| 1. |
- Ackelid, U, et al.
(författare)
-
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
-
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
-
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
-
Ingår i: Surface Science. - 0039-6028. ; 406:1-3, s. 48-56
-
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
-
Ingår i: Journal of Vacuum Science and Technology A. - : American Vacuum Society. - 0734-2101. ; 15:2, s. 394-401
-
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)
-
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
-
Ingår i: Journal of Materials Research. - 0884-2914. ; 7, s. 3235-3241
-
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)
-
Strain relaxation and thermal stability of the 3C-SiC(001)/Si(001) interface : A molecular dynamics study
- 1997
-
Ingår i: Thin Solid Films. - 0040-6090. ; 294:1-2, s. 47-49
-
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)
-
Simulation of electron diffraction patterns from III–V alloys with CuPt ordering : Effect of clusters and antiphase boundaries
- 2001
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89, s. 2653-2664
-
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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| 11. |
- Ferrow, Embaie A., et al.
(författare)
-
Crystal chemistry and defect structure of ekmanite : New data from transmission electron microscopy and Mossbauer spectroscopy
- 1999
-
Ingår i: European Journal of Mineralogy. - 0935-1221. ; 11:2, s. 299-308
-
Tidskriftsartikel (refereegranskat)abstract
- Ekmanite is a member of the 2:1 type modulated layer silicates such as ganophyllite and bannisterite. Its chemical composition can be represented by K(M20)[Si32O76](OH)16 (M = Fe2+, Mg2+, Mn2+) where three of eight Si-tetrahedra are inverted across the interlayer sharing an apical oxygen with similarly inverted tetrahedra from the adjacent layers. The arrangement of the regular, D, and inverted, R, tetrahedra has the configuration 4D2R1D1R4D... along the b-axis. In local regions of possibly high Mg/(Mn+Fe) ratio, this configuration is interrupted by the absence of inverted tetrahedra. Ekmanite typically contains a multitude of defects; twinning and both regular and irregular stacking arrangements are the most common ones. Ekmanite is sensitive to oxidation and an unidentified phase, chemically related to it, is always found lining its grain boundaries. This texture results in intergrown rods defining polygons where the central parts do not contain ekmanite. The Mossbauer spectrum consists of Fe2+ and Fe3+ absorption doublets with the Fe2+ absorption composed of two Gaussian line pairs and the Fe3+ absorption of a single but broad line pair.
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| 12. |
- Ferrow, EA, et al.
(författare)
-
Compositional control of plane group symmetry in tourmalines : an experimental and computer simulated TEM, crystallographic image processing and Mossbauer spectroscopy study
- 1993
-
Ingår i: European Journal of Mineralogy. - 0935-1221. ; 5:3, s. 479-492
-
Tidskriftsartikel (refereegranskat)abstract
- Tourmalines with different compositions show different plane group symmetries in experimental high resolution transmission electron microscopy (HRTEM) when projected along the c-axis. Fe-poor elbaite shows p31m symmetry, while Fe-bearing elbaite shows p3m1 symmetry. Rubellite shows p6 symmetry, while Fe-Mg-Al-bearing tourmaline shows a `pseudo' p6 type of symmetry. Symmetries p3m1 and p6 are not compatible with the space group R3m assigned to tourmaline from X-ray structural determination studies. The perturbations of symmetry from p31m to p6 and `pseudo' p6 depend on the magnitude of the scattering amplitude of the atoms occupying the 3a and 9b sites. Furthermore, computer simulations of elbaite, schorl and dravite show different projected potentials for images down the c-axis. Regions with high mean concentration of light or heavy elements a few unit cells apart are common in Fe-poor elbaite. This results in a marked difference of the distribution contrast in the HRTEM image of elbaite. The Mossbauer effect (ME) spectra of tourmaline are different with different Mossbauer parameters, reflecting the difference in composition. Experimental HRTEM, computer simulation and ME indicate that composition controls symmetry, ME parameters and atomic coordinates in tourmaline, an observation not recorded in other minerals.
