| 1. |
- Guimond, S., et al.
(författare)
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Vanadium oxide surfaces and supported vanadium oxide nanoparticles
- 2006
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Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 38:1-3, s. 117-125
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Tidskriftsartikel (refereegranskat)abstract
- The information obtained from the characterization of vanadium oxide single crystal surfaces is related to the study of vanadia nanoparticles supported on silica and alumina thin films, model systems for the so-called “supported monolayer vanadia catalysts”. It is found that these particles have properties similar to V2O3 surfaces, where the topmost V ions are involved in vanadyl groups and have a 5+ oxidation state. A vibrational spectroscopy investigation combined with DFT calculations show that the accepted interpretation of vibrational spectra from vanadia catalysts must be revised.
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| 2. |
- Martynova, Y., et al.
(författare)
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CO Oxidation Over Monolayer Manganese Oxide Films on Pt(111)
- 2013
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Ingår i: Catalysis Letters. - : Springer. - 1011-372X .- 1572-879X. ; 143:11, s. 1108-1115
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Tidskriftsartikel (refereegranskat)abstract
- Ultrathin manganese oxide films grown on Pt(111) were examined in the low temperature CO oxidation reaction at near atmospheric pressures. Structural characterization was performed by X-ray photoelectron spectroscopy, Auger electron spectroscopy, high-resolution electron energy loss spectroscopy, and temperature programmed desorption. The results show that the reactivity of MnOx ultrathin films is governed by a weakly bonded oxygen species, which may even be formed at low oxygen pressures (similar to 10(-6) mbar). For stable catalytic performance at realistic conditions the films required highly oxidizing conditions (CO:O-2 < 1:10), otherwise the films dewetted, ultimately resulting in the catalyst deactivation. Comparison with other thin films on Pt(111) shows, that the desorption temperature of weakly bonded oxygen species can be used as a benchmark for its activity in this reaction.
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| 3. |
- Kaya, S., et al.
(författare)
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Formation of an ordered ice layer on a thin silica film
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:2, s. 759-764
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of water on a thin silica film grown on a Mo(112) single crystal was studied by temperature-programmed desorption, infrared reflection absorption spectroscopy, and photoelectron spectroscopy using synchrotron radiation. Water does not dissociate on the defect-free oxygen-terminated silica surface. In contrast to adsorption at 100 K, where water follows a zero-order desorption kinetics, water adsorbed at 140 K exhibits a pseudo-first-order kinetics and induces a strong blue shift of the silica phonon. Even larger spectral changes were observed for D2O adsorption. The results were rationalized in terms of the formation of an amorphous solid water film at 100 K and a crystalline ice monolayer film at 140-150 K. This film is well-ordered as revealed by low-energy electron diffraction showing a c(2 x 2) superstructure with respect to the silica substrate.
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| 4. |
- Kaya, S., et al.
(författare)
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Formation of one-dimensional molybdenum oxide on Mo(112)
- 2008
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 602:21, s. 3338-3342
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structure of a reconstructed Mo(112)-O(2 x 3) surface has been revisited using photoelectron spectroscopy with synchrotron radiation, scanning tunneling microscopy, infrared reflection absorption spectroscopy and density functional theory. In contrast to previous models, the results are rationalized in terms of the formation of one-dimensional, Mo=O terminated molybdenum oxide involving corner sharing distorted [MoO(6)] octahedra on the (1 x 3) reconstructed Mo(112) surface.
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| 5. |
- Kaya, S., et al.
