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  • 1
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nanocrystalline thick-film SnO2 sensors with different dopants were fabricated by an optimized screen printing process and subsequent annealing. Powders were used as starting materials which were prepared by a wet chemical process from SnCl4. Microanalysis was performed of both, the precursors and the final sensor materials with their different annealing conditions. Gas sensing tests with CO, CH4 and NO2 in air with controlled humidity were correlated with results from X-ray photoemission spectroscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). As an interesting result, the distribution of the transition metal dopants Pd and Pt (as deduced from TEM and XPS data) rules out the existence of metallic clusters or even atoms in the metallic state at the surface. This finding does not allow to explain the sensor effects on SnO2 based materials as usually done by means of spill-over effects or Fermi energy control.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 833-840 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the properties of strained Si1−yCy(0≤y≤0.02) alloy layers grown on silicon after wet oxidation between 750 and 1100 °C. Both secondary ion mass spectrometry and x-ray photoelectron spectroscopy prove the presence of carbon in the oxide. The growth rates and refractive indices of the oxides obtained from ellipsometry show no significant differences compared with oxides grown on silicon. Infrared absorption measurements reveal decreasing stress in the oxides with rising oxidation temperature and a slight dependence of the stress in the oxide upon the carbon concentration. For the Si1−yCy layer, x-ray diffraction measurements show a decrease of the substitutional carbon concentration with increasing oxidation temperature and duration. This loss of substitutional carbon is enhanced near the SiO2/Si1−yCy interface. The formation of silicon carbide precipitates in the Si1−yCy layer is demonstrated by infrared absorption. For short oxidation times, we find an increase of the intensity of the local vibrational absorption mode of substitutional carbon. We observe discrepancies between the determination of the substitutional carbon concentration in the x-ray diffraction and infrared absorption measurements. © 1999 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3962-3964 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion implantation followed by high temperature annealing can be used to synthesize group IV semiconducting nanoparticles in SiO2. The density and the size distribution of these nanocrystals obviously depend on the implantation and annealing conditions. While their size can be measured by "classical" transmission electron microscopy techniques, their density cannot because no diffraction occurs in the amorphous matrix. In this letter, we use electron energy loss spectroscopy to overcome this problem. We have measured the evolution of the size distribution, the density, and the atomic fraction occupied by the Ge precipitates during annealing. We show that the nanocrystals grow in size and reduce their density, while the overall number of atoms they contain remains constant. This observation proves that the nanoparticles undergo a conservative ripening during annealing. © 2000 American Institute of Physics.
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  • 4
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of In0.52Al0.48As films grown on InP (100) by molecular beam epitaxy, at growth temperatures in the range of 530–590 °C, are analyzed by transmission electron microscopy. The existence of contrast inhomogeneities along the 〈010〉 fcc soft directions, the appearance of which depends on the temperature and the distance to the substrate, is reported. It is shown that these contrast irregularities in InAlAs are related directly to the existence of precipitates in the InAlAs/InP interface, whose origin can be found in the formation of an InAs layer under an As-stabilized InP surface.
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  • 5
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical characterization of silicon-on-insulator structures formed by sequential implantation and annealing (SIA) has been carried out. The infrared transmission spectra show peaks characteristic of a thermal oxide, and confirm the high quality of the buried oxide. Moreover, the spectra obtained from these SIA samples, in comparison to those obtained from equivalent samples made with a single implant, show a shift of the main absorption peak to higher wave numbers, which can be attributed to excess oxygen. The higher concentration of oxygen in the SIA samples is corroborated by photoluminescence measurements which show the presence of dislocation-related bands broadened by the presence of oxygen.
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use transmission electron microscopy to characterize the morphology of InGaP epitaxial layers grown by metal-organic vapor-phase epitaxy over misoriented GaAs (001) substrates, with a cutoff angle in a range from 0° to 25°. The occurrence of phase separation and CuPt-type ordered superstructures has been observed. The most ordered configuration has been found to appear in layers grown on 2° off substrates, and the strength of order decreases with increasing the misorientation angle beyond α=2°. Conversely, whereas the phase separation is less evident in the layer grown at 2°, the sample grown with a misorientation of 25° exhibits the most phase separated configuration. The completion between these two phenomena is discussed depending on the misorientation angle. © 1996 American Institute of Physics.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical absorption spectra and transmission electron microscopy (TEM) observations on InGaAs/InP layers under compressive strain are reported. From the band-gap energy dispersion, the magnitude of the strain inhomogeneities, σε, is quantified and its microscopic origin is analyzed in view of the layer microstructure. TEM observations reveal a dislocation network at the layer interface the density of which correlates with σε. It is concluded that local variations of dislocation density are responsible for the inhomogeneous strain field together with another mechanism that dominates when the dislocation density is very low. © 1995 American Institute of Physics.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-dose carbon-ion-implanted Si samples have been analyzed by infrared spectroscopy, Raman scattering, and x-ray photoelectron spectroscopy (XPS) correlated with transmission electron microscopy. Samples were implanted at room temperature and 500 °C with doses between 1017 and 1018 C+/cm2. Some of the samples were implanted at room temperature with the surface covered by a capping oxide layer. Implanting at room temperature leads to the formation of a surface carbon-rich amorphous layer, in addition to the buried implanted layer. The dependence of this layer on the capping oxide suggests this layer to be determined by carbon migration toward the surface, rather than surface contamination. Implanting at 500 °C, no carbon-rich surface layer is observed and the SiC buried layer is formed by crystalline β-SiC precipitates aligned with the Si matrix. The concentration of SiC in this region as measured by XPS is higher than for the room-temperature implantation. © 1995 American Institute of Physics.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thick (∼3 μm) films of InxGa1−xAs grown on GaAs(100) substrates, across the whole composition range, have been examined by transmission electron microscopy and double-crystal x-ray diffraction. The results were compared with the observed growth mode of the material determined by in situ reflection high-energy electron diffraction in the molecular beam epitaxy growth system. The quality of the material degraded noticeably for compositions up to x∼0.5 associated with an increased density of dislocations and stacking faults. In contrast, improvements in quality as x approached 1.0 were correlated with the introduction of an increasingly more regular array of edge dislocations.
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  • 10
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed analysis of the photocapacitance signal at the near-band and extrinsic energetic ranges in Schottky barriers obtained on horizontal Bridgman GaAs wafers, which were implanted with boron at different doses and annealed at several temperatures, has been carried out by using the optical isothermal transient spectroscopy, OITS. The optical cross sections have been determined as well as the quenching efficiency of the EL2 level which has been found to be independent of the annealing temperature. Moreover, the quenching relaxation presents two significant features: (i) a strong increase of the quenching efficiency from 1.35 eV on and (ii) a diminution of the quenching transient amplitude in relation with that shown by the fundamental EL2 level. In order to explain this behavior, different cases are discussed assuming the presence of several energy levels, the existence of an optical recuperation, or the association of the EL2 trap with two levels located, respectively, at Ev+0.45 eV and Ec−0.75 eV. The theoretical simulation, taking into account these two last cases, is in agreement with the experimental photocapacitance data at low temperature, as well as at room temperature where the EL2 filling phototransient shows an anomalous behavior. Moreover, unlike the previous data reported for the EL2 electron optical cross section, the values found using our experimental technique are in agreement with the behavior deduced from the theoretical calculation. The utilization of the OITS method has also allowed the determination of another level, whose faster optical contribution is often added to that of the EL2 level when the DLOS or standard photocapacitance is used.
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