsorbate induced workfunction change as found theoretically and experimentally for alkali adsorbates. The influence on the shift of the workfunction and initial energy of the surface state is studied by preadsorbing Na on the Cu(111) surface.
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| 3. |
- Paul, Jan, et al.
(författare)
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Catalytic active sites on sputtered metal surfaces
- 1983
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 127:1, s. L93-L97
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Tidskriftsartikel (refereegranskat)abstract
- By the use of Hartree-Fock-Slater (HFS) cluster calculations, the symmetry of adatom induced electronic states and their possible role in catalytic processes have been investigated. For iron adsorbed on a close packed iron single crystal surface we find an increased density of occupied "π" as well as "σ" states at the Fermi level. Simple group theoretical arguments give that the "π" states, which represent the highest occupied molecular orbitais (HOMO) will mix with the lowest unoccupied molecular orbital (LUMO) of CO, 2π*, assuming CO bound normal to the surface in a terminal position with respect to the adatom. Such a system with an adsorbed atom on a flat surface is a model for a sputtered surface and these "π" states may thus explain the experimentally observed high rate of dissociation for CO on sputtered iron surfaces. A comparative study shows that no such increased density of states (DOS) is found when the Fe adatom is replaced by potassium. Finally for Cu adsorbed on Cu(111) only 4s derived "σ" states are introduced close to the Fermi level.
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| 4. |
- Paul, Jan, et al.
(författare)
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The reactivity of adsorbed Na atoms probed by coadsorbed CH3OH
- 1984
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 146:1, s. 43-60
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Tidskriftsartikel (refereegranskat)abstract
- The chemical properties of sodium atoms adsorbed on a Cu(111) surface have been probed by coadsorbed methanol. Methoxide, stoichiometrically close to CH3ONa2, is identified as a product by photoemission spectroscopy. Sodium atoms are found to react in the same manner at all submonolayer coverages, i.e. independent of atomic charge. Films of closely packed Na atoms - the first sp-metal substrate probed by methanol - are slightly less reactive. Hartree-Fock-Slater cluster calculations as well as observed energy shifts of a Cu electronic surface state indicate a transfer of charge from the copper substrate to the methoxide group. The desorption temperature for a monolayer of methanol molecules from a Cu(111) surface is enhanced by the presence of low sodium concentrations (1/20 of a monolayer). CH3OH is found to adsorb associatively on the uncovered Cu(111) surface.
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| 5. |
- Petersson, L-G, et al.
(författare)
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Hydrogen dissociation on clean and contaminated Pd studied with a Pd-MOS structure.
- 1982
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 117, s. 676-
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Tidskriftsartikel (refereegranskat)abstract
- We show how a new combination of methods can be used in order to gain information on hydrogen dissociation on Pd and on its dependence on the electronic structure. With this method we can also detect changes in hydrogen pressure of about 1×10−11 Torr H2 corresponding to hydrogen coverages on the Pd surface of about 0.001 of a monolayer.
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