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- Lundwall, Marcus, et al.
(författare)
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Photon energy dependent intensity variations observed in Auger spectra of free argon clusters
- 2006
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:16, s. 3321-3333
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Tidskriftsartikel (refereegranskat)abstract
- Photon energy dependent intensity variations are experimentally observed in the L2,3M2,3M2,3 Auger spectra of argon clusters. Two cluster sizes are examined in the present study. Extrinsic scattering effects, both elastic and inelastic, involving the photoelectron are discussed and suggested as the explanation of the variations in the Auger signal. The atoms in the first few coordination shells surrounding the core-ionized atom are proposed to be the main targets for the scattering processes.
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- Lundwall, Marcus, et al.
(författare)
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Preferential site occupancy observed in coexpanded argon-krypton clusters
- 2006
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 74:4, s. 043206-
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Tidskriftsartikel (refereegranskat)abstract
- Free heterogeneous argon-krypton clusters have been produced by coexpansion and investigated by means of x-ray photoelectron spectroscopy. By examining cluster surface and bulk binding energy shifts, relative intensities, and peak widths, we show that in the mixed argon-krypton clusters the krypton atoms favor the bulk and argon atoms are pushed to the surface. Furthermore, we show that krypton atoms in the surface layer occupy high-coordination sites and that heterogeneous argon-krypton clusters produced by coexpansion show the same surface structure as argon host clusters doped with krypton. These observations are supported by site-dependent calculations of chemical shifts.
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- Lundwall, Marcus, 1977-
(författare)
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Rare-gas Clusters Studied by Electron Spectroscopy : Structure of Heterogeneous Clusters and Effects of Electron Scattering on Auger Decay
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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- Lundwall, Marcus, et al.
(författare)
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Self-assembled heterogeneous argon/neon core-shell clusters studied by photoelectron spectroscopy
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:21, s. 214706-
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Tidskriftsartikel (refereegranskat)abstract
- Clusters formed by a coexpansion process of argon and neon have been studied using synchrotron radiation. Electrons from interatomic Coulombic decay as well as ultraviolet and x-ray photoelectron spectroscopy were used to determine the heterogeneous nature of the clusters and the cluster structure. Binary clusters of argon and neon produced by coexpansion are shown to exhibit a core-shell structure placing argon in the core and neon in the outer shells. Furthermore, the authors show that 2 ML of neon on the argon core is sufficient for neon valence band formation resembling the neon solid. For 1 ML of neon the authors observe a bandwidth narrowing to about half of the bulk value.
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- Peredkov, Sergey, et al.
(författare)
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Free nanoscale sodium clusters studied by core-level photoelectron spectroscopy
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:23, s. 235407-
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Tidskriftsartikel (refereegranskat)abstract
- Free sodium metal clusters have been studied by probing the Na2p core level using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The development of electronic structure with size has been studied and discussed in comparison with the atom, dimer, and solid. Information on cluster metallic properties, size, and temperature has been deduced from the XPS measurements. For the large ⟨N⟩>103 Na clusters, the surface and bulk sites have been separated in the photoelectron signal. Auger spectra allowed extracting the information on the valence band. The present study introduces core-level spectroscopies XPS and AES into the field of free neutral metal cluster research.
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