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Sökning: WFRF:(Kikas A.)

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1.
  • Maiste, A, et al. (författare)
  • 3d-resonant photo- and Auger emission of Ce in CeO2
  • 1995
  • Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. ; 76, s. 583-587
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The Ce 3d-edge resonant photoelectron and Auger electron emission spectra in CeO2 have been measured. The 4s-, 4p- and 4d-emission at off-resonance excitations consists of two parts separated by about 13 eV, which correspond to different final-state confi
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2.
  • Ruus, R, et al. (författare)
  • Ti 2p and O 1s X-ray absorption of TiO2 polymorphs
  • 1997
  • Ingår i: SOLID STATE COMMUNICATIONS. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0038-1098. ; 104:4, s. 199-203
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • We present and discuss the Ti 2p and O 1s X-ray absorption spectra (XAS) and resonant photoelectron emission spectra (RPES) of the various polymorphic forms (TiO2-II, rutile and anatase) of TiO2. The largest differences between the Ti 2p XAS of polymorphs
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3.
  • Elango, M., et al. (författare)
  • Autoionization phenomena involving the 2p53d configuration of argonlike ions in ionic solids
  • 1993
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 47:18, s. 11736-11748
  • Tidskriftsartikel (refereegranskat)abstract
    • The photon-induced Auger and photoelectron spectra of the argonlike ions Cl- (in NaCl), K+ (in KCl), Ca2+ (in CaCl2 and CaF2), and Sc3+ (in Sc2O3) have been measured in the vicinity of the L23 absorption edges of these ions. It is shown that at the 2p6→2p53d(4s) resonance a spectator structure appears in the L23M23M23 Auger spectra, which shifts to higher kinetic energies with increasing photon energy. This structure originates from the 3p-23d(4s) final configuration arising as a product of the Auger resonant-inelastic-scattering process of the incident photons. We demonstrate that the peculiarities of this process and the role of the collapsing 3d electron in it can be largely understood in terms of an atomic treatment. The solid-state effects, caused by the crystal field and the lattice polarization, may play an additional role.
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4.
  • Kook, M., et al. (författare)
  • Ion fragmentation study of [EMMIM][TFSI], [EMIM][OTf] and [EMIM][DCA] by vacuum ultraviolet light
  • 2022
  • Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 471
  • Tidskriftsartikel (refereegranskat)abstract
    • The ionic liquids (ILs) 1-Ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide [EMMIM][TFSI], 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM][OTf] and 1-Ethyl-3-methylimidazolium dicyanamide [EMIM][DCA] were evaporated by effusion and a time-of-flight (TOF) instrument was employed as the mass analyzer while vacuum ultraviolet (VUV) light in the energy range 9–20 eV was used to excite the IL molecules. Fragmentation patterns with respect to excitation energy are discussed and decomposition products are analyzed. Hydrogenated and dehydrogenated fragments are discussed. Our experiment seems to show that the ionic liquids with larger anions have less cation fragmentation. [EMMIM][TFSI] was studied for the first time and it produces different fragments than 1-Ethyl-3-methylimidazolium based ionic liquids. Surprisingly 1-Ethyl-3-methylimidazolium or 1-Ethyl-2-methylimidazolium cations were not detected in the [EMMIM][TFSI] fragmentation pattern.
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5.
  • Kukk, E, et al. (författare)
  • Auger decay of the dissociating core-excited states in the HCl and DCl molecules
  • 1996
  • Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. ; 104:12, s. 4475-4480
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • High-resolution Auger electron spectra from the decay of the Cl 2p-->sigma* excitation in HCl and DCl have been measured. The spectra are analyzed, separating molecular and atomic features, which are assigned to transitions to the HCl (5 sigma 2 pi)(4) si
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6.
