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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 90 (2001), S. 1550-1557 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The complete Raman spectrum of SnO2 nanoparticles in presented and analyzed. In addition to the "classical" modes observed in the rutile structure, two other regions shown Raman activity for nanoparticles. The Raman bands in the low-frequency region are attributed to acoustic modes associated with the vibration of the individual nanoparticle as a whole. The high-frequency region is activated by surface disorder. A detailed analysis of these regions and the changes in the normal modes of SnO2 are presented as a function nanoparticle size. © 2001 American Institute of Physics.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The analysis of SiC films obtained by carbon ion implantation into amorphous Si (preamorphized by Ge ion implantation) has been performed by infrared and Raman scattering spectroscopies, transmission electron microscopy, Rutherford backscattering, and x-ray photoelectron spectroscopy (XPS). The data obtained show the formation of an amorphous Si1−xCx layer on top of the amorphous Si one by successive Ge and C implantations. The fitting of the XPS spectra indicates the presence of about 70% of Si–C bonds in addition to the Si–Si and C–C ones in the implanted region, with a composition in the range 0.35〈x〈0.6. This points out the existence of a partial chemical order in the layer, in between the cases of perfect mixing and complete chemical order. Recrystallization of the layers has been achieved by ion-beam induced epitaxial crystallization (IBIEC), which gives rise to a nanocrystalline SiC layer. However, recrystallization is not complete, observing still the presence of Si–Si and C–C bonds in an amorphous phase. Moreover, the distribution of the different bonds in the IBIEC processed samples is similar to that from the as-implanted ones. This suggests that during IBIEC homopolar bonds are not broken, and only regions with dominant Si–C heteropolar bonds recrystallize. © 1996 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 463-465 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The supralinear dependence of visible photoluminescence intensity from amorphous silicon nanopowder produced in plasma enhanced chemical vapor deposition on excitation power and its exponential dependence on pressure is reported. It is shown that this new material emits two different kinds of photoluminescence that dominate at different pressures.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 3488-3490 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this letter, we report the ion-beam synthesis and the structural characterization of ZnS nanocrystals in SiO2. Both electron diffraction and x-ray diffraction measurements show the precipitation of ZnS nanocrystals having a wurtzite–2H structure and infrared spectroscopy confirms the presence of Zn–S bonding. Upon annealing, transmission electron microscopy observations show the Ostwald ripening of the precipitates coupled with a self-organization in two layers parallel to the free surface. This self-organization has been also detected by secondary ion mass spectroscopy, and its origin is discussed in terms of a pure Ostwald ripening process and/or a consequence of the implantation damage. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 676-681 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution electron microscopy technique has been applied to a detailed study of the 60° dislocations at the atomic layer molecular-beam-epitaxial GaAs/Si interface. Their deformation fields strongly interact with neighbor dislocations inducing irregular spacing between the cores and possible dissociations. Biatomic silicon steps were observed at the interface, but never inside 60° dislocation cores. Computer image simulation and elasticity calculations of the atomic displacement field have been used in order to determine the structure of the 60° dislocation; however, due to the Eshelby effect and to interaction with some neighbor dislocations, in many cases no theoretical model could explain some observations. © 1996 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2441-2446 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Previously reported results on deep level optical spectroscopy, optical absorption, deep level transient spectroscopy, photoluminescence excitation, and time resolved photoluminescence are reviewed and discussed in order to know which are the mechanisms involved in electron capture and emission of the Ti acceptor level in GaP. First, the analysis indicates that the 3T1(F) crystal-field excited state is not in resonance with the conduction band states. Second, it is shown that both the 3T2 and 3T1(F) excited states do not play any significant role in the process of electron emission and capture. © 1995 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4018-4020 
    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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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2978-2984 
    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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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3393-3398 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The validity of optical absorption (OA) as a technique for the measurement of strain e11, alloy composition x, and relaxation in InxGa1−xAs epilayers on InP has been examined by comparison with similar measurements by double-crystal x-ray diffraction (DCXD). Provided that the strain arising from differences in the thermal contraction of the substrate and epilayer are taken into account, measurements of strain by OA show good agreement with DCXD results, with a dispersion of Δe11=±0.27×10−3. Comparison of alloy compositions given by the two techniques shows similarly good agreement, with a dispersion in the values of x of less than Δx=±0.7%. OA may also be used to determine lattice relaxation. The degree of uncertainty in the measurement of this parameter increases as lattice match is approached and decreases as the lattice relaxes. Our studies indicate that OA may be used as an independent technique to evaluate strain, alloy composition, and the degree of lattice relaxation in InxGa1−xAs epilayers. © 1995 American Institute of Physics.
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