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  • 1
    Electronic Resource
    Electronic Resource
    Dynamics of atoms in YBa"2Cu"3O"7"-"x
    Amsterdam : Elsevier
    Physica C: Superconductivity and its applications 153-155 (1988), S. 300-301 
    Details
    ISSN: 0921-4534
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0921-4534(88)90602-8
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  • 2
    Electronic Resource
    Electronic Resource
    Physical properties of semi-insulating polycrystalline silicon. II. Optical studies of thin films (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7690-7700 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical properties of semi-insulating polycrystalline silicon (SIPOS), i.e., SiOx with 0≤x≤2 are studied in the spectral range from the infrared to the UV region. The refractive index n(x,E) and the absorption coefficient α(x,E) are evaluated as a function of the oxygen content x and the photon energy E. The actual shape of the n(x) and α(x) curves are determined by two counteracting effects: (1) the increase of n(x) and α(x) caused by the transition from c-Si to a-Si of the Si grains in SIPOS in the range 0.02≤x≤0.2, and (2) the decrease of n(x) and α(x) due to the increasing insulating character of SIPOS with increasing x. The infrared vibrational modes of bulk SIPOS are described on the basis of an oscillator model with effective parameters. Both, the vibrational frequencies ν˜1(x) of the asymmetrical stretching motion and the total oscillator strength S˜(x) increase with increasing x. While ν˜1(x) can be qualitatively described on the basis of a simple mixture model, this is neither the case for the shape of the frequency-dependent conductivity σ(ν˜,x) nor for S˜(x). Both, σ(ν˜,x) and S˜(x) depend sensitively on the real defect structure consisting of Si grains embedded in the oxide matrix consisting of SiO2, SiO, and other suboxides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353966
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  • 3
    Electronic Resource
    Electronic Resource
    Physical properties of semi-insulating polycrystalline silicon. I. Structure, electronic properties, and electrical conductivity (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7677-7689 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semi-insulating polycrystalline silicon (SIPOS) are thin SiOx films (0≤x≤2), deposited by means of low pressure chemical vapor deposition on suitable substrates (silicon or sapphire). Although SIPOS has important applications in the semiconductor and solar cell technology, its physical properties which depend strongly on the oxygen content x, are not well known. In the present contribution, SIPOS as deposited at 660 °C in the range 0≤x≤1 is investigated by using different and complementary methods, namely nuclear reaction analysis, secondary ion mass spectrometry, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and electrical conductivity measurements. On the basis of these experiments it is found that SIPOS consists of a nanometer-scale mixture containing Si, SiO2, and at least one suboxide (SiO1−Δ with Δ≈0.14). SIPOS with x≤0.034 is polycrystalline, while SIPOS with x≥0.4 is completely amorphous. In the range 0.034≤x≤0.4 there is a transition from crystalline Si grains to amorphous Si grains which is accompanied with a drastic decrease in grain size. The microstructure of SIPOS is consistent with a shell model, in which the Si grains are embedded in an amorphous oxide matrix consisting of SiO2 and SiO1−Δ. The latter oxide is located at the grain boundaries of the Si grains, i.e., it forms the transition oxide between the Si grains and the SiO2 matrix. Within the shell model, conduction proceeds by tunneling of thermally activated carriers through the oxide barriers separating adjacent grains. The model is able to qualitatively reproduce the observed low-bias conductivity σ(x,T) in the high-temperature regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353965
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  • 4
    Electronic Resource
    Electronic Resource
    Physical properties of semi-insulating polycrystalline silicon. III. Infrared diagnosis of the polycrystalline-Si/c-Si interface (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7701-7707 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to investigate the interface between polycrystalline-silicon (poly-Si) and crystalline silicon (c-Si), which is of crucial importance for the passivation of high-voltage devices, an infrared diagnostic method has been developed which is based on a modified attenuated total reflection configuration. This interface is shown to consist of silicon oxides (mainly SiO2) in the monolayer range with a thickness of 7±2 A(ring). The interpretation of the experimental results is based on a direct comparison of the infrared reflectivity spectrum of the interface to be studied with that of a reference sample containing a 100-A(ring) thick SiO2 interface layer, as well as on extensive computer calculations. Such calculations have been performed for a three-layer system as well as for a simplified system consisting of a single absorbing layer sandwiched between two transparent half-spaces. The latter system can be solved analytically and provides detailed insight into the physics of the interaction of light with the vibrational excitations of the interface layer. The existence and properties of such a silicon oxide interface layer are compatible with our secondary ion mass spectrometry experiments (oxygen segregation at the interface) and its thickness is in excellent agreement with the thickness of the amorphous interface layer observed by transmission electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353967
