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  • 1.
    Almqvist, Nils
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Fractal analysis of scanning probe microscopy images1996Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 355, nr 1-3, s. 221-228Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The accuracy and precision of several algorithms, including newly developed, for calculating the fractal dimension from scanning probe microscopy images of material surfaces are investigated. The algorithms are based on the area-perimeter method, a variance method or versions of the structure function method. The latter two methods show good correspondence to computer simulated images, with known fractal dimensions, and have successfully been applied also on real images. The results show that these two methods give reliable fractal dimensions and are well suited to describe surface roughness quantitatively.

  • 2.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Katainen, Jukka
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology, Laboratory of Physics, Aalto University.
    Hautojärvi, Pekka
    Laboratory of Physics, Helsinki University of Technology.
    An experimental study on adsorption of benzene on Co(0001)2002Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 507, s. 57-61Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption of benzene on Co(0 0 0 1) was studied by X-ray photoelectron spectroscopy, temperature programmed desorption, low energy electron diffraction (LEED) and work function measurements. The adsorption was found to be molecular at room temperature and to saturate at a fractional coverage of 0.125 ML. With LEED a c(2root3 x 4) overlayer structure was seen. Below 220 K at high exposures a p(root7 x root7)R19degrees LEED pattern was observed corresponding to a coverage of 0.143 ML. Temperature programmed desorption measurements stated that benzene starts to decompose around 340 K to hydrogen and a hydrocarbon fragment, most likely C6H5. While the hydrogen desorbed, the hydrocarbon stayed at the surface. The desorption of molecular benzene was negligible. The activation energy for the dehydrogenation was calculated to be about 102 kJ/mol. The work function of Co(0 0 0 1) decreased by 1.3 eV upon saturation with benzene. The induced dipole moment was calculated to be 1.9 Debye/molecule.

  • 3.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology.
    Sulfur poisoning of the CO adsorption on Co(0001)2004Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 573, nr 2, s. 183-190Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    CO adsorption on a sulfur covered cobalt surface at 185 K has been studied using XPS, TDS, LEED, and WF measurements. As in the case of CO adsorption on the clean Co(0001) surface, CO adsorbs and desorbs molecularly and no dissociation was observed. The saturation coverage of CO decreases linearly from 0.54 ML to 0.27 ML when the S pre-coverage increases to 0.25 ML. The WF increased during CO adsorption, but did not reach the value obtained for CO adsorption on the clean surface. The smaller work function change is explained by the reduced adsorption of CO on the sulfur-precovered surface. A reduction in the activation energy of desorption for CO from 113 kJ/mol to 88 kJ/mol was observed indicating weaker bonding of the CO molecules to the surface. The behavior of the CO/S/Co(0001) system was explained by a combination of steric and electronic effects.

  • 4.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology, Laboratory of Physics, Aalto University.
    Hautojärvi, Pekka
    Laboratory of Physics, Helsinki University of Technology.
    Coadsorption of CO and C6H6 on Co(0 0 0 1)2005Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 584, nr 1, s. 70-76Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied the influence of CO on the adsorption of benzene on the Co(0 0 0 1) surface using LEED, XPS, TDS and work function measurements. CO was found to reduce the benzene adsorption, but even at saturation CO exposure no complete blocking was observed. Thermal desorption of the coadsorbed layer featured CO and H2 peaks indicating partial dehydrogenation of benzene and retaining of the CO bond. Ordered LEED structures were found with all coverages: Pre-adsorption of CO led to patterns already seen for pure carbon monoxide adsorption. Pre-adsorption of benzene showed the known (7×7)R19°structure of pure benzene also with small CO exposures, but higher CO exposures yielded a mixture of (7×7)R19°and (3×3)R30°patterns

