| 1. |
- Ackelid, U, et al.
(författare)
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Kinetics of ethylene oxidation on plane Pt/SiO2 catalysts in the viscous pressure regime: Evidence of support activity
- 1996
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Ingår i: Catalysis Letters. - 1011-372X. ; 39:1-2, s. 129-139
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Tidskriftsartikel (refereegranskat)abstract
- C2H4 oxidation on plane Pt/SiO2 model catalysts with various Pt loadings was studied at T = 373-473 K and in the pressure ranges 10-6-102 Torr C2H4 and 0.3-1500 Torr O2 (1 Torr = 133.3 Pa). Mass spectrometry combined with spatially resolved gas sampling enabled kinetic data to be collected far into the viscous pressure regime. Reaction orders and activation energies were similar to those of a macroscopic Pt surface. However, under fuel-lean conditions the global reaction rate decreases faster than the decrease in metal area. On the other hand, the global rate was independent of Pt loading and metal surface area in fuel-rich gas mixtures. This is interpreted in terms of a spillover effect.
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| 2. |
- Berg, LK, et al.
(författare)
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GP-zones in Al-Zn-Mg alloys and their role in artificial aging
- 2001
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Ingår i: Acta Materialia. - 1359-6454. ; 49:17, s. 3443-3451
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Tidskriftsartikel (refereegranskat)abstract
- The structure of GP-zones in an industrial, 7xxx-series Al–Zn–Mg alloy has been investigated by transmission electron microscopy methods: selected area diffraction, conventional and high-resolution imaging. Two types of GP-zones, GP(I) and (II) are characterized by their electron diffraction patterns. GP(I)-zones are formed over a wide temperature range, from room temperature to 140–150°C, independently of quenching temperature. The GP(I)-zones are coherent with the aluminum matrix, with internal ordering of Zn and Al/Mg on the matrix lattice, suggested to be based on AuCu(I)-type sub-unit, and anti-phase boundaries. GP(II) are formed after quenching from temperatures above 450°C, by aging at temperatures above 70°C. The GP(II)-zones are described as zinc-rich layers on {111}-planes, with internal order in the form of elongated domains. The structural relation to the η′-precipitate is discussed.
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| 3. |
- Birch, J., et al.
(författare)
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Structural characterization of precious-mean quasiperiodic Mo/V single-crystal superlattices grown by dual-target magnetron sputtering
- 1990
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Ingår i: Physical Review B. - 1098-0121. ; 41:15, s. 10398-10407
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Tidskriftsartikel (refereegranskat)abstract
- A class of quasiperiodic superlattice structures, which can be generated by the concurrent inflation rule A→AmB and B→A (where m=positive integer), has been studied both theoretically and experimentally. Given that the ratios between the thicknesses of the two superlattice building blocks, A and B, are chosen to be γ(m)=[m+(m2+4)1/2]/2 (known as the ‘‘precious means’’), then the x-ray- and electron-diffraction peak positions are analytically found to be located at the wave vectors q=2πΛ−1r[γ(m)]k, where r and k are integers and Λ is an average superlattice wavelength. The analytically obtained results have been compared to experimental results from single-crystalline Mo/V superlattice structures, generated with m=1, 2, and 3. The superlattices were grown by dual-target dc-magnetron sputtering on MgO(001) substrates kept at 700 °C. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) showed that the analytical model mentioned above predicts the peak positions of the experimental XRD and SAED spectra with a very high accuracy. Furthermore, numerical calculations of the diffraction intensities based on a kinematical model of diffraction showed good agreement with the experimental data for all three cases. In addition to a direct verification of the quasiperiodic modulation, both conventional and high-resolution cross-sectional transmission electron microscopy (XTEM) showed that the superlattices are of high crystalline quality with sharp interfaces. Based on lattice resolution images, the width of the interfaces was determined to be less than two (002) lattice-plane spacings (≊0.31 nm).
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| 4. |
- Carlsson, A, et al.
(författare)
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Strain state in semiconductor quantum dots on surfaces : a comparison of electron microscopy and finite element calculations
- 1998
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Ingår i: Surface Science. - 0039-6028. ; 406:1-3, s. 48-56
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Tidskriftsartikel (refereegranskat)abstract
- The strain distribution in InP quantum dots, coherently grown on a GaInP substrate, was determined by image analysis of high-resolution electron microscopy images. Image simulations were used to verify the obtained results. The measured strain values were compared with values obtained from finite element calculations, using the dot shape determined by electron microscopy. The measured and calculated strain values are in good agreement, supporting the use of finite element calculations for strain determination in quantum dots.
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| 5. |
- Carlsson, JRA, et al.
