| 1. |
- Hedin, Lars, et al.
(författare)
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Sudden approximation in photoemission and beyond
- 2002
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 124:2-3, s. 289-315
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Tidskriftsartikel (refereegranskat)abstract
- The conditions behind sudden approximation are critically examined. The fuzzy band expression is derived in detail from first principles. We go beyond the sudden approximation to account for both extrinsic losses and interference effects. In an extension of earlier work we discuss both core and valence satellites including both intrinsic and extrinsic amplitudes, and high energy excitations as well as low energy electron-hole pairs. We show how the extrinsic losses in photoemission can be connected with the electron energy loss function. This is achieved by three approximations, to connect the dynamically screened potential in the bulk solid to the loss function, to account for the surface, and lastly to extrapolate zero momentum loss data to include dispersion. The extrinsic losses are found to be weak for small loss energies. For larger loss energies the extrinsic losses can be strong and have strong interference with the intrinsic losses depending on the nature of the solid. The transition from the adiabatic to the sudden regime is discussed for atoms and localized systems and compared with the situation for solids. We argue that in solids for photoelectron energies above some 10 eV the external losses are mainly connected with spacially extended excitations. We discuss strongly correlated quasi-two-dimensional solids with Bi2212 as example, and find an asymmetric broadening of the main peak from shake up of acoustic three-dimensional plasmons. In the superconducting state the loss function is assumed to have a gap, which then leads to a peak-dip-hump structure in the photoemission spectrum. This structure is compared with a corresponding structure in tunneling. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 2. |
- Zakharov, Alexei, et al.
(författare)
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Anisotropy of the electronic structure of low-dimensional Sr(Ca)CuO2 single crystals studied by scanning photoelectron spectromicroscopy
- 2002
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 122:3, s. 203-208
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Tidskriftsartikel (refereegranskat)abstract
- The energy band structure of superconducting (T-c(onset) = 80 K), low-dimensional Sr(Ca)CuO2 single crystals was studied by photoelectron spectromicroscopy. The sample consists of double parallel Cu-O chains, and spectra show a strong anisotropy for electron momenta k parallel and perpendicular to the chain direction q. Spectra were collected with two experimental setups: kparallel toq (Aperpendicular toq) and kperpendicular toq (Aparallel toq), where A is the electric field vector of the incident photon beam. By imaging the surface on the micrometer scale we find significant variations in the valence band intensity in the vicinity of about 2 eV below the Fermi level for kparallel toq. For this geometry, Aperpendicular toq and the spectra are very sensitive to beam damage. This effect can be related to the breaking of weak inter-chain bonds with the high flux density (similar to10(18) photons s(-1) cm(-2)) beam focused on the sample surface.
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| 3. |
- Crispin, Xavier, et al.
(författare)
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Understanding the initial stages of polymer grafting on metals : A photoelectron spectroscopy study of acrylonitrile adsorption on transition metal surfaces
- 2001
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 121:1-3, s. 57-74
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Tidskriftsartikel (refereegranskat)abstract
- X-ray and UV photoelectron spectroscopies show that acrylonitrile is chemisorbed on iron, nickel and copper polycrystalline surfaces via the carbon and nitrogen atoms. Depending on the conditions used, different adsorption geometries are found. The molecules can either be adsorbed flat on the surface and chemically bound by a (2pp)-(3d/4s) overlap via both the C=C double bond and the C=N nitrile group or they can be adsorbed perpendicular to the surface via a covalent interaction between the nitrogen lone pair and the 3d-4s levels of the metals. Analysis of the XPS data obtained on molecular mono-layers chemisorbed on metal surfaces emphasizes the importance of initial-state effects (charge transfer upon chemisorption, contribution of the metal surface dipole) and final-state effects (metal screening and polarization effect within the mono-layer). The correlation between the XPS and UPS data illustrates the importance of the metal surface dipole in understanding the workfunction changes upon molecular adsorption on metal surfaces. © 2001 Elsevier Science B.V. All rights reserved.
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| 4. |
- Giovanelli, L., et al.
(författare)
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Electronic structure of self-assembled organic/inorganic semiconductor interfaces : lead phthalocyanine on InSb and InAs(100)-4X2/c(8 X2)
- 2001
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 114, s. 375-381
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial properties of ultra thin films of lead-phthalocyanine deposited in situ onto InSb and InAs(100)-4X2/c(8X2) clean surfaces have been studied by synchrotron radiation core level and valence band photoelectron spectroscopy. The interaction between the overlayers and the substrates was determined upon analyzing the changes in the photoemission spectra between room and higher annealing temperatures, leading to ordered monolayer films. While weaker than on other substrates, a reactivity is nevertheless present: the organic macrocycle preserves its integrity up to 320 degreesC but the Pb central atom first leaves the molecules most probably to be incorporated in the substrate surface, before being desorbed at higher temperatures.
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| 5. |
- Greczynski, G., et al.
