| 1. |
- Andersson, M P, et al.
(författare)
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Surface-induced C–O bond anharmonicity of methoxy adsorbed on Cu(100): Experiments and density-functional theory calculations
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:22, s. 1-224714
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Tidskriftsartikel (refereegranskat)abstract
- The anharmonic properties of a surface intermediate, methoxy, adsorbed on Cu(100) are investigated by surface infrared overtone spectroscopy and density-functional-theory electronic structure calculations. The anharmonicity is measured in the zero-coverage limit, and it is observed that the anharmonicity is increased upon adsorption as compared with the free methanol. By combining experiments with calculations we demonstrate that modifications of the anharmonicity of the methoxy species is indeed induced by adsorption onto the copper surface and not by the formation of the methoxy species.
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| 2. |
- Blomquist, Jakob, et al.
(författare)
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Inducing H/D Exchange in Ultrathin Ice Films by Proton Deficiency
- 2011
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Ingår i: Physical Review Letters. - 1079-7114. ; 107:21
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Tidskriftsartikel (refereegranskat)abstract
- We show that H/D exchange between H2O and D2O in ultrathin ice films adsorbed on Cu(100) does not occur through autoionization at temperatures below 140 K. The exchange is, however, facile if a proton deficiency is induced in the ice films by having small amounts of OH preadsorbed on the copper surface. The system was studied using surface infrared vibrational spectroscopy with the aid of density functional theory calculations.
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| 3. |
- Blomquist, Jakob
(författare)
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Infrared and Photoelectron Spectroscopic Studies of Adsorbates on Solid Surfaces: Experiments and DFT Calculations
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In general, the more complex and real a system is, with all its interactions with solvents and contaminations etc., the harder it is to accurately model it and reproduce the experimental results by calculations. Similarly, modern sophisticated, advanced and higher order calculations are done for very specialized systems, often removed from any experimental equivalent. This dissertation deals with the description of chemistry and physics of adsorbed molecules on solid surfaces from a theoretical as well as experimental point of view, using density-functional calculations together with vibrational and photoelectron spectroscopy of model systems. These model systems have made it possible to let the calculations and experiments effectively overlap, for example, to accurately describe the anharmonic behaviour of the vibrational transitions. The calculations have been performed using density-functional theory methods for adsorbate/surface systems represented by clusters. In the course of the dissertation an effort has been to increase the accuracy of the calculations. The result was that the surface vibrational spectra of two model systems, methoxy and carbon monoxide adsorbed on Cu(100), were accurately reproduced. The ethanol oxidation on Rh(111), forming adsorbed acetate, was studied by photoelectron spectroscopy, Fourier transform infrared spectroscopy and calculations. Adsorbed water have been studied by DFT calculations, surface vibrational spectroscopy as well as with photoelectron spectroscopy. In the former case the growth, self-diffusion and H/D exchange of very thin films (< 50 Å) of amorphous solid water vapor, deposited on Cu(100), were investigated by Fourier transform infrared spectroscopy and water-dimer DFT calculations. In the latter case the dissociative and non-dissociative adsorption of water on reconstructed TiO2(001)-(4x1) films, grown by chemical vapor deposition, was studied by photoelectron spectroscopy.
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| 4. |
- Blomquist, Jakob, et al.
(författare)
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Surface adsorbate vibrations explored by infrared spectroscopy and DFT cluster calculations at the anharmonic level: CO on Cu(100).
- 2010
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Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12, s. 14162-14168
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Tidskriftsartikel (refereegranskat)abstract
- The vibrational properties of the CO/Cu(100) surface adsorbate system have been explored by infrared spectroscopy and DFT cluster calculations. We show that all four fundamental, FT(x,y), FR(x,y), FT(z) and ν(C-O), vibrational modes are very well reproduced with respect to experiments by the present calculations and they are at the highest level reported to date. Our work demonstrates that it is essential to include both anharmonicity and cluster relaxation when modeling the CO/Cu(100) system. The absence and presence of binary modes: 2 ×ν(C-O) and FT(z) + ν(C-O) in our experimental data are discussed as well.
