1. |
- Abu-samha, M, et al.
(author)
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Lineshapes in carbon 1s photoelectron spectra of methanol clusters
- 2006
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 8:21, s. 2473-2482
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Journal article (peer-reviewed)abstract
- A general protocol for theoretical modeling of inner-shell photoelectron spectra of molecular clusters is presented and applied to C1s spectra of oligomers and medium-sized clusters of methanol. The protocol employs molecular dynamics for obtaining cluster geometries and a polarizable force field for computing site-specific chemical shifts in ionization energy and linewidth. Comparisons to spectra computed from first-principle theories are used to establish the accuracy of the proposed force field approach. The model is used to analyze the C1s photoelectron spectrum of medium-sized clusters in terms of surface and bulk contributions. By treating the surface-to-bulk ratio as an adjustable parameter, satisfactory fits are obtained to experimental C1s spectra of a beam of methanol clusters.
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2. |
- Andersson, Tomas, 1984-
(author)
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Free Metal Clusters Studied by Photoelectron Spectroscopy
- 2012
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Doctoral thesis (other academic/artistic)abstract
- Clusters are aggregates of a finite number of atoms or molecules. In the present work, free clusters out of metallic parent materials have been created and studied by synchrotron radiation-based photoelectron spectroscopy. The clusters have been formed and studied in a beam and the electronic structure of the clusters has been investigated. Conclusions have been drawn about the spatial distribution of atoms of different elements in bi-component clusters, about the development of metallicity in small clusters, and about the excitation of plasmons.Bi-component alloy clusters of sodium and potassium and of copper and silver have been produced. The site-sensitivity of the photoelectron spectroscopy technique has allowed us to probe the geometric distribution of the atoms of the constituent elements by comparing the responses from the bulk and surface of the clusters. In both cases, we have found evidence for a surface-segregated structure, with the element with the largest atoms and lowest cohesive energy (potassium and silver, correspondingly) dominating the surface and with a mixed bulk.Small clusters of tin and lead have been probed to investigate the development of metallicity. The difference in screening efficiency between metals and non-metals has been utilized to determine in what size range an aggregate of atoms of these metallic parent materials stops to be metallic. For tin this has been found to occur below ~40 atoms while for lead it happened somewhere below 20-30 atoms.The excitation of bulk and surface plasmons has been studied in clusters of sodium, potassium, magnesium and aluminium, with radii in the nanometer range. The excitation energies have been found to be close to those of the corresponding macroscopic solids. We have also observed spectral features corresponding to multi-quantum plasmon excitation in clusters of Na and K. Such features have in macroscopic solids been interpreted as due to harmonic plasmon excitation. Our observations of features corresponding to the excitation of one bulk and one surface plasmon however suggest the presence of sequential excitation in clusters.
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3. |
- Andersson, Tomas, et al.
(author)
-
Plasmon single- and multi-quantum excitation in free metal clusters as seen by photoelectron spectroscopy
- 2011
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:9, s. 094511-
-
Journal article (peer-reviewed)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. |
- Andersson, Tomas, et al.
(author)
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The electronic structure of free aluminum clusters: Metallicity and plasmons
- 2012
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:20
-
Journal article (peer-reviewed)abstract
- The electronic structure of free aluminum clusters with similar to 3-4 nm radius has been investigated using synchrotron radiation-based photoelectron and Auger electron spectroscopy. A beam of free clusters has been produced using a gas-aggregation source. The 2p core level and the valence band have been probed. Photoelectron energy-loss features corresponding to both bulk and surface plasmon excitation following photoionization of the 2p level have been observed, and the excitation energies have been derived. In contrast to some expectations, the loss features have been detected at energies very close to those of the macroscopic solid. The results are discussed from the point of view of metallic properties in nanoparticles with a finite number of constituent atoms. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4718362]
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5. |
- Babenkov, Sergey V., et al.
(author)
-
Hybrid organic-inorganic systems formed by self-assembled gold nanoparticles in CuPcF4 molecular crystal
- 2016
-
In: Organic Electronics. - : Elsevier BV. - 1566-1199. ; 32, s. 228-236
-
Journal article (peer-reviewed)abstract
- In this work we have fabricated and studied hybrid organic-inorganic nanocomposite system formed by gold nanoparticles self-assembled in organic semiconductor thin film - copper tetrafluorophthalocyanine (CuPcF4). By means of Photoelectron Spectroscopy and Transmission Electron Microscopy (TEM) the evolution of the morphology and electronic structure of the system as a function of nominal gold content have been investigated. The gold atoms, deposited onto the CuPcF4 surface, diffuse into the organic matrix and self-assemble to nanoparticles in a well-defined manner with a narrow size distribution, which depends on the amount of deposited gold. Using High-Resolution TEM, we were able to observe the atomic planes of single gold nanoparticles and their coalescence processes. Photoelectron spectroscopy has not revealed any detectable chemical reaction between gold and organic. However, the strong upward band bending, induced by gold nanoparticles in the organic film, takes place.
