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| 2. |
- Andersson, Tomas, et al.
(författare)
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Photon energy influence on valence photoelectron spectra of silver clusters
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:15, s. 152028-
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Tidskriftsartikel (refereegranskat)abstract
- Silver clusters in the size range of ∼102 constituent atoms have been studied using photoelectron spec-troscopy. The 5s and 4d valence bands have been probed with 40 and 60.5 eV photon energies. Differences in the valence band spectral features have been observed and are discussed in view of earlier results on copper clusters and in terms of differences in mean free path for electrons of different energies.
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| 3. |
- Andersson, Tomas, et al.
(författare)
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Plasmon single- and multi-quantum excitation in free metal clusters as seen by photoelectron spectroscopy
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:9, s. 094511-
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Tidskriftsartikel (refereegranskat)abstract
- Plasmons are investigated in free nanoscale Na, Mg, and K metal clusters using synchrotron radiation-based x-ray photoelectron spectroscopy. The core levels for which the response from bulk and surface atoms can be resolved are probed over an extended binding energy range to include the plasmon loss features. In all species the features due to fundamental plasmons are identified, and in Na and K also those due to either the first order plasmon overtones or sequential plasmon excitation are observed. These features are discussed in view of earlier results for planar macroscopic samples and free clusters of the same materials.
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| 4. |
- Arion, Tiberiu, et al.
(författare)
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New insight into the Auger decay process in O-2: The coincidence perspective
- 2012
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 185:8-9, s. 234-243
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron-Auger electron coincidence spectroscopy is a powerful tool for the investigation of Auger decay processes with different core-ionized intermediate states. In this paper we describe an investigation into the Auger decay of the O-2 molecule, with the purpose of bringing new insight into the dynamics of the core hole decay mechanism. Using a novel experimental approach to measuring such coincidence spectra we report the highest resolution Auger spectrum of O-2 recorded hitherto. In our approach, we have combined the advantages of these coincidence spectra with the high resolution and excellent signal-to-noise ratios of non-coincident Auger spectra and a state-of-the-art fit analysis. In this way we have derived information about the potential energy curves of the final states W-3 Delta(u), B-3 Pi(g), and B' (3)Sigma(-)(u) and concluded that the corresponding Auger transitions are formed to a large part by strongly overlapping vibrational progressions. The present findings are compared to earlier results reported in the literature confirming some theoretical predictions. (C) 2012 Elsevier B.V. All rights reserved.
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| 6. |
- Bergersen, Henrik, et al.
(författare)
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A photoelectron spectroscopic study of aqueous tetrabutylammonium iodide
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:32, s. 326101-
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectra of tetrabutylammonium iodide (TBAI) dissolved in water have been recorded using a novel experimental set-up, which enables photoelectron spectroscopy of volatile liquids. The set-up is described in detail. Ionization energies are reported for I− 5p, I− 4d, C 1s and N 1s. The C 1s spectrum shows evidence of inelastic scattering of the photoelectrons, that differs from the case of TBAI in formamide.
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| 7. |
- Bergersen, Henrik, et al.
(författare)
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First observation of vibrations in core-level photoelectron spectra of free neutral molecular clusters
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 429:1-3, s. 109-113
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Tidskriftsartikel (refereegranskat)abstract
- Core-level photoelectron spectra of free neutral methane clusters have been recorded. These spectra exhibit well-resolved surface and bulk features as well as vibrational fine structure. The vibrational structure in the cluster signal is well reproduced by a theoretical model that assumes independent contributions from inter- and intramolecular modes. The intramolecular contribution to the vibrational line-shape is taken to be equal to that of the monomer in the gas phase, while the intermolecular part is simplified to line broadening. An estimate of the cluster size has been made on the basis of the observed surface-to-bulk intensity ratio.
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| 8. |
- Bergersen, Henrik, 1978-
(författare)
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Free Neutral Clusters and Liquids Studied by Electron Spectroscopy and Lineshape Modeling
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electronic and geometrical structure of free neutral clusters and liquids have been studied using synchrotron-radiation based photoelectron and Auger electron spectroscopy in combination with lineshape modeling. A novel experimental setup has been developed for studies of liquids, based on the liquid microjet technique. Theoretical lineshapes have been computed using both classical (molecular dynamics) and quantum mechanical (mainly density functional theory) methods.Clusters are finite ensembles of atoms or molecules, ranging in size from a few to several thousand atoms. Apart from being fundamentally interesting, clusters are also promising as building blocks for nano-technology. In this thesis results are presented for rare-gas and molecular clusters, ranging from weakly van-deer-Waals bonded to hydrogen bonded. It is shown that the combination of core-level photoelectron spectroscopy (XPS) and lineshape modeling can be used to estimate the sizes of clusters. A model for treating the effect of inter-molecular nuclear relaxation upon ionization is proposed. The structure of single-component molecular clusters are investigated by molecular dynamics simulations, validated against XPS data. Finally, the radial structure of a two-component molecular cluster is investigated by XPS.Liquids have been studied for centuries, but still many questions remain regarding the microscopic properties. With the recent development of the liquid microjet technique, new insight into the atomic structure can be obtained. In this thesis we study aqueous solutions using photoelectron and Auger electron spectroscopy (AES). We investigate the structure of surface active molecules by XPS, study the Auger decay after core-level ionization in aqueous potassium chloride (KCl), and follow the changes in molecular structure of glycine as a function of pH.
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| 9. |
- Bergersen, Henrik, et al.
(författare)
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Two size regimes of methanol clusters produced by adiabatic expansion
- 2006
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:18, s. 184303-
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Tidskriftsartikel (refereegranskat)abstract
- Free neutral methanol clusters produced by adiabatic expansion have been studied by photoelectron spectroscopy and line shape modeling. The results show that clusters belonging to two distinct size regimes can be produced by changing the expansion conditions. While the larger size regime can be well described by line shapes calculated for clusters consisting of hundreds of molecules, the smaller size regime corresponds to methanol oligomers, predominantly of cyclic structure. There is little contribution from dimers to the spectra.
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| 10. |
- Björneholm, Olle, et al.
(författare)
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Deeper Insight into Depth-Profiling of Aqueous Solutions Using Photoelectron Spectroscopy
- 2014
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:50, s. 29333-29339
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) is widely used to probe properties such as molecular stoichiometry, microscopic distributions relative to the surface by so-called depth-profiling, and molecular orientation. Such studies usually rely on the core-level photoionization cross sections being independent of molecular composition. The validity of this assumption has recently been questioned, as a number of gas-phase molecules have been shown to exhibit photon-energy-dependent nonstochiometric intensity oscillations arising from EXAFS-like modulations of the photoionization cross section. We have studied this phenomenon in trichloroethanol in both gas phase and dissolved in water. The gas-phase species exhibits pronounced intensity oscillations, similar to the ones observed for other gas-phase molecules. These oscillations are also observed for the dissolved species, implying that the effect has to be taken into account when performing depth-profiling experiments of solutions and other condensed matter systems. The similarity between the intensity oscillations for gas phase and dissolved species allows us to determine the photoelectron kinetic energy of maximum surface sensitivity, approximate to 100 eV, which lies in the range of pronounced intensity oscillations.
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