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| 4. |
- Karlsson, L. S., et al.
(författare)
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Structural Characterisation of GaP <111 > B Nanowires by HRTEM
- 2008
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Ingår i: Microscopy of Semiconducting Material 2007. - 0930-8989. - 9781402086144 ; 120, s. 229-232
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Konferensbidrag (refereegranskat)abstract
- GaP < 111 > B nanowires are dominated by (111) twins orthogonal to the growth direction and show well-developed {111} side-facets. Based on this, a 3D-model has been constructed with a cross-section of an octahedron used as a building block. The twins can be of ortho- or para type i.e. by 60 degrees about the growth axis or 180 degrees in the twin plane. The segment thickness variation follows an exponential distribution with a clear dependence oil growth ternperature. Multislice simulations show different features of the twin types that are useful for further characterisation.
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- Mårtensson, T, et al.
(författare)
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III-V nanowires on Si and nanowire arrays
- 2005
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Ingår i: Book of abstracts: 342nd WE-Heraeus-Seminar Sci and Technol of Inorganic Nanowires, Bad Honnef, Germany (2005).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Sanati, Mehri, et al.
(författare)
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Zirconia-Supported Vanadium Oxide Catalysts for Ammoxidation and Oxidation of Toluene: A Characterization and Activity Study
- 1993
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Ingår i: Applied Catalysis A: General. - 0926-860X. ; 106:1, s. 51-72
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Tidskriftsartikel (refereegranskat)abstract
- A series of samples of vanadia supported on monoclinic zirconia were prepared with nominal loadings from a half up to sixteen theoretical vanadia layers. The samples were characterized with X-ray diffraction, scanning electron microscopy combined with energy dispersive X-ray analysis, high-resolution electron microscopy, Raman and diffuse reflectance infrared spectroscopy, and were used in the oxidation and the ammoxidation of toluene. At loadings in the monolayer range, Raman and infrared bands from decavanadate-like and dehydrated tetrahedral vanadia species were at ca. 990 and ca. 1025 cm−1, respectively. Raman bands at 821 and 880 cm−1 were present only at the lowest loading and are characteristic of orthovanadate and pyrovanadate species, respectively. X-ray diffraction, Raman and infrared spectroscopic results revealed formation of some crystalline V2O5 and ZrV2O7 at loadings exceeding a theoretical monolayer. In this case, consideration of Raman intensity variations allowed the conclusion that additional non-crystalline vanadia must be present. According to high-resolution electron micrographs, this vanadia consists of an amorphous overlayer, 4–8 atomic layers thick. In toluene oxidation zirconia-supported vanadia compared with crystalline V2O5 was found less selective for benzaldehyde formation. In toluene ammoxidation, on the other hand, vanadia on zirconia was found to possess good activity and selectivity for benzonitrile formation. Amorphous vanadia was the most active structure on zirconia, while the selectivities for nitrile and aldehyde formations were almost independent of the loading for one theoretical layer and above.
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- Tchaplyguine, M., et al.
(författare)
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Tin-oxide nanoparticles deposited from a beam : what happens to the composition?
- 2019
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Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 21:11, s. 6287-6295
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Tidskriftsartikel (refereegranskat)abstract
- The debate around the oxidation states occurring in laboratory-prepared tin-oxide samples has been for a long time an obstacle for an unambiguous assignment of characterization studies performed on such samples. In particular the changes in the Sn core-level energies caused by oxidation - i.e. the chemical shifts - as measured by photoelectron spectroscopy (PES) have been under discussion. The assignment problem is especially pronounced for nanoscale structures, which are important for photovoltaics, electronics, catalysis, and gas sensing. The reasons for the difficulties lie both in the natural properties of tin oxides, which can have substantial deficiencies of oxygen and tin in the lattice, and in the shortcomings of the fabrication and PES-characterization procedures themselves. Our recent PES study on tin-oxide nanoparticles fabricated by vapour-aggregation gave a chemical shift two times larger than earlier reported for Sn(iv) oxide for the Sn 4d level. The implemented fabrication technique forms an in-vacuum beam of particles whose composition can be both controlled and characterized by PES. In the present work SnO and SnO2 nanoparticles fabricated this way were deposited from the beam and probed by PES directly, as well as after exposure to air. The deposited nanoparticle films were also imaged by TEM (Transmission Electron Microscopy). The effects of the deposition process and exposure to air on the chemical composition were studied. The PES study of deposited SnO2 nanoparticles in the Sn 4d and Sn 3d core-level regions revealed the same core level shift as for unsupported nanoparticles, indicating that the chemical composition is preserved in the deposition process. The TEM study demonstrated a crystalline structure of separate SnO2 particles with lattice constants close to the macroscopic Sn(iv)-oxide. The PES study on the particles exposed to air showed changes in the composition. For the film of initially SnO particles a higher intermediate oxide was created. For the SnO2 nanoparticle film a lower, but strong, intermediate oxide was observed, likely at the surface.
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