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6. |
- Bergersen, Henrik, et al.
(author)
-
First observation of vibrations in core-level photoelectron spectra of free neutral molecular clusters
- 2006
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 429:1-3, s. 109-113
-
Journal article (peer-reviewed)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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7. |
- Bergersen, Henrik, 1978-
(author)
-
Free Neutral Clusters and Liquids Studied by Electron Spectroscopy and Lineshape Modeling
- 2008
-
Doctoral thesis (other academic/artistic)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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8. |
- Bergersen, Henrik, et al.
(author)
-
Two size regimes of methanol clusters produced by adiabatic expansion
- 2006
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:18, s. 184303-
-
Journal article (peer-reviewed)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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9. |
- Björneholm, Olle, et al.
(author)
-
Free clusters studied by core-level spectroscopies
- 2009
-
In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576 .- 0167-5087. ; 601:1-2, s. 161-181
-
Research review (peer-reviewed)abstract
- In this review we describe the development and current status of free clusters studied using core-level spectroscopies. This topic ranges from simple model systems, such as rare gas clusters, to molecular clusters, and clusters of solids, held together by ionic, covalent and metallic bonding.
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10. |
- Feifel, Raimund, et al.
(author)
-
From localised to delocalised electronic states in free Ar, Kr and Xe clusters
- 2004
-
In: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 30:3, s. 343-351
-
Journal article (peer-reviewed)abstract
- We present new results for the inner valence levels of clusters of the three inert gases Ar, Kr and Xe based on photoelectron spectroscopy studies. The inner valence levels are compared to the localised core levels and to the delocalised outer valence levels. This comparison shows a gradual change from a relatively localised behaviour for Ar inner valence 3s, over the intermediate case of Kr inner valence 4s, to a more delocalised behaviour for Xe inner valence 5s. This change correlates well with the ratio between the orbital sizes and the interatomic distances. The Kr4s intermediate case is found to exhibit characteristics of both localised and delocalised behaviour.
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11. |
- Foehlisch, A., et al.
(author)
-
Charge transfer dynamics in molecular solids and adsorbates driven by local and non-local excitations
- 2012
-
In: Surface Science. - : Elsevier BV. - 0039-6028. ; 606:11-12, s. 881-885
-
Journal article (peer-reviewed)abstract
- Charge transfer pathways and charge transfer times in molecular films and in adsorbate layers depend both on the details of the electronic structure as well as on the degree of the initial localization of the propagating excited electronic state. For C6F6 molecular adsorbate films on the Cu(111) surface we determined the interplay between excited state localization and charge transfer pathways. In particular we selectively prepared a free-particle-like LUMO band excitation and compared it to a molecularly localized core-excited C1s -> pi* C6F6 LUMO state using time-resolved two-photon photoemission (tr-2PPE) and core-sole-clock (CHC) spectroscopy, respectively. For the molecularly localized core-excited C1s -> pi* C6F6 LUMO state, we separate the intramolecular dynamics from the charge transfer dynamics to the metal substrate by taking the intramolecular dynamics of the free C6F6 molecule into account Our analysis yields a generally applicable description of charge transfer within molecular adsorbates and to the substrate. (C) 2011 Published by Elsevier B.V.
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12. |
- Gisselbrecht, Mathieu, et al.
(author)
-
Charge migration and decay of doubly charged ammonia clusters
- 2012
-
In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:2, s. 022112-
-
Journal article (peer-reviewed)abstract
- The photo-fragmentation of ammonia molecular clusters ionized with soft x-rays is studied for photon energies near the N-1s threshold. The fragmentation is studied with a 3D momentum mass spectrometer to access the energy and angular correlations between fragments. By choosing the cluster sizes below or above the critical size of stable dication, we investigate the coulomb explosion dynamics and the interplay between charge delocalization and mobility of molecules in the clusters.
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13. |
- Gisselbrecht, Mathieu, et al.
(author)
-
Photon energy dependence of fragmentation of small argon clusters
- 2005
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:19
-
Journal article (peer-reviewed)abstract
- Photofragmentation of small argon clusters with size below ten atoms is reported. In this size range significant modifications from the electronic properties and geometry take place. When tuning the photon energy through the argon 2p edge, the fragmentation pattern is changed. Specifically, cation dimer production is enhanced at the 2p(3/2)-> 4s resonance, while above the 2p edge almost complete atomization is observed. In both cases, the widths of the peaks in the mass spectra indicate that a large amount of kinetic energy is imparted to the fragment due to the formation of multiply charged clusters. A model based on "Coulomb explosion"-charge separation, simply resulting in a complete atomization of the cluster with no dependence on the photon energy-is insufficient to explain the observed photofragmentation of small clusters.
