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  • American Institute of Physics (AIP)  (13.800)
  • 2015-2019
  • 1985-1989  (13.800)
  • 1988  (7.806)
  • 1987  (5.994)
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  • 2015-2019
  • 1985-1989  (13.800)
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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4243-4244 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is pointed out that it is inappropriate to use the third-derivative functional form derived by Aspnes [Surf. Sci. 37, 418 (1973)] to fit the photoreflectance data of GaAs at the fundamental absorption edge when the low-field condition is not satisfied. Instead, the Franz–Keldysh oscillations can be used to determine the carrier concentration of the material.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4241-4243 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: ZnSe epitaxial layers were successfully grown on (111) Si substrates by low-pressure metalorganic chemical vapor deposition. It is not necessary that the reactant inlet tubes project to near the substrates. From x-ray and scanning electron microscopy examinations, single-crystalline ZnSe epilayers with mirrorlike surfaces can be obtained. The carrier concentration profile shows that the carrier distribution in the epilayer is very uniform. The electron mobility of the epilayer at room temperature is 280 cm2 /V s. The efficient 77-K photoluminescence indicates that the ZnSe epilayers are of good quality.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4244-4245 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Compliance to the low electric field regime necessary for application of the third derivative functional form formalism is demonstrated for ion-implanted samples used to determine the doping level by photoreflectance spectroscopy. Due to field and doping inhomogeneity, the proper line shape is speculated to be described by a superposition of Franz–Keldysh oscillations.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4245-4247 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Neutron irradiation induced degradation in the responsivity of Si and Ge p-i-n photodetectors has been studied. The responsivity of an irradiated photodetector normalized to its preirradiation responsivity was found to have a spectral dependence in the case of the Si photodetector. In the case of the Ge photodetector, the relative responsivity was found to be independent of wavelength in the most part of the spectrum covered in the experiment.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4257-4257 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4251-4253 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Small silicon-stabilized amorphous iron particles in a silica matrix have been produced by cosputtering under conditions that apparently disturb the Si:O stoichiometry obtained from the SiO2 source. The amorphous iron particles can be converted to α-Fe by annealing in vacuum at high temperatures. As-deposited films with iron volume fractions around 45% have small coercive force and exhibit a magnetic switching phenomena.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4253-4256 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We show that measurements of minority-carrier lifetimes in thin layer (Al,Ga)As double heterostructures grown by organometallic vapor-phase epitaxy can be severely influenced by modulation doping of the layer studied. Samples where this effect has been eliminated exhibit a dominantly nonradiative luminescence decay, from which we deduce an interface recombination velocity of only 18 cm s−1, which is among the lowest ever reported for a GaAs/(Al,Ga)As interface.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4248-4250 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We propose and demonstrate an odd-harmonic resistive multiplier that exploits the unique current-voltage (I-V) relation of resonant-tunneling diodes. It is shown that efficient odd-harmonic conversion is possible and that even harmonics do not appear because of the antisymmetry of the I-V curve. In addition, with the proper choice of resonant-tunneling structure and pump amplitude, most of the harmonic output power can be confined to a single, odd-harmonic frequency. Fifth-harmonic multiplication has been demonstrated with output at 21.75 GHz and a power conversion efficiency of 0.5% in a coaxial circuit. Circuit simulation using an improved I-V curve yields a fifth-harmonic efficiency of 2.7%, suggesting that useful harmonic output in the millimeter and submillimeter spectrum should be achievable.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3341-3344 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The range profile of Hg+ implanted at energies from 50 to 400 keV in glass was measured by 4He+ Rutherford backscattering. The measured projected ranges are in good agreement with those predicted by the Biersack model. A marked improvement in the range straggling fit is obtained after considering the second-order energy loss.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3345-3352 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Doppler shifts and widths of strong spectral lines have been measured on JET (Joint European Torus) both in the x-ray (resonance line of He-like Ni xxvii at 1.5886 A(ring)) and in the XUV region (several Ni, C, and He ion lines are available between 100 and 330 A(ring)). Time-resolved measurements of impurity ion temperature Tz and plasma toroidal angular velocity ω are presented. Radial profiles of both Tz and ω are inferred in combination with numerical simulations obtained using an impurity transport code, which allows radial localization of the emitting shells.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3398-3401 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Finite element techniques are used to calculate the thermal stresses generated in single-layer, optical storage thin films. The calculations predict that the thermal stresses generated by laser heating may reach values well beyond the strength of the media in times much less than that for pit formation by melting. Both dye-polymer and metal-based systems are considered with either air or substrate incident laser sources.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3402-3406 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A maskless etch process for diffraction gratings in n-InP is described in detail which permits simple and reliable large-area fabrication of gratings for distributed feedback (DFB) or Bragg-reflector (DBR) lasers. With respect to processes reported earlier the exposure and etching times are reduced by an order of magnitude without sacrificing resolution, modulation depth, or surface morphology. In accordance with the recently published diffusion theory for minority-carriers generated under holographic illumination, a high etch rate is found to be advantageous with respect to high spatial resolution. In addition, however, the results demonstrate that the chemical stability of the In-rich (211) and (111) planes as against the (100) surface is of final importance for obtaining good first-order DFB gratings.
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  • 13
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3407-3410 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Optical constants (3000–8000 A(ring)) and layer thicknesses of TiO2/Ag/TiO2 optical coatings are determined using variable angle of incidence spectroscopic ellipsometry. Ellipsometrically determined silver layer thicknesses agree well with those obtained by cross-sectional transmission electron microscopy. Also, spectral characteristics, absent in bulk silver data, are observed in n and k spectra for the thin silver layers. It is suggested that these structures may be caused by plasmon effects from the silver layers.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3411-3418 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Selected experimental results are presented from an extensive experimental investigation of dc prebreakdown and breakdown processes in vacuum along solid insulators made of a variety of alumina ceramics and polymers. The investigations included measurements of predischarge current, x-ray intensity, insulator surface charge density, breakdown behavior as influenced by insulator surface characteristics and insulator profiles, and the analysis of the spectral characteristics associated with insulator surface luminescence. The prebreakdown and breakdown phenomena were found to be strongly influenced by surface microstructure and the chemical state of the insulator surface. The experimentally observed phenomena in our studies strongly point to a new breakdown model based on collision-ionization by electrons of defect sites and/or traps within the dielectric subsurface at the vacuum interface.