  • 5.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Laboratory of Physics, Helsinki University of Technology.
    Hautojärvi, Pekka
    Laboratory of Physics, Helsinki University of Technology.
    Methanol on Co(0 0 0 1): XPS, TDS, WF and LEED results2005Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 598, nr 1-3, s. 128-135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption and decomposition of methanol on clean Co(0 0 0 1) was studied as a function of temperature and exposure by means of TDS (thermal desorption spectroscopy), XPS (X-ray photoelectron spectroscopy), WF (work function measurements) and LEED (low energy electron diffraction). Methanol was adsorbed by OH-bond scission as methoxide on the cobalt surface. TD and XP spectra revealed that beside a small amount of molecularly desorbing methanol, it decomposed during heating to the final products: CO and H2. Desorption of H2 took place around 356 K and desorption of CO around 390 K. These temperatures are characteristic for desorption of these species on clean cobalt. Work function measurements showed that the adsorption of methanol resulted in a lowering of the WF by 1.1 eV. Heating - and therewith decomposition - led to an increase in the WF of +0.4 eV. After all decomposition products had desorbed, the WF returned to the value for the clean Co(0 0 0 1) surface. LEED exhibited a combination of two ordered structures: p(2 × 2) and (7×7)19.1°. The (7×7)19.1° pattern was formed by methoxide or hydrogen and vanished below 340 K. The p(2 × 2) structure was still found above 380 K and was therefore assigned to CO

  • 6. Hoffmann, F.M.
    et al.
    Weisel, M. D.
    Paul, Jan
    The activation of CO2 by potassium-promoted Ru(001) I. FT-IRAS and TDMS study of oxalate and carbonate intermediates1994Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 316, nr 3, s. 277-293Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interaction of CO2 with the clean and alkali promoted Ru(001) surface has been studied with time-evolved Fourier transform-infrared reflection absorption spectroscopy (FT-IRAS) and thermal desorption mass spectrometry (TDMS). CO2 adsorbs on the clean Ru(001) surface at 85 K in a physisorbed CO2 monolayer, which desorbs undissociated at 100 K. The interaction of CO2 with a √3 × √3-R30° monolayer of potassium on Ru(001) results in the facile formation of oxalate at 85 K. Oxalate decomposes to carbonate after heating above 150 K, i.e. C2O4 → CO3 + CO. Vibrational spectra suggest, in agreement with theoretical calculations, an ionic carbonate species with D3h symmetry and the molecular plane oriented perpendicular to the surface, although alternate coordinations cannot be completely ruled out. Decomposition of the carbonate starts at 700 K and results in the simultaneous desorption of K and CO2 as major decompositions products, suggesting a reaction pathway of CO3 → CO2 + O and a K:CO3 stoichiometry of ≈1:1. The interaction of CO2 with a multilayer of potassium adsorbed on Ru(001), exhibits similar intermediates as observed for the monolayer, i.e. oxalate and carbonate. However, the overall reaction behavior is more complex and controlled by the penetration of CO2 into the potassium layer, which limits the reaction to only a few (4-5) of the topmost potassium layers. Reaction at 85 K reveals the formation of oxalate, CO2-2 and possibly CO-2 species. Annealing of the multilayer to 425 K results in the formation of carbonate, and the desorption of unreacted potassium. Vibrational spectra characterize an essentially ionic carbonate species with a preferential orientation of the molecular plane perpendicular to the surface, although the vibrational linewidths suggest imperfect ordering of the layer. Further annealing to 550 K results in a well-ordered "bilayer", containing two carbonate species with the molecular plane perpendicular (C2v, first layer) and parallel (C3v, second layer) to the surface, respectively. Decomposition of this layer at 700 K leaves a carbonate monolayer which subsequently decomposes at 750 K. The overall decomposition behavior of the multilayer is complex and is sensitive to the preparation and thickness of the potassium multilayer.