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14. |
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15. |
- Gisselbrecht, Mathieu, et al.
(author)
-
Size dependent fragmentation of argon clusters in the soft x-ray ionization regime.
- 2008
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:4
-
Journal article (peer-reviewed)abstract
- Photofragmentation of argon clusters of average size ranging from 10 up to 1000 atoms is studied using soft x-ray radiation below the 2p threshold and multicoincidence mass spectroscopy technique. For small clusters (N=10), ionization induces fast fragmentation with neutral emission imparting a large amount of energy. While the primary dissociation takes place on a picosecond time scale, the fragments undergo slow degradation in the spectrometer on a microsecond time scale. For larger clusters (N>/=100) we believe that we observe the fragmentation pattern of multiply charged species on a time-scale which lasts a few hundred nanoseconds. The reason for these slower processes is the large number of neutral atoms which act as an efficient cooling bath where the excess energy ("heat") dissipates among all degrees of freedom. Further degradation of the photoionic cluster in spectrometer then takes place on the microsecond time scale, similar to small clusters.
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16. |
- Hautala, Lauri, et al.
(author)
-
Probing RbBr solvation in freestanding sub-2 nm water clusters
- 2017
-
In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:36, s. 25158-25167
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Journal article (peer-reviewed)abstract
- Concentration dependent solvation of RbBr in freestanding sub-2 nm water clusters was studied using core level photoelectron spectroscopy with synchrotron radiation. Spectral features recorded from dilute to saturated clusters indicate that either solvent shared or contact ion pairs are present in increasing amount when the concentration exceeds 2 mol kg-1. For comparison, spectra from anhydrous RbBr clusters are also presented.
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17. |
- Hautala, Lauri, et al.
(author)
-
Surface site coordination dependent responses resolved in free clusters: applications for neutral sub-nanometer cluster studies
- 2015
-
In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 17:10, s. 7012-7022
-
Journal article (peer-reviewed)abstract
- In this paper we demonstrate how surface site specific experimental information can be obtained from free low nanometer scale clusters using photoelectron spectroscopy utilising synchrotron radiation. In addition, we show how it can be used to gain insight into the geometry and surface structure of the clusters. The present experiments were conducted on alkali metal halides, RbCl and CsCl, which were chosen as advantageous test cases due to their simple electronic and geometric structures. These heavy alkali metal salts provide additional clarity since the surface and bulk responses can be separated, which is not the case for clusters of lighter alkali metal salts. Computational chemical shift calculations and simple alkali halide cluster size modelling were used to interpret the experimental results.
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18. |
- Huttula, Marko, et al.
(author)
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Size-varied photoelectron spectroscopy of metal clusters using the Exchange Metal Cluster Source
- 2010
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 181:2-3, s. 145-149
-
Journal article (peer-reviewed)abstract
- The recently developed Exchange Metal Cluster Source (EXMEC) is described. The source is designed for electron-spectroscopic studies of neutral metal clusters. Preliminary results on the rubidium and tin clusters using synchrotron radiation excited photoelectron spectroscopy show the capability for cluster production in the size regime of few tens to few hundred of atoms per cluster. A wide range of metal evaporation temperatures is covered applying resistive and induction heating methods. (C) 2010 Elsevier B.V. All rights reserved.
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19. |
- Jankala, K., et al.
(author)
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Photon Energy Dependent Valence Band Response of Metallic Nanoparticles
- 2011
-
In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 107:18
-
Journal article (peer-reviewed)abstract
- We show that the valence band response to photon impact in metallic nanoparticles is highly energy dependent. This is seen as drastic variations of cross sections in valence photoionization of free and initially charge-neutral nanosized metal clusters. The effect is demonstrated in a combined experimental and theoretical study of Rb clusters. The experimental findings are interpreted theoretically using a jellium model and superatom description. The variations are attributed to the changing overlap with the photon energy between the wave functions of diffuse delocalized valence electrons and continuum electrons producing a series of minima in the cross section.
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20. |
- Lindblad, Andreas, 1978-
(author)
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A Treatise on the Geometric and Electronic Structure of Clusters : Investigated by Synchrotron Radiation Based Electron Spectroscopies
- 2008
-
Doctoral thesis (other academic/artistic)abstract
- Clusters are finite ensembles of atoms or molecules with sizes in the nanometer regime (i.e. nanoparticles). This thesis present results on the geometric and electronic structure of homogeneous and heterogeneous combinations of atoms and molecules. The systems have been studied with synchrotron radiation and valence, core and Auger electron spectroscopic techniques.The first theme of the thesis is that of mixed clusters. It is shown that by varying the cluster production technique both structures that are close to that predicted by equilibrium considerations can be attained as well as far from equilibrium structures.Electronic processes following ionization constitute the second theme. The post-collision interaction phenomenon, energy exchange between the photo- and the Auger electrons, is shown to be different in clusters of argon, krypton and xenon. A model is proposed that takes polarization screening in the final state into account. This result is of general character and should be applicable to the analysis of core level photoelectron and Auger electron spectra of insulating and semi-conducting bulk materials as well.Interatomic Coloumbic Decay is a process that can occur in the condensed phases of weakly bonded systems. Results on the time-scale of the process in Ne clusters and mixed Ar/Ne clusters are herein discussed, as well observations of resonant contributions to the process. In analogy to Auger vis-à-vis Resonant Auger it is found that to the ICD process there is a corresponding Resonant ICD process possible. This has later been observed in other systems and by theoretical calculations as well in subsequent works by other groups.Delocalization of dicationic valence final states in the hydrogen bonded ammonia clusters and aqueous ammonia has also been investigated by Auger electron spectroscopy. With those results it was possible to assign a previously observed feature in the Auger electron spectrum of solid ammonia.