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| 13. |
- Georgsson, K, et al.
(författare)
-
TRANSMISSION ELECTRON-MICROSCOPY INVESTIGATION OF THE MORPHOLOGY OF INP STRANSKI-KRASTANOW ISLANDS GROWN BY METALORGANIC CHEMICAL-VAPOR-DEPOSITION
- 1995
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 67:20, s. 2981-2982
-
Tidskriftsartikel (refereegranskat)abstract
- We have used transmission electron microscopy to determine the morphology of InP Stranski–Krastanow islands in GaInP, grown by metalorganic chemical vapor deposition at 580 °C. We investigated both capped and uncapped islands. It was found that the fully developed islands have the principal shape of truncated pyramids with a hexagonal base both before and after overgrowth. The planes defining the islands are of {001}, {110}, and {111} types. The base dimensions are 40–50 nm and 55–65 nm in the [1̄10] and [110] directions, respectively, and the height is 12–18 nm.
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| 14. |
- Georsson, K, et al.
(författare)
-
Transmission electron microscopy of InP Stranski‐Krastanow islands buried in GaInP
- 1995
-
Ingår i: Physica Status Solidi (A) Applied Research. - : Wiley. - 0031-8965. ; 150:1, s. 479-487
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- InP islands in a matrix of GaInP are investigated by transmission electron microscopy (TEM). The islands are uniform in size and shape, and are formed though self‐organized Stranski‐Krastanow growth. The introduction of a 4 ML intermediate GaP layer eliminates the bimodal distribution found in films where the InP was grown directly on the GaInP layer. The achieved island density is around 2 × 109 cm−2, and the basal plane of the InP islands is around 40 × 50 nm2. A model is suggested for the shape where the islands are in a truncated pyramidal form, showing {111}, {110}, and (001) facets, with an island height of 10 to 15 nm. A fast and simple specimen preparation method is suggested, based on laser assisted chemical etching.
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| 15. |
- Henning, P, et al.
(författare)
-
Compositional information from amorphous Si-Ge multilayers using high-resolution electron microscopy imaging and direct digital recording
- 1996
-
Ingår i: Ultramicroscopy. - 0304-3991. ; 66:3-4, s. 221-235
-
Tidskriftsartikel (refereegranskat)abstract
- A simple method for extracting compositional information from high-resolution electron microscopy images of an amorphous two-element system using a slow-scan CCD camera has been developed. The method has been evaluated on amorphous Si/Ge multilayers. The characterisation of the multilayers provided information about thickness of the layers, maximum concentrations within the layers and elemental profiles across the boundaries. It was shown that the intensity profiles could be corrected for the wedge shape of the specimen and that the derived compositional profile was independent of average sample thickness variation within the range of the cross-section sample thickness.The results have been compared to analysis performed by Auger electron spectroscopy depth profiling on as-prepared multilayers as well as by energy-dispersive X-ray analysis and electron energy filtered images of cross-sections. The proposed HREM image contrast evaluation method gave spatial resolution in chemical analysis across the thin layers comparable in accuracy to the other methods, whereas the oscillation amplitude for the concentration is slightly less due to specimen preparation artifacts.
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| 16. |
- Hultman, L., et al.
(författare)
-
Formation of polyhedral voids at surface cusps during growth of epitaxial TiN/NbN superlattice and alloy films
- 1992
-
Ingår i: Journal of Vacuum Science and Technology A. - : American Vacuum Society. - 0734-2101. ; 10:4, s. 1618-1624
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial TiN/NbN(001) superiattice thin films with periods A between 0 (alloy) and 9.6 nm have been grown by ultrahigh vacuum reactive magnetron sputter deposition on MgO(OOl) substrates in mixed Ar/N2 discharges. Cross-sectional transmission electron microscopy was used for characterizing layer and defect structure. Coherency strain relaxation close to the film/substrate interface resulted in nonplanar growth with surface cusps and the creation of apparent column boundaries at which TiN and NbN layers curved towards the substrate, but across which the basic lattice was ordered. Also, a fraction of the boundaries were associated with threading defects along the growth direction. The column boundaries and threading defects were decorated by voids that exhibited an orthorhombohedral shape, were elongated in the growth direction, and typically had flat surfaces on {100} planes. The origin of voids is suggested to be through self-shadowing at surface cusps in combination with limited adatom mobility. The voids subsequently attained equilibrium shape as the result of surface and bulk diffusion. The void density varied withλ and the void length in the growth direction was generally an integer number of periods, indicating that the void formation was influenced by the superiattice layers. The formation of limited voids is suggested to be characteristic of thin film growth close to the epitaxial temperature.
