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Search: WFRF:(Schnadt J.)

  • Result 1-50 of 59
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  • Schnadt, J, et al. (author)
  • Excited-state charge transfer dynamics in systems of aromatic adsorbates on TiO2 studied with resonant core techniques
  • 2003
  • In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:23, s. 12462-12472
  • Journal article (peer-reviewed)abstract
    • Resonant core spectroscopies are applied to a study of the excited electron transfer dynamics on a low-femtosecond time scale in systems of aromatic molecules (isonicotinic acid and bi-isonicotinic acid) adsorbed on a rutile TiO2(110) semiconductor surface. Depending on which adsorbate state is excited, the electron is either localized on the adsorbate in an excitonic effect, or delocalizes rapidly into the substrate in less than 5 fs (3 fs) for isonicotinic acid (bi-isonicotinic acid). The results are obtained by the application of a variant of resonant photoemission spectroscopy. (C) 2003 American Institute of Physics.
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  • Schnadt, Joachim, et al. (author)
  • Structural study of adsorption of isonicotinic acid and related molecules on rutile TiO2(110) I: XAS and STM
  • 2003
  • In: Surface Science. - 0039-6028. ; 540:1, s. 39-54
  • Journal article (peer-reviewed)abstract
    • X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) have been used to study the absorption of monolayers of the pyridinecarboxylic acid monomers (isonicotinic acid, nicotinic acid, and picolinic acid) and benzoic acid on a rutile TiO2(1 1 0) surface. We find that the pyridine and phenyl rings are oriented with their planes largely perpendicular to the surface. The azimuthal orientations are strongly influenced by adsorbate-adsorbate interactions, which in each case leads to at least two different molecular species. In order to reach this conclusion a detailed strategy has been developed for the interpretation of angle-dependent XAS data, which does not rely on any curve fitting procedures. (C) 2003 Elsevier B.V. All rights reserved.
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  • O'Shea, J. N., et al. (author)
  • Hydrogen-bond induced surface core-level shift in isonicotinic acid
  • 2001
  • In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:10, s. 1917-1920
  • Journal article (peer-reviewed)abstract
    • Intermolecular hydrogen-bonding in thick films of isonicotinic acid evaporated onto rutile TiO2(110) has been investigated with X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The rate of deposition is found to be a key factor in overcoming the kinetic barriers to extensive hydrogen-bond formation, which, when present, gives rise to large energy shifts between bulk and surface in both the N1s XPS and XAS. The origin of the surface core-level shift is attributed to the presence of non-hydrogen-bonded nitrogen atoms in the surface layer.
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  • O'Shea, J. N., et al. (author)
  • Hydrogen-bond induced surface core-level shift in pyridine carboxylic acids
  • 2001
  • In: Surface Science. - 0039-6028 .- 1879-2758. ; 486:3, s. 157-166
  • Journal article (peer-reviewed)abstract
    • Intermolecular hydrogen bonding in thick films of pyridine carboxylic acids (isonicotinic; picolinic and bi-isonicotinic acid) evaporated onto rutile TiO2(1 1 0) has been investigated with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. These molecules are shown to be strongly H-bonded in the condensed phase, and a surface core-level shift is observed due to the presence of non-H-bonded nitrogen atoms in the surface layer. Density functional theory calculations are used to relate the experimental data to the proposed bonding configurations based on the surface termination of the known equilibrium solid-state structure. A kinetic barrier, attributed to the high degree of molecular orientation required for the formation of extended H-bonding networks, has also been investigated.
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  • Schiessling, J, et al. (author)
  • Bulk and surface charge states of K3C60
  • 2005
  • In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 71:16
  • Journal article (peer-reviewed)abstract
    • We detect a significant angle-dependence in the core level and valence line shapes of photoelectron spectra of single crystal K3C60. This allows the identification of bulk and surface components in the data, and allows us to explain the anomalous line shapes observed for this system. The states near the Fermi level are associated with the bulk of the sample. There is strong evidence of an insulating surface layer, which we ascribe to intermolecular electron correlations. These results simplify the interpretation of previous, apparently conflicting observations.