  • 7.
    Lahtinen, J.
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Kantola, P.
    Laboratory of Physics, Helsinki University of Technology.
    Jaatinen, S.
    Laboratory of Physics, Helsinki University of Technology.
    Habermehl-Cwirzen, K.
    Laboratory of Physics, Helsinki University of Technology.
    Salo, P.
    Laboratory of Physics, Helsinki University of Technology.
    Vuorinen, J.
    Institute of Physics, Tampere University of Technology.
    Lindroos, M.
    Institute of Physics, Tampere University of Technology.
    Pussi, K.
    Laboratory of Electronics Materials Technology, Lappeenranta University of Technology.
    Seitsonen, A. P.
    Institute of Mineralogy and Condensed Matter Physics, CNRS and University of Pierre and Marie Curie.
    LEED and DFT investigation on the (2 × 2)-S overlayer on Co(0 0 0 1)2005Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 599, nr 1-3, s. 113-121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The geometric surface structure of a (2 × 2)-S layer formed by adsorption of hydrogen sulfide at 185 K on the Co(0 0 0 1) surface has been determined by low energy electron diffraction (LEED) experiments and density-functional theory (DFT) calculations. The favored atomic configuration consists of sulfur atoms residing at the fcc-hollow sites with S-Co distance of 2.2 ± 0.1 Å. Buckling in the first layer is negligible and the three nearest-neighbor Co atoms below the S atom are symmetrically moved by 0.05 ± 0.09 Å along the surface away from the S atom. The DFT calculations confirm the hollow-site adsorption and give further information on the electronic structure of the system. © 2005 Elsevier B.V. All rights reserved.

  • 8. Lindgren, S.Å.
    et al.
    Paul, Jan
    Walldén, L.
    Sodium induced structure in UPS spectra of Cu(111)/Na1985Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 155, nr 1, s. 165-172Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    UPS Spectra of sodium monolayers evaporated onto Cu(111) are presented. We interpret sodium induced structure below the Cu d-band as due to photoemitted 3d electrons which have experienced an energy loss by exciting a sodium monolayer plasmon. An experimental difficulty is that even small amounts (<1/10 monolayers) of water contamination produces structure in the same energy range. This emission is due to the OH 1π orbital. Hydroxide groups may also origin from the alkali source if this is operated at too elevated temperatures.

  • 9. Lindgren, S.Å.
    et al.
    Paul, Jan
    Walldén, L.
    Surface state energy shifts by molecular adsorption: CO on clean and Na covered Cu(111)1982Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 117, nr 1-3, s. 426-433Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Angle resolved photoelectron energy spectra recorded in the near UV show that the surface state 0.4 eV below EF of Cu(111) shifts to higher energy upon CO adsorption. The surface band related emission intensity is reduced by the adsorption at a rate suggesting that each adsorbed molecule wipes out the surface state over an area corresponding to seven surface layer Cu atoms. The surface state energy shift is not as closely related to the adsorbate induced workfunction change as found theoretically and experimentally for alkali adsorbates. The influence on the shift of the workfunction and initial energy of the surface state is studied by preadsorbing Na on the Cu(111) surface.

  • 10. Paul, Jan
    UPS spectra of H2O, CH3OH and C5H9OH adsorbed onto Cu(111)/Na and Na(cp)1985Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 160, nr 2, s. 599-617Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present communication presents ultraviolet photoemission spectra (UPS) of three different "alcohols"; water (H2O), methanol (CH3OH), and cyclopentanol (C5H9OH), chemisorbed onto a Cu(111) surface partially covered by sodium atoms as well as onto closely packed sodium films, a free electron adsorbent. Whereas all three alcohols ROH bind reversibly and associatively to Cu(111) they react with adsorbed sodium atoms to metal bound alcoxides RO. The chemisorption bond, characterized by the interaction between O 2pπ orbitals and metal atoms as an electron donor, the alcoxide being the acceptor, is similar for all groups R. The O 2pπ orbitals shift to higher UPS binding energies with increasing electron density, i.e. decreasing rs/ao of the sodium overlayer. Only for HONa, the sterically smallest group R, does the alcoxide growth continue in three dimensions. Although, possibly failing to reproduce the electron density profile of a free electron surface, Hartree-Fock-Slater cluster calculations of small models ROH and RONa3 enable correlations to be made between UPS intensity peaks and one electron orbitals.