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  • 15
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3419-3423 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this paper we comment on recently reported experimental data about some characteristic magnitudes of plasma columns produced and maintained by surface microwaves. We then compare them with theoretical values obtained from the diffusion-recombination model of Mateev, Zhelyazkov, and Atanassov [J. Appl. Phys. 54, 3049 (1988)] and Zhelyazkov, Benova, and Atanassov [J. Appl. Phys. 59, 1466 (1986)] for the same magnitudes, in a wide range of operating conditions. Such a comparison allows us to make conclusions about the results of the model and its hypothesis.
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  • 16
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3461-3467 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The permeation of hydrogen, deuterium, and hydrogen-deuterium through iron coated with thin surface films of palladium has been measured. The experimental steady-state fluxes show the expected isotope diffusivity dependence in iron. A new observation is that hydrogen and deuterium react on the palladium surface to form HD, and this affects the permeation fluxes. The results are in good agreement with a model incorporating second-order surface kinetics which allow for competition between hydrogen and deuterium for surface sites. The theory predicts that the hydrogen/deuterium surface coverage ratio on palladium is ∼4 at room temperature for equal H2 and D2 pressures.
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  • 17
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3487-3491 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A series of Nb/Al multilayered samples made by a sputter-deposition or a cold-rolling technique was used to simulate reactions in powder metallurgy processed Nb/Al superconducting wires. The sequence of phase formation observed in the Nb/Al multilayered samples was explained using knowledge about the crystal structure of each compound. Three different controlling mechanisms were proposed: the activation energy for nucleation, the energy barrier associated with short range order, and the diffusion barrier by the previously formed phase layer.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3564-3569 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Numerical solution of the time-dependent Schrödinger equation for resonant-tunneling diodes has been impeded by the difficulty in handling open-system boundary conditions. This paper presents a boundary condition method to simulate the interaction with ideal particle reservoirs at the device boundaries. A switching transient is calculated where the device is switched from the peak current state to the valley current state. In addition, this method was used to develop a small-signal analysis of resonant-tunneling diodes. Results for the small-signal equivalent circuit of a particular device versus frequency are presented.
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  • 19
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3574-3580 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A study of electrical transport properties in MoSi2 thin films revealed a large resistivity difference of 57 vs 157 μΩ cm at room temperature between films formed from a codeposited Mo/Si structure and layers formed by reaction of deposited Mo with Si. The resistivity difference was found to be temperature independent. The Hall effect in the films formed from deposited Mo was a factor of four larger than in films formed from a codeposited alloy. The temperature dependencies of the Hall effect were also found to be different. Analyses of the films by Rutherford backscattering and transmission electron microscopy revealed no significant differences in thickness or grain size of the layers. The only microstructural difference is the stacking fault density, which is very high in the high-ohmic films. The mechanism by which the stacking faults influence the electrical properties of MoSi2 and other refractory metal silicides is discussed, and relations are established between the method of deposition, the microstructure of the films, and the electrical transport properties.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3589-3592 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The measurements of x-ray diffraction, the temperature dependence of the dc resistance and the ac susceptibility have been performed for the single-phase 3D-metal doping systems YBa2 Cu3−x Mx Oy (M=Fe, Co, and Ni; x=0.025, 0.05, 0.075, 0.10, 0.25, and 0.50 for Ni and Co and 0.05, 0.075, 0.10, 0.15, and 0.20 for Fe). With an increase of impurity content, two structural transitions were observed for the Co and Fe dopants but only one for the Ni dopant. The resistivity in the normal state changes from metallic to semiconductinglike behavior and the depression of Tc is linear with the impurity concentration (x) when x〈0.10. A weak Curie–Weiss type paramagnetism, which is enhanced with impurity content, exists in the samples studied. Incorporating other work on oxygen defects, we suggest that a change of oxygen content induced by doping was the dominant effect on superconductivity in these samples.
    Materialart: Digitale Medien
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  • 21
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3598-3601 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report Raman scattering and resistance measurements on a YBa2Cu3O7−δ film in which δ is varied by repeated annealing in oxygen or argon. As oxygen is removed, the resistance rises, the transition moves to lower temperature and broadens, and "forbidden'' Raman modes are observed. Group theory, the Raman activity of another oxygen rich (δ∼0) film of different orientation, and comparison with results on single crystals allow us to assign each Raman phonon. We hence demonstrate that several "forbidden'' Raman peaks are associated with depletion of oxygen chain sites. Our results establish that the oxygen concentration δ, and hence the superconducting properties, can be varied reversibly by reannealing in oxygen or argon with the Raman spectra providing a useful microscopic probe of the lattice.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3610-3613 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: At the boundary of a ferromagnetic material, the local change in the surroundings of the atomic magnetic moments induces an additional magnetic anisotropy. The dipole-dipole interaction, responsible for the form-dependent demagnetizing field inside the ferromagnet, differs for magnetic moments at the boundary and magnetic moments inside the bulk material. By calculation it is shown that the demagnetization factor for an ultrathin ferromagnetic film is thickness dependent. However, the anisotropy resulting from the dipole-dipole interaction can be interpreted as a surface and a volume anisotropy which depend on the crystalline structure and orientation of the film, but are independent of the thickness of the film.
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  • 23
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3620-3628 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: This paper presents results on the magnetic properties of NiCu and NiCo alloys with compositions in the range 70%–100% Ni. Measurements include coercivity initial susceptibility, maximum differential susceptibility, magnetostriction, and Barkhausen effect emissions. Results revealed a surprising increase in the magnetostriction as a function of magnetic induction B as the copper content increased. The saturation magnetostriction λs was nevertheless found to decrease with copper content. The addition of cobalt reduced the magnitude of the magnetostriction resulting in a change of sign from negative to positive at between 20% and 30% cobalt. Coercivity was found to be little affected by elastic stress, but strongly affected by plastic deformation such as occurs, for example, in cold working. A similar result was true for initial susceptibility. Maximum differential susceptibility was, however, found to be strongly dependent on elastic stress. Results were interpreted in terms of stress induced uniaxial anisotropy. As the tensile stress increased the magnetization became more reversible, but the susceptibility decreased.
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  • 24
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3637-3640 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this work experimental results in infrared absorption at low temperatures on the layered compounds of the MPX3 (M=Fe,Ni and X=S,Se) family are reported. The absorption spectra in the far infrared (between 50 and 500 cm−1) recorded on thin slabs of these compounds (10 μm thick) are compared with the corresponding Raman spectra and this comparison confirms the hypothesis of the phonon branches folding in the antiferromagnetic phase of FePS3 below the Néel transition at 118 K. In the midinfrared (between 700 and 4000 cm−1), broad bands have been observed at low temperatures for the iron phosphorus trichalcogenide compounds. These absorption bands are attributed to electronic transitions for both FePS3 and FePSe3 lamellars, which are mainly due to the splitting of the 3d-metal levels by the pseudooctahedral field created by the nearest-neighbor sulfur atoms.
