| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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