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Tsud N, Skála T, Veltruská K, Skoda M, Prince KC, Matolín V. Sn/Pt(110) bimetallic surfaces: formation and oxygen adsorption. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:215002. [PMID: 21555834 DOI: 10.1088/0953-8984/23/21/215002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Submonolayer coverage of Sn on a Pt(110) surface was studied by photoemission and low-energy electron diffraction. Deposition of less than 0.6 ML at 300 K gives rise to a c(2 × 2) surface reconstruction with weak diffraction spots at the very beginning of growth, and no other LEED patterns were found at this temperature. A new (4 × 1) Sn/Pt(110) surface structure was observed after flashing to 570 K a coverage of 0.64 ML. The total Sn coverage decreased to 0.58 ML after flashing as some of the atoms diffused into deeper layers. Different Sn phases were identified on the (4 × 1) Sn/Pt(110) surface: two types of surface Sn atoms in different adsorption sites, a subsurface Sn-Pt intermetallic layer and Sn-Pt surface islands. To investigate chemical reactivity, 0.25 ML Sn/Pt(110) and 0.58 ML (4 × 1) Sn/Pt(110) surfaces were exposed to 1000 L of O(2) at 300 K. Analyses of the photoemission data provide evidence for the formation of tin oxide. The interaction with oxygen of the two surfaces is similar, independent of surface structure and the composition of the subsurface layers. The Sn concentration in the interface intermetallic layer is the main factor which influences the oxygen adsorption.
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Skála T, Tsud N, Prince KC, Matolín V. Interaction of tungsten with CeO2(111) layers as a function of temperature: a photoelectron spectroscopy study. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:215001. [PMID: 21555841 DOI: 10.1088/0953-8984/23/21/215001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The interaction of tungsten with CeO(2)(111) layers grown on Cu(111) was studied in the temperature range between 300 and 870 K by photoelectron spectroscopy of the core levels and resonant valence band spectroscopy. The interaction was found to be very strong even at 300 K, leading to the formation of cerium tungstate Ce(6)WO(12) in which the metal atoms were in Ce(3+) and W(6+) chemical states. The growth was limited by the diffusion of W atoms into the ceria layer, so subsequent tungsten deposition led to formation of W suboxides with consecutively lower chemical oxidation states, i.e. W(4+), W(2+) and metallic W(0) with an almost negligible contribution of W(5+). Step-wise annealing of the layer showed that due to stimulated diffusion of tungsten into ceria at higher temperature, Ce(6)WO(12) was formed more easily. Larger W overlayer thicknesses needed higher annealing temperature to promote diffusion. The thickest sample studied, 1.4 nm W/CeO(2), was transformed by annealing to 870 K to the Ce(6)WO(12)/W system with a tungsten monoxide (WO) interface, whereas the rest of the tungsten was converted to the W(6 + ) oxidation state.
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Bolognesi P, O'Keeffe P, Ovcharenko Y, Coreno M, Avaldi L, Feyer V, Plekan O, Prince KC, Zhang W, Carravetta V. Pyrimidine and halogenated pyrimidines near edge x-ray absorption fine structure spectra at C and N K-edges: experiment and theory. J Chem Phys 2010; 133:034302. [PMID: 20649325 DOI: 10.1063/1.3442489] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The inner shell excitation of pyrimidine and some halogenated pyrimidines near the C and N K-edges has been investigated experimentally by near edge x-ray absorption fine structure spectroscopy and theoretically by density functional theory calculations. The selected targets, 5-Br-pyrimidine, 2-Br-pyrimidine, 2-Cl-pyrimidine, and 5-Br-2-Cl-pyrimidine, allow the effects of the functionalization of the pyrimidine ring to be studied either as a function of different halogen atoms bound to the same molecular site or as a function of the same halogen atom bound to different molecular sites. The results show that the individual characteristics of the different spectra of the substituted pyrimidines can be rationalized in terms of variations in electronic and geometrical structures of the molecule depending on the localization and the electronegativity of the substituent.