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21. |
- Lindblad, A., et al.
(author)
-
Charge delocalization dynamics of ammonia in different hydrogen bonding environments : free clusters and in liquid water solution
- 2009
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 11:11, s. 1758-1764
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Journal article (peer-reviewed)abstract
- Valence and core level photoelectron spectra and Auger electron spectra of ammonia in pure clusters have been measured. The Auger electro spectra of gas-phase ammonia, pure ammonia clusters and ammonia in aqueous solution are compared and interpreted via ab initio calculations of the Auger spectrum of the ammonia monomer and dimer. The calculations reveal that the final two-hole valence states can be delocalized over both ammonia molecules. Features at energies pertaining to delocalized states involving one, or more, hydroge bonding orbitals can be found in both the ammonia cluster Auger electron spectrum and in that of the liquid solvated molecule. The lower Coulombic repulsion between two delocalized valence final state holes gives higher kinetic energy of the Auger electrons which is also observed in the spectra. This decay path-specific to the condensed phase-is responsible for more than 5% of the total cluster Auger intensity. Moreover, this interpretation is also applicable to the solid phase since the same features have been observed, but not assigned, in the Auger spectrum of solid ammonia.
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22. |
- Lindblad, A, et al.
(author)
-
Postcollision interaction in noble gas clusters: Observation of differences in surface and bulk line shapes
- 2005
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:21
-
Journal article (peer-reviewed)abstract
- The surface and bulk components of the x-ray photoelectron spectra of free noble gas clusters are shown to display differences in the influence of postcollision interaction between the photoelectron and the Auger electron on the spectral line shape; the bulk component is observed to be less affected than the surface and atomic parts of the spectra. A model for postcollision interaction in nonmetallic solids and clusters is also provided which takes the polarization screening into account. Core-level photoelectron spectra of Ar, Kr, and Xe have been recorded to verify the dependence of the postcollision interaction effect on the polarizability of the sample.
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23. |
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24. |
- Lindblad, A, et al.
(author)
-
The far from equilibrium structure of argon clusters doped with krypton or xenon
- 2006
-
In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 8:16, s. 1899-1905
-
Journal article (peer-reviewed)abstract
- Heterogeneous clusters created by doping Ar host clusters with Kr or Xe are shown to have radically different structures from the mixed clusters of the same type created by co-expansion of Ar-Kr or Ar-Xe gas mixtures. In contrast to the co-expansion case, the doped mixed clusters can be produced with Kr or Xe on the surface and Ar in the bulk. With the doping technique it is thus possible to control the surface composition of a specific cluster. A study of the cluster properties as a function of the doping pressure is also reported for the case of Ar clusters doped with Xe. The clusters have been studied by means of synchrotron radiation based X-ray photoelectron spectroscopy.
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25. |
- Lindblad, A, et al.
(author)
-
The geometric structure of pure SF6 and mixed Ar/SF6 clusters investigated by core level photoelectron spectroscopy
- 2009
-
In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 603:3, s. 433-436
-
Journal article (peer-reviewed)abstract
- The S 2p core level photoelectron spectra of Sulphurhexafluoride Clusters have been investigated together with heterogeneous Ar/SF6 clusters, created by doping Ar host clusters (with a mean size of 3600 atoms) with the molecule. Surface and bulk features are resolved both in the argon 2p and the sulphur 2p core level photoelectron spectra. For the latter level such features were only observed in the pure cluster case; a single feature characterizes the S 2p core level spectra of SF6 doped argon clusters. From the chemical shifts, investigated with respect to SF6 doping pressure. It can be concluded that the host clusters get smaller with increasing doping pressures and that the SF6 molecules predominantly stay below the cluster surface, whereas the Argon core stays intact. We have neither observed features corresponding to SF6 on the cluster Surface, nor features corresponding to molecules deep inside the bulk in any of the spectra from the pick-up experiments.
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26. |
- Lundwall, M, et al.