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| 17. |
- Hultman, L, et al.
(författare)
-
Growth and electronic properties of epitaxial TiN thin films on 3C-SiC(001) and 6H-SiC(0001) substrates by reactive magnetron sputtering
- 1996
-
Ingår i: Journal of Materials Research. - 0884-2914. ; 11:10, s. 2458-2462
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial TiN films were grown on cubic (3C)-SiC(001) and hexagonal (6H)-SiC(0001) substrates by ultrahigh vacuum reactive magnetron sputtering from a Ti target in a mixed Ar and N2 discharge at a substrate temperature of 700°C. Cross-sectional transmission electron microscopy, including high-resolution imaging, showed orientational relationships TiN(001) ∥ 3C-SiC(001), and TiN[110] ∥ 3C-SiC[110], and TiN(111) ∥ 6H-SiC(0001) and TiN[110],[101] ∥ 6H-SiC[1210]. In the latter case, twin-related TiN domains formed as the result of nucleation on SiC terraces with an inequivalent stacking sequence of Si and C. The TiN/SiC interface was locally atomically sharp for both SiC polytypes. Defects in the TiN layers consisted of threading double positioning domain boundaries in TiN(111) on 6H-SiC. Stacking faults in 3C-SiC did not propagate upon growth of TiN. Room-temperature resistivity of TiN films was ρ = 14 μΩ cm for 6H-SiC(0001) and ρ = 17 μΩ cm for 3C-SiC(001) substrates. Specific contact resistance of TiN to 6H-SiC(0001) was 1.3 × 10-3 Ω cm2 for a 6H-SiC substrate with an n-type doping of 5 × 1017 cm-3.
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| 18. |
- Håkansson, G., et al.
(författare)
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Ion irradiation effects during growth of Mo/V(001) superlattices by dual-target magnetron sputtering
- 1992
-
Ingår i: Journal of Crystal Growth. - 0022-0248. ; 121:3, s. 399-412
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial (001)-oriented Mo/V superlattice films with wavelengths of ≈ 5 nm have been grown on MgO(001) substrates, kept at 700°C, by dual-target unbalanced magnetron sputter deposition in Ar discharges. Low-energy (15-250 eV) Ar ion irradiation with incident ion-to-metal flux ratio of ≈ 1 during film growth was obtained through the application of a negative potential Vs to the substrate. The effects of ion bombardment on interface roughness and mixing, resputtering rates, and defect structure were investigated using a combination of cross-sectional transmission electron microscopy (XTEM), X-ray diffraction (XRD), and simulation of XRD patterns. High-resolution XTEM images showed that the interfaces were relatively sharp for Vs ≤ 100 V while higher Vs values resulted in more diffuse interfaces indicating ion-induced intermixing. By using a kinematical model of diffraction, and comparing with experimental XRD results, it could be concluded that the intermixing increased from ≈ 0.3 nm (2 monolayers) at Vs = 15 V to & 0.9 nm (6 monolayers) at Vs = 250 V. The inhomogeneous strain showed a large increase for Vs & 50 V. This is explained by an incorporation of point defects. Coherency strain relaxation between layers is suggested to take place through the formation of edge dislocations with Burgers vector 〈110〉 by climb processes. Finally, increasing Vs also resulted in resputtering, preferentially from the V layers.
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| 19. |
- Jacobsen, SN, et al.
