| 1. |
- Hoffmann, F.M., et al.
(författare)
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A FT-IRAS study of the vibrational properties of CO adsorbed on Cu/Ru(001) : II: The dispersion of copper
- 1987
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 87:3, s. 1857-1865
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Tidskriftsartikel (refereegranskat)abstract
- The dispersion of copper adsorbed on a Ru(001) substrate has been investigated by using Fourier transform-infrared reflection absorption spectroscopy (FT-IRAS) and carbon monoxide as a molecular probe. Copper films evaporated at 85 K show a drastically different CO adsorption behavior compared to annealed films and exhibit a variety of adsorption sites. Characteristic C-O stretching frequencies allow us to identify small copper clusters of 1-4 atoms (2138-2123 cm-1), two-dimensional (2120-2110 cm-1) and three-dimensional (2098 cm-1) copper aggregates. After annealing to 250 K copper films at sub- and monolayer coverages form well-ordered small two- and three-dimensional copper aggregates. Formation of the epitaxial monolayer or islands of copper (2082 cm-1) requires a surprizingly mild annealing temperature of 350 K. Further annealing to 540 K results in increasing domain size of the copper islands or annealing of defect sites of the epitaxial monolayer. Multilayer coverages of copper evaporated at 85 K exhibit C-O stretching frequencies found for high-index copper single crystal surfaces, e.g., (211) and (755). This indicates a large number of surface steps and protruding copper atoms associated with rough films. Annealing to 540 K results in a smooth copper layer with preferential (111) orientation (2075 cm-1). The vibrational data presented here for Cu-Ru(001) agree well with previous reports of CO adsorption on copper single crystals, supported or evaporated films, and matrix-isolated clusters. They further allow us to determine the dispersion of supported Cu-Pt and Cu-Ni catalysts from data in the literature.
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| 2. |
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| 3. |
- Larsson, C.G., et al.
(författare)
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Diffraction of UV excited photoelectrons by an ordered overlayer
- 1983
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T4, s. 44-46
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Tidskriftsartikel (refereegranskat)abstract
- Angle resolved UV photoemission spectra obtained from Cu(111)-(√3 × √3)R30° Xe and Cu(111)-(√3 × √3)R30° CO samples are compared with spectra obtained from the clean substrate. Interest is focussed on the adsorbate induced changes in the Cu3d band range of initial energies. From the similarity between the spectra observed for the ordered Xe and CO overlayers we conclude that the changes are primarily due to diffraction of the photoexcited Cu3d electrons by the adsorbate. This is supported also by calculated photoelectron energy distributions.
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| 4. |
- Lindgren, S.Å., et al.
(författare)
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Low-energy electron diffraction from close-packed Na
- 1982
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Ingår i: Journal of Physics. C, Solid State Physics. - : IOP Publishing. - 0022-3719. ; 15:30, s. 6285-6291
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Tidskriftsartikel (refereegranskat)abstract
- The authors obtain a homogeneously thick film of close-packed Na with close-packed planes parallel to the surface by evaporating Na onto Cu(111) held at LN2 temperature. Comparison between measured LEED intensity spectra, recorded at LN2 temperature, and theoretical ones, calculated under the assumption that the crystal structure of Na is FCC or HCP, favours the HCP structure. The authors UPS results indicate that if Na is evaporated onto Cu(111) held at RT, it will form three-dimensional clusters on top of a Na film only few atomic layers thick.
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| 5. |
- Lindgren, S.Å., et al.
(författare)
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Photoemission of backbonding electrons from CO chemisorbed on Cu(III)
- 1981
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 84:3, s. 487-490
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved photoclectron energy spectra recorded in the normal direction for a CO-exposed Cu(111) sample show a peak at the Fermi edge for high monolayer coverages. We associate this peak with a filled part of a resonance-broadened CO 2π level.
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| 6. |
- Lindgren, S.Å., et al.
(författare)
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Sodium induced structure in UPS spectra of Cu(111)/Na
- 1985
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 155:1, s. 165-172
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Tidskriftsartikel (refereegranskat)abstract
- UPS Spectra of sodium monolayers evaporated onto Cu(111) are presented. We interpret sodium induced structure below the Cu d-band as due to photoemitted 3d electrons which have experienced an energy loss by exciting a sodium monolayer plasmon. An experimental difficulty is that even small amounts (<1/10 monolayers) of water contamination produces structure in the same energy range. This emission is due to the OH 1π orbital. Hydroxide groups may also origin from the alkali source if this is operated at too elevated temperatures.
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| 7. |
- 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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