(författare)
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Photoelectron spectroscopy of thin films of PEDOT-PSS conjugated polymer blend : A mini-review and some new results
- 2001
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 121:1-3
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Forskningsöversikt (refereegranskat)abstract
- We present an overview of the photoelectron spectroscopy studies of thin films of the commercially important, electrically conducting polymer blend poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate), PEDOT-PSS. The issues discussed include the study of thermal effects, the influence of hydrochloric acid on the chemical and electronic structures of the films, phase segregation, as well as the energy level alignment at interfaces employing a PEDOT-PSS layer. All of these issues are important in applications of PEDOT-PSS as a hole-injecting electrode in polymer-based, light-emitting devices. Among the most important results are the identification of the three chemically different species in pristine PEDOT-PSS, namely poly(4-styrenesulfonic acid), poly(sodium 4-styrenesulfonate) and poly(3,4-ethylenedioxythiophene), the conversion of the sodium salt into free poly(styrenesulfonic acid) upon HCl treatment, and the decomposition of the free sulfonic acid component (presumably through loss of SO3H) induced by annealing. It is also shown that phase segregation occurs in the PEDOT-PSS system, resulting in a predominance of PSS in the surface region. This issue has been studied using different approaches, including X-ray photoelectron spectroscopy studies of the sulfur S(2p) and oxygen O(1s) core levels, ultraviolet photoelectron spectroscopy of the valence band region combined with reference measurements and quantum chemical calculations, as well as variable photon energy investigations of sulfur S(2p) core levels. It is demonstrated that, in the context of the energy level alignment at the polymer-metal interfaces, PEDOT-PSS shows metallic-like behavior. Due to the latter, the insertion of a thin PEDOT-PSS layer between the hole-injecting electrode ITO and a polymer layer of poly(bis-(2-dimethyloctylsilyl)-1,4-phenylenevinylene) leads to the lowering of the barrier for hole injection, independent of the work function of the underlying ITO. PEDOT-PSS is also used to show the alignment of the electrochemical potential across metal-polymer-metal structures. © 2001 Elsevier Science B.V. All rights reserved.
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| 6. |
- Gunnarsson, O., et al.
(författare)
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Information from photoemission spectral weights and shapes
- 2001
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 117-118, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Photoemission line shapes can be used to extract important information about ground-state and low-energy properties. This is illustrated for the electron–phonon interaction in C60 molecules, the occupancy and hybridization of the 4f-level in Ce compounds, the effect of the Cu–O network on core-level photoemission in cuprates and the properties of one-dimensional conductors.
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| 7. |
- Hemmers, O., et al.
(författare)
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Dipole and nondipole angular-distribution effects in valence photoemission from neon
- 2002
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048. ; 123:2-3, s. 257-264
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Tidskriftsartikel (refereegranskat)abstract
- Nondipole angular-distribution parameters γ and δ for neon 2s and 2p photoelectrons have been measured and are compared to all available theoretical data. The agreement is very good throughout the 150-1200 eV photon-energy range studied. Furthermore, the neon 2p dipole angular-distribution parameter β and the 2s to 2p cross-section ratio have been measured throughout the same photon-energy range. The agreement between theoretical data and experiment is excellent.
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| 8. |
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| 9. |
- Petoral, Rodrigo Jr, et al.
(författare)
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XPS and NEXAFS study of tyrosine-terminated propanethiol assembled on gold
- 2003
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 128:2-3, s. 159-164
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Tidskriftsartikel (refereegranskat)abstract
- Tyrosine-terminated propanethiol (TPT), tyrosine linked to 3-mercaptopropionic acid through an amide bond, is adsorbed to gold surfaces. The adsorbates are characterized by means of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). XPS is used to investigate the chemical binding and electronic structure of the monolayer. Strong molecular binding of the tyrosine derivative on the gold surface through the sulfur atom is attained. Angle-dependent XPS results shows that TPT molecules are oriented with the sulfur atoms molecularly oriented close to the gold surface and that the phenol moiety is oriented away from the gold surface. Average orientation of the adsorbate on gold is deduced using the NEXAFS results. It shows that the main molecular axis is tilted approximately 38° relative to the Au surface normal. The ring plane of the phenol moiety exhibits a preferential orientation with an average tilt angle of the normal of the ring plane from the surface normal of about 60°.
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| 10. |
- Plashkevych, O., et al.
(författare)
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Calculations of valence electron binding energies using Kohn-Sham theory and transition potentials
- 2000
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 106:1, s. 51-63
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the success in computing X-ray photoelectron binding energies and chemical shifts in the core region we apply the Kohn-Sham density functional and transition potential methodology to calculations of binding energies in the valence electron region. Accurate predictions of binding energies over a large energy interval are obtained for a set of molecules for which the quasi-particle approximation holds, but which still have been considered notoriously difficult. The accuracy is found to be a few tenths of an eV in the outermost valence region, slightly poorer in the intermediate region, and seems to be maintained with increasing size of the system.
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