(författare)
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Sharp microfaceting of (001)-oriented cerium dioxide thin films and the effect of annealing on surface morphology
- 1999
-
Ingår i: Surface Science. - 0039-6028. ; 429:1-3, s. 22-33
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Tidskriftsartikel (refereegranskat)abstract
- Cerium dioxide, CeO2, is a chemically stable oxygen-ion-conducting material, which has been extensively used as an additive or support in oxidation catalysts. The fact that catalytic behaviour is often surface structure sensitive and/or edge atom dependent suggests that different surfaces might be discernible in associated redox processes. Thus, it is desirable to realise CeO2 films with a well-defined microstructure and with crystallographically uniform surfaces. In this paper we present evidence of extremely sharp microfaceting on the surface of thin CeO2 films grown by r.f. magnetron sputtering, and the effect of annealing on the formed sharp ridges. The results show that nominally designated crystallographic surfaces may in fact not coincide with the surfaces exposed as-grown. Thus, there is a clear risk for erroneous interpretation of various orientation-dependent surface properties. Carefully controlled annealing of these films can be utilised as a method for tailoring the resulting surface morphology on the atomic scale.
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| 20. |
- Li, XZ, et al.
(författare)
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HREM study and structure modeling of the η′ phase, the hardening precipitates in commercial Al-Zn-Mg alloys
- 1999
-
Ingår i: Acta Materialia. - 1359-6454. ; 47:9, s. 2651-2659
-
Tidskriftsartikel (refereegranskat)abstract
- The structure of the η′ phase, one of the most important age-hardening precipitates in commercial Al-Zn-Mg alloys, has been studied at the atomic level by means of high-resolution electron microscopy (HREM). A structural model of the η′ phase has been constructed on the basis of the structural characteristics in the observed images and the structure of the η-MgZn2 phase. Image simulation of this model shows a good agreement between calculated and experimental images. Comparison of this model with the early existing model on the basis of the X-ray diffraction is also given.
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| 21. |
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| 22. |
- Ni, W.-X., et al.
(författare)
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δ-function-shaped Sb-doping profiles in Si(001) obtained using a low-energy accelerated-ion source during molecular-beam epitaxy
- 1992
-
Ingår i: Physical Review B. - 0163-1829. ; 46:12, s. 7551-7558
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) buried delta-function-shaped Sb-doping profiles have been obtained in Si using a low-energy accelerated Sb-ion source during molecular-beam epitaxy. A combination of secondary-ion mass spectrometry (SIMS), capacitance-voltage (C-V) measurements, and cross-sectional transmission electron microscopy (XTEM) was used to investigate dopant distributions and to determine profile widths. The 2D-sheet Sb-doping concentration N(Sb), obtained by integrating SIMS delta-doping profiles in samples grown with substrate temperature T(s) = 620-degrees-C and Sb-ion acceleration potentials V(Sb) = 200 and 300 V, was found to vary linearly with the product of the Sb-ion flux and the exposure time (i.e., the ion dose) over the N(Sb) range from 5 X 10(12) to 2 X 10(14) cm-2. The full width at half maximum (FWHM) concentration of 8-doping profiles in Si(001) films was less than the depth resolution of both SIMS and C-V measurements (approximately 10 and 3 nm, respectively). High-resolution XTEM lattice images show that the FWHM was less-than-or-equal-to 2 nm. This is consistent with dopant incorporation simulations, based upon a multisite transition-state dopant incorporation model, which show that accelerated-beam dopant species are trapped in near-surface substitutional sites with atomic mobilities between those of surface and bulk atoms. Dopant surface segregation during growth is strongly suppressed, and the dopant distribution is determined primarily by the straggle in ion trapping distributions. The present results are compared with profile broadening observed in 8-doped layers obtained by solid-phase epitaxy of amorphous Si containing a buried Sb layer.
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| 23. |
- 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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| 24. |
- 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
-
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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| 25. |
- Radnoczi, G., et al.
