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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 394-399 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman scattering has been carried out on PbTiO3 thin films prepared on platinum-coated (100) silicon by radio-frequency (rf)-magnetron sputtering without substrate heating and a post-deposition thermal treatment. The Raman spectra obtained from the thin film are characteristic of powder Raman spectra: In comparison with the single crystal spectra, the intensity of the background is relatively high at low frequencies and the Raman lines are broad. The lattice phonon modes corresponding to the observed lines are identified by comparison with the data on single crystals and powder. The Raman frequencies for the thin film remarkably shift to low frequencies compared with single-crystal data. It is shown that the phenomenon of the frequency shifts is similar with the hydrostatic pressure effect on single crystals of PbTiO3. The result indicates that the thin films are composed of grains that are stressed depending on the grain size by neighboring grains of different orientations when they are split up into ferroelectric domains at the paraelectric-to-ferroelectric transition. This stress effect is significant even for a grain size of ∼0.5 μm. It is found that the lowest frequency E transverse optical (TO) mode in the thin film shows softening with increasing temperature as was reported in previous studies on single crystals.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2042-2047 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical and optical spectroscopic studies of TiO2 anatase thin films deposited by sputtering show that the metastable phase anatase differs in electronic properties from the well-known, stable phase rutile. Resistivity and Hall-effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self-trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2945-2951 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoemission spectromicroscopy was used to investigate the electronic structure of TiO2 anatase single crystals and polycrystalline thin films. The stoichiometry and the degree of oxidation of as-grown crystals, as-deposited films, as well as of thermally annealed samples in different atmospheres, were analyzed, based on the Ti 2p and O 1s core levels, with an energy resolution of 0.4 eV. The experimental density of states (DOS) was found to be in agreement with the theoretical DOS reported in the literature for anatase crystals, and shows some characteristics similar to the experimental DOS reported for rutile crystals. In reduced samples, the experimental DOS is characterized by intense emission in the region of O 2p bonding orbitals, and does not exhibit an appreciable density of states in the band gap. As-grown crystals exhibit small band gap emission (a few percent of the valence band VB signal) at about 0.8 eV, which is attributed to Ti3+ (3d) defect states. Annealing the crystals at high temperatures in O2 or subsequent thermal reduction in an Ar–H2 mixture (95%–5%) produces nearly stoichiometric surfaces with smaller or undetectable density of Ti3+ states. In addition, some redistribution of the spectral weight is observed in the VB spectra.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 633-635 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Resistivity, thermopower, and Hall-effect measurements on large single crystals of the anatase form of TiO2 all indicate high mobility n-type carriers that are produced by thermal excitation from a density of ∼1018 cm−3 putatively present shallow donor states. The decrease of the mobility with increasing temperature is consistent with the scattering of carriers by the optical phonons of TiO2.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6625-6631 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman scattering is used to characterize thin films of PbTi1−xZrxO3. The films have been prepared on platinum-coated (100) silicon by radio-frequency (rf)-magnetron sputtering without substrate heating followed by a post-deposition annealing at 600–650 °C. As the concentration of Zr is increased, the Raman peaks broaden and their intensities decrease more rapidly compared with bulk ceramic or powder samples, while the background intensity increases. The observations show that the crystal structure of the films is locally deformed and significantly disordered. With increasing x, the soft E(TO) mode shifts to lower frequencies. An additional Raman peak appears besides the phonon peaks expected in a perfect crystal. The soft mode strongly couples with the extra mode, similarly with the case of ceramic samples. The results are related to features of the thin films such as a frustrated phase transition, i.e., smaller differences between the lattice parameters a and c in comparison with powder data, and an electrical behavior showing a diffuse ferroelectric-to-paraelectric transition with a broad peak.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3997-4003 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We used the novel experimental technique of photoemission spectromicroscopy to investigate the active area of SnOx thin films for gas sensors, deposited by dc sputtering. First, we analyzed the degree of oxidation and the homogeneity of as-deposited films in a high lateral resolution (30 μm) spectromicroscopy mode with an energy resolution of 0.4 eV. This led to a surprising discovery of a large amount of tin monoxide on the film surface. Then we studied the interaction of H2 and H2O with the surface of polycrystalline SnO2 films used as sensitive layers in actual gas sensor devices. These results have been related to the resistivity changes of the corresponding devices: we found that such changes are primarily due to a reduction process in the film rather than to mere chemisorption.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 1820-1825 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The TiSi2/Si system is investigated using high-resolution transmission electron microscopy (HRTEM) and electron diffraction in both cross-section and flat-on modes. The results show that the large crystallographic differences between both crystals and the complexity of the reaction path are not obstacles to the formation of flat and well-defined interfaces. (1¯01) TiSi2 proves to be a preferential plane for epitaxial growth on Si (111). In this case, the terminal TiSi2 plane at the interface is composed of single atomic species. It is proposed that the reasons leading to such an epitaxy are related to the small discrepancy of atomic densities and interplanar spacings characteristic of these planes. Observation of local epitaxial relationships are reported and investigated using a lattice matching model. It turns out that they minimize the two-dimensional misfit at the interface.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 979-981 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We explored the reactivity of gold on cleaved 2212 BiCaSrCuO by synchrotron-radiation photoemission spectroscopy. We found no evidence for reactivity when the substrate was at room temperature, similar to what has been reported for very low temperatures (20 K). At intermediate temperatures (100 K), however, clear evidence was found of a chemical reaction with formation of a localized nonmetallic phase. These findings have potentially important implications for the manufacturing of devices based on BiCaSrCuO.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 60 (1990), S. 907-914 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on Time Differential Perturbed Angular Correlation measurements of the nuclear quadrupole interaction of181Hf(β−)181 and its temperature dependence in the low dimensional Hf- trichalcogenides HfS3, HfSe3 and HfTe3. In HfS3 the temperature dependence of the precession frequency is a slowly decreasing function with a negative curvature, the deviation from axial symmetry of the electric field gradient is practically temperature independent. In HfSe3 the NQI shows a peculiar behaviour; between 10K and 300K the quadrupole frequency and the asymmetry parameter increase, between 300K and 400K the frequency decreases while the deviation from axial symmetry increases, indicating a structural phase transition near room temperature. In HfTe3 the quadrupole frequency is practically temperature independent below 600K and increases linearely at higher temperatures, the asymmetry parameter increases steadily in the temperature range from 10K to 600K and then decreases. There is a strong correlation between the strength and the asymmetry of the electric field gradient so that the system depends on one control parameter only.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 144 (1990), S. 137-143 
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We recently reported that the growth of normal rat pleural mesothelial cells (RPMCs) is inhibited by conditioned media from either in vivo or in vitro transformed RPMCs. In this study we report that the growth of normal RPMCs is inhibited by epidermal growth factor (EGF). This was demonstrated by using three methods of investigation. Two types of studies were carried out with growing cells. First, cell counts indicated that the number of cells was reduced in EGF-treated cultures when compared with untreated cultures. Second, the percentage of S cells detected by flow cytometry following treatment with EGF was lower than without EGF. In other experiments, incorporation of tritiated thymidine in confluent cells was decreased by EGF treatment, either in the presence or absence of fetal calf serum; these effects were dose dependent and were observed from 2 ng/ml EGF. Lower EGF concentrations did not significantly modify thymidine incorporation when compared with untreated cells. Analysis of 125I EGF binding experiments by the Scatchard method indicated that RPMCs possess EGF receptors (about 105 per cell) with low ligand binding affinity (Kd = 1.7 ± 0.4 nM). These results indicate that EGF might modulate the growth of RPMCs.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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