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Pacilé D, Papagno M, Skála T, Matolín V, Sainsbury T, Ikuno T, Okawa D, Zettl A, Prince KC. Excitons at the B K edge of boron nitride nanotubes probed by x-ray absorption spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:295301. [PMID: 21399297 DOI: 10.1088/0953-8984/22/29/295301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We have performed a near-edge x-ray absorption fine-structure (NEXAFS) investigation of multi-walled boron nitride nanotubes (BNNTs). We show that the one-dimensionality of BNNTs is clearly evident in the B K edge spectrum, while the N K edge spectrum is similar to that of layered hexagonal BN (h-BN). We observe a sharp feature at the σ* onset of the B K edge, which we ascribe to a core exciton state. We also report a comparison with spectra taken after an ammonia plasma treatment, showing that the B K edge becomes indistinguishable from that of h-BN, due to the breaking of the tubular order and the formation of small h-BN clusters.
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Tsud N, Šutara F, Matolínová I, Veltruská K, Dudr V, Prince KC, Matolín V. Interaction of oxygen with Au/Ti(0001) surface alloys studied by photoelectron spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:265002. [PMID: 21386468 DOI: 10.1088/0953-8984/22/26/265002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The interaction of oxygen with gold adsorbed on Ti(0001) was studied by synchrotron radiation photoelectron spectroscopy. Two kinds of surfaces were explored: as-deposited 0.38, 1.16 and 1.85 monolayer (ML) thick Au overlayers on the Ti(0001) surface, and the same samples after thermal treatment, which resulted in the formation of Au-Ti intermetallic surfaces. The Ti 3p core level was strongly affected by reaction with oxygen, while the Au 4f core level showed only minor changes other than a decrease in intensity. The Ti 3p peak was fitted with several components which were identified as Ti atoms in different oxidation states, namely TiO, Ti(2)O(3), TiO(2) and Ti-OH. Titanium oxide phase formation is accompanied by Au-Ti bond dissociation and outward diffusion of Ti. The presence of an Au-Ti intermetallic phase on the Ti(0001) surface promotes oxidation of the Ti atoms.
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Bolognesi P, Mattioli G, O'Keeffe P, Feyer V, Plekan O, Ovcharenko Y, Prince KC, Coreno M, Amore Bonapasta A, Avaldi L. Investigation of halogenated pyrimidines by X-ray photoemission spectroscopy and theoretical DFT methods. J Phys Chem A 2010; 113:13593-600. [PMID: 19929014 DOI: 10.1021/jp908512v] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The inner shell ionization of pyrimidine and some halogenated pyrimidines has been investigated experimentally by X-ray photoemission spectroscopy (XPS) and theoretically by density functional theory (DFT) methods. The selected targets-5-Br-pyrimidine, 2-Br-pyrimidine, 2-Cl-pyrimidine, and 5-Br-2-Cl-pyrimidine-allowed the study of the effect of the functionalization of the pyrimidine ring by different halogen atoms bound to the same molecular site, or by the same halogen atom bound to different molecular sites. The theoretical investigation of the inductive and resonance effects in the C(1s) ionization confirms the soundness of the resonance model for a qualitative description of the properties of an aromatic system. Moreover, the combination of the experimental results and the theoretical analysis provides a detailed description of the effects of the halogen atom on the screening of a C(1s) hole in the aromatic pyrimidine ring.
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Stenuit G, Castellarin-Cudia C, Plekan O, Feyer V, Prince KC, Goldoni A, Umari P. Valence electronic properties of porphyrin derivatives. Phys Chem Chem Phys 2010; 12:10812-7. [DOI: 10.1039/c004332j] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Prince KC, Feyer V, Tadich A, Thomsen L, Cowie BCC. Photoabsorption and photoemission of magnesium diboride at the Mg K edge. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:405701. [PMID: 21832421 DOI: 10.1088/0953-8984/21/40/405701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The Mg K edge photoabsorption spectrum and the B 1s, Mg 1s, Mg 2p and valence band photoemission spectra of polycrystalline magnesium diboride have been measured. The photoabsorption spectra of the diboride and the oxide, which is present as an impurity, were separated by measuring the Auger electron partial yield at electron energies characteristic of each phase. The spectra are consistent with published calculations of the density of unoccupied p symmetry states. Better agreement is obtained with calculations for the ground state of the system than with ones for the excited state. Valence band photoemission spectra were measured at photon energies corresponding to core resonances, but, within the signal to noise level of the spectra, no resonant enhancement was observed. This is consistent with the delocalized nature of the valence band.