(författare)
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Defect formation in al-doped SI(100) films grown by molecular-beam epitaxy and solid-phase epitaxy
- 1989
-
Ingår i: Institute of Physics Conference Series. - 0951-3248. ; :100, s. 235-240
-
Tidskriftsartikel (refereegranskat)abstract
- Aluminium doped Si layers grown either by solid phase epitaxy (SPE) or molecular beam epitaxy (MBE) have been investigated over wide ranges of Al fluxes (J(Al) = 1 x 10(10)-3 x 10(13) cm-2s-1) and growth temperatures (T(s) = 500-900-degrees-C), using RHEED, LEED and AES during growth and cross section TEM of the as-deposited layers. For MBE growth, defect free films could be grown almost in the whole interval of J(Al) and T(s). In the SPE case Al is completely incorporated in the amorphous films. Upon crystallization dislocations and stacking faults/twins, as well as small voids are formed. For all concentrations and annealing temperatures TEM shows similar defect structures.
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| 26. |
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| 27. |
- Selinder, T.I., et al.
(författare)
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Structural characterization of yttria (Y2O3) inclusions in YBa2Cu3O7−x films : Growth model and effect on critical current density
- 1993
-
Ingår i: Thin Solid Films. - 0040-6090. ; 229:2, s. 237-248
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Tidskriftsartikel (refereegranskat)abstract
- A higher critical current and enhanced pinning was obtained in c-axis-oriented YBa2Cu3O7−x (YBCO)films having a higher density of semicoherent yttria (Y2O3) inclusions. The films were grown by sputtering and the inclusion density depends on the fraction of N2O in the sputtering gas. The inclusions were studied by transmission electron microscopy, both in planar sections and in cross-sections. They are embedded in the YBCO matrix without disturbing its structure appreciably, and the inclusion density is up to about 1017 cm−3, comprising about 4% of the film volume. From the appearance of moiré fringes and from high resolution transmission electron micrographs, it is concluded that the inclusions are highly oriented and have coherent or semicoherent interfaces towards matrix. A model for formation of the yttria inclusions during film growth is presented, which includes nucleation of epitaxial coherent yttria islands, layer-by-layer growth and finally overgrowth by advancing steps of the YBCO film. The enhanced pinning and transport critical current densities, relation to film microstructure and the possible flux-pinning mechanisms by these yttria inclusions are discussed.
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| 28. |
- Selinder, T.I., et al.
(författare)
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Yttrium oxide inclusions in YBa2Cu3Ox thin films : Enhanced flux pinning and relation to copper oxide surface particles
- 1992
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Ingår i: Physica C: Superconductivity and its Applications. - 0921-4534. ; 202:1-2, s. 69-74
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Tidskriftsartikel (refereegranskat)abstract
- Semi-coherent Y2O3 (yttria) inclusions are identified in high quality epitaxial YBa2Cu3Ox (YBCO) thin films by using transmission electron microscopy and energy dispersive X-ray analyses. Magnetization measurements show enhanced flux pinning in films containing an increasing number density of inclusions. The inclusions are incorporated into the films without disturbing the YBCO structure appreciably. The number density is ≈ 1017 cm-3 in films having transport critical currents of 4x106 A cm-2 at 77 K. Nucleation of the yttria inclusions is suggested to occur spontaneously during film growth. The abundance of yttria inclusions is connected to the occurrence of large Cu-rich surface particles in films that have optimum superconducting properties.
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| 29. |
- Selinder, TI, et al.
(författare)
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Microstructure and microwave loss studies on epitaxial YBa2Cu3Ox thin films
- 1992
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Ingår i: High Tc superconductor thin films. - 0444893539 ; , s. 219-224
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Konferensbidrag (refereegranskat)abstract
- Thin YBa2Cu3Ox films were grown on SrTiO3 or LaAlO3 single crystals by dc-magnetron reactive sputtering in argon/oxygen gas mixtures. Deposition temperatures ranged from 540 °C to 780 °C. After deposition and subsequent cool down, films grown above 680 °C are superconducting below 86–88 K. All films are oriented with the [001] direction parallel to the [001] substrate normal. The best films have critical current densities well above 106 A/cm2, and effective 6 GHz surface resistance values below 300 μω, at 77 K. Despite good electrical properties, the films are littered with copper rich particles on a smooth and epitaxial single crystalline surface. Cross-section Transmission Electron Microscopy (X-TEM) was used to study the crystalline quality on a microscopic level, and the nature of particles occurring on/in the as grown film. Small misaligned YBa2Cu3Ox grains often occur in the films. The large copper rich particles on the film surface seem to have nucleated at such grains on the film surface. Their occurrence can, at least partly, be explained by a nonstoichiometric flow to the substrate. The number density of the particles decreased with increasing growth temperature but the volume density seemed to be constant in the investigated temperature interval.