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  • 5
    Electronic Resource
    Electronic Resource
    Electrical activity of aluminum implanted in silicon: An interface problem in high-power devices (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2226-2234 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Because of its high diffusivity in silicon, aluminum is best suited for deep diffusions often required in high-voltage-power semiconductor devices. The ion implantation technique allows the reproducible low dosage doping necessary, e.g., for the new concepts of junction termination systems. The most important drawback of using aluminum as a p-type dopant in silicon is its low electrical activity after the anneal. In order to obtain a deeper insight into the mechanisms responsible for the loss of the electrical activity, we have studied the states of aluminum implanted into silicon before and after annealing by means of spreading resistance, secondary-ion mass spectroscopy, transmission electron microscopy, and energy-dispersive x-ray techniques. The case study presented here [Czochralski grown (100) silicon, implanted dose 3×1015 cm−2, junction depth 6 μm] reveals that the major source for the loss of the electrical activity is out-diffusion, i.e., segregation into the native silicon oxide layer and/or evaporation into the vacuum. In addition, the activity is reduced by the formation of aluminum oxide precipitates. The results are discussed in the light of optical studies on the same materials performed previously as well as on the basis of a diffusion model which allows for out-diffusion. The large rate constant for out-diffusion indicates that the native oxide layer represents a highly reactive surface for aluminum. From the diffusion model it is possible to calculate an approximate electrical activity A˜(xj) as a function of junction depth xj, which qualitatively reproduces well the observed activity A(xj). This demonstrates that our case study is representative for a large number of samples which were implanted and annealed under widely different conditions. Some technical processes which could possibly enhance the electrical activity are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346526
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  • 6
    Electronic Resource
    Electronic Resource
    Optical properties of aluminum-implanted and annealed silicon (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2074-2080 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The main problem associated with the use of aluminum as a p-type dopant in silicon power devices is its low electrical activity in silicon after the anneal process. In order to obtain a deeper insight into the possible mechanisms responsible for the loss of electrical activity, it is necessary to study three different states of the p-n junction fabrication: (1) the unimplanted starting or reference material; (2) the aluminum-implanted material; and (3) the implanted and annealed material. In this paper we present a detailed analysis of reflectivity and transmission measurements of the three different states extending from the far-infrared to the UV region, as well as depth profiles of the reflectivity from as-implanted and bevelled samples. From these investigations we have obtained information about two important aspects, namely lattice damage and free-carrier properties. The refractive index across the implanted layer is essentially constant and considerably larger than that of the crystalline state; together with recent transmission electron microscopy studies it is suggested that this change in refractive index is due to the formation of broken or weakened bonds. In the annealed state those defects induced by implantation which produce a change of the optical properties are healed out to a high degree. From the free-carrier absorption observed in the far-infrared direct information is obtained about the electrical properties, i.e., the mean concentration and mobility of the holes associated with the electrically active aluminum atoms in the thin p-type layer produced by annealing. We obtain an electrical activity (percentage of electrically active Al atoms) of 17%. This result is discussed and compared with recent sheet resistance-, spreading resistance-, and secondary-ion mass spectrometry data obtained from the same sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345595
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamics of atoms in the high-temperature superconductor YBa2Cu3O7−δ (1988)
    Springer
    The European physical journal 70 (1988), S. 1-8 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In order to obtain insight into the role played by the phonons in the superconducting phase transition, we have performed infrared reflectivity and inelastic neutron scattering experiments on single phase YBa2Cu3O7−δ(δ≊0.1,T c =94 K, ΔT 10–90=1 K). These experimental results, together with published Raman scattering and specific heat data are used to determine the parameters of a rigid-ion model; the model is able to reproduce qualitatively the experimental data. On the basis of our model we derive and discuss the phonon density of states and the pattern of atomic displacements of some important vibrational modes. In particular, the model reveals the existence of high-frequency oxygen breathing modes and of low-frequency copper dimerization modes in both the CuO3-chains and the CuO2-planes. Furthermore, Jahn-Teller like oxygen modes exist in the chains. The possible role of these modes with respect to the pairing mechanism is discussed. In addition there exist low-frequency “chain-degrading” modes which favour jumps of oxygen atoms out of the CuO3-chains into neighbouring vacant sites in the basal plane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320530