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  • Schiessling, J, et al. (author)
  • Insulating surface layer on single crystal K3C60
  • 2004
  • In: European Physical Journal B. Condensed Matter and Complex Systems. - : Springer Science and Business Media LLC. - 1434-6028. ; 41:4, s. 435-438
  • Journal article (peer-reviewed)abstract
    • Using angle-dependent photoemission spectra of core and valence levels we show that metallic, single crystal K3C60 is terminated by an insulating or weakly-conducting surface layer. We attribute this to the effects of strong intermolecular correlations combined with the average surface charge state. Several controversies on the electronic structure are thereby resolved.
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  • Schnadt, J, et al. (author)
  • Structural study of adsorption of isonicotinic acid and related molecules on rutile TiO2(110) II: XPS
  • 2003
  • In: Surface Science. - : Elsevier BV. - 0039-6028. ; 544:1, s. 74-86
  • Journal article (peer-reviewed)abstract
    • The adsorption of monolayers of the pyridine-carboxylic acid monomers (isonicotinic acid, nicotinic acid, and picolinic acid) on rutile TiO2(1 1 0) has been studied by means of X-ray photoemission spectroscopy. An investigation of the O 1s spectra shows that the molecular carboxylic groups are deprotonated and, hence, that the molecules bind to the surface in a bidentate mode. Moreover, the binding energy of those core levels that are related to the pyridine ring atoms shift as a function of molecule relative to the substrate O 1s and Ti 3p levels, while the position of the core levels related to emission from the carboxylic group are constant relative to the substrate levels. The molecule-dependent shifts are attributed to local intermolecular interactions that determine the proximity of adjacent molecular rings and thus the core-hole screening response of the neighbouring molecules. We propose a simple molecular arrangement for each case which satisfies the known constraints. (C) 2003 Elsevier B.V. All rights reserved.
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27.
  • Snezhkova, O., et al. (author)
  • Iron phthalocyanine on copper nitride: geometry, spin state, and modification by pyridine adsorption
  • Other publication (other academic/artistic)abstract
    • Using a monolayer of iron phthalocyanine adsorbed on the Au(111) surface and on a Cu(111)-supported two-dimensional copper nitride layer, we show how the modification of the support can influence the electronic and magnetic properties of an adsorbed transition metal complex. The two systems have been studied by a combination of electron spectroscopy and first principles theoretical calculations, which included modelling of the van der Waals interactions. For adsorption of iron phthalocyanine on the Cu(100)c(2x2)-2N/Cu(111) surface we find several different adsorbate structures at different surface sites, which all have very similar energies. Depending on the adsorption site - above a support nitrogen or a support copper atom - the spin magnetic moment of the molecular iron ion assumes different values. Although pyridine adsorption on the iron phthalocyanine monolayer reduces the spin magnetic moments for all phthalocyanine adsorption sites, the difference between the different sites persists: only for the iron phthalocyanine adsorbates with the central iron ion above a support nitrogen atom the spin is quenched completely, while a residual spin magnetic moment is found for the adsorption structures with the iron ion above a copper atom. The results illustrate clearly the relevance of the support as a ligand to the central ion.
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  • Mayor, Louise C., et al. (author)
  • Photoemission, resonant photoemission, and x-ray absorption of a Ru(II) complex adsorbed on rutile TiO2 (110) prepared by in situ electrospray deposition
  • 2008
  • In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 129:11
  • Journal article (peer-reviewed)abstract
    • An experimental study of the bonding geometry and electronic coupling of cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium( II) (N3) adsorbed on rutile TiO2(110) is presented, along with supporting theoretical calculations of the bonding geometry. Samples were prepared in situ using ultrahigh vacuum electrospray deposition. Core-level photoemission spectroscopy was used to characterize the system and to deduce the nature of the molecule-surface bonding. Valence band photoemission and N 1s x-ray absorption spectra were aligned in a common binding energy scale to enable a quantitative analysis of the bandgap region. A consideration of the energetics in relation to optical absorption is used to identify the photoexcitation channel between the highest occupied and lowest unoccupied molecular orbitals in this system, and also to quantify the relative binding energies of core and valence excitons. The core-hole clock implementation of resonant photoemission spectroscopy is used to reveal that electron delocalization from N3 occurs within 16 fs. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.2975339]
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30.