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  • 25
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3641-3646 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Absorptive optical nonlinearity in InP doping superlattices grown by vapor-phase epitaxy is investigated in a 2–300 K temperature range. The absorption spectra have tails below InP band-gap energy, caused by the Franz–Keldysh effect due to the internal electric field. The absorption tail is almost temperature independent. This means that the periodic electric potential in the doping superlattice, responsible for the nonlinearity, is unchanged across this temperature range. Nonlinear absorption is evaluated by the pump-probe method. The large reduction in absorption coefficient is obtained even with a weak excitation light intensity. This enhancement in nonlinearity is due to prolongation of the excited-carrier lifetime. Nonlinear absorption increases as temperature decreases. This is due to the temperature dependence of the carrier lifetime.
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  • 26
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4364-4374 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An electrical breakdown on a highly charged dielectric surface can result in a discharge along the surface, i.e., a flashover arc. We construct a simple circuit model for such an arc: the discharge of a capacitor C (related to the initial charged area) through a series inductor L and resistor R (related to the arc considered as a plasma). The arc current assumes a very simple form over most of its dynamic range, and such measured arc quantities as total charge transport, pulse width, peak current, and rise time are easily calculated. Moreover, straightforward a priori estimates of C, L, and R values give calculated arc quantities in good agreement with observation, for both typical magnitudes and areal scaling. We also analyze the effect on areal scaling of allowing the arc resistance R to "switch'' during the evolution of the arc, from a small value characteristic of the arc plasma to a large value characteristic of the dielectric surface. Finally, we consider some aspects of the electromagnetic radiation generated by the arc.
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  • 27
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4375-4383 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Fermi acceleration is considered as an underlying mechanism for electron heating in rf discharges, in which the heating arises from the reflection of electrons from moving sheaths. By examining the dynamics of the electron collisions with the sheaths, the map that describes the electron motion is derived. For high-frequency discharges (ω/2π〉50 MHz), the electron motion is shown to be stochastic. By combining these dynamics with collisional effects in the bulk plasma and incorporating self-consistent physical constraints, a self-consistent model of the discharge is developed. The model is used to calculate physically interesting quantities, such as the electron temperature and average lifetime, and to predict the minimum pressure necessary to sustain the plasma. The distribution of electron energies is shown to be non-Maxwellian. These results can be applied to experimentally interesting parallel-plate rf plasma discharges to predict the operating conditions necessary for stochastic heating to occur.
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  • 28
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4398-4403 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The behavior of electron-cyclotron resonant (ECR) and non-ECR H2 plasmas generated in a microwave plasma chemical-vapor deposition reactor have been studied as a function of magnetic field strength and absorbed microwave power. Plasma diagnostics were performed with a planar electrostatic probe, microwave power measurements, and visual inspection. The probe measurements were concerned with the plasma impingent on a sample table placed downstream from the active core of the plasma. ECR plasmas were found to be more efficient, stable, uniform, and dense than plasmas not generated by ECR. All properties of the ECR plasmas measured by the downstream probe showed a gentle monotonic increase with the magnetic field strength. This was attributed to a reduction in the spacing between the probe and the resonant zone. In the ECR plasmas the average electron temperature was 3 eV and the average density was 1016 m−3. The degree of ionization was on the order of 5×10−4.
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  • 29
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4415-4423 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Cross-sectional high-resolution transmission electron microscopy and related diffraction techniques are applied to the characterization of argon implantation-induced amorphization of silicon at room temperature. Damage calculations have been performed to provide a theoretical support for the cross-sectional transmission electron microscopy observations. It is shown that the amorphous-crystalline interfacial roughness is strongly dependent on ion dose and hence on its depth location. The a-c transition region was found to have sharply defined boundaries and sometimes exhibits defects such as dislocations and stacking-fault nuclei. Combining the experimental measurement of the extension of the a layer for increasing dose, with concepts arising from the "critical damage energy density'' model leads to a value of about 10 eV/atom for the c→a transformation. It is suggested that temperature effects are responsible for the observation that higher damage energy densities are apparently needed to produce a first continuous a layer than to extend this layer to greater depth.
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  • 30
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2833-2837 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Calculations show that even a modest-sized laboratory rotor can exhibit stability comparable to that of good frequency standards if it is sufficiently undisturbed and if its moment of inertia is constant enough. Further, they show that electronic cooling, by derivative feedback, can cause these properties to be exhibited in much more useful regimes of time and frequency. This paper describes theoretical and experimental efforts to evaluate the effects of such feedback on a practical rotor, presently far from ideal. The stability measurements are presented in the context of averaging or observing times and are given as Allan variances. Representative results for a small (few centimeters) rotor with a magnetic suspension bearing show noise 4–5 orders of magnitude above the ideal, i.e., noise caused only by molecular bombardment. These analyses are in the region of averaging times from 10 to 100 000 s, and the measurements were in a laboratory in which the temperature fluctuates a few degrees Centigrade. Measured and calculated transfer functions from temperature variations show that a significant part of the excess noise is caused by these variations. Electronic cooling by feedback behaves as expected in modifying the noise spectrum. The changes in the excess noise are the same as those calculated for molecular bombardment noise, thus indicating that the excess noise comes from frequency-independent driving torques.
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  • 31
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2854-2860 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Data are presented on the thermal characteristics of p-n AlxGa1−xAs-GaAs quantum well heterostructure (QWH) diode lasers grown on Si substrates. Continuous 300-K operation for over 10 h is demonstrated for lasers mounted with the junction side away from the heat sink ("junction-up'') and the heat dissipated through the Si substrate. "Junction-up'' diodes that are grown on Si substrates have measured thermal impedances that are 38% lower than those grown on GaAs substrates, with further reductions possible. Thermal impedance data on "junction-down'' diodes are presented for comparison. Measured values are consistent with calculated values for these structures. Low sensitivity of the lasing threshold current to temperature is also observed, as is typical for QWH lasers, with T0 values as high as 338 °C.
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  • 32
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4509-4515 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thin low-temperature heteroepitaxial film growth of Si on sapphire (SOS) was investigated by using the reactive ion beam deposition method proposed recently. This method uses low-energy controlled ionized species produced from reactive SiH4 gas plasma. By accommodating the ion energy to two film growth stages, i.e., an initial heteroepitaxial growth stage followed by a homoepitaxial growth stage, thin SOS films about 200 nm in thickness with no superficial microtwins can be grown at the low temperature of 600 °C. The energy level is adjusted to 300 eV in the initial heteroepitaxial film growth stage (about 50 nm in thickness), and then to 100 eV until the total film thickness is about 200 nm.