(author)
-
Enhanced surface sensitivity in AES relative to XPS observed in free argon clusters
- 2005
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In: Surface Science. - : Elsevier BV. - 0039-6028. ; 594:1-3, s. 12-19
-
Journal article (peer-reviewed)abstract
- The surface-to-bulk intensity ratio in Auger electron spectra has been studied in comparison with core-level photoelectron spectra using free argon clusters of sizes ranging over two orders of magnitude. Enhanced surface sensitivity is observed in L2,3M2,3M2.3 Auger electron spectra compared to 2p photoelectron spectra where electrons of similar kinetic energies were recorded. This is discussed in terms of the effective attenuation length of the electrons.
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27. |
- Lundwall, Marcus, et al.
(author)
-
Photon energy dependent intensity variations observed in Auger spectra of free argon clusters
- 2006
-
In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:16, s. 3321-3333
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Journal article (peer-reviewed)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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28. |
- Lundwall, Marcus, et al.
(author)
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Preferential site occupancy observed in coexpanded argon-krypton clusters
- 2006
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 74:4, s. 043206-
-
Journal article (peer-reviewed)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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29. |
- Lundwall, M., et al.
(author)
-
Preferential site occupancy of krypton atoms on free argon-cluster surfaces
- 2006
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:1
-
Journal article (peer-reviewed)abstract
- Argon clusters have been doped with krypton atoms in a pick-up setup and investigated by means of ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). The width of the krypton surface feature in the XPS spectra from mixed krypton/argon clusters has been studied and found to be narrower than in the case of homogeneous krypton clusters. By considering known spectral broadening mechanisms of the cluster features and the electron binding energy shift of the cluster surface feature relative to the atomic signal, we conclude that krypton ad-atoms preferentially occupy high-coordination surface sites on the argon host-cluster. (c) 2006 American Institute of Physics.
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30. |
- Lundwall, M, et al.
(author)
-
Radial surface segregation in free heterogeneous argon/krypton clusters
- 2004
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 392:4-6, s. 433-438
-
Journal article (peer-reviewed)abstract
- Free clusters produced by a co-expansion of argon and krypton have been studied by means of core level photoelectron spectroscopy. In this study we have determined: (i) the produced clusters are heterogeneous; (ii) the radial distribution of the two atomic species in the cluster differs. The proposed structure model places the majority of the krypton atoms in the bulk, leaving the argon atoms to be found more frequently on the cluster surface. The suggested structure is qualitatively discussed using the cohesive energies of the two-components. (C) 2004 Elsevier B.V. All rights reserved.
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31. |
- Lundwall, Marcus, 1977-
(author)
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Rare-gas Clusters Studied by Electron Spectroscopy : Structure of Heterogeneous Clusters and Effects of Electron Scattering on Auger Decay
- 2007
-
Doctoral thesis (other academic/artistic)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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32. |
- Lundwall, Marcus, et al.
(author)
-
Self-assembled heterogeneous argon/neon core-shell clusters studied by photoelectron spectroscopy
- 2007
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:21, s. 214706-
-
Journal article (peer-reviewed)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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33. |
- Lundwall, M., et al.
(author)
-
Shell-dependent core-level chemical shifts observed in free xenon clusters
- 2006
-
In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:24, s. 5225-5235
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Journal article (peer-reviewed)abstract
- Photoelectron and Auger electron spectra following Xe-3d and Xe-4d ionization of free xenon clusters have been measured using synchrotron radiation. The atom-to-surface and atom-to-bulk binding energy shifts found in the Xe-3d and the subsequent M5N4,5N4,5 Auger decay are about 15% larger than those observed in the Xe-4d and N4,5O2,3O2,3 measurements. This experimental result is also considered theoretically.
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34. |
- Mikkela, M-H, et al.
(author)
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Photoelectron spectroscopy of unsupported bismuth clusters: Size related effects of metallic properties
- 2012
-
In: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 112:8
-
Journal article (peer-reviewed)abstract
- Evolution of metallic properties of free and initially neutral nanoscale Bi clusters has been studied using synchrotron radiation excited photoelectron spectroscopy. The 4f and 5d core as well as the valence levels have been probed. The cross-level analysis indicates metallic properties in Bi clusters in the observed size range from 0.5 nm to 1.4 nm. The behavior of the core-level and valence binding energies as a function of cluster size has been observed to be smooth and relatively consistent. Valence responses for the largest clusters have their shape and width similar to those of the polycrystalline solid Bi. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4759324]
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35. |
- Mikkela, M. -H., et al.
(author)
-
Size-dependent study of Rb and K clusters using core and valence level photoelectron spectroscopy
- 2011
-
In: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 64:2-3, s. 347-352
-
Journal article (peer-reviewed)abstract
- Electronic structure of free and neutral Rb and K clusters containing from few tens to few hundred atoms has been studied using synchrotron radiation. Core-level photoelectron spectroscopy has been used to probe the metallic nature of Rb and K clusters. We show that the metallicity exists down to the dimensions of few nanometers. Simultaneously the emergence and evolution of the valence band structure has been monitored by the valence-level photoelectron spectroscopy.