  • O'Shea, JN, et al. (author)
  • Hydrogen-bond induced surface core-level shift in isonicotinic acid
  • 2001
  • Other publication (other academic/artistic)abstract
    • Intermolecular hydrogen-bonding in thick films of isonicotinic acid evaporated onto rutile TiO2(110) has been investigated with X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The rate of deposition is found to be a key fac
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  • O'Shea, JN, et al. (author)
  • Hydrogen-bond induced surface core-level shift in pyridine carboxylic acids
  • 2001
  • In: SURFACE SCIENCE. - : ELSEVIER SCIENCE BV. - 0039-6028. ; 486:3, s. 157-166 Language: English
  • Journal article (peer-reviewed)abstract
    • Intermolecular hydrogen bonding in thick films of pyridine carboxylic acids (isonicotinic; picolinic and bi-isonicotinic acid) evaporated onto rutile TiO2(1 1 0) has been investigated with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy
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  • Persson, Petter, et al. (author)
  • N1s x-ray Absorption Study of the Bonding Interaction of Bi-Isonicotinic Acid on Rutile TiO2 (110)
  • 2000
  • In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 112:9, s. 3945-3948
  • Journal article (peer-reviewed)abstract
    • N1s x-ray absorption spectra of bi-isonicotinic acid (2,28-bipyridine–4,48-dicarboxylic acid! on rutile TiO2(110) have been studied experimentally and quantum chemically. Differences between multilayer and monolayer spectra are explained by the adsorbate bonding to the substrate. A connection to the electronic coupling in dye-sensitized electrochemical devices is made.
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  • Ueda, K., et al. (author)
  • Adsorption and Reaction of CO and NO on Ir(111) under Near Ambient Pressure Conditions
  • 2016
  • In: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 59:5-7, s. 487-496
  • Journal article (peer-reviewed)abstract
    • The adsorption and reaction of CO and NO on Ir(111) have been studied by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) together with low-energy electron diffraction, scanning tunneling microscopy, and mass spectroscopy (MS). Under both ultrahigh vacuum (UHV) and NAP conditions CO molecules occupy on-top sites of the Ir(111) surface at room temperature (RT) by forming two-dimensional clusters. Exposure to NO under UHV conditions at RT induces partially dissociative adsorption, while NAP NO exposure leads to a Ir(111) surface that is covered by molecular NO. We conducted in-operando NAP-XPS/MS observation of the NO + 13CO reaction under a NAP condition as a function of temperature. Below 210 °C adsorption of NO is inhibited by CO, while above 210 °C the CO inhibition is released due to partial desorption of CO and dissociative adsorption of NO starts to occur leading to associative formation of N2. Under the most active condition studied here the Ir surface is covered by a dense co-adsorption layer consisting of on-top CO, atomic N and O, which suggests that this reaction is not a NO-dissociation-limited process but a N2/CO2 formation-limited process.
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  • Westerström, Rasmus, et al. (author)
  • Stressing Pd atoms: Initial oxidation of the Pd(110) surface
  • 2008
  • In: Surface Science. - : Elsevier BV. - 0039-6028. ; 602:14, s. 2440-2447
  • Journal article (peer-reviewed)abstract
    • We have investigated the oxygen induced structures of the Pd(1 1 0) surface in the pressure range of 10(-5)-10(-3) mbar of oxygen, at a sample temperature of around 300 degrees C. These structures, denoted as "(7 x root 3)" and "(9 x root 3)", are studied in detail by the use of a combination of low-energy electron diffraction, scanning tunneling microscopy, high-resolution core level spectroscopy, and ab-initio simulations. Based on our data a model is proposed for these structures containing segments of Pd atoms in the [1 (1) over bar0] direction, in which the Pd rows are decorated by O atoms in a zig-zag pattern. The segments are periodically separated by displaced Pd atoms. Density functional theory calculations show that the displacements reduce the oxygen induced stress significantly, as compared to a structure with no displacements. The calculations also suggest that the new structures are stabilized by domain formation. (C) 2008 Elsevier B.V. All rights reserved.