  • 11. Paul, Jan
    Vibrational spectra of CO and CO2 adsorbed on potassium modified Fe(100)1989Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 224, nr 1-3, s. 348-358Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High resolution electron energy loss (EEL) spectra for CO adsorbed on potassium modified Fe(100) are presented. Five CO vibrational bands are clearly distinguishable. Two bands at or above 2000 cm-1 correspond to the *1- and *2-states on the clean surface. Two more bands, residing between 1450 and 1850 cm-1, reveal adsorption at potassium modified sites. The response of these bands to changes in potassium coverage and annealing temperature is highly predictable and similar to the situation on Fe(111) [1]. This suggests a local K: CO coordination. A fifth band is observed around 950 cm-1 and interpreted as CO adsorbed at potassium modified *3-sites, redshifted from 1200 cm-1 at unmofidied sites. The present results are complementary to a previous study of the same adsorption system utilizing photoemission spectroscopy and thermal desorption spectroscopy [2]. Finally, we present novel vibrational and thermal desorption (TDS) data for Fe(100)/K exposed to CO2 and point at similarities between intermediate states following CO and CO2 adsorption on different potassium promoted iron surfaces.

  • 12. Paul, Jan
    et al.
    Cameron, S.D.
    Dwyer, D. J.
    Hoffmann, F.M.
    The interaction of CO and O2 with the (111) surface of Pt3Ti1986Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 177, nr 1, s. 121-138Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic properties of clean and partly oxidized Pt3Ti(111) surfaces have been studied utilizing carbon monoxide both as a probe and as a reducing agent. Vibrational frequencies and desorption profiles of chemisorbed CO as well as ion scattering and angular resolved X-ray photoelectron spectroscopy (XPS) suggest that the first atomic layer of annealed Pt3Ti(111) is quasi-pure platinum. Scarcely any (θ ≈ 0.01) dissociation of CO was observed. Minor shifts of vibrational frequencies and desorption temperatures compared to Pt(111) and a p(2 × 2) "reconstruction" of the clean surface reveal some influence of the bulk. Auger spectroscopy, XPS, and ion scattering all show an increased titanium signal as a result of oxidation. Surface bound atomic oxygen gives a vibrational band around 650 cm-1 which coincides with infrared absorption spectra of TiO2. Flashing with CO shifts the band to 500 cm-1. Correlated with this shift we observe (i) CO2 desorption at a temperature well above that observed for Pt(111)/O, (ii) an altered Ti XPS signal, and (iii) a reduced oxygen concentration. Subsequently adsorbed CO molecules vibrate at the same frequencies as on the bare surface, give the same c(4 × 2) LEED pattern, and desorb at the same temperatures but with reduced intensity, in all proving that the surface oxide only acts as a site-blocker with respect to the metal surface. Our current understanding of these observations is that oxygen creates "islands of TiO2", segregated to the surface but with no electronic influence on remaining areas of the platinum enriched metal surface. The hexacoordinated Ti4+ ions on the surface of these islands are reduced by CO to pentacoordinated Ti3+ species. The vibrational shift, 650 to 500 cm-1, can be understood by the dipole active bands of a triatomic O-Ti4+ -O vibrator compared to a diatomic Ti3+-O vibrator.

  • 13. Paul, Jan
    et al.
    Hoffmann, F.M.
    Hydrogen adsorption on alkali modified aluminum1988Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 194, nr 3, s. 419-437Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Coadsorption experiments of alkali metals and hydrogen on Al(100) are reported. The probability for H-H (D-D) dissociation and subsequent atomic adsorption is less than 1:104 at all alkali coverages. As a consequence, each overlayer had to be prepared by exposing the sodium or potassium modified surface to a beam of hydrogen (deuterium) atoms. We observed an attractive alkali-hydrogen interaction at all coverages. This interaction is best described as the formation of an alkali hydride in the presence of excess alkali atoms. The formation of the hydride shifts the recombination and desorption temperature of hydrogen adatoms on Al(100) from around 350 to around 500 K. While no isotope effect was detected on the clean aluminum surface (diffusion limited recombination), a significant 10-15 K shift was observed for both alkali hydrides (bond breaking). Furthermore, both alkali hydrides observed intense vibrational losses, thus revealing the ionic character of the metal-hydrogen bond. Electron energy loss spectra of an annealed monolayer of sodium hydride (deuteride) showed metal-hydrogen stretching bands at 1850 (1350) cm-1 and 1715 (1250) cm-1, a deformation band at 800 (600) cm-1, and a metal-metal band at 200 (200) cm-1. Corresponding peak positions for potassium hydride (deutride) were 1650 (1200) cm-1, 1500 (1100) cm-1, and 775 (585) cm-1. The metal-metal vibration could not be separated from the elastic peak because of the larger mass of potassium compared to sodium.