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36. |
- Mikkelä, Mikko-Heikki, et al.
(author)
-
Bismuth-oxide nanoparticles: study in a beam and as deposited
- 2024
-
In: Physical chemistry chemical physics : PCCP. - 1463-9084. ; 26:13, s. 10369-10381
-
Journal article (peer-reviewed)abstract
- Bi2O3 is a promising material for solid-oxide fuel cells (SOFC) due to the high ionic conductivity of some phases. The largest value is reached for its δ-phase, but it is normally stable at temperatures too high for SOFC operation, while nanostructured oxide is believed to have more suitable stabilization temperature. However, to manufacture such a material with a controlled chemical composition is a challenging task. In this work, we investigated the fabrication of nanostructured Bi2O3 films formed by deposition of free Bi-oxide nanoparticles created in situ. The particle-production method was based on reactive sputtering and vapour aggregation. Depending on the fabrication conditions, the nanoparticles contained either a combination of Bi–metal and Bi-oxide, or only Bi-oxide. Prior to deposition, the free particles were probed in the beam – by synchrotron-based photoelectron spectroscopy (PES), which allowed assessing their composition “on the-fly”. The nanoparticle films obtained after deposition were studied by PES, scanning electron microscopy, transmission electron microscopy, and electron diffraction. The films' chemical composition, grain dimensions, and crystal structure were probed. Our analysis suggests that our method produced Bi-oxide films in more than one polymorph of Bi2O3.
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37. |
- Mikkelä, Mikko Heikki, et al.
(author)
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Free silver nanoparticles doped by potassium : Work-function change in experiment and theory
- 2021
-
In: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 154:23
-
Journal article (peer-reviewed)abstract
- The composition-dependent change in the work-function (WF) of binary silver-potassium nanoparticles has been studied experimentally by synchrotron-based x-ray photoelectron spectroscopy (PES) and theoretically using a microscopic jellium model of metals. The Ag-K particles with different K fractions were produced by letting a beam of preformed Ag particles pass through a volume with K vapor. The PES on a beam of individual non-supported Ag-K nanoparticles created in this way allowed a direct absolute measurement of their WF, avoiding several usual shortcomings of the method. Experimentally, the WF has been found to be very sensitive to K concentration: Already at low exposure, it decreased down to approximate to 2 eV-below the value of pure K. In the jellium modeling, considered for Ag-K nanoparticles, two principally different adsorption patterns were tested: without and with K diffusion. The experimental and calculation results together suggest that only efficient surface alloying of two metals, whose immiscibility was long-term textbook knowledge, could lead to the observed WF values.
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38. |
- Ohrwall, G, et al.
(author)
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Femtosecond interatomic Coulombic decay in free neon clusters: Large lifetime differences between surface and bulk
- 2004
-
In: Physical Review Letters. - 1079-7114. ; 93:17
-
Journal article (peer-reviewed)abstract
- A quantitative determination of 2s vacancy lifetimes in surface and bulk atoms of free Ne clusters has been made. While for free atoms the 2s inner-valence hole has a ps lifetime, it reduces to 6+/-1 fs for cluster bulk atoms. For surface atoms, the lifetime is on average longer than 30 fs. The lifetime estimate was obtained from fits of high-resolution photoelectron spectra of Ne clusters. The shortening of the lifetime is attributed to the coordination dependent interatomic Coulombic decay, which is extremely sensitive to internuclear distances.
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39. |
- Ohrwall, G, et al.
(author)
-
Observation of elastic scattering effects on photoelectron angular distributions in free Xe clusters
- 2003
-
In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 36:19, s. 3937-3949
-
Journal article (peer-reviewed)abstract
- We report an observation of substantial deviations in the photoelectron angular distribution for photoionization of atoms in free Xe clusters compared to the case of photoionization of free atoms. The cross section, however, seems not to vary between the cluster and free atoms. This observation was made in the vicinity of the Xe 4d Cooper minimum, where the atomic angular distribution is known to vary dramatically. The angular distribution of electrons emitted from atoms in the clusters is more isotropic than that of free atoms over the entire kinetic energy range studied. Furthermore, the angular distribution is more isotropic for atoms in the interior of the clusters than for atoms at the surface. We attribute this deviation to elastic scattering of the outgoing photoelectrons. We have investigated two average cluster sizes, (N) approximate to 4000 and 1000 and found no significant differences between these two cases.
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40. |
- Osmekhin, S., et al.