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Matolín V, Matolínová I, Sedlácek L, Prince KC, Skála T. A resonant photoemission applied to cerium oxide based nanocrystals. NANOTECHNOLOGY 2009; 20:215706. [PMID: 19423945 DOI: 10.1088/0957-4484/20/21/215706] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Cerium 4f level occupation determines the properties of cerium oxide based catalysts in a significant way. The Ce 4f level of nanosized cerium oxide particles was investigated with the use of resonant photoelectron spectroscopy in the Ce 4d-4f photoabsorption region. A strong interaction of ceria with different additives, e.g. Pd and Sn, led to a partial Ce4+-->Ce3+ transition that was observed as a significant resonance enhancement of 4f photoemission intensity. Increases of the CO oxidation catalytic activity were observed simultaneously. The ratio of resonance enhancement of Ce photoemission intensity DCe(3+)/DCe(4+) was used to monitor Ce(3+) and Ce(4+) state occupation. The relative parameter DCe(3+)/DCe(4+) was found to be particularly useful in the case of photoemission studies of nanopowder ceria catalysts.
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Tsud N, Skála T, Sutara F, Veltruská K, Dudr V, Yoshitake M, Prince KC, Matolín V. Low pressure oxidation of ordered Sn/Pd(110) surface alloys. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:185011. [PMID: 21825457 DOI: 10.1088/0953-8984/21/18/185011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The reaction of oxygen at low pressure with the Sn/Pd(110) system has been examined by photoelectron spectroscopy using synchrotron radiation. The c(2 × 2) and (3 × 1) reconstructions of the Sn/Pd(110) surface at 0.5 and 0.7 monolayers (ML) Sn coverage and a 1.75 ML Sn overlayer on the Pd(110) surface after flashing to 470 K were studied. The Sn 4d core level is strongly affected by O(2) adsorption while the Pd 3d core level shows very little change other than a decrease in intensity. Starting with a 10 L dose of oxygen, prominent changes in the spectra were observed for all Sn/Pd(110) surface alloys. Analysis of the Sn 4d core levels indicates that oxidation proceeds with the formation of well-defined states of Sn, which were identified as a Pd-Sn-O interface layer, SnO and SnO(2) oxides. The valence band spectra confirm this assignment. The Sn(2+) and Sn(4+) component signals originate from the topmost surface layer, i.e. tin atoms in more highly oxidized states constitute the topmost surface layer on top of the Pd-Sn-O interface. The presence of a sub-surface PdSn intermetallic alloy facilitates the tin oxide formation; the Sn-O phase formation is accompanied by Pd-Sn bond dissociation.
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Alagia M, Coreno M, Farrokhpour H, Franceschi P, Mihelic A, Moise A, Omidyan R, Prince KC, Richter R, Söderström J, Stranges S, Tabrizchi M, Zitnik M. Excitation of 1S and 3S metastable helium atoms to doubly excited states. PHYSICAL REVIEW LETTERS 2009; 102:153001. [PMID: 19518627 DOI: 10.1103/physrevlett.102.153001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2008] [Indexed: 05/27/2023]
Abstract
We present spectra of triplet and singlet metastable helium atoms resonantly photoexcited to doubly excited states. The first members of three dipole-allowed ;{1,3}P;{o} series have been observed and their relative photoionization cross sections determined, both in the triplet (from 1s2s ;{3}S;{e}) and singlet (from 1s2s ;{1}S;{e}) manifolds. The intensity ratios are drastically different with respect to transitions from the ground state. When radiation damping is included the results for the singlets are in agreement with theory, while for triplets spin-orbit interaction must also be taken into account.