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  • 33
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4574-4579 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Semi-insulating In0.53Ga0.47As with carrier concentration n=1.2×1012 cm−3, resistivity up to 1090 Ω cm, and mobility up to 9500 cm2/V s at 300 K is grown by liquid-phase epitaxy and doping with Fe. The influence of Fe doping on the photoluminescence of In0.53Ga0.47As is systematically investigated. An acceptor level at Ev+150 meV, tentatively assigned to Fe by some of us earlier, is definitively identified as an Fe-related complex. This acceptor level, however, is not responsible for the semi-insulating behavior of In0.53Ga0.47As as shown by statistical calculations. High-resolution deep-level transient spectroscopy experiments show two deep acceptors at EC−ET=0.44 and 0.30 eV, respectively. The first one, which dominates, is identified as being caused by the Fe3+/Fe2+ acceptor level. The second, somewhat weaker one, might be caused by the O-related trap recently discovered by Loualiche et al. [Appl. Phys. Lett. 51, 1361 (1987).] Combining the Fe acceptor energy position in In0.53Ga0.47As with its known value in InP and the known conduction-band discontinuity of the InP/In0.53Ga0.47As heterointerface we find that the vacuum referred binding energy model is approximately but not strictly valid. In this model the transition-metal impurity levels are aligned with respect to the vacuum level across interfaces regardless of the surrounding host crystal environment.
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  • 34
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2995-3004 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Vapor-grown carbon fibers possessing a high degree of preferential orientation have been prepared using either a catalyzed substrate or a fluidized catalytic method, yielding fibers with diameters of about 10 and 1 μm, respectively. After heat treatment at 2600–2960 °C, the fibers were used as a host material for bromine intercalation to yield highly conductive filaments. Intercalation was carried out at room temperature by direct immersion into liquid bromine. Through bromination, the room-temperature electrical conductivity of these fibers measured under ambient conditions increased by a factor of about 6 relative to their pristine state. Typical values for the resistivity of the brominated fibers are ∼10 μΩ cm. Of particular importance is the stability of these brominated fibers under ambient conditions; the fibers showed less than a 3% increase in resistivity after 1 month of exposure to air. The fibers also displayed a high degree of thermal stability up to 500 °C, which was established by measuring the change in resistivity and the weight loss with increasing temperature. Whereas the thick fibers prepared by the substrate method showed a high degree of staging structure, the thin fibers prepared by the fluidized seeding method did not show significant staging fidelity, based on x-ray, Raman, and TEM observations. Nevertheless, the increase in conductivity observed for the thin fibers is almost as large as for the thick fibers. The fiber preparation and intercalation method used in this work, as well as the chemical and thermal stability that has been achieved, offer attractive possibilities for practical applications of these materials in light weight, highly conducting composites.
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  • 35
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3024-3030 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report on an x-ray diffraction study of GaAs/GaAs1−xSbx superlattices grown by molecular-beam epitaxy on miscut GaAs (100) substrates. The fundamental reflections of the superlattice lie on a reciprocal lattice rod which is tilted with respect to the reciprocal lattice rod of the substrate. The satellite reflection, in turn, lies on lines making a constant angle with the reciprocal lattice rod containing the fundamental reflections. This result is attributed to a terraced superlattice which, in addition, is tilted with respect to the substrate. We describe a model which approximates the misfit strain imposed on the superlattice at the interfacial step, and which is capable of relating the average tilt angle to the misfit strain. The same model can also explain the transverse broadenings observed for the superlattice peaks.
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  • 36
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3043-3050 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A model, based on energy considerations, to determine the critical thickness for pseudomorphic growth of Si/Ge alloys and superlattices is introduced. Comparison with experiments shows a good agreement between the theory and experiment. It is also shown that in films which are initially dislocation-free, the energy barrier for the nucleation of dislocation loops can be crossed by thermal activation if the film is thicker than the critical value provided by the model.
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  • 37
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3067-3071 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using a Raman microscope we have studied Raman scattering from plasmon-LO-phonon coupled modes in the cross section of GaP diodes. The line shape analysis of the coupled mode has provided the thermal-equilibrium carrier concentration and mobility. Their distribution is determined from the spatial variation of the spectra. The carrier distribution thus obtained is consistent with that estimated from capacitance measurements. The result demonstrates that the Raman microprobe is a powerful method for determining the distribution of the carrier concentration and mobility in semiconductor devices without electric measurements using electrodes.
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  • 38
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4640-4645 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It has been shown theoretically as well as experimentally that microwalls with linear dimensions of the order of 10−6–10−8 m can be nucleated in KNbO3 single crystals under the influence of the electric dc fields applied externally at the sites of the impurity ions. The critical field for nucleation is found to be about 8×103 V m−1. Since such low fields already exist in crystals at the nonferroelectric to ferroelectric phase transition, the mechanism is expected to be operative at that time, and a photographic evidence of it is also obtained. A model has been developed to explain the nucleation. Employing thermodynamic considerations, expressions have been derived for the critical length of the domain wall nucleated, and the activation energy of nucleation, both for 60° and 90° walls. The photomicrographs obtained after applying the dc fields show microwalls nucleated at the impurity sites, with their linear dimensions of the order given by the theory. Many other aspects of the domain wall nucleation have been made clear by the photomicrographs. Particularly, it has been found that the microwalls move after nucleation to lie linearly to reduce the strain energy of the crystal. The microwalls are not pinned at the impurities, and extend themselves so that they meet each other end to end, producing a continuous wall. It is possible to distinquish these microwalls from the microwalls nucleated by the dislocation loops. The expression for the activation energy of nucleation is also verified experimentally. It is suggested that the mechanism of domain wall nucleation can occur in other ferroelectric crystals also, and shown that the memory of domain walls, commonly observed in ferroelectrics, can be readily attributed to the impurity ions present in the crystals, and the phenomenon of domain wall nucleation operative at their sites.