(author)
-
Size-dependent transformation of energy structure in free tin clusters studied by photoelectron spectroscopy
- 2010
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 81:2, s. 023203-
-
Journal article (peer-reviewed)abstract
- Free nanoscale tin clusters in the average size range of a few tens up to similar to 500 atoms are studied by means of valence and core-level photoelectron spectroscopy. A self-consistent picture arises from comparison of the work functions derived from the 4d core-level spectra, the experimental ionization energies extracted from the 5p valence spectra, and the expectations from the metallic sphere model for the clusters. The present studies demonstrate that the 4d core-level energy changes are a sensitive probe of the metal-to-semiconductor transition in the size range under investigation.
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41. |
- Partanen, Leena, et al.
(author)
-
Solvation at nanoscale : alkali halides in water clusters
- 2013
-
In: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 138:4, s. 044301-
-
Journal article (peer-reviewed)abstract
- The solvation of alkali-halides in water clusters at nanoscale is studied by photoelectron spectroscopy using synchrotron radiation. The Na 2p, K 3p, Cl 2p, Br 3d, and I 4d core level binding energies have been measured for salt-containing water clusters. The results have been compared to those of alkali halide clusters and the dilute aqueous salt solutions. It is found that the alkali halides dissolve in small water clusters as ions.
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42. |
- Peredkov, Sergey, et al.
(author)
-
Free nanoscale sodium clusters studied by core-level photoelectron spectroscopy
- 2007
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:23, s. 235407-
-
Journal article (peer-reviewed)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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43. |
- Peredkov, Sergey, et al.
(author)
-
Ioniclike energy structure of neutral core-excited states in free Kr clusters
- 2005
-
In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 72:2
-
Journal article (peer-reviewed)abstract
- The development of electronic states in krypton clusters is investigated by high-resolution core-level electron spectroscopy. The energy ordering of bulk versus surface 3d(-1)np(n > 5) core-excited states in neutral clusters is demonstrated to be reversed to the 3d(-1)5p level situation. The cluster 3d(-1)6p,7p states are proven to be at a lower energy than the corresponding atomic levels. These findings reveal the ioniclike energy structure of the neutral cluster core-excited levels. The phenomenon is explained by a spatial spread of the excited orbitals over the cluster lattice.
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44. |
- Peredkov, Sergey, et al.
(author)
-
Size determination of free metal clusters by core-level photoemission from different initial charge states
- 2007
-
In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 1550-235X. ; 76:8
-
Journal article (peer-reviewed)abstract
- We present the study of free nanoscale lead clusters using photoelectron spectroscopy and synchrotron radiation. Pb 5d core-level spectra reveal the presence of different initial charge states of the clusters created by the magnetron-based source. We suggest a method for determining the cluster size from the charge-dependent core level binding energies. Both the core-level and the valence spectra demonstrate that we have created free metallic clusters with essentially the same electronic structure as the solid.
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45. |
- Pokapanich, Wandared, et al.
(author)
-
Auger Electron Spectroscopy as a Probe of the Solution of Aqueous Ions
- 2009
-
In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:21, s. 7264-7271
-
Journal article (peer-reviewed)abstract
- Aqueous potassium chloride has been studied by synchrotron-radiation excited core-level photoelectron and Auger electron spectroscopy. In the Auger spectrum of the potassium ion, the main feature comprises the final states where two outer valence holes are localized on potassium. This spectrum exhibits also another feature at a higher kinetic energy which is related to final states where outer valence holes reside on different subunits. Through ab initio calculations for microsolvated clusters, these subunits have been assigned as potassium ions and the surrounding water molecules. The situation is more complicated in the Auger spectrum of the chloride anion. One-center and multicenter final states are present here as well but overlap energetically.
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46. |
- Pokapanich, Wandared, et al.
(author)
-
Core level photoelectron spectroscopy probed heterogeneous xenon/neon clusters
- 2017
-
In: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 135, s. 45-48
-
Journal article (peer-reviewed)abstract
- Binary rare gas clusters; xenon and neon which have a significant contrariety between sizes, produced by a co-expansion set up and have been studied using synchrotron radiation based x-ray photoelectron spectroscopy. Concentration ratios of the heterogeneous clusters; 1%, 3%, 5% and 10% were controlled. The core level spectra were used to determine structure of the mixed cluster and analyzed by considering screening mechanisms. Furthermore, electron binding energy shift calculations demonstrated cluster aggregation models which may occur in such process. The results showed that in the case of low mixing ratios of 3% and 5% of xenon in neon, the geometric structures exhibit xenon in the center and xenon/neon interfaced in the outer shells. However, neon cluster vanished when the concentration of xenon was increased to 10%.