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Fronzoni G, Stener M, Decleva P, Simone MD, Coreno M, Franceschi P, Furlani C, Prince KC. X-ray Absorption Spectroscopy of VOCl3, CrO2Cl2, and MnO3Cl: An Experimental and Theoretical Study. J Phys Chem A 2009; 113:2914-25. [DOI: 10.1021/jp808720z] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Skála T, Sutara F, Skoda M, Prince KC, Matolín V. Palladium interaction with CeO(2), Sn-Ce-O and Ga-Ce-O layers. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:055005. [PMID: 21817292 DOI: 10.1088/0953-8984/21/5/055005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Using photoemission, we have studied the interaction of palladium with thin layers of stoichiometric ceria (Ce(4+) character) and two mixed oxides, Ga-Ce-O and Sn-Ce-O, where cerium in the Ce(3+) oxidation state is present. Palladium was found to partially reduce the CeO(2) layer by introducing oxygen vacancies most probably in the vicinity of the growing Pd particles. In mixed oxide systems palladium very strongly interacts with both added metals-gallium and tin-leading to a breaking of metal-ceria bonds and the establishment of Pd-Ga(Sn) intermetallic compounds. As a consequence the ceria reoxidizes back to a Ce(4+) oxidation state.
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Škoda M, Cabala M, Matolínová I, Prince KC, Skála T, Šutara F, Veltruská K, Matolín V. Interaction of Au with CeO2(111): A photoemission study. J Chem Phys 2009; 130:034703. [DOI: 10.1063/1.3046684] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Prümper G, Fukuzawa H, Rolles D, Sakai K, Prince KC, Harries JR, Tamenori Y, Berrah N, Ueda K. Is CO carbon KVV Auger electron emission affected by the photoelectron? PHYSICAL REVIEW LETTERS 2008; 101:233202. [PMID: 19113548 DOI: 10.1103/physrevlett.101.233202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2008] [Indexed: 05/27/2023]
Abstract
Angular distributions (ADs) of O+ fragments from C 1s photoexcited CO detected in coincidence with carbon KVV Auger electrons emitted in the horizontal direction were measured at photon energies of 298, 305, 320, and 450 eV. At 450 eV, the ADs are polarization-independent and coincide with the molecular-frame Auger electron angular distribution. All measured ADs can be rationalized as a product of the same molecular-frame Auger electron angular distribution and the axial selectivity in the photoionization process. Thus the interaction between the photoelectron and the Auger electron for the normal Auger decay of CO can be neglected, and the two-step model is a good approximation.
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Caruso T, Lenardi C, Agostino RG, Amati M, Bongiorno G, Mazza T, Policicchio A, Formoso V, Maccallini E, Colavita E, Chiarello G, Finetti P, Šutara F, Skála T, Piseri P, Prince KC, Milani P. Electronic structure of cluster assembled nanostructured TiO2 by resonant photoemission at the Ti L2,3 edge. J Chem Phys 2008; 128:094704. [DOI: 10.1063/1.2832321] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Matolín V, Cabala M, Cháb V, Matolínová I, Prince KC, Škoda M, Šutara F, Skála T, Veltruská K. A resonant photoelectron spectroscopy study of Sn(Ox) doped CeO2 catalysts. SURF INTERFACE ANAL 2008. [DOI: 10.1002/sia.2625] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Feyer V, Bolognesi P, Coreno M, Prince KC, Avaldi L, Storchi L, Tarantelli F. Effects of nuclear dynamics in the low-kinetic-energy Auger spectra of CO and CO2. J Chem Phys 2007; 123:224306. [PMID: 16375475 DOI: 10.1063/1.2137311] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The CO and CO(2) carbon and oxygen Auger spectra have been measured by electron impact and compared with accurate theoretical calculations accounting for the effects of the dynamics of the nuclei on the energy and linewidth of the Auger bands. The calculations for CO were previously published [L. S. Cederbaum et al., J. Chem. Phys. 95, 6634 (1991)], while for CO(2) they are new and presented here for the first time. For both molecules, particular attention has been paid to the low-kinetic-energy region of the spectra, which corresponds to doubly charged ion states with the two holes mainly localized in the inner valence region. New bands have been observed. It is shown that a proper consideration of the vibrational broadening and shift of the bands due to the dynamics of the nuclei is needed to assign these features. For CO, very large energy shifts between corresponding features in the C 1s and O 1s spectra have been observed, confirming the theoretical predictions of 1991. The new computed spectra of CO(2) allow a very accurate analysis of the experiments over the whole energy range.
