| 1. |
- Chen, W, et al.
(författare)
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Pressure dependence of Mn2+ fluorescence in ZnS:Mn2+ nanoparticles
- 2000
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Ingår i: Journal of Luminescence. - 0022-2313. ; 91:3-4, s. 139-145
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Tidskriftsartikel (refereegranskat)abstract
- The photoluminescence of Mn2+ in ZnS : Mn2+ nanoparticles with an average size of 4.5 nm has been measured under hydrostatic pressure from 0 to 6 GPa. The emission position is red-shifted at a rate of −33.3±0.6 meV/GPa, which is in good agreement with the calculated value of −30.4 meV/GPa using the crystal field theory.
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| 2. |
- Andersson, Arne, et al.
(författare)
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Ammoxidation of 3-Picoline: An Activity and High-Resolution Electron Microscopic Investigation of Vanadium Oxide Catalysts
- 1986
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Ingår i: Journal of Catalysis. - 1090-2694. ; 98:1, s. 204-220
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Tidskriftsartikel (refereegranskat)abstract
- A V2O5 catalyst was used in the ammoxidation of 3-picoline to nicotinonitrile. It was observed that the selectivity for the formation of CO2 as a function of temperature passed through a minimum. This is explained to be due to the existence of weakly bonded electrophilic oxygen species at low temperatures, and an increasing degradation involving O2− at high temperatures. A comparison of two different V2O5 preparations shows the beneficial effect of the V2O5(010) plane on the formation of nicotinonitrile. The exposure of planes other than the (010) plane as the source of formation of CO2 is discussed by consideration of bond strength values. The activity, selectivity, and composition of the charged V2O5 catalyst were followed as a function of time-on-stream at various temperatures. It was found that the V2O5 phase was reduced in the course of the reaction. V4O9, VO2(B), VO2 (tetragonal), and even more reduced phases were formed depending upon the reaction temperature used. Of the pure oxides, V4O9 was found to be both less active and less selective than V2O5. VO2(B), however, is more active but less selective compared to V2O5. The phases formed were characterized by various methods including high-resolution transmission electron microscopy (HRTEM). This technique made it possible to image the View the MathML source phase boundary for the first time. The general direction of this boundary is parallel to the (301) plane of V2O5. Micrographs of VO2(B) show that the nature of defects formed depends on the reaction temperature. After use at 695 K two types of planar twin lamellae were formed. At a slightly higher temperature partly amorphous defects appeared. The influence on the catalytic reaction of the phase boundaries and defects formed is discussed.
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| 3. |
- Bovin, JO, et al.
(författare)
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Imaging of atomic clouds outside the surfaces of gold crystals by electron microscopy
- 1985
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 317, s. 47-49
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Tidskriftsartikel (refereegranskat)abstract
- The structure of small metal crystals has been intensively examined by high-resolution electron microscopy (HREM). In particular, multiply-twinned gold and silver crystals have been characterized using the profile-imaging method1,2 at atomic resolution, and reconstructed metal surfaces observed2. Crystal structure images of large gold clusters consisting of 55 gold atoms arranged in a cubeoctahedron have been recorded3 using 2.5 Å resolution, and crystal growth, row by row, on a {111} surface has been documented4 using a low-light-level silicon-intensified target television (TV) camera and video system with an on-line image processor. Direct imaging of rearrangements of atomic columns on extended gold surface5 established that profile imaging can provide information about surface self-diffusion. The motion of surface atoms, recorded with a real-time video tape-recorder (VTR) system, and the formation of surface atom steps on {100} surfaces, although not {111}, has also been reported recently6. Dynamic HREM observations at TV rate showing defect motion in gold7 and CdTe (refs. 8, 9) has given information on ‘in-lattice’ rearrangements of columns of atoms. We report here surface profile images recorded with the electron beam along the 〈110〉 direction with spatial resolution of ∼2.0 Å which reveal changes in occupancy of the atom columns often within periods of less than 0.1 s. Surfaces with several adjacent atom columns involved in rapid structural changes frequently interacted with a cloud of atoms extending out to 9 Å off the crystal and changes in shape and density of the clouds were recorded. Although these clouds have already been described6,10, the present work is the first to analyse these events properly and to describe them in detail. The motion of atomic columns and the existence of atom clouds revealed here may have important consequences for crystal growth, surface science and catalysis studies.
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| 4. |
- Cesar, F, et al.
(författare)
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Synthesis and characterization of carbon filaments grown from Pd3P colloids
- 2000
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Ingår i: Journal of Materials Research. - 0884-2914. ; 15:9, s. 1857-1859
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous carbon filaments were synthesized by catalytic pyrolysis of propene over Pd3P colloids. The channel close to the center of the filaments usually contained particles, which were analyzed by analytical electron microscopy to be palladium. The palladium particles could be found anywhere along the filament. The carbon filaments were of two types and of different diameters, about 8-15 nm and about 40-80 nm. The thinner type of filament shows a channel diameter of about 5 nm. The type of filament produced depends on the reaction conditions. Increased reaction time results in a large number of filaments, whereas an increased propene gas flow results in more of the thicker type of filaments.