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| 5. |
- Blomquist, Jakob, et al.
(författare)
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Water Dissociation on Single Crystalline Anatase TiO2(001) Studied by Photoelectron Spectroscopy
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:42, s. 16616-16621
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of water on the anatase TiO2(001)-(4 x 1) surface is studied using synchrotron radiation-excited core level photoelectron spectroscopy. The coverage-dependent adsorption of water at low temperature is monitored and compared to the sequence obtained after heating of a water multilayer. Two adsorption phases of submonolayer coverage can be defined: Phase 1 consists only of dissociated water, observed as OH-groups. This phase is found at low coverage at low temperature (190 K) and is the only state of adsorbed water above similar to 230 K. The saturation coverage of phase 1 is consistent with dissociation on the 4-fold-coordinated Ti ridge atoms of the (4 x 1) surface reconstruction. Phase 2 is found at higher coverage, reached at lower temperature. It consists of a mixture of dissociated and molecular water with a ratio of 1:1 at 170 K. The molecular water is found to bond to the hydroxyl groups. The hydroxyl coverage of phase 2 is approximately 2 times that of phase 1. The results suggest that the OH and H2O species of phase 2 are confined to the ridges of the surface.
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| 6. |
- Karlsson, P G, et al.
(författare)
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Interfacial properties of the nanostructured dye-sensitized solid heterojunction TiO2/RuL2(NCS)(2)/CuI
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:23, s. 11224-11232
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Tidskriftsartikel (refereegranskat)abstract
- The interfaces of the nanostructured dye-sensitized solid heterojunction TiO2/Ru-dye/CuI have been studied using photoelectron spectroscopy of core and valence levels, x-ray absorption spectroscopy and atomic force microscopy. A nanostructured anatase TiO2 film sensitized with RuL2(NCS)(2) [cis-bis(4,4'-dicarboxy-2,2'-bipyridine)-bis(isothio-cyanato)-ruthenium(II)] was prepared in a controlled way using a novel combined in-situ and ex-situ (Ar atmosphere) method. Onto this film CuI was deposited in-situ. The formation of the dye-CuI interface and the changes brought upon the dye-TiO2 interface could be monitored in a stepwise fashion. A direct interaction between the dye NCS groups and the CuI is evident in the core level photoelectron spectra. Concerning the energy matching of the valence electronic levels, the photoelectron spectra indicate that the dye HOMO overlaps in energy with the Cu 3d-I 5p hydrid states. The CuI grow in the form of particles, which at the initial stages displace the dye molecules causing dye-TiO2 bond breaking. Consequently, the very efficient charge injection channel provided by the dye-TiO2 carboxylic bonding is directly affected for a substantial part of the dye molecules. This may be of importance for the functional properties of such a heterojunction. (C) 2004 American Institute of Physics.
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| 7. |
- Karlsson, P. G., et al.
(författare)
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Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(100) and Si(111) studied by electron spectroscopy
- 2007
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 601:4, s. 1008-1018
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Tidskriftsartikel (refereegranskat)abstract
- The growth of ultrathin ZrO2 films on Si(100)-(2 x 1) and Si(111)-(7 x 7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50 angstrom thick film leads in both cases to tetragonal ZrO2 (t-ZrO2), whereas significant differences are found for thinner films. On Si(111)-(7 x 7) the local structure of t-ZrO2 is not observed until a film thickness of 51 angstrom is reached. On Si(100)-(2 x 1) the local geometric structure of t-ZrO2 is formed already at a film thickness of 11 angstrom. The higher tendency for the formation of t-ZrO2 on Si(100) is discussed in terms of Zr-O valence electron matching to the number of dangling bonds per surface Si atom, The Zr-O hybridization within the ZrO2 unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C-O scission on Si(100), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(111) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range. (c) 2006 Elsevier B.V. All rights reserved.