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| 30. |
- Sjostrom, H., et al.
(författare)
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Characterization of interfaces between hydrogenated amorphous carbon films and steel substrates using high resolution cross-sectional transmission electron microscopy
- 1993
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Ingår i: Diamond and Related Materials. - 0925-9635. ; 2:2-4, s. 562-566
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Tidskriftsartikel (refereegranskat)abstract
- Cross-sectional transmission electron microscopy, including high resolution microscopy, was employed to characterize the interfaces between hydrogenated amorphous carbon (a-C:H) films and steel substrates. Films were deposited both by ion beam decomposition of large hydrocarbon molecules and by magnetron plasma decomposition of C2H2. The latter method was also used to deposit Mo- and W-containing a-C:H films onto steel substrates with interlayers of the pure metals between the steel substrate and the a-C:H films. The films were found to be amorphous except for the metal-containing films where 1–4 nm crystalline clusters were present in an a-C:H matrix. The metal interlayers had a columnar microstructure with column widths of ∼30 nm. The interfaces between the a-C:H films and the Mo or W interlayers were found to extend over 20–40 nm with a gradual crystalline-to-amorphous transition. In most of the a-C:H film-substrate interface regions a thin (less than 10 nm) layer was observed which was predominantly amorphous, but contained a small fraction of crystalline grains. Additional analyses carried out using Auger electron spectroscopy showed an increase in both O and N close to the interface. However, for the cases with Mo and W interlayers, the substrate surface contaminants were less localized and on some parts of the substrate surface the lattice fringes were continuous across the atomically sharp interface.
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| 31. |
- Sjöström, H., et al.
(författare)
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Microstructure of amorphous C:H and metal-containing C:H films deposited on steel substrates
- 1993
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Ingår i: Thin Solid Films. - 0040-6090. ; 232:2, s. 169-179
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Tidskriftsartikel (refereegranskat)abstract
- Cross-sectional transmission electron microscopy (XTEM), including high-resolution microscopy (HREM), was employed to characterize the interface between different amorphous hydrogenated carbon (a-C:H) films and steel substrates. Additional analyses using Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were also performed. Films were deposited both by high-energy (50 keV) nitrogen ion-beam decomposition of large hydrocarbon molecules and by magnetron plasma decomposition of C2H2 in mixed Ar-C2H2 discharges. The latter method was also used to deposit Mo- or W-containing a-C:H films (Me-C:H films) onto steel substrates with interlayers of the pure metals between the substrate and Me-C:H film. The films were found to be truly amorphous except for the cases of the metal-containing films, where 1–2 nm crystalline clusters were present in an a-C:H matrix. In the case of Mo the clusters were identified from HREM micrographs to have a bcc-like structure, characteristic of metallic Mo. The metal interlayers had a columnar microstructure with column widths of ∼ 30 nm. The interfaces between the Mo and W interlayers and the a-C:H films were found to extend over 20–40 nm with a gradual crystalline-to-amorphous transition. In most of the a-C:H film-substrate interface regions a thin layer ( < 10 nm) was observed which was predominantly amorphous but contained a small fraction of crystalline grains. AES showed an increase of both O and N close to the interface. However, for the cases with Mo and W interlayers, the substrate surface contaminants were less localized, and on some parts of the substrate surface the lattice fringes of the substrate and metal interlayer phase were continuous across a sharp interface.
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| 32. |
- Sjöström, H, et al.