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Vall-Llosera G, Melero García E, Kivimäki A, Rachlew E, Coreno M, de Simone M, Richter R, Prince KC. Fluorescence emission from photo-fragments after resonant S 2p excitations in H2S. Phys Chem Chem Phys 2007; 9:389-95. [PMID: 17199155 DOI: 10.1039/b610199b] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Visible-UV fluorescence emission of gas-phase hydrogen sulfide, H(2)S, has been studied at the S 2p edge with synchrotron radiation excitation. Dispersed fluorescence measurements in the wavelength range 300-900 nm were taken at several photon energies corresponding to the excitations of the S 2p electrons to the unoccupied molecular and Rydberg orbitals. The spectra reveal fluorescence from the H, S, S(+), HS and HS(+) photo-fragments. H is found to be the strongest emitter at Rydberg excitations, while the emission from S(+) is dominant at the molecular resonances and above the S 2p ionization thresholds. The intensities of hydrogen Lyman-alpha (122 nm), Balmer-alpha (656 nm), Balmer-beta (486 nm) transitions as well as the visible-UV total fluorescence yield (300-900 nm) and the total ion yield were measured by scanning the photon energy in small steps across the S 2p edge. The different Balmer lines show some sensitivity to the specific core excitations, which is, however, not so strong as that recently observed in the water molecule [E. Melero García, A. Kivimäki, L. G. M. Pettersson, J. Alvarez Ruiz, M. Coreno, M. de Simone, R. Richter and K. C. Prince, Phys. Rev. Lett., 2006, 96, 063003].
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Masek K, Fabík S, Masková A, Tsud N, Veltruská K, Prince KC, Cháb V, Vyskocil J, Matolín V. Photoelectron spectroscopy characterization of diamond-like carbon films. APPLIED SPECTROSCOPY 2006; 60:936-40. [PMID: 16925932 DOI: 10.1366/000370206778062129] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
The electronic states of diamond-like hydrogenated carbon (DLC) films were studied by synchrotron radiation photoelectron spectroscopy. The valence band spectra measured at different excitation energies show the gradual emergence of the p-pi band in relation to the sample annealing and ion bombardment amorphization. The p-pi band of the annealed DLC was characterized by localized p(z) states, while the formation of the amorphous carbon surface was accompanied by appearance of the delocalized p(z) states, which reduce the optical gap. A simple approach permitting the extraction of the 2p band shape from the photoelectron spectra is proposed.
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Prince KC, Coreno M, Richter R, de Simone M, Feyer V, Kivimäki A, Mihelic A, Zitnik M. Detection of the 1pe series of doubly excited helium states below N=2 via the stark effect. PHYSICAL REVIEW LETTERS 2006; 96:093001. [PMID: 16606259 DOI: 10.1103/physrevlett.96.093001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2005] [Indexed: 05/08/2023]
Abstract
The Stark effect on the doubly excited states of helium below the N=2 threshold has been studied by vacuum ultraviolet fluorescence yield spectroscopy. Two new series of states are observed at moderate fields (<10 kV/cm), and assigned to the previously unobserved even 1pe series, and a group of 1De series. The 1Se states are observed indirectly via their mixing with nearby 1 po states. The observations at moderate field contradict theoretical predictions that field strengths about an order of magnitude greater are necessary to observe the Stark effect on He doubly excited states at low quantum numbers.
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Melero García E, Kivimäki A, Pettersson LGM, Alvarez Ruiz J, Coreno M, de Simone M, Richter R, Prince KC. Fluorescence emission of excited hydrogen atoms after core excitation of water vapor. PHYSICAL REVIEW LETTERS 2006; 96:063003. [PMID: 16605990 DOI: 10.1103/physrevlett.96.063003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Indexed: 05/08/2023]
Abstract
The Balmer emission from atomic hydrogen has been recorded across the resonances at the oxygen K edge of the water molecule using synchrotron radiation excitation. The emission is observed to be strongest at excitations to Rydberg resonances. The observations are interpreted using a qualitative model for the dynamics of the core-to-Rydberg excited molecule. The model links the quantum state of the core-excited water molecule via resonant Auger decay and subsequent dissociation to the state of the fluorescing hydrogen atom.