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| 8. |
- Karlsson, P. G., et al.
(författare)
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TiO2 chemical vapor deposition on Si(111) in ultrahigh vacuum: Transition from interfacial phase to crystalline phase in the reaction limited regime
- 2011
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 605:13-14, s. 1147-1156
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between the metal organic precursor molecule titanium(IV) isopropoxide (TTIP) and three different surfaces has been studied: Si(111)-(7 x 7), SiOx/Si(111) and TiO2. These surfaces represent the different surface compositions encountered during TTIP mediated TiO2 chemical vapor deposition on Si(111). The surface chemistry of the titanium(IV) isopropoxide precursor and the film growth have been explored by core level photoelectron spectroscopy and x-ray absorption spectroscopy using synchrotron radiation. The resulting film morphology has been imaged with scanning tunneling microscopy. The growth rate depends on both surface temperature and surface composition. The behavior can be rationalized in terms of the surface stability of isopropoxy and isopropyl groups, confirming that growth at 573 K is a reaction limited process. (C) 2011 Elsevier B.V. All rights reserved.
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| 9. |
- Karlsson, P G, et al.
(författare)
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UHV-MOCVD growth of TiO2 on SiOx/Si(111): Interfacial properties reflected in the Si 2p photoemission spectra
- 2005
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 580:1-3, s. 207-217
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Tidskriftsartikel (refereegranskat)abstract
- Metal-organic chemical vapour deposition growth of titanium oxide on moderately pre-oxidised Si(1 1 1) using the titanium(IV) isopropoxide precursor has been studied for two different growth modes, reaction-limited growth at 300 degrees C and flux-limited growth at 500 degrees C. The interfacial properties have been characterized by monitoring synchrotron radiation excited Si 2p photoemission spectra. The cross-linking from oxidised Si to bulk Si after TTIP exposure has been found to be very similar to that of SiOx/Si(1 1 1). However, the results show that the additional oxidation of Si most probably causes a corrugation of the SiOx/Si interface. Those conclusions are valid for both growth modes. A model is introduced in which the amorphous interface region is described as (TiO2)(x)(SiO2)(y) where x and y changes linearly and continuously over the interface. The model quantifies how (TiO2)(x)(SiO2)(y) mixing changes the relative intensities of the signals from silicon oxide and silicon. The method can be generalised and used for the analyses of other metal-oxides on silicon. (c) 2005 Elsevier B.V. All rights reserved.
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| 10. |
- Karlsson, P. G., et al.
(författare)
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Ultrathin ZrO2 films on Si-rich SiC(0001)-(3x3): Growth and thermal stability
- 2007
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 601:11, s. 2390-2400
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Tidskriftsartikel (refereegranskat)abstract
- The growth and thermal stability of ultrathin ZrO2 films on the Si-rich Si(0001)-(3 x 3) surface have been explored using photoelectron spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The films were grown in situ by chemical vapor deposition using the zirconium tetra tert-butoxide (ZTB) precursor. The O 1s XAS results show that growth at 400 degrees C yields tetragonal ZrO2. An interface is formed between the ZrO2 film and the SiC substrate. The interface contains Si in several chemically different states. This gives evidence for an interface that is much more complex than that formed upon oxidation with O-2. Si in a 4+ oxidation state is detected in the near surface region. This shows that intermixing of SiO2 and ZrO2 occurs, possibly under the formation of silicate. The alignment of the ZrO2 and SiC band edges is discussed based on core level and valence PES spectra. Subsequent annealing of a deposited film was performed in order to study the thermal stability of the system. Annealing to 800 degrees C does not lead to decomposition of the tetragonal ZrO2 (t-ZrO2) but changes are observed within the interface region. After annealing to 1000 degrees C a laterally heterogeneous layer has formed. The decomposition of the film leads to regions with t-ZrO2 remnants, metallic Zr silicide and Si aggregates. (c) 2007 Elsevier B.V. All rights reserved.
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