  • Ristinmaa Sörensen, Stacey, et al. (författare)
  • Site-Selective Participator Decay of Core-Excited Butadiene
  • 1996
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 105, s. 10719-10724
  • Tidskriftsartikel (refereegranskat)abstract
    • The decay of core-excited electronic states in free 1,3 trans butadiene molecules has been studied using high-resolution synchrotron radiation and electron spectrometry. The core-level energy shift between the terminal and central carbon atoms is 0.64 eV making selective excitation of core electrons from these atoms possible. Resonant excitation to the au(*) valence state leads to autoionizing decay channels which proceed according to the atomic site in the molecule. The radiationless decay is localized, and certain molecular orbitals are excluded from the decay depending upon the site of the core hole. This phenomenon is confirmed by semiempirical INDO calculations based upon the equivalent core approximation. The vibrational structure of the resonances below the carbon K edge has been measured and fit to extract vibrational energies and intensities, chemical shifts, and the lifetimes of the centrally and terminally excited states. The C 1s spectrum is also measured with vibrational resolution and the energies of the normal vibrational modes are extracted. The bond lengths are derived by application of a linear coupling analysis.
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7.
  • Ruus, R., et al. (författare)
  • M4,5N4,5N4,5 Auger decay spectra of the resonantly excited 3d94f configuration of xenonlike ions in solids
  • 1994
  • Ingår i: Physical Review B (Condensed Matter). - 0163-1829. ; 49:21, s. 14836-14844
  • Tidskriftsartikel (refereegranskat)abstract
    • The synchrotron-radiation-induced Auger and photoelectron spectra of the xenonlike ions I- (in CsI), Cs+ (in CsI), Ba2+ (in BaF2), and La3+ (in LaF3) have been measured in the vicinity of the M4,5 absorption edges of these ions. It is shown that the spectra of La and Ba measured at 3d10→3d94f resonances exhibit a very intense 4f-spectator structure which changes its energy and intensity with the energy of the exciting photons. Calculation of the Auger decay of the 3d-14f configuration shows that this structure is due to transitions to the 4d-24f+4p-1 final ionic configuration, the high-energy part of which overlaps the 4d-2 continuum. In the case of Ba this structure coexists with the normal Auger structure which appears as a result of the M4M5N6,7 Coster-Kronig transitions. The spectra of I- contain only the normal M4,5N4,5N4,5 Auger structure related to the 3d-1→4d-2 transitions. The spectra of Cs+ are similar to those of I- with a small admixture of the 4f-spectator-like structure.
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8.
  • Sammelselg, V, et al. (författare)
  • Study of thin oxide films by electron, ion and synchrotron radiation beams
  • 2002
  • Ingår i: Microchimica Acta. - : Springer Science and Business Media LLC. - 1436-5073 .- 0026-3672. ; 139:1-4, s. 165-169
  • Tidskriftsartikel (refereegranskat)abstract
    • Titanium oxide and zirconium oxide thin films deposited on silicon substrates were characterised using electron probe microanalysis (EPMA), Rutherford backscattering spectroscopy (RBS), time-of-flight elastic recoil detection analysis (TOF-ERDA) and scanning photoelectron microscopy (SPEM). The composition and mass thickness of the films were determined and the results of different methods compared. It was revealed that the synchrotron radiation used for SPEM studies caused considerable modification of zirconia films grown at low temperatures.
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9.
  • Ausmees, A., et al. (författare)
  • Secondary photoelectron spectra of NaCl and KBr excited by XUV radiation : Experiments and computer simulations
  • 1990
  • Ingår i: Solid State Communications. - 0038-1098. ; 76:12, s. 1383-1386
  • Tidskriftsartikel (refereegranskat)abstract
    • Energy distributions of slow electrons (0 to 10eV) emitted by thin layers of NaCl and KBr irradiated by monochromatic XUV photons with various energies in the interval of 50 to 300 eV are measured. For all cases the photoelectron spectrum starts with an intense peak of slow secondaries and has a hot-secondary structure at the energies 1 to 5 eV. The smaller the photon absorption depth, the stronger is this structure. An attempt is made to reproduce such a behaviour of spectra by a Monte Carlo simulation of electron-electron and electron-phonon scattering sequences induced in solids by XUV photon absorption. It appears that for high-energy ( > 2 to 3 eV) conduction electrons the electron-phonon scattering is mainly due to acoustic phonons.
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10.