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  • 39
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3201-3204 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Liquid-phase epitaxy has been used to grow four-layer GaAs/AlGaAs double heterostructures on Si substrates that had been precoated with GaAs by molecular-beam epitaxy and coating the remaining exposed parts of the Si wafer with SiO2. Direct growth of GaAs on Si by liquid-phase epitaxy is not feasible because of the dissolution of the Si substrate by the Ga melt. As with the other growth techniques, photoluminescence from the GaAs cap layer and electroluminescence from the 0.2-μm-thick GaAs active layer indicate the luminescence peaks are shifted to lower energy as a result of the tensile strain in the plane of the layers that is caused by the different thermal contraction of the GaAS and Si layers as the wafer is cooled from the growth temperature. Optically pumped stimulated emission is observed from the cap layer at 80 K. The efficiency of the electroluminescence from the active layer was low, indicating the p-n junction was displaced from the active layer due to the accidental excess doping resulting from a slight dissolution of the Si substrate in the Ga melt.
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  • 40
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3224-3228 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Amorphous Ni-Zr powders have been prepared by mechanical alloying from crystalline elemental powders. The glass-forming range has been determined by x-ray diffraction, differential scanning calorimetry and saturation magnetization measurements. From 27 to 83 at. % Ni the powders become amorphous. This shows that deep eutectics do not play any role, contrary to amorphization by melt spinning. Crystallization temperatures, crystallization enthalpies, and wave numbers Qp, obtained from x-ray diffraction investigations, are compared with the data received for rapidly quenched samples. In addition, the effect of the milling intensity on the glass formation has been studied for the first time. If the intensity is too high, crystalline intermetallic phases are formed. On the other hand, the powder needs an extended milling time to become completely amorphous if the milling intensity is too low. Conclusions on the actual temperature of the individual particle during mechanical alloying and on the glass-forming process are drawn from these results.
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  • 41
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3273-3276 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Single electromagnetic pulses propagating in a spatially modulated nonlinear dielectric are compressed temporally. The system discussed may generate very short, high-power electromagnetic pulses.
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  • 42
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4795-4795 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
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  • 43
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3299-3301 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The change of second-order Doppler shift with temperature in Mössbauer effect measurements was estimated by using the two-band model with two characteristic temperatures, θ1 and θ3, rather than the Debye model. The experimental results for Fe83B17, Fe80B20, and Fe80P20 amorphous alloys were in good agreement with the calculated ones. The isomer shift was also obtained and the bonding characteristics and s-electron density of the iron atoms in these substances were discussed.
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  • 44
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3309-3311 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Huge gain values (〉107) are evidenced in parametric amplification of infrared subpicosecond pulses using two successive organic N-(4-nitrophenyl)-L-prolinol crystals acting as parametric amplifiers. Temporal analysis of parametric emission in the first crystal is performed in the second one. Application to the detection of long-wavelength pulses (〉1.6 μm) is demonstrated with a high temporal resolution.
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  • 45
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3327-3329 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Thermochromic VO2−xFx thin films were prepared by reactive rf magnetron sputtering followed by annealing post-treatment. Electrical and optical properties were measured as a function of temperature. The transmittance and reflectance were essentially wavelength independent at 65 °C, i.e., at the metal-insulator transition.
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  • 46
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2279-2285 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: KDP, KD*P, and LiNbO3, three nonlinear optical materials that have been difficult to coat, are treated with polymeric surface layers. These layers hermetically seal the hygroscopic crystal surfaces. Their optical properties, thermal compatibility, high-power laser damage behavior, abrasive resistance, and suitability for overcoating with traditional, dielectric antireflection multilayers are reported.
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  • 47
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2291-2297 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A fast-beam deflection technique is used to investigate the transient behavior of a laser-induced surface plasma generated by CO2-laser pulses of 2-kW average power near an aluminum surface in various protective gas atmospheres, with a typical pulse energy of 3.3×10−2 J, a pulse repetition rate of 60 kHz, and an average peak power per pulse of 30 kW, corresponding to an intensiy of 6×1012 W/m2. As a laterally probing beam, a cw 10-W CO2 laser is used, whose beam is focused into a small volume in front of the surface. The electrons of the laser-induced plasma passing this volume diffract the cw CO2 laser beam, and the resulting beam deflection is determined by means of a partially absorbing CaF2 wedge in connection with a fast infrared detector. The evaluation of beam deflection 0.15 cm above the surface renders a maximum electro density of 2×1023 m−3 for a surrounding argon atmosphere and 0.7×1023 m−3 for pure helium. Additives of O2 reduce the attainable electron density even more. No plasma can be detected below a threshold of, say, 10 mJ energy per laser pulse. It is verified that high electron density as in the case of argon shields the surface against the incoming CO2 laser pulses so that material processing, such as welding, is rather poor. Better welding results are achieved in helium-oxygen mixtures.
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  • 48
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3845-3850 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: This paper describes the application of phase-amplitude imaging to the measurement of self-generated magnetic fields in laser-produced plasmas. The magnitude of the magnetic field is determined by polarimetry and the plasma density profile by interferometry. Both pieces of information are recorded on a single interferogram in a form that can be analyzed automatically using computer-based image processing. We describe a method for successfully determining the magnetic field profile in plasmas generated by 70-ps Nd laser pulses at high intensity on planar targets when plasma motion or turbulence introduces an additional difficulty by reducing the visibility of the fringes.
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  • 49
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3831-3844 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Controlled, ultrahigh axial magnetic fields have been produced and measured in a gas-puff Z pinch. A 0.5-MA, 2-cm-radius annular gas-puff Z pinch with a 3-min repetition rate was imploded radially onto an axial seed field, causing the field to compress. Axial magnetic field compressions up to 180 and peak magnetic fields up to 1.6 MG were measured. Faraday rotation of an Argon laser (5154 A(ring)) in a quartz fiber on-axis was the principal magnetic field diagnostic. Other diagnostics included a nitrogen laser interferometer, x-ray diodes, and magnetic field probes. The magnetic field compression results are consistent with simple snowplow and self-similar analytic models, which are presented here. Even small axial fields help stabilize the pinches, some of which exhibit several stable radial bounces during a current pulse. The method of compressing axial fields in a gas-puff Z pinch is extrapolable to the order of 100 MG. Scaling laws are presented. Potential applications of ultrahigh axial fields in Z pinches are discussed for x-ray lasers, inertial confinement fusion, gamma-ray generators, and atomic physics studies.
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  • 50
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3928-3933 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The growth and structure properties of Cd1−xFexTe thin films prepared by rf sputtering were studied. Films with thicknesses in the range 0.75–2.45 μm were grown onto Corning glass substrates at temperatures between 50 and 300 °C in an argon atmosphere at a pressure of 3 mTorr. The deposition rate was determined by film thickness profile analysis. Transmission electron microscopy and x-ray diffractometry techniques were used to evaluate the structure, grain size, and orientation of the films. These properties were found to be related to the substrate deposition temperature.
