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Enhanced surface sensitivity in AES relative to XPS observed in free argon clusters
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
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2005 In: Surf. Sci., Vol. 594, 12-19 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2005. Vol. 594, 12-19 p.
URN: urn:nbn:se:uu:diva-95323OAI: oai:DiVA.org:uu-95323DiVA: diva2:169493
Available from: 2007-01-16 Created: 2007-01-16Bibliographically approved
In thesis
1. Rare-gas Clusters Studied by Electron Spectroscopy: Structure of Heterogeneous Clusters and Effects of Electron Scattering on Auger Decay
Open this publication in new window or tab >>Rare-gas Clusters Studied by Electron Spectroscopy: Structure of Heterogeneous Clusters and Effects of Electron Scattering on Auger Decay
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this Thesis experimental studies of nano-clusters using synchrotron radiation based photoelectron (UPS and XPS) and Auger Electron Spectroscopy (AES) are presented. The investigations may be divided into two parts where the first reports on the structure of heterogeneous two component clusters, and the second concerns electronic decay processes.

Using photoelectron spectroscopies as investigative tools the radial composition of heteroclusters of argon mixed with xenon, krypton or neon has been determined. Two methods of heterogeneous cluster production were employed: co-expansion and doping/pick-up. By analyzing the line shapes, energy positions, and widths of the spectral cluster features the radial composition of the clusters produced by co-expansion were found to form close-to-equilibrium structures, placing the component with larger cohesive energy in the cluster core while the second component was to varying degree segregated toward the surface. By instead using the doping/pick-up technique the opposite radial structures, i.e. far-from-equilibrium structures, may be formed. In the case of argon/krypton clusters a similar surface structure is formed regardless of production technique.

The second part of the Thesis concerns post-ionization decay processes. Experimental evidence for the Interatomic Coulombic Decay process, a theoretically predicted decay channel, is presented in a study of homogeneous neon clusters. The time scale of the decay was determined to 6±1 fs for bulk atoms and >30 fs for surface atoms in the neon cluster, showing the connection between local geometry and dynamics of the decay.

Another channel for electronic relaxation is Auger decay. This Thesis presents a method of disentangling the spectral surface and bulk responses from clusters in Auger spectra. Studies of argon clusters show that the AES technique is more surface sensitive than XPS, even at the same electron kinetic energy. Furthermore, the effect scattering of the photoelectron has on the Auger spectra was investigated. Special effort was put into explaining an experimentally observed photon energy dependent intensity appearing on the high-kinetic energy side on the Auger signal. We propose that this intensity is due to a solid state-specific photoelectron recapture process we name Pre-Auger Recapture (PAR), which affects the kinetic energy of the Auger electrons.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 85 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 260
Physics, Nano-particles, Clusters, Heterogeneous clusters, Core-shell clusters, XPS, UPS, AES, Electron scattering, Radial structure, Surface structure, Surface sensitivity, Synchrotron radiation, Ne, Ar, Kr, Xe, Fysik
National Category
Natural Sciences
urn:nbn:se:uu:diva-7431 (URN)978-91-554-6769-2 (ISBN)
Public defence
2007-02-09, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Available from: 2007-01-16 Created: 2007-01-16 Last updated: 2016-08-24Bibliographically approved

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