  • Kaambre, T., et al. (författare)
  • Resonant inelastic X-ray scattering at the Be 1s edge in BeO
  • 2007
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 156, s. 299-302
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the resonant inelastic X-ray scattering (RIXS) spectra of BeO at the Be 1s photoabsorption edge. The RIXS spectra excited in the vicinity of the core exciton resonance show two principal features: the scattering on a valence exciton (which at higher excitation energies verges into the characteristic K alpha emission), and a remarkably strong energy loss side-band to the elastic scattering peak, which has a maximum width of 6 eV and has intensity, at resonance, comparable to the valence scattering. The energy loss side-band appears to result from rapid lattice relaxation at the absorption site on the X-ray scattering time-span. (c) 2006 Elsevier B.V. All rights reserved.
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11.
  • Kikas, A., et al. (författare)
  • Auger Spectra of K+ L23 Excitations in Potassium Halides
  • 1991
  • Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 15:6, s. 683-686
  • Tidskriftsartikel (refereegranskat)abstract
    • The L23M23M23 Auger spectra of K+ L23 excitation in potassium halides are measured using photon excitation with different energies in the region of the K+ L23 absorption edge (around 300 eV). It is shown that the screening of the two 3p holes caused by the collapsed 3d electron of the K+ L23 exciton leads to a considerable shift (by about (6÷7) eV) of the K+ L23M23M23 Auger bands to higher energies. Only the low-energy component of the crystal-field-split K+ 3d orbital forms a genuine bound state with 2p holes, whereas its high-energy component lies in the conduction band continuum and behaves like a shape resonance.
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12.
  • Kikas, A, et al. (författare)
  • High-resolution study of the correlation satellites in photoelectron spectra of the rare gases
  • 1996
  • Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 77:3, s. 241-266
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • High-resolution, synchrotron radiation excited valence photoelectron satellite spectra, taken at the magic angle, of all the rare gases, He, Ne, Ar, Kr and Xe, are presented. The facilities at the Finnish beam line at the MAX laboratory have been used to
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13.
  • Kikas, A, et al. (författare)
  • NaK photoabsorption and resonant KLL Auger spectra in naf and NaCl
  • 2002
  • Ingår i: Surface Review and Letters. - 0218-625X. ; 9:2, s. 1303-1308
  • Tidskriftsartikel (refereegranskat)abstract
    • The nature of Na Is photoabsorption in NaF and NaCl is investigated using the resonant Auger decay of Na Is core excitations. The appearance of new peaks in Auger spectra, when the energy of excitation coincides with the photoabsorption thresholds, shows that the core excitons are created in the threshold region of the Na 1s photoabsorption spectrum. The core excitons around 1074.2 eV originate from the dipole-forbidden 1s(-1)3s final state, the population of which is made possible by the symmetry disruption at the photoabsorption site. Another core exciton, excited at photon energies of 1076.8 eV in NaF and 1076.3 eV in NaCl, originates from 1s(-1)3p states similar to atoms of Ne and Na. Resonant Auger spectra show also that in NaCl the first sharp photoabsorption maximum at 1076.6 eV has only partially excitonic character.
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14.
  • Kikas, A., et al. (författare)
  • Resonant inelastic x-ray scattering at the F 1s photoabsorption edge in LiF : Interplay of excitonic and conduction states, and Stokes' doubling
  • 2004
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 70:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The excitation-decay processes at the F 1s photoabsorption edge in LiF crystal are studied using resonant inelastic x-ray scattering spectroscopy. The Raman-type linear dispersion and the narrowing of the x-ray fluorescence peak are observed at resonant excitation. A theoretical model based on the Kramers-Heisenberg formula describes well the main features in fluorescence spectra and allows one to separate the contributions of the exciton and the conduction states in the scattering spectra. At the same time, the role of the shape of the spectral distribution within the incident radiation is emphasized as being critically sensitive to the number, kind, and onset of the spectral features which finally appear in the scattering spectra at a particular incident photon energy, particularly in the subthreshold excitation region.
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15.
  • Kikas, A, et al. (författare)
  • Resonant inelastic X-ray scattering at the K edge of oxygen and fluorine in insulators
  • 2005
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 144-147, s. 845-848
  • Tidskriftsartikel (refereegranskat)abstract
    • Here we present the results of a study of the electronic structure using the resonant inelastic scattering process at the F 1s photoabsorption edge in LiF and O 1s edge of MgO crystals. In case of excitations in the sub-threshold region, the Raman-type linear dispersion of X-ray fluorescence peak was observed for the studied compounds. In LiF, the narrowing of the X-ray fluorescence peak is observed at pre-threshold excitation, which can be related to the creation of a core exciton, but no core excitons were identified in MgO.