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| 5. |
- Hansen, Staffan, et al.
(författare)
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Oxidation Catalysis on YBa2Cu3O6 + x
- 1988
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 334:6178, s. 143-145
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Tidskriftsartikel (refereegranskat)abstract
- Mild oxidation catalysts are used to product a wide range industrial chemicals from hydrocarbons, whereas deep oxidation catalysts yield CO2 and are becoming important in the cleaning of emissions from combustion of carbonaceous fuels. Here we report on a catalyst1 that facilitates both mild and deep oxidation of toluene in the presence of molecular oxygen and ammonia. At low partial pressures of O2a YBa2Cu3O6+x catalyst is very active in the formation of benzonitrile, but at higher O2 partial pressures it preferentially catalyses formation of CO2. This sharp transition in product selectivity is reversible and occurs at a defined partial pressure of O2. At transition the bulk compostition of the catalyst is close to YBa2Cu3O6 (x≈0). Increasing the content of lattice oxygen (x > 0) makes the catalyst selective for CO2 formation
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| 6. |
- Oku, T, et al.
(författare)
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Modulated structure of Ag2SnO3 studied by high-resolution electron microscopy
- 2000
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Ingår i: Acta Crystallographica. Section B: Structural Science. - 0108-7681. ; 56:3, s. 363-368
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Tidskriftsartikel (refereegranskat)abstract
- The modulated structure of Ag2SnO3, disilver tin trioxide, was investigated by high-resolution electron microscopy and electron diffraction along four different directions. Electron diffraction showed an incommensurate one-dimensional modulated structure with a modulation wavevector of 1/6.4a*. High-resolution images showed a large number of superstructure domains with the size range 10-100 nm and orientations related by hexagonal rotation. The modulation was determined to be displacements along the c axis of the Ag atoms both in octahedral and linear coordination. An approximate structure model with a commensurate sixfold superstructure, with an orthorhombic cell (P2(1)2(1)2(1), a = 2.922, b = 1.267, c = 0.562 nm), is proposed. Calculated images and electron diffraction patterns, based on this model, agree well with experimental observations.
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| 7. |
- Petfordlong, Amanda K., et al.
(författare)
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On the growth of small crystals of Cd, Zn, Pt and Rh during electron microscope observations
- 1987
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 80:2, s. 218-224
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Tidskriftsartikel (refereegranskat)abstract
- The growth of small supported metal crystals under the influence of an electron beam has been studied in real-time using a 400 keV ultra-high-resolution electron microscope. Samples of Pt, Rh, Cd and Zn supported on amorphous C or Si films were prepared ex situ and crystal growth in situ was recorded directly using a TV imaging/video system attached to the microscope. The different types of observed crystal growth are reported: the fcc metals (Pt and Rh) grow by coalescence, or by the addition of atoms along the particle surface followed by structural rearrangements which result in approximately spherical particles. The hcp metals (Cd and Zn) grow in the form of long rafts along the surface of the substrate film.
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| 8. |
- Skårman, Björn, et al.
(författare)
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Carbon monoxide oxidation on copper oxide thin films supported on corrugated cerium dioxide {111} and {001} surfaces
- 1999
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 1090-2694 .- 0021-9517. ; 181:1, s. 6-15
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of CeO2 with and without a thin layer of copper oxide were prepared by rf magnetron sputtering on surfaces of alpha-Al2O3 (sapphire) substrates. Careful characterisation of the surfaces was performed down to the atomic level using high-resolution electron-microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Surprisingly, the as-deposited, corrugated ceria surfaces, nominally (001), consist exclusively of {111}-type lattice planes, but, upon annealing at 800 degrees C, a well-defined portion of (001) surfaces are formed. Oxidation of carbon monoxide to carbon dioxide was studied, having the prepared films in a stirred batch reactor. A batch reactor was chosen so that the conversion over the small sample surface area (ca 10(-4) m(2)) could be monitored as a function of the reaction time. The activity of copper oxide on annealed ceria surfaces is markedly higher than on nonannealed surfaces, indicating a favourable synergetic effect between the ceria (001) surface and the copper oxide phase. (C) 1999 Academic Press.
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| 9. |
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| 10. |
- Wallenberg, LR, et al.
(författare)
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Atomic-resolution study of structural rearrangements in small platinum crystals
- 1986
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991. ; 20:1-2, s. 71-75
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Tidskriftsartikel (refereegranskat)abstract
- Structural rearrangements in small Pt crystals, which were initiated by the incident electron beam, have been studied in real time with a 400 kV high-resolution electron microscope equipped with TV image viewing and videorecording facilities. The phenomena of crystal growth, particle coalescence and atomic clouds above particular surfaces were recorded at the atomic level and have been analysed using frame-by-frame playback facilities.
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