(författare)
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Reactive magnetron sputter deposition of CNx films on Si(001) substrates : film growth, microstructure and mechanical properties
- 1994
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 246:1-2, s. 103-109
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Tidskriftsartikel (refereegranskat)abstract
- There is currently considerable interest in producing new materials with extreme combinations of mechanical properties such as high hardnesses and moduli. One example of such a material is crystalline C3N4, which has been predicted to have a bulk modulus higher than that of diamond. In this paper we report on experiments carried out to synthesize CNx thin films. The films were grown in an unbalanced magnetron-sputtering system by reactive sputtering of C in N2 discharges. Si(001) substrates with the native oxide removed by thermal desorption and then kept at temperatures ranging from 150 to 600°C and substrate bias voltages Vs between 7.5 and -200 V were used. The films were analysed using X-ray diffraction, transmission electron microscopy (TEM). Auger electron spectroscopy, Rutherford backscattering and nano-indentation tests. Typically the films were grown at rates of 5 nm s-1 to total thicknesses of 300 nm. Owing to an extensive re-sputtering, only low negative bias voltages (-80
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| 33. |
- Skårman, B, et al.
(författare)
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Evaluation of intermittent contact mode AFM probes by HREM and using atomically sharp CeO2 ridges as tip characterizer
- 2000
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 16:15, s. 6267-6277
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Tidskriftsartikel (refereegranskat)abstract
- The imaging process of the atomic force microscope (AFM) in contact, noncontact, and intermittent contact mode is still debated after more than a decade of widespread use, in particular when imaged features are approaching atomic dimensions. Several models for the interaction between the tip and the surface have been suggested, but generally they all need an exact description of the geometry of either the tip, the surface, or both. We present here a tip characterizer with close to reproducible geometry, exactly known angles of all surfaces, and sharp features with close to atomic dimension. It has been tested on three commercial AFM probes and a laboratory-made electron-beam-deposited tip, sharpened by oxygen plasma etching. High-resolution transmission electron microscopy has been used to unambiguously verify the tip shapes down to atomic dimensions, both before and after imaging in intermittent contact mode. The effect on the recorded AFM images is shown of tip shape, tip wear, spallation, and accumulation on the tip of amorphous and crystalline debris. The imaging is shown to be a dynamic event, with a continuously changing tip and occasional catastrophic events that give abrupt changes in imaging conditions. The tips are severely worn down already after scanning a few centimeters, but accumulated amorphous material may still give it imaging capabilities in the nanometer range, even with having a tip radius exceeding 130 nm. Accumulated amorphous material seems to be more important than previously believed. Procedures for tip in situ characterization and reliable imaging are suggested.
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| 34. |
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| 35. |
- Suenaga, K, et al.
(författare)
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Carbon nitride nanotubulite - densely-packed and well-aligned tubular nanostructures
- 1999
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Ingår i: Chemical Physics Letters. - 0009-2614. ; 300:5-6, s. 695-700
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Tidskriftsartikel (refereegranskat)abstract
- Tubular carbon nitride (CNx, x=0.01–0.32) nanoparticles were successfully synthesized by d.c. magnetron sputtering. These tubes were grown in a highly packed form perpendicularly on a sodium chloride substrate. Their number density is estimated to be ∼1×104 per μm2 and is constant over macroscopic regions. Sub-nanometer scale chemical mapping shows that the nitrogen to carbon atomic ratio is rather constant across these tubes. This successful synthesis of a nanotubulite – made of a rather compact aggregation of tubular nanoparticles – could facilitate experimental approaches to measure mechanical or electrical transport properties of such nanotubes and to open the way to variable nanotube applications.
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| 36. |
- Vavra, I, et al.
(författare)
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Electron-beam mixing of W1 - xSix Si multilayers
- 1995
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Ingår i: Vacuum. - 0042-207X. ; 46:8-10, s. 1063-1064
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Tidskriftsartikel (refereegranskat)abstract
- The high energy electron beam was used for the local amorphisation of metallic multilayer. The observed effect is proposed for the application in nanometer-scale technology.