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  • Faraggi, M. N., et al. (author)
  • Role of Deprotonation and Cu Adatom Migration in Determining the Reaction Pathways of Oxalic Acid Adsorption on Cu(111)
  • 2011
  • In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:43, s. 21177-21182
  • Journal article (peer-reviewed)abstract
    • Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and first principles theoretical calculations have been used to gain insight into the fundamental processes involved in the adsorption and self-assembly of oxalic acid on Cu(111). The experimental data demonstrate that several reaction pathways are involved in the chemisorption of oxalic acid on Cu(111), one of which leads to deprotonation of the acid into oxalate molecules that form ordered structures on the surface. Theoretical calculations indicate that the adsorption of oxalate molecules is not stable on the surface unless copper adatoms are taken into consideration. Coordination with copper adatoms prevents oxalate molecules from getting closer to the substrate, precluding the expected decomposition of oxalate into carbon dioxide. Our results, thus, suggest that the 2D gas of diffusing copper adatoms might play a very important role in the self-assembly of the molecules not only by catalyzing the deprotonation of oxalic acid but also by decreasing the surface reactivity.
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  • Kjeldgaard, Lisbeth, et al. (author)
  • Intramolecular vibronic dynamics in molecular solids: C60
  • 2005
  • In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:20
  • Journal article (peer-reviewed)abstract
    • Vibronic coupling in solid C60 has been investigated with a combination of resonant photoemission spectroscopy (RPES) and resonant inelastic x-ray scattering (RIXS). Excitation as a function of energy within the lowest unoccupied molecular orbital resonance yielded strong oscillations in intensity and dispersion in RPES, and a strong inelastic component in RIXS. Reconciling these two observations establishes that vibronic coupling in this core hole excitation leads to predominantly inelastic scattering and localization of the excited vibrations on the molecule on a femtosecond time scale. The coupling extends throughout the widths of the frontier valence bands.
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  • Kokkonen, E., et al. (author)
  • Ambient pressure x-ray photoelectron spectroscopy setup for synchrotron-based in situ and operando atomic layer deposition research
  • 2022
  • In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 93:1
  • Journal article (peer-reviewed)abstract
    • An ambient pressure cell is described for conducting synchrotron-based x-ray photoelectron spectroscopy (XPS) measurements during atomic layer deposition (ALD) processes. The instrument is capable of true in situ and operando experiments in which it is possible to directly obtain elemental and chemical information from the sample surface using XPS as the deposition process is ongoing. The setup is based on the ambient pressure XPS technique, in which sample environments with high pressure (several mbar) can be created without compromising the ultrahigh vacuum requirements needed for the operation of the spectrometer and the synchrotron beamline. The setup is intended for chemical characterization of the surface intermediates during the initial stages of the deposition processes. The SPECIES beamline and the ALD cell provide a unique experimental platform for obtaining new information on the surface chemistry during ALD half-cycles at high temporal resolution. Such information is valuable for understanding the ALD reaction mechanisms and crucial in further developing and improving ALD processes. We demonstrate the capabilities of the setup by studying the deposition of TiO2 on a SiO2 surface by using titanium(IV) tetraisopropoxide and water as precursors. Multiple core levels and the valence band of the substrate surface were followed during the film deposition using ambient pressure XPS.
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  • Käämbre, Tanel, et al. (author)
  • Bulk electronic structure of K3C60 as revealed by soft x-rays
  • 2007
  • In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:19, s. 195432-
  • Journal article (peer-reviewed)abstract
    • We present C 1s x- ray absorption, x- ray emission, and resonant inelastic x- ray scattering (RIXS ) spectra of single- phase crystalline K3C60. The comparison to valence- band photoelectron spectra from the same sample facilitates identification of the contribution from surface and bulk electronic states in the latter. Bulk- sensitive techniques show that the valence bands of K3C60 and pure C-60 are characterized by spectral features of similar width, in agreement with the predictions of band- structure calculations. Symmetry selectivity in the RIXS process allows us to assign peaks in the C 1s absorption spectrum, demonstrating a close correspondence with pure C-60 also in the conduction band. The symmetry selectivity is as pronounced in K3C60 as in pure C-60, indicating that the local C-60 symmetry is not appreciably affected by the K doping, either in the ground state or intermediate state, on the time scale of 6 fs.