  • 14. Paul, Jan
    et al.
    Hoffmann, F.M.
    TDS and EELS observations for CO, O2, and CH3OH bound to Ru(0001)/Cu1986Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 172, nr 1, s. 151-173Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic properties of monolayers of copper atoms adsorbed onto a Ru(0001) single crystal surface have been studied with thermal desorption spectroscopy (TDS) and high resolution electron energy loss spectroscopy (EELS) utilizing carbon monoxide (CO), dioxygen (O2), methanol (CH3OH), and to some extent water (H2O) as chemical probes. Whereas a three-monolayer-thick film exhibits most properties of a Cu(111) crystal distinct deviations are found at lower Cu coverages. TDS as well as EELS show a weakened Ru---CO bond and a strengthened Cu---CO bond as a result of metal-metal interaction. The stronger Cu---CO bond is accompanied by a higher probability for O2 dissociation. The mobilities of copper and oxygen atoms are such that annealing to 650 K produces an overlayer structure which is independent of adsorption sequence: Cu/O2 or O2/Cu, but where Ru---O as well as Cu---O vibrations can be identified. Methanol adsorbs reversibly on a monolayer of copper atoms. Metal bound methoxy species are formed in the presence of oxygen atoms. The decomposition paths of such methoxy intermediates alter towards more formaldehyde (CH2O) relative to CO with increasing copper and methoxy coverages.

  • 15. Paul, Jan
    et al.
    Rosén, A.
    Catalytic active sites on sputtered metal surfaces1983Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 127, nr 1, s. L93-L97Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By the use of Hartree-Fock-Slater (HFS) cluster calculations, the symmetry of adatom induced electronic states and their possible role in catalytic processes have been investigated. For iron adsorbed on a close packed iron single crystal surface we find an increased density of occupied "π" as well as "σ" states at the Fermi level. Simple group theoretical arguments give that the "π" states, which represent the highest occupied molecular orbitais (HOMO) will mix with the lowest unoccupied molecular orbital (LUMO) of CO, 2π*, assuming CO bound normal to the surface in a terminal position with respect to the adatom. Such a system with an adsorbed atom on a flat surface is a model for a sputtered surface and these "π" states may thus explain the experimentally observed high rate of dissociation for CO on sputtered iron surfaces. A comparative study shows that no such increased density of states (DOS) is found when the Fe adatom is replaced by potassium. Finally for Cu adsorbed on Cu(111) only 4s derived "σ" states are introduced close to the Fermi level.

  • 16. Paul, Jan
    et al.
    Walldén, L.
    Rosén, A.
    The reactivity of adsorbed Na atoms probed by coadsorbed CH3OH1984Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 146, nr 1, s. 43-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The chemical properties of sodium atoms adsorbed on a Cu(111) surface have been probed by coadsorbed methanol. Methoxide, stoichiometrically close to CH3ONa2, is identified as a product by photoemission spectroscopy. Sodium atoms are found to react in the same manner at all submonolayer coverages, i.e. independent of atomic charge. Films of closely packed Na atoms - the first sp-metal substrate probed by methanol - are slightly less reactive. Hartree-Fock-Slater cluster calculations as well as observed energy shifts of a Cu electronic surface state indicate a transfer of charge from the copper substrate to the methoxide group. The desorption temperature for a monolayer of methanol molecules from a Cu(111) surface is enhanced by the presence of low sodium concentrations (1/20 of a monolayer). CH3OH is found to adsorb associatively on the uncovered Cu(111) surface.