(författare)
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Ice-assisted preparation of silica-supported vanadium oxide particles
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:14, s. 5337-5344
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Tidskriftsartikel (refereegranskat)abstract
- Vanadium oxide particles were prepared by physical vapor deposition of vanadium in oxygen ambient onto ice-precovered well-ordered silica thin films. Morphology, electronic structure, and vibrational properties of the vanadia deposits were studied by scanning tunneling microscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, and infrared reflection absorption spectroscopy. The results show that the ice behaves as an oxidative agent, that favors vanadium oxidation up to V4+, and as a buffer layer that precludes strong interaction of the V adatoms with the silica film. At room temperature, upon desorption of the unreacted water, nanosized particles of vanadia hydroxide-like gel, containing V-OH and, to a lesser extent, vanadyl (VO) species, are formed. Vacuum annealing at 550 K leads to the total dehydration and partial reduction of the particles to V2O3, which expose the V-terminated surface. Subsequent reoxidation in 10(-6) mbar of O-2 irreversibly transforms the surface to the VO terminated, that is, the same as for the reactive deposition onto the clean silica surface. The results suggest that the structure of silica-supported vanadia catalysts is determined by a calcination step and should be considered under low oxygen pressure conditions as vanadium sesquioxide nanoparticles with the VO terminated surface.
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| 6. |
- Kaya, S., et al.
(författare)
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On the geometrical and electronic structure of an ultra-thin crystalline silica film grown on Mo(112)
- 2007
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 601:21, s. 4849-4861
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structure of a well-ordered silica film grown on a Mo(112) single crystal substrate is discussed in detail using the experimental and theoretical results available to date. New photoelectron spectroscopy results using synchrotron radiation and ultraviolet spectroscopy data are presented. The analysis unambiguously shows that the ultra-thin silica film consists of a two-dimensional network of corner-sharing [SiO4] tetrahedra chemisorbed on the unreconstructed Mo(112) surface. The review also highlights the important role of theoretical calculations in the determination of the atomic structure of the silica films and in interpretation of experimental data.
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| 7. |
- Lu, J. -L, et al.
(författare)
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Formation of one-dimensional crystalline silica on a metal substrate
- 2006
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 600:13, s. L164-L168
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Tidskriftsartikel (refereegranskat)abstract
- We have observed formation of one-dimensional silica structures of 0.5 nm in width on Mo(112) single crystal surface. Combination of high-resolution scanning tunneling microscopy, photoelectron and infrared spectroscopy, and density functional theory provides strong evidence for formation of paired rows of corner sharing [SiO4] tetrahedra chemisorbed on a metal substrate.
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| 8. |
- Lu, J. -L, et al.
(författare)
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Low temperature CO induced growth of Pd supported on a monolayer silica film
- 2006
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 600:12, s. L153-L157
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Tidskriftsartikel (refereegranskat)abstract
- Nucleation, growth and sintering of Pd deposited on an ultra-thin silica film were studied by scanning tunneling microscopy and infrared reflection absorption spectroscopy. No preferential nucleation of Pd on the silica surface was observed both at 90 and 300 K deposition. When adsorbed on Pd clusters formed at 90 K, CO causes a strong sintering effect even at this temperature. The results are rationalized on the basis of a high mobility of Pd carbonyl-like species on the silica film. At a given Pd coverage, the extent of CO induced sintering cannot be achieved by annealing in vacuum. In addition, vacuum sintering, which commences above 700 K, goes simultaneously with interdiffusion of Pd and support.
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| 9. |
- Lu, J. -L., et al.
(författare)
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Structure, thermal stability, and CO adsorption properties of Pd nanoparticles supported on an ultra-thin SiO2 film
- 2007
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Ingår i: Surface review and letters. - 0218-625X. ; 14:5, s. 927-934
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Tidskriftsartikel (refereegranskat)abstract
- Nucleation, growth, and thermal stability of Pd particles vapor-deposited on an ultra-thin crystalline silica film grown on Mo(112) have been studied by scanning tunneling microscopy, X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and temperature-programmed desorption of CO. No preferential nucleation of Pd on the silica film is found at room temperature deposition: the hemispherical Pd nanoparticles are homogenously dispersed on the support at all coverages studied (0.01-1ML(mono layer)). The Pd particles are resistant toward sintering up to 700K as judged by STM; however, CO adsorption studies have revealed surface chemical modification at temperatures as low as 550K. Strong morphological changes are observed above 800K (ultimately resulting in elongated rectangular islands at similar to 1000 K), which is accompanied by strong alterations of CO adsorption properties. The results are rationalized in terms of Pd and Mo substrate interdiffusion at elevated temperatures, while the silica film basically preserves its structure.