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  • 51
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4278-4284 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Uniform charged liquid-hydrogen drops are produced using the method of field injection electrostatic spraying. This method consists of forming a meniscus of liquid hydrogen at the end of a glass nozzle and injecting charge into the liquid using a sharp electrode raised to a high voltage. A small pressure drop across the nozzle results in a constant volume flow rate of liquid through the nozzle allowing a drop to form and drip off. As the amount of charge injection increases with the raised needle electrode voltage, the drop size decreases due to the increased electrostatic forces compensating for the surface tension forces. As a result, the drops drip off at an increased frequency. Eventually a charged jet forms which in turn breaks up into small uniform charged drops. A detailed description of the experimental apparatus is presented. Experimental results are presented and discussed.
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  • 52
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4031-4040 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A scanning minority-carrier transient spectroscopy with optical injection and full transient analysis is developed. The continuity equation is solved with adequate injection and boundary conditions in order to determine the optimum experimental conditions and the corresponding optimum spatial resolution. A numerical treatment is implemented which filters out the noise component of the transient, improving the sensitivity of the technique. It allows us to make a fit to the transient, to check its exponential character and to treat certain cases of nonexponential behavior. The technique is applied first to a step distribution of laser-induced defects and results can be obtained which are in good agreement with theoretical predictions. Finally, the gettering of gold to dislocations during a rapid thermal annealing is illustrated using this technique.
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  • 53
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4056-4064 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effects of valence-band mixing on the gain and on the refractive index change of the quantum-well laser and the effect of an applied electric field perpendicular to the quantum wells for gain switching are studied theoretically. Our calculations are based on the multiband effective-mass theory (k⋅p method) and the density-matrix formalism with the intraband relaxation taken into account. First, we calculate the nonparabolic valence-band structure by the finite difference method after making a unitary transformation of the Luttinger-Kohn Hamiltonian. The calculated gain for our model shows remarkable differences in both spectral shape and peak amplitude as compared with those for the conventional model of the parabolic valence band. The peak gain is reduced considerably and the gain spectrum is more symmetric in our model compared with that for the conventional model. The refractive index change shows a negative increment in the active region for both the TE and TM polarizations resulting in the antiguidance. However, the TM polarization shows more negative change which would result in the suppression of the TM modes as compared with the TE modes. As another example, the perpendicular electric field effects on the quantum-well laser with lateral current injection are also calculated. A red shift and a reduction of the gain spectrum are shown when an electric field is applied. This may have applications as a tunable and high-speed switching quantum-well laser.
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  • 54
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4065-4074 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: AlGaAs/InGaAs/GaAs heterojunction bipolar transistors (HBTs) with lattice-mismatched InGaAs bases have been studied for determining the effect of misfit defects on device performance. Defect structures were investigated using scanning cathodoluminescence and transmission electron microscopy. Misfit dislocations were found to form at the bottom interface between n-InGaAs and n-GaAs in the collector. Electrical properties of lattice-misfitted n-GaAs/n-InGaAs heterojunctions were studied using p+-GaAs/n-GaAs/n-InGaAs diode structures. Deep-level transient spectroscopy measurements revealed electron traps (Et=0.49–0.55 eV) and hole traps associated with the lattice-misfitted interface. Devices showed high dc current gains in spite of the presence of misfit dislocations. Poorer saturation of collector current was observed with increasing defect density. HBTS with lattice-mismatched InGaAs bases are considered to be relatively insensitive to the introduction of misfit dislocations in terms of dc characteristics.
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  • 55
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4082-4085 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Increasing the effective Schottky-barrier height of epitaxial CoSi2/Si(111) diodes by the use of thin, highly doped Si layers in close proximity to the metal-semiconductor interface has been studied. Intrinsic Si, Si doped by coevaporation of Ga, and epitaxial CoSi2 layers have all been grown in the same molecular-beam epitaxy system. Current-voltage and photoresponse characterization yield barrier heights ranging from 0.61 eV for a sample with no p+ layer to 0.89 eV for a sample with a 20-nm-thick p+ layer. These results are compared to theoretical values based on a one-dimensional solution of Poisson's equation under the depletion approximation.
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  • 56
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4075-4081 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The interrelationship between mechanical and electronic properties of crystalline semiconductors has been explored through indentation of doped single-crystal silicon. The indentations were etched and the damage that extended beyond the immediate contact zone has been measured as a function of isothermal temperature of the silicon during the indentation. The damage zone exhibited a maximum at 150 °C. The surface properties of the silicon have been modeled with a finite, fixed number of surface states which possess an energy within the band gap. The spatial extent (Debye length) of the space-charge region has been calculated as a function of temperature, doping level, surface state energy, and density. The temperature variation of the Debye length is similar to that of the experimentally measured damage zone size when the indentation load was 0.49 N; both range in the 10−6 m and exhibit a maximum with temperature. The model implies that the deformation mode of silicon may be additionally influenced by external applied voltages, suitable doping, and/or surface preparation.
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  • 57
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4086-4090 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A practical numerical method is presented for obtaining the scattering matrix for an electron at a junction between two regions having different confining potentials in the transverse direction. The scattering matrix should find general use in models describing electron transport in semiconductor microstructures whenever changes in channel dimensions or structure are important. As an illustrative example, the method is applied to electron transfer from a narrow channel into a wide contact including the effects of the contact potential.
    Materialart: Digitale Medien
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  • 58
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4091-4094 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The magnetron sputtering method has been used for fabricating YBa2Cu3O7−y superconducting thin films. Their critical current and superconducting phase with relation to temperature have been investigated. Experimental results show, for some samples, the proportionality between critical current Ic and temperature as (1−T/Tc)3/2 in the vicinity of Tc and the typical proximity tunneling effect. While at temperatures much lower than Tc, the current-temperature relation corresponds well with the Ambegaokar–Baratoff theory.
    Materialart: Digitale Medien
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  • 59
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4095-4102 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The high-Tc superconductor LaBa2Cu3Oy has been prepared under various conditions, and characterized by x-ray and neutron powder diffraction techniques, dc and ac magnetic susceptibility measurements, and dc resistivity measurement. It has been found that samples with excellent superconducting characteristics and also with good structural properties are obtained in a reproducible way if the following three procedures are performed: preheat treatment of La2O3 powders, sintering in N2, and low-temperature annealing in dried O2. Long-time annealing in undried O2 was sometimes found to degrade the grain boundaries and to lead to a lower zero-resistance temperature.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4103-4107 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The strong relaxation of the ac magnetic permeability, observed in amorphous ferromagnets at very short times after demagnetization, is studied under different experimental conditions. The behavior of the fast permeability relaxation with temperature, applied stress, and driving field frequency clearly shows that this effect has a predominant dissipative character, very different from the diffusive permeability aftereffect, ascribed instead to activated processes of directional ordering. Optical measurements of domain wall motion at the sample surface suggest that the dissipative relaxation of the permeability is to be ascribed to a progressive reduction in the number of the domain walls participating in the magnetization process.