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  • Muraro, Antonella, et al. (author)
  • Managing food allergy: GA2LEN guideline 2022.
  • 2022
  • In: The World Allergy Organization journal. - : Elsevier BV. - 1939-4551. ; 15:9
  • Journal article (peer-reviewed)abstract
    • Food allergy affects approximately 2-4% of children and adults. This guideline provides recommendations for managing food allergy from the Global Allergy and Asthma European Network (GA2LEN). A multidisciplinary international Task Force developed the guideline using the Appraisal of Guidelines for Research and Evaluation (AGREE) II framework and the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach. We reviewed the latest available evidence as of April 2021 (161 studies) and created recommendations by balancing benefits, harms, feasibility, and patient and clinician experiences. We suggest that people diagnosed with food allergy avoid triggering allergens (low certainty evidence). We suggest that infants with cow's milk allergy who need a breastmilk alternative use either hypoallergenic extensively hydrolyzed cow's milk formula or an amino acid-based formula (moderate certainty). For selected children with peanut allergy, we recommend oral immunotherapy (high certainty), though epicutaneous immunotherapy might be considered depending on individual preferences and availability (moderate certainty). We suggest considering oral immunotherapy for children with persistent severe hen's egg or cow's milk allergy (moderate certainty). There are significant gaps in evidence about safety and effectiveness of the various strategies. Research is needed to determine the best approaches to education, how to predict the risk of severe reactions, whether immunotherapy is cost-effective and whether biological therapies are effective alone or combined with allergen immunotherapy.
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48.
  • O'Shea, James N, et al. (author)
  • Molecular damage in bi-isonicotinic acid adsorbed on rutile TiO2(110)
  • 2008
  • In: Surface Science. - : Elsevier BV. - 0039-6028. ; 602:9, s. 1693-1698
  • Journal article (peer-reviewed)abstract
    • Here we present the characteristic signatures in X-ray absorption and photoemission spectroscopy for molecular damage in adsorbed monolayers of bi-isonicotinic acid on a rutile TiO2(110) surface. Bi-isonicotinic acid is the anchor ligand through which many important inorganic complexes are bound to the surface of TiO2 in dye-sensitized solar cells. The nature of the damage caused by excessive heating of the adsorbed monolayer is consistent with splitting the molecule into two adsorbed isonicotinic acid molecular fragments. The effect on the lowest unoccupied molecular orbitals (involved in electron transfer in the molecule) can be understood in terms of the adsorption geometry of the reaction products and their nearest neighbor interactions.
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  • O'Shea, James N., et al. (author)
  • Ultra-fast intramolecular vibronic coupling revealed by RIXS and RPES maps of an aromatic adsorbate on TiO2(110)
  • 2018
  • In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:20
  • Journal article (peer-reviewed)abstract
    • Two-dimensional resonant inelastic x-ray scattering (RIXS) and resonant photoelectron spectroscopy (RPES) maps are presented for multilayer and monolayer coverages of an aromatic molecule (bi-isonicotinic acid) on the rutile TiO2(110) single crystal surface. The data reveal ultra-fast intramolecular vibronic coupling upon core excitation from the N 1s orbital into the lowest unoccupied molecular orbital (LUMO) derived resonance. In the RIXS measurements, this results in the splitting of the participator decay channel into a purely elastic line which disperses linearly with excitation energy and a vibronic coupling channel at constant emission energy. In the RPES measurements, the vibronic coupling results in a linear shift in binding energy of the participator channel as the excitation is tuned over the LUMO-derived resonance. Localisation of the vibrations on the molecule on the femtosecond time scale results in predominantly inelastic scattering from the core-excited state in both the physisorbed multilayer and the chemisorbed monolayer.
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  • O'Shea, JN, et al. (author)
  • X-ray photoelectron spectroscopy of low surface concentration mass-selected Ag clusters
  • 2000
  • In: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. - 0021-9606. ; 113:20, s. 9233-9238
  • Journal article (peer-reviewed)abstract
    • We have developed an experimental setup for the study of small mass-selected clusters delivered by soft landing to a model oxide support. An automated deposition system to achieve accurately quantified homogeneous surfaces is described which also overcome
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