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Takács AF, Neumann M, Postnikov AV, Kuepper K, Scheurer A, Sperner S, Saalfrank RW, Prince KC. Electronic structure study by means of x-ray spectroscopy and theoretical calculations of the “ferric star” single molecule magnet. J Chem Phys 2006; 124:044503. [PMID: 16460181 DOI: 10.1063/1.2155340] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The electronic structure of the single molecule magnet system {M[Fe(L(1))(2)](3)}4CHCl(3) [M=Fe,Cr;L(1)=CH(3)N(CH(2)CH(2)O)(2) (2-)] has been studied using x-ray photoelectron spectroscopy, x-ray-absorption spectroscopy, soft-x-ray emission spectroscopy, as well as theoretical density-functional-based methods. There is a good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O,N) exhibit a magnetic polarization yielding effective spin S=52 per iron atom, giving a high-spin state molecule with a total S=5 effective spin for the case of M=Fe.
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Kuepper K, Bondino F, Prince KC, Zangrando M, Zacchigna M, Takás AF, Crainic T, Matteucci M, Parmigiani F, Winiarski A, Galakhov VR, Mukovskii YM, Neumann M. Direct Investigation of Orbital Ordering in a Colossal Magnetoresistance Manganite by Means of X-ray Linear Dichroism at the Mn L Edge. J Phys Chem B 2005; 109:15667-70. [PMID: 16852985 DOI: 10.1021/jp052762s] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have investigated for the first time the orbital ordering in a three-dimensional colossal magnetoresistance manganite, namely La(7/8)Sr(1/8)MnO3, by applying soft X-ray linear dichroism (XLD) to the Mn L edge. We found that the cooperative Jahn-Teller distorted orthorhombic phase, which is present at a temperature of 240 K, is probably accompanied by a predominantly cross type (x2 - z2)/(y2 - z2) orbital ordering. This result is discussed in the light of different exchange interaction models.
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Kuepper K, Falub MC, Prince KC, Galakhov VR, Troyanchuk IO, Chiuzbaian SG, Matteucci M, Wett D, Szargan R, Ovechkina NA, Mukovskii YM, Neumann M. Electronic Structure of A- and B-Site Doped Lanthanum Manganites: A Combined X-ray Spectroscopic Study. J Phys Chem B 2005; 109:9354-61. [PMID: 16852120 DOI: 10.1021/jp044447w] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The electronic properties of a series of colossal magnetoresistance (CMR) compounds, namely LaMnO3, La(1-x)Ba(x)(MnO3 (0.2 < or = x < or = 0.55), La(0.76)Ba(0.24)Mn(0.84)Co(0.16)O3, and La(0.76)Ba(0.24)Mn(0.78)Ni(0.22)O3, have been investigated in a detailed spectroscopic study. A combination of X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS), and resonant inelastic X-ray scattering (RIXS) was used to reveal a detailed picture of the electronic structure in the presence of Ba, Co, and Ni doping in different concentrations. The results are compared with available theory. The valence band of La(1-x)()Ba(x)MnO3 (0 < or = x < or = 0.55) is dominated by La 5p, Mn 3d, and O 2p states, and strong hybridization between Mn 3d and O 2p states is present over the whole range of Ba concentrations. Co-doping at the Mn site leads to an increased occupancy of the e(g) states near the Fermi energy and an increase in the XPS valence band intensity between 0.5 and 5 eV, whereas the Ni-doped sample shows a lower density of occupied states near the Fermi energy. The Ni d states are located in a band spanning the energy range of 1.5-5 eV. XAS spectra indicate that the hole doping leads to mixed Mn 3d-O 2p states. Furthermore, RIXS at the Mn L edge has been used to probe d-d transitions and charge-transfer excitations in La(1-x)Ba(x)MnO3.
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