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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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
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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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| 6. |
- Kiros, Yohannes, 1956-, et al.
(författare)
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Cobalt and cobalt-based macrocycle blacks as oxygen-reduction catalysts in alkaline fuel cells
- 1993
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 45:2, s. 219-227
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical reduction of oxygen on high surface are carbons catalyzed by cobalt and pyrolyzed macrocycles has been studied in alkaline fuel cells. Tests were also carried out with 'green black', i.e., pyrolyzed phyto-biomass. Galvanostatic polarization curves show that cobalt from cobalt acetate and fine cobalt metal power exhibit a high catalytic activity. The activity of pyrolyzed cobalt tetraphenylporphyrin (CoTPP) is due to the combined effects of the cobalt additive and the charred residue of the macrocycle. 'Green black', with chlorophyll as macrocycle black precursor, has a similar effect. The dissolution of cobalt from the electrode surface has been established. Life tests with these electrodes are reported. © 1993.
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| 7. |
- Kiros, Yohannes, 1956-, et al.
(författare)
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Pyrolyzed macrocycles on high surface area carbons for the reduction of oxygen in alkaline fuel cells
- 1991
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 36:4, s. 547-555
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Tidskriftsartikel (refereegranskat)abstract
- Polarization characteristics and preparation methods of double-layer porous gas diffusion electrodes on various carbon materials in alkaline fuel cells were investigated. The electrodes with active carbon carriers were catalyzed with cobalt/iron tetraphonylporphyrin or silver. These electrodes show a potential of - 186 mV (versus Hg/HgO) at 1.0 A/cm2 when operated with oxygen at 40 °C and 5 M KOH. Various techniques such as surface area measurements, scanning (SEM) and transmission (TEM) electron microscopy in combination with energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) were used to characterize the structure and morphology of the catalyst layer.
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| 8. |
- Montelius, L., et al.
(författare)
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Direct observation of the atomic force microscopy tip using inverse atomic force microscopy imaging
- 1994
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Ingår i: Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures. - : American Vacuum Society. - 0734-211X. ; 12:3, s. 2222-2226
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Tidskriftsartikel (refereegranskat)abstract
- It is a well‐known fact in scanning probe microscopy that the tip geometry will be convoluted with the shape of the sample. In this study we report on a clear‐cut in situ direct observation of the real shape of the atomic force microscopy (AFM) tip using the AFM technique itself, utilizing a specially designed sample. The sample was an array of columns fabricated using aerosol deposition of metal particles and subsequent plasma etching. In this article we report on the so‐called inverse AFM mode in which the tip is actually used as the sample and vice versa. We will present results using ordinary AFM tips and ‘‘tapping‐mode’’ tips as well as high‐aspect‐ratio supertips (Nanoprobe). We propose how this method can, with a very high accuracy, be used for studying objects, e.g., biomolecules, that are deliberately attached to the usual AFM cantilever tip. Finally, we discuss how this method can significantly increase the reliability of the obtained AFM images.
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| 9. |
- 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
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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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