    Materialart: Digitale Medien
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  • 61
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4108-4112 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: This paper presents an experimental investigation into the magnetic properties of Ni/Fe//SiO2 multilayer films. An increase in magnetic anisotropy and a decrease in hard-axis coercivity are observed with decreasing the Ni/Fe layer thickness in Ni/Fe//SiO2 multilayer films. By sandwiching thinner Ni/Fe and 5-nm SiO2 layers together, relative permeability is tremendously increased to a range of 3500–4500. This permeability improvement corresponds well to the minor loop in the M-H characteristics. The magnetic domain observation indicates that the domain structure is widely changed, and several 180° and reduced 90° walls exist in the pole tip of thin-film head patterns. The higher relative permeability of over 3000 and the higher saturation magnetization of 1.7 T are confirmed in the thickness range of 0.1–2.0 μm.
    Materialart: Digitale Medien
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  • 62
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4113-4122 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Transition-metal–magnesium (TM-Mg) thin films, Fe-Mg, Co-Mg, and Ni-Mg, with an artificially layered structure are formed by the magnetron sputtering method. TM and Mg grow epitaxially on the closest planes in films with a thicker Co layer than a Mg layer. Crystallographic structures of the films are the bcc with the 〈110〉 direction normal to the film plane for Fe-Mg films, the hcp with the 〈001〉 normal for Co-Mg films, and the fcc with the 〈111〉 normal for Ni-Mg films. The films, composed of a monatomic layer of Mg and then several atomic layers of TM in an alternating way, show a clearly separated spot pattern in the reflection high-energy electron diffraction analysis. The artificial superlattice structure of the films is thermally stable at temperatures up to 700 K. The films composed of a thicker TM layer than a Mg layer are ferromagnetic with an easy magnetization direction in the film plane. The magnetization of TM in all films is smaller than that of the bulk. The paramagnetism or the nonmagnetism is observed in the films composed of a thinner TM layer than a Mg layer. Small magnetization, i.e., paramagnetism or nonmagnetism, originates from decreases both in magnetization and in Curie temperature of the TM due to lattice deformation.
    Materialart: Digitale Medien
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  • 63
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4128-4134 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A new approach is described for the prediction of the optical properties of amorphous tetrahedrally bonded materials over the entire experimental energy range, in which a model of the imaginary part of the dielectric constant is assigned and the real part is obtained by the Kramers–Kronig transform. Tight-binding theory provides direct interpretation of the model parameters. The model provides good insight into the physics of the problem and a quantitative account of experimental data as well. Results are presented for Si, Ge, Si3N4, and GaAs.
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4123-4127 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Infrared intersubband absorption in modulation-doped MOVPE-grown AlxGa1−xAs/GaAs single-quantum wells have been studied by Fourier transform infrared spectroscopy. High signal to noise ratio was obtained by utilizing the multiple internal reflection (MIR) technique and a quantitative model of the absorption for this geometry was developed. Overlapping from multiphonon absorption was eliminated by using radiation polarized in two orthogonal directions and taking the difference between the resulting spectra, only one of them exhibiting the intersubband peak. The absorption wavelengths and intensities were fitted to theoretical expressions and the dimensions of the quantum wells were compared with independent determinations by photoluminescence, double crystal x-ray diffraction, and Hall-effect measurements. A narrow linewidth of about 6 meV was measured, corresponding to a 0.1-ps lifetime of electrons in the excited state.
    Materialart: Digitale Medien
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  • 65
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4562-4566 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a simple analytic model for calculating the trapped-charge density as a function of free-carrier concentration for realistic density-of-states distributions in hydrogenated amorphous silicon. This is necessary to understand the behavior of amorphous silicon devices as their characteristics are largely determined by the high concentration of charge trapped by the localized stages in the band gap. Such a model is useful as an aid in exploring the nature of the charge-trapping process and for the efficient numerical simulation of amorphous-silicon devices such as thin-film transistors.
    Materialart: Digitale Medien
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  • 66
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4135-4140 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Low-temperature photoluminescence (PL) spectra of Ga1−xInxAs/GaAs single heterostructures with 0.07≤x≤0.19 and thicknesses ranging from 10 nm to 5 μm have been analyzed to study strain relaxation. Two series of samples were grown simultaneously on GaAs substrates oriented exactly on (100) and misoriented by 2° towards 〈110〉. In both kinds of samples, the strain induced exciton shift decreases first slowly with increasing thickness and then drops abruptly. This variation is analyzed in terms of the equilibrium critical thickness where misfit dislocations are generated and the kinetics of these dislocations in the relaxation process. The decrease of the exciton energy shift is accompanied by a large reduction of the PL intensity and broadening of the emission. In thicker layers, however, the behavior of the two series of samples is strikingly different. While the layers grown on misoriented substrates have all the characteristics of high-quality unstrained crystals, those grown on (100) substrates have PL spectra dominated by a low-energy emission. These results show that the critical thickness for the generation of misfit dislocations is the same for layers grown on both kinds of substrates but that the relaxation process is different and results in inhomogeneous layers on (100) substrates.
    Materialart: Digitale Medien
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  • 67
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4150-4153 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ultraviolet photoelectron spectra have been measured for monomolecular films of perfluorinated carboxylic acids prepared by vacuum deposition. Their threshold ionization potentials were determined to be 8.5 eV and their work functions larger than those for other organic compounds. The escape depth of photoelectrons through the perfluorocarbon chain was evaluated at 2.3 nm. These results are interpreted in relation to the large electronegativity of constituent fluorine atoms.
    Materialart: Digitale Medien
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  • 68
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4144-4149 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The optical properties of reactively sputtered InN thin films were measured in the spectral region 2.5–5.5 eV using spectroscopic ellipsometry. The measured pseudodielectric function data of the InN films were found to vary with deposition power. The effective medium approximation theory, which describes a random aggregate microstructure, was able to relate the differences in the measured optical properties to the surface microroughness and porosity of the InN films. The relationship between microstructure and deposition power was subsequently verified by scanning electron microscopy. The analysis and electron microscopy indicate that the film deposited at 90 W was most representative of InN.