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| 37. |
- Vavra, I, et al.
(författare)
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Structural and electrical properties of superconducting Nb/Si multilayers
- 1998
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Ingår i: Vacuum. - 0042-207X. ; 50:1-2, s. 31-33
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Tidskriftsartikel (refereegranskat)abstract
- We have found the deposition technology at which the interface roughness of Nb/Si multilayer is strongly correlated and decreases with deposited layer number. On the basis of our Nb/Si multilayer we succeeded to prepare ten-fold stacked Josephson junction (JJ). Basic electric properties of stacked JJ are presented.
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| 38. |
- Vavra, I, et al.
(författare)
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The influence of thermal processing on structural and electrical properties of WxSi1−x/Si multilayers
- 1994
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0168-9002. ; 350:1-2, s. 379-390
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal stability of WxSi1−x/Si multilayers (MLs) with x varying from 1 to 0.11 is studied by TEM and LAXS. The structure of the prepared samples is amorphous. Doping of W sublayers with silicon affects the interdiffusion process as well as the crystallization in these sublayers. We investigated these two processes (which have a detrimental influence on e.g. X-ray mirror stability) by annealing our samples at 400°C for 40 min. The structural changes were monitored by resistance measurement in the temperature range of 1.5–300 K. A correlation between structural and electrical characteristics was found, which is based on the comparison between three different R(T) curves. It is shown in our paper that the R(T) curve of a ML lies between the R(T) curves of two extreme types of single layers. The first single layer is the analogue of a fully intermixed ML and the second one represents a parallel connection of all conductive sublayers. Thus, a simple resistance measurement can give additional information about the quality of interfaces. We claim that in MLs with ultrathin sublayers the reported highest thermal stability of the amorphous mixture W0.72Si0.28 cannot be utilized because interdiffusion dominates over crystallization so that the superlattice structure is not retained.
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| 39. |
- 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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| 40. |
- Wallenberg, LR, et al.
(författare)
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Aurivillius-type-high-tc superconductor containting bismuth
- 1988
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Ingår i: EUREM 88 : proceedings of the 9th European Congress on Electron Microscopy held in York, England, 4-9 September 1988 - proceedings of the 9th European Congress on Electron Microscopy held in York, England, 4-9 September 1988. - 085498187X ; 93, s. 237-237
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Konferensbidrag (refereegranskat)
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| 41. |
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| 42. |
- Wallenberg, LR, et al.
(författare)
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On the crystal structure of small gold crystals and large gold clusters
- 1985
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 156:1, s. 256-264
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Tidskriftsartikel (refereegranskat)abstract
- A large gold cluster with the formula Au55[(C6H5)3P]12Cl6, was imaged with a high-resolution transmission electron microscope (HRTEM) and a proposed model was confirmed. Growth of gold crystals of approximately 4.0 nm size could be followed, row by row of atoms, with the use of a low light level TV camera and on-line image processing.
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| 43. |
- Withers, RL, et al.
(författare)
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Microdomains, Solid Solutions and the "Defect Fluorite" to C-Type Sesquioxide Transition in CeO2-RO1.5 and ZrO2-RO1.5 Systems
- 1995
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596. ; 120:2, s. 290-298
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Tidskriftsartikel (refereegranskat)abstract
- Satellite dark field (SDF) imaging is used to show that there is a definite change in symmetry on moving across the two-phase region separating the so-called "defect fluorite" and C-type sesquioxide solid solution regions in (1 - x)CeO2 · xRO1.5 and (1 - x )ZrO2 · xRO1.5 systems. SDF images of the "defect fluorite" side of the two-phase region are characterized by a microdomain texture on the ∼100-200 Å scale and the local symmetry within any one of these microdomains is shown to be lower than cubic. Corresponding SDF images of the C-type sesquioxide side of the two-phase region are by contrast homogeneous and consistent with Ia3 space group symmetry. The nature of the local oxygen vacancy distribution on either side of the two-phase region is discussed and a possible model for the "defect fluorite" side of the two-phase region proposed.
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