(författare)
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A new silicon phosphide, Si12P5 : Formation conditions, structure, and properties
- 1997
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Ingår i: Journal of Vacuum Science and Technology A. - : American Vacuum Society. - 0734-2101. ; 15:2, s. 394-401
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Tidskriftsartikel (refereegranskat)abstract
- The formation conditions, structure, and properties of the recently discovered phosphide, Si12P5 (initially assigned Si7P3), have been studied using x-ray diffraction, high-resolution transmission electron microscopy, photospectrometry, and a four-point probe. The phosphide formed in amorphous Si-P alloy thin films with 30, 35 and 44 at. % P after annealing at 1000°C for 30 min. During annealing at 1100°C, the phosphide dissociated through P evaporation. The Si12P5 phase is proposed to have rhombohedral symmetry with a P31m space group and a C5W12 structure. The hexagonal lattice parameters measured were a = 6.16±0.05 Å and c = 13.17±0.01 Å. The optical band gap and the electrical resistivity of the phosphide were determined to be 1.55 eV and 5 mΩ cm, respectively. The Gibbs free energy diagram for the Si-P system was modified to include this new Si12P5 phase.
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| 6. |
- 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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| 7. |
- Cheng, Y.F., et al.
(författare)
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TEM study of the early stages of the precipitation process in strip-cast Al3003 alloys
- 1992
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Ingår i: Journal of Materials Research. - 0884-2914. ; 7, s. 3235-3241
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Tidskriftsartikel (refereegranskat)abstract
- The precipitation behavior, especially the early nucleation stages, of the industrial strip-cast Al3003 alloys was investigated by using transmission electron microscopy (TEM). An icosahedral quasicrystalline phase was found as secondary particles in these strip-cast alloys after heat treatment for a few seconds. Three different nucleation paths are proposed based on the TEM observations. They have the same origin, viz. (Mn, Fe)-containing Mackay icosahedra, and are governed by the composition of alloys, especially the Mn and Si content.
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| 8. |
- Chirita, V, et al.
(författare)
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Strain relaxation and thermal stability of the 3C-SiC(001)/Si(001) interface : A molecular dynamics study
- 1997
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Ingår i: Thin Solid Films. - 0040-6090. ; 294:1-2, s. 47-49
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics (MD) and high-resolution electron microscopy (HREM) imaging are used to investigate the mechanism of strain relaxation of a model 3C-SiC(001)/Si(001) interface. It is found that the essential atomic mechanism governing this process is the formation of undulations in planes parallel and perpendicular to the interface. The net effect is the generation of misfit-accommodating dislocations, of the [removed] type, which allow for structure relaxation at 2, 700 and 1000 K. MD configurations are then used for HREM image simulations. Comparisons with actual HREM images of the interface support the model interface and relaxation mechanisms proposed herein.
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| 9. |
- Christiansson, M, et al.
(författare)
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Reduction of surface sulphur upon microbial devulcanization of rubber materials
- 1998
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Ingår i: Biotechnology Letters. - 0141-5492. ; 20:7, s. 637-642
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Tidskriftsartikel (refereegranskat)abstract
- Thiobacillus ferrooxidans, T. thioparus, Acidianus brierleyi and TH2 Lund, an archaeal isolate, were tested for sulphur oxidising capacity on ground rubber from spent car tyres. T. ferrooxidans converted 8% (w/w) of the sulphur in cryo-ground spent rubber to sulphate in 20 days. Desulphurization of fresh made natural rubber was studied with scanning electron microscope with energy-dispersive x-ray spectrometer and electron spectroscopy for chemical analysis. The average depletion of sulphur on the treated surface was 24% compared to the bulk region. Oxidised sulphur species were detected on the surface after microbial treatment.
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| 10. |
- Dobrocka, E, et al.
(författare)
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Simulation of electron diffraction patterns from III–V alloys with CuPt ordering : Effect of clusters and antiphase boundaries
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89, s. 2653-2664
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Tidskriftsartikel (refereegranskat)abstract
- A method for the simulation of electron diffraction patterns from partially ordered semiconductor compounds with CuPt-type ordering is proposed. The simulation procedure is based on the generation of two-dimensional model structures containing different types of imperfections. The defects are randomly dispersed in the structure and they are characterized by statistical parameters (density, average size, shape, etc.). Performing the intensity calculations for electron diffraction, the influence of the selected types of defects on the diffuse scattering in the transmission electron microscopy (TEM) diffraction patterns can be analyzed and the correlation between the statistical parameters describing the defects and the fine structure of the diffuse scattering can be established. By means of this method the influence of the plate-like clusters and of the antiphase boundaries (APBs) on the TEM diffraction pattern is analyzed. It is shown that the slope of the diffuse streaks around the ordering diffraction spots is determined by the mean orientation of the cluster boundaries irrespective of the type of clusters. The role of the fine structure of the inclined APBs in the formation of the diffraction patterns is established. (C) 2001 American Institute of Physics.
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