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  • 8
    Electronic Resource
    Electronic Resource
    Three-dimensional antiferromagnetic ordering in the light rare-earth high-T c superconductor NdBa2Cu3O6.86 (1989)
    Springer
    The European physical journal 74 (1989), S. 183-189 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Powder neutron diffraction investigations performed in the temperature range from 20 mK to 300K prove that the magnetic Nd moments of the superconductor NdBa2Cu3O6.86 withT c=88 K order three-dimensionally (3D) antiferromagnetic belowT N=(551±10) mK. As in similar Gd and Dy compounds the corresponding wave vector isk=[1/2, 1/2, 1/2]. In approximate agreement with crystal field calculations the ordered magnetic moment of Nd amounts at saturation to (1.14±0.06) μ B and at 25 mK the magnetic moments are oriented parallel [0,0,1]. The transition to the magnetically ordered state corresponds to the Landau type critical exponent β≈0.5, in contrast to the predominant 2D character of such heavy rare-earth systems. The crystal structure of NdBa2Cu3O6.86 is orthorhombic similar to the one of YBa2Cu3O7−x.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307384
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  • 9
    Electronic Resource
    Electronic Resource
    Electrical and infrared dielectrical properties of silica aerogels and of silica-aerogel-based composites (1993)
    Springer
    Applied physics 57 (1993), S. 329-337 
    Details
    ISSN: 1432-0630
    Keywords: 72.20.Ht ; 72.80.Sk ; 78.30.Ly
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract In this contribution we have studied the key electrical parameters of silica aerogels and of silica-aerogel-based composites, namely the dielectric constants ɛ, the dielectric losses tan δ (at 1 kHz), and the breakdown fields E b (at 50 Hz). For low-density bulk silica aerogels we find ɛ=1.25 and tan δ=0.0005. E b is about 500 kV/cm in quasi-homogeneous fields, and of the order of MV/cm in strongly inhomogeneous fields. The dielectric constants of partially densified aerogels increase linearly with density; their dielectric losses are relatively large and their breakdown fields are comparativiely low. The same results are found for aerogels in the form of settled materials, i.e. aerogel granules and powders in air. Acrylate-based aerogel composites with volume fractions larger than 70% have low dielectric constants but their losses are at least 10 times higher than those of low-density aerogels. These materials sustain high local fields in the MV/cm region, while in quasihomogeneous fields, breakdown occurs at about 100 kV/cm. Based on the present results and the interplay with other physical properties (low mechanical resistance, low thermal conductivity, adsorption of water, etc.), silica aerogels and silica aerogel-acrylate-based composites are predicted to have a low potential for electrical insulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00332286
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  • 10
    Electronic Resource
    Electronic Resource
    Corrosion of stainless steels in chloride solution: An XPS investigation of passive films (1985)
    Springer
    Applied physics 38 (1985), S. 1-18 
    Details
    ISSN: 1432-0630
    Keywords: 68.45.v ; 81.60.Bn
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Five commercial steels ranging from the martensitic stainless steel containing 12% chromium to the superferrite containing 29% chromium, 4% molybdenum, and 2% nickel have been studied by XPS. In addition, a pure iron-chromium alloy containing 7% chromium has been investigated. Armco iron and pure chromium (99.99%) were included as references. The formation of the passive films (or corrosion) occurred in deoxygenated 0.1 M NaCl solution (pH=5.6), from which the samples were transferred directly to the XPS chamber under controlled atmosphere (Ar). Concentration profiles (at.-%) of the alloy constituents in their oxidized and metallic states have been determined separately from the measured XPS depth profiles. Forc≳= 12% chromium the passive films have the following structure: there is a depletion of Cr in the inner region, followed by an enrichment (concentration maximum) in the central region of the films. The height of this maximum increases, and its position shifts towards the surface with increasing chromium content in the alloy. The outermost monolayers are rich in water and hydroxyl groups. Various significant properties of the films change drastically at the critical chromium concentration of about 12%. This behaviour is rather independent of the other components (Mo, Ni, Cu) present in the alloys and is discussed in terms of a phase transition in the films which is controlled by the chromium concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618720
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