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| 10. |
- Sierka, M., et al.
(författare)
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Interplay between theory and experiment in the quest for silica with reduced dimensionality grown on a Mo(112) surface
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 424:1-3, s. 115-119
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Tidskriftsartikel (refereegranskat)abstract
- The stability of ordered one- and two-dimensional silica structures formed on a Mo(112) surface as a function of silicon coverage and oxygen pressure (phase diagram) is derived from density functional theory. At elevated oxygen pressures formation of a new, previously not considered structure of two-dimensional silica film is predicted. It contains additional oxygen atoms adsorbed directly on the Mo(112) surface underneath a two-dimensional network of corner sharing [SiO4] tetrahedra. The existence of the new phase is confirmed experimentally using infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy.
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| 11. |
- Stacchiola, D. J., et al.
(författare)
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Growth of stoichiometric subnanometer silica films
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a method to grow stoichiometric SiO(2) films of only similar to 0.6-0.9 nm in thickness on a metal substrate. Based on photoelectron and infrared spectroscopy studies, we conclude that the similar to 0.6-nm-thick silica films exhibit characteristics only observed for > 2.0-nm-thick films grown on conventional Si substrates. The films can be used as model oxides for fundamental studies and may have implications on the further miniaturization of metal-oxide-semiconductor transistors.
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| 12. |
- Todorova, T. K., et al.
(författare)
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Atomic structure of a thin silica film on a Mo(112) substrate : A combined experimental and theoretical study (vol 73, pg 165414, 2006)
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:16
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structure of the thin SiO2 film on a Mo(112) substrate has been determined based on a combination of density functional theory calculations and high-quality experimental data obtained from scanning tunneling microscopy, infrared reflection absorption spectroscopy, and x-ray photoelectron spectroscopy. The film consists of a honeycomblike, two-dimensional network of corner-sharing [SiO4] tetrahedra. One oxygen atom of each tetrahedron binds to the Mo(112) substrate and is located in a bridge position between Mo atoms located in rows protruding from the metal surface. The other three oxygen atoms form Si-O-Si bonds with the neighboring tetrahedra.
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| 13. |
- Todorova, T K, et al.
(författare)
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Atomic structure of a thin silica film on a Mo(112) substrate : A combined experimental and theoretical study
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:16, s. 165414-
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structure of the thin SiO2 film on a Mo(112) substrate has been determined based on a combination of density functional theory calculations and high-quality experimental data obtained from scanning tunneling microscopy, infrared reflection absorption spectroscopy, and x-ray photoelectron spectroscopy. The film consists of a honeycomblike, two-dimensional network of corner-sharing [SiO4] tetrahedra. One oxygen atom of each tetrahedron binds to the Mo(112) substrate and is located in a bridge position between Mo atoms located in rows protruding from the metal surface. The other three oxygen atoms form Si-O-Si bonds with the neighboring tetrahedra.
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| 14. |
- Weissenrieder, Jonas, et al.
(författare)
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Atomic structure of a thin silica film on a Mo(112) substrate : A two-dimensional network of SiO4 tetrahedra
- 2005
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 95:7, s. 1-4
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Tidskriftsartikel (refereegranskat)abstract
- The structure of a thin single crystalline SiO2 film grown on Mo(112) has been studied by scanning tunneling microscopy, infrared reflection absorption spectroscopy, and x-ray photoelectron spectroscopy. In excellent agreement with the experimental results, density functional theory calculations show that the film consists of a two-dimensional network of corner sharing [SiO4] tetrahedra, with one oxygen of each tetrahedron binding to the protruding Mo atoms of the Mo(112) surface.
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| 15. |
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| 16. |
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