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47. |
- Pokapanich, Wandared, 1976-
(author)
-
Solvent–Solute Interaction : Studied by Synchrotron Radiation Based Photo and Auger Electron Spectroscopies
- 2011
-
Doctoral thesis (other academic/artistic)abstract
- Aqueous solutions were studied using photoelectron and Auger spectroscopy, based on synchrotron radiation and a liquid micro-jet setup. By varying the photon energy in photoelectron spectra, we depth profiled an aqueous tetrabutylammonium iodide (TBAI) solution. Assuming uniform angular emission from the core levels, we found that the TBA+ ions were oriented at the surface with the hydrophobic butyl arms sticking into the liquid. We investigated the association between ions and their neighbors in aqueous solutions by studying the electronic decay after core ionization. The (2p)−1 decay of solvated K+ and Ca2+ ions was studied. The main features in the investigated decay spectra corresponded to two-hole final states localized on the ions. The spectra also showed additional features, related to delocalized two-hole final states with vacancies on a cation and a neighboring water molecule. These two processes compete, and by comparing relative intensities and using the known rate for the localized decay, we determined the time-scale for the delocalized process for the two ions. We compared to delocalized electronic decay processes in Na+, Mg2+, and Al3+, and found that they were slower in K+ and Ca2+, due to different internal decay mechanisms of the ions, as well as external differences in the ion-solute distances and interactions. In the O 1s Auger spectra of aqueous metal halide solutions, we observed features related to delocalized two-hole final states with vacancies on a water molecule and a neighboring solvated anion. The relative intensity of these feature indicated that the strength of the interaction between the halide ions and water correlated with ionic size. The delocalized decay was also used to investigate contact ion pair formation in high concentrated potassium halide solutions, but no concrete evidence of contact ion pairs was observed.
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48. |
- Preobrajenski, Alexei, et al.
(author)
-
FlexPES : a versatile soft X-ray beamline at MAX IV Laboratory
- 2023
-
In: Journal of Synchrotron Radiation. - 0909-0495. ; 30, s. 831-840
-
Journal article (peer-reviewed)abstract
- FlexPES is a soft X-ray beamline on the 1.5 GeV storage ring at MAX IV Laboratory, Sweden, providing horizontally polarized radiation in the 40-1500 eV photon energy range and specializing in high-resolution photoelectron spectroscopy, fast X-ray absorption spectroscopy and electron-ion/ion-ion coincidence techniques. The beamline is split into two branches currently serving three endstations, with a possibility of adding a fourth station at a free port. The refocusing optics provides two focal points on each branch, and enables either focused or defocused beam on the sample. The endstation EA01 at branch A (Surface and Materials Science) is dedicated to surface- and materials-science experiments on solid samples at ultra-high vacuum. It is well suited not only to all flavours of photoelectron spectroscopy but also to fast (down to sub-minute) high-resolution X-ray absorption measurements with various detectors. Branch B (Low-Density Matter Science) has the possibility to study gas-phase/liquid samples at elevated pressures. The first endstation of this branch, EB01, is a mobile setup for various ion-ion and electron-ion coincidence techniques. It houses a versatile reaction microscope, which can be used for experiments during single-bunch or multi-bunch delivery. The second endstation, EB02, is based on a rotatable chamber with an electron spectrometer for photoelectron spectroscopy studies on primarily volatile targets, and a number of peripheral setups for sample delivery, such as molecular/cluster beams, metal/semiconductor nanoparticle beams and liquid jets. This station can also be used for non-UHV photoemission studies on solid samples. In this paper, the optical layout and the present performance of the beamline and all its endstations are reported.
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49. |
- Rander, T, et al.
(author)
-
A dose dependence study of O-2 adsorbed on large Ar clusters
- 2009
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:22, s. 224305-
-
Journal article (peer-reviewed)abstract
- An investigation of the behavior of O-2 molecules in and on O-2-doped large (< N > similar or equal to 8000) Ar host clusters has been performed by means of core and valence photoelectron spectroscopy. Data from pure O-2 and Ar clusters, as well as from O-2-doped Ar clusters, are presented. The experimental data together with calculations of the binding energy shifts of oxygen molecular ions in and on the surface of a large host Ar cluster show that the diffusion behavior has a strong dependence on the doping pressure. We conclude that the oxygen molecules in the doped Ar host do not partake in band formation, since there is clear vibrational resolution in the spectral features stemming from screened O-2(+) ions. This implies that valence photoelectron spectroscopy can be used to determine the geometrical structure of this and certain, similar, cluster systems. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3148883]
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50. |
- Rander, Torbjörn, et al.
(author)
-
Core-level electron spectroscopy on the sodium dimer Na 2p level
- 2007
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 75:3, s. 032510-
-
Journal article (peer-reviewed)abstract
- The lifetime broadening and molecular field splitting of the sodium dimer 2p core level is studied by x-ray photoelectron spectroscopy and by Auger electron spectroscopy. The lifetime of the Na 2p core hole has been determined to be 15±8fs , much shorter than what has previously been reported for solid sodium. The molecular field splitting of this core level has been determined to be 42±10meV . The Auger measurements have experimentally confirmed that the sodium dimer is a good example of when the Coulomb explosion mechanism determines the spectral shape.
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