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16.
  • Kikas, A, et al. (författare)
  • Resonant photoemission of CoCl2
  • 1999
  • Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 103, s. 745-749
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • We present the results of a study of the resonant photoemission from polycrystalline in situ evaporated thin him of CoCl2 excited at 2p photoabsorption edges of Co and Cl. At the Co 2p-->3d resonance strong enhancement was observed for the Co 3p, valence
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17.
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18.
  • Osborne, SJ, et al. (författare)
  • The vibrationally resolved C 1 s core photoelectron spectra of methane and ethane
  • 1997
  • Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 106:5, s. 1661-1668
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Recent progress in the development of high-resolution electron spectrometers in combination with highly monochromatized undulator radiation has allowed observation of the vibrationally resolved gas-phase C Is photoelectron spectra of methane and ethane. F
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19.
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20.
  • Ruus, R., et al. (författare)
  • Cs 3d absorption and resonant photoemission study of caesium halogenides
  • 2005
  • Ingår i: Physica Scripta. - 0031-8949. ; T115, s. 396-398
  • Tidskriftsartikel (refereegranskat)abstract
    • The highly localized 4f electrons play an important role in forming of the electronic structure and properties of compounds. The 3d photoabsorption and resonant decay spectra of Cs halides represent an interesting case showing both the localized and spatially extended f wave function features. We present and discuss the Cs 3d X-ray absorption and resonant photoelectron emission spectra of the Cs halides. The Cs 3d absorption spectra exhibit a strong atom-like shape resonance behavior, solid-state effects play a minor role. The appearance of the spectral features, which are intrinsic to a localized state, in the decay spectra show that the Cs 3d photoelectron, temporally and spatially trapped in the Cs 3d shape resonance due to the potential barrier for epsilon f electrons near threshold, has substantially localized nature.
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21.
  • Ruus, R, et al. (författare)
  • Potential barrier effects in Cs 3d resonance photoemission of CsF
  • 2004
  • Ingår i: ICESS-9 Proceedings of the 9th International Conference on Electronic Spectroscopy and Structure (Journal of Electron Spectroscopy and Related Phenomena). - : Elsevier BV. - 0368-2048. ; 137-40, s. 377-381
  • Konferensbidrag (refereegranskat)abstract
    • We present and discuss the Cs 3d X-ray absorption spectra and resonant photoelectron emission spectra of CsF. The resonant photoelectron spectra excited at the Cs 3d absorption maxima, exhibit a strong resonance behavior. The different behaviour of participator and spectator channels and interference effects of the 4d partial photoionisation cross-section at the 3d resonances are discussed. The experimental evidence of the phenomenon of spin-orbit activated interchannel coupling in the 3d photoionization of Cs is presented. (C) 2004 Elsevier B.V. All rights reserved.
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22.
  • Sorensen, SL, et al. (författare)
  • Continuum resonance in ethylene: Evidence from vibrationally resolved core photoionization
  • 1998
  • Ingår i: PHYSICAL REVIEW A. - : AMERICAN PHYSICAL SOC. - 1050-2947. ; 58:3, s. 1879-1884
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The carbon Is photoelectron spectrum of gas-phase ethylene has been measured with high resolution in order to study changes in vibrational structure arising from core photoionization through a continuum resonance. By evaluating the changes in vibrational
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23.
  • Sorensen, SL, et al. (författare)
  • Site-selective participator decay of core-excited butadiene
  • 1996
  • Ingår i: JOURNAL OF CHEMICAL PHYSICS. - 0021-9606. ; 105:24, s. 10719-10724
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The decay of core-excited electronic states in free 1,3 trans butadiene molecules has been studied using high-resolution synchrotron radiation and electron spectrometry. The core-level energy Shift between the terminal and central carbon atoms is 0.64 eV
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24.