  • 17.
    Paul, Jan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Williams, G. P.
    Jefferson Lab.
    Hoffmann, F. M.
    SCI-MED, New York.
    Carbon dioxide activation and alkali compound formation. I: Vibrational characterization of oxalate intermediates2003Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 531, nr 3, s. 244-264Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The activation of CO2 in thin potassium layers adsorbed on Cu(1 1 1) has been studied with time-evolved Fourier transform-infrared reflection absorption spectroscopy. The growth of thin layers by reactive evaporation of potassium in a CO2 atmosphere permits control of the K:CO2 stoichiometry, which strongly affects the selectivity in the formation of intermediates and the decomposition pathways of the layer. Layers grown in a CO2 rich atmosphere exhibit the preferential growth of stoichiometric potassium oxalate K2C2O4 (D2h). The molecular identity of oxalate with D2h symmetry is confirmed by vibrational spectra utilizing isotopic substitution methods (13CO2 and C18O2) and by the use of isotopic mixtures of CO2/C18O2 and CO2/13CO2. A comparison of the isotope data with theoretical calculations gives an estimated OCO bond angle in oxalate of 132°. Far-IR spectra obtained with synchrotron radiation indicate the equivalent interaction of all oxygen atoms with the potassium. A comparison of the vibrational data with theoretical ab initio calculations confirms the structural model of an oxalate species that is bulk coordinated with no strong directional bonding and all oxygen atoms equally interacting with potassium. At medium and low CO2:K ratios, very complex vibrational spectra are observed, indicating the formation of an oxalate surface species with C2v symmetry in addition to D2h- oxalate, CO2- and CO22- species.

  • 18.
    Pussi, Katariina
    et al.
    Laboratory of Electronics Materials Technology, Lappeenranta University of Technology, Institute of Physics, Tampere University of Technology.
    Lindroos, Matti
    Institute of Physics, Tampere University of Technology.
    Katainen, Jukka
    Laboratory of Physics, Helsinki University of Technology.
    Habermehl-Cwirzen, Karin
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology, Laboratory of Physics, Aalto University.
    Seitsonen, Ari Paavo
    Université Pierre et Marie Curie, Physikalisch Chemisches Institut, Universität Zürich.
    The (√7 × √7)R19.1°-C6H6 adsorption structure on Co{0001}: A combined tensor LEED and DFT study2004Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 572, nr 1, s. 1-10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The geometric structure of a Co{0001}-(√7 × √7)R19.1°-C6H6 surface formed by adsorption of benzene to the saturation coverage at 170 K has been determined by low energy electron diffraction (LEED). The favored model consists of a flat laying, nearly undisturbed benzene molecule, with the hydrogen-carbon bonds bent away from the substrate by 0.3 ± 0.2 Å. The carbon ring lies at a hcp-site with the two parallel C-C bonds aligned with [1̄100] direction. Buckling between the inequivalent carbon atoms in the molecular ring is within the experimental uncertainty (0.01 ± 0.11 Å). The experimental results are supported by density functional calculations

  • 19. Söderberg, Hans
    et al.
    Birch, Jens
    Thin Film Physics Division, IFM, Linköping University.
    Hultman, Lars
    Thin Film Physics Division, IFM, Linköping University.
    Odén, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    RHEED studies during growth of TiN/SiNx/TiN trilayers on MgO(001)2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 11, s. 2352-2356Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    TiN/SiNx/TiN(0 0 1) trilayers have been deposited on MgO(0 0 1) substrates using ultra-high vacuum based reactive magnetron sputtering and studied by in situ reflection high energy electron diffraction (RHEED). Depositions were carried out at 500 °C and 800 °C, with SiNx layer thicknesses between 3 and 300 Å. Here, we find that SiNx(0 0 1) layers grown at 800 °C exhibit 1 × 4 surface reconstructions along orthogonal (1 1 0) directions up to a critical thickness of ≈9 Å, where an amorphous phase forms. Growth of TiN overlayers on the reconstructed SiNx(0 0 1) layers yield RHEED patterns indicating the growth of (0 0 1)-oriented epitaxial layers with a 1 × 1 reconstruction. For the case of amorphous SiNx layers the TiN overlayers grow polycrystalline.

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