  • Sundin, S, et al. (författare)
  • Auger decay of core-excited higher Rydberg states of carbon monoxide
  • 1997
  • Ingår i: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. - : IOP PUBLISHING LTD. - 0953-4075. ; 30:19, s. 4267-4278
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The de-excitation of higher core-excited C 1s(-1)np Rydberg states of carbon monoxide has been studied. It is found that already with a main quantum number of 4 or higher, Rydberg states of p-symmetry can be successfully treated within the single-particle
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25.
  • Sundin, S, et al. (författare)
  • Collapse of vibrational structure in the Auger resonant Raman spectrum of CO by frequency detuning
  • 1997
  • Ingår i: PHYSICAL REVIEW LETTERS. - : AMER INST PHYSICS. - 0031-9007. ; 79:8, s. 1451-1454
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Observations made in the C1s-->pi* Auger resonant Raman spectra of carbon monoxide demonstrate that the vibrational structure in such spectra is strongly frequency dependent. In the limit of narrow bandpass photon excitation, the vibrational excitations o
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26.
  • Sundin, S, et al. (författare)
  • Influences from the C 1s shape resonance on the vibrational progression in the Auger decay of CO
  • 1998
  • Ingår i: PHYSICAL REVIEW A. - : AMERICAN PHYSICAL SOC. - 1050-2947. ; 58:3, s. 2037-2042
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Auger decay from the C Is con-ionized state of CO has been studied with vibrational resolution both at the C Is shape resonance and far above. Variations in the vibrational intensity distribution with photon energy are observed. This observation is explai
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27.
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28.
  • Sundin, S, et al. (författare)
  • Vibrationally selective resonant Auger spectroscopy of the 3p core-to-Rydberg excitation in CO
  • 1997
  • Ingår i: PHYSICAL REVIEW A. - : AMER INST PHYSICS. - 1050-2947. ; 56:1, s. 480-487
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The Auger decay of the C 1s-->3p excitation in CO has been studied by means of vibrationally selective angle-resolved electron spectroscopy. It is shown that for these highly excited Rydberg states the strict spectator model works excellently in describin
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29.
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30.
  • Kikas, A., et al. (författare)
  • Effect of phase composition on X-ray absorption spectra of ZrO2 thin films
  • 2007
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 156, s. 303-306
  • Tidskriftsartikel (refereegranskat)abstract
    • The X-ray photoabsorption spectra of ZrO2 films with different phase compositions were measured. The analysis of the results obtained shows that due to the site-sensitivity the X-ray photoabsorption spectroscopy is an attractive method for characterization of the ZrO2 structure. This allows application of the X-ray spectroscopy in investigation of the crystal structure in the various stages of the thin film growth including the initial stage of the ZrO2 growth. (c) 2006 Elsevier B.V. All rights reserved.
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31.
  • Kikas, A., et al. (författare)
  • Resonant inelastic x-ray scattering and UV-VUV luminescence at the Be 1s edge in BeO
  • 2010
  • Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 22:37
  • Tidskriftsartikel (refereegranskat)abstract
    • We carried out a combined study of UV-VUV luminescence and resonant x-ray emission from BeO single crystals with incident photon energies in the vicinity of the Be 1s absorption edge. The x-ray emission spectra show that at the Be 1s photoabsorption edge the lattice relaxation processes in the excitation site take place already on the timescale of the radiative decay of the core excitation. Comparison of the x-ray emission and the luminescence spectra indicates that the maximum energy loss of the process of lattice relaxation during the decay of inner-shell holes is similar to the loss that occurs in the self-trapping process of valence excitons. The possible decay channels of core excitations have been discussed and the mechanism for the creation of 5.2 eV luminescence at the photoabsorption resonances has been suggested.
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32.
  • Reisberg, L., et al. (författare)
  • UPS and DFT investigation of the electronic structure of gas-phase trimesic acid
  • 2016
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 213, s. 11-16
  • Tidskriftsartikel (refereegranskat)abstract
    • Benzene-1,3,5-tricarboxylic acid (trimesic acid, TMA) molecules in gas-phase have been investigated by using valence band photoemission. The photoelectron spectrum in the binding energy region from 9 to 22 eV is interpreted by using density functional theory calculations. The electronic structure of TMA is compared with benzene and benzoic acid in order to demonstrate changes in molecular orbital energies induced by addition of carboxyl groups to benzene ring.
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