    Materialart: Digitale Medien
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  • 69
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4154-4160 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Undoped and boron-doped polycrystalline silicon films were prepared on a fused quartz at 500–840 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) from a SiH4+B2H6+H2 mixture, using the same fabrication system. The effects of plasma (rf power) supply on the structural and electrical properties were investigated. Below 700 °C, all films show a 〈110〉 preferential orientation (P.O.), increasing with an increase in rf power. Particularly between 650 and 700 °C, an extremely stronger 〈110〉 P.O. is found at a rf power 〉15 W. Above 730 °C, undoped LPCVD and PECVD films and boron-doped LPCVD films represent a nearly random orientation. On the other hand, for boron-doped PECVD films, a strong 〈111〉 texture is observed in the intermediate doping range. The 〈110〉 texture increasing with rf power in undoped PECVD films is interpreted as indicating enhanced nucleation at the surface in contact with the gas phase. The plasma supply also has essential effects for smoothing the surface and improving the boron-doping efficiency. The effects of plasma supply are discussed in terms of increased surface diffusion of adsorbates, sputtering effect, and a contribution of hydrogen covering the surface. PECVD films are more stable for foreign contamination after fabrication than LPCVD films.
    Materialart: Digitale Medien
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  • 70
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4161-4167 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The thermal reaction of sputtered platinum with silicon to form platinum silicide by rapid thermal processing (RTP) has been investigated. A platinum film of 800 A(ring) was sputter deposited on undoped single-crystal silicon substrates. A wide range of RTP cycles were used in N2 ambient to study the formation kinetics and determine the phase growth sequence. The composition, thickness, impurity content, platinum-silicon interface quality, grain size, and surface oxide of the Ptx Siy layer were characterized by Auger electron spectroscopy, transmission electron microscopy, and x-ray diffraction analysis. All the analysis techniques used were consistent in determining the platinum silicide system evolution. Initially, the reaction between platinum and silicon results in the formation of an intermediate phase of Pt2Si, the growth of which continues until the entire platinum film has been transformed into Pt2Si. Then the evolution of a final phase of PtSi starts at the Pt2 Si/Si interface and the reaction between Pt2 Si and Si proceeds towards the surface until the entire Pt2 Si is converted to PtSi film. No simultaneous presence of the three phases, Pt, Pt2Si, and PtSi, was observed in any sample studied. An enhanced diffusion coefficient of Pt through Pt2 Si was observed as a result of rapid thermal processing. It was determined that 1 A(ring) of Pt results in the formation of 1.9 A(ring) of PtSi and 1 A(ring) of Si results in 1.44 A(ring) of PtSi. This small rate of Si consumption is desirable for silicidation of shallow junctions formation. The resistivity of PtSi was determined to be in the range 31–38 μΩ cm which is similar to furnace annealed values. Reactive ion etching selectivity between silicon dioxide and PtSi was determined to be 33:1. The high etching selectivity combined with small Si consumption make PtSi a potential candidate for submicron applications.
    Materialart: Digitale Medien
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  • 71
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4175-4180 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The purpose of this paper is twofold. First, we report on the successful application of variable angle spectroscopic ellipsometry to quantitative thin-film hermeticity evaluation. Secondly, it is shown that under a variety of film preparations and moisture introduction conditions water penetrates only a very thin diamondlike carbon (DLC) top surface-roughness region. Thus DLC is an excellent candidate for use as protective coatings in adverse chemical and aqueous environments.
    Materialart: Digitale Medien
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  • 72
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4168-4174 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Amorphous silicon dioxide films were deposited from oxygen, disilane (Si2H6), and perfluorosilanes (Si2F6 or SiF4) by photochemical vapor deposition using a deuterium lamp at a substrate temperature of as low as 200 °C. It was found that by mixing Si2F6, defects such as H and OH in the films were effectively removed with an enhancement in the growth rate and a slight doping of fluorine into the films, while SiF4 had no effect except a little doping of fluorine. The generation and extinction of defects including H, OH, and SiSi were investigated quantitatively by measuring infrared spectra and vacuum ultraviolet absorptions at the optical band edge. The model on the deposition process was proposed that photodissociated F-containing radicals eliminate H and activate the growing surface, resulting in enhancing the deposition rate.
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  • 73
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4194-4198 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Electron-beam deposited films of phosphosilicate (PSG) have been investigated as dielectrics for the encapsulation of Si-implanted GaAs for the purpose of post-implant annealing. The processing parameters that were optimized included the thickness of PSG film, the substrate temperature, and the annealing time and temperature. PSG films deposited at temperatures ≥300 °C showed no signs of deterioration up to temperatures in excess of 900 °C for 30-min anneals carried out in a forming gas and/or nitrogen ambient. Depth profiles in excellent agreement with the Lindhard–Scharff–Schiott curves were obtained with 1000-A(ring)-thick films when annealed at 850 °C for 30 min. The diffusion coefficient of implanted silicon was found to be an order of magnitude smaller for the PSG films than that for the conventional plasma assisted chemical vapor deposited SiO2 films at 850 °C.
    Materialart: Digitale Medien
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  • 74
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4199-4207 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A generalized plasma etching model has been developed. The new model is a generalization of our previous model presented in a recent paper [E. Zawaideh and N. S. Kim, J. Appl. Phys. 62, 2498 (1987)]. The new model includes the effects of multi-ion and multineutral gas species. New generalized plasma transport equations are also introduced. These equations are derived for multi-ion species. No restrictions on the anisotropy of the ion distribution functions are imposed. The new generalized plasma transport equations are valid for collisional to weakly collisional plasma [λ/L≤0(1)], where λ is the ion mean free path and L is the smallest of the scale lengths of the gradient in the electric field or in the macroscopic plasma parameters. A new particle balance model has also been introduced which incorporates the effects of gas composition, gas flowrate, pumping rate, ion and neutral gas chemistry, and atomic reactions on the neutral gas and plasma parameters (e.g., densities and pressures of the various neutral gas and plasma species). As an example, silicon dioxide (SiO2) plasma etching using carbon tetrafluoride (CF4) gas is used to illustrate this new generalized model. The model has shown good agreement with the experimental etch rates of SiO2 for various plasma and reactor parameters (e.g., neutral gas pressure, CF4 flowrate, and rf power).
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  • 75
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4726-4732 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The complex wave number of magnetostatic waves propagating in multiple lossy ferrite layers is found by solving the dispersion equation using Davidenko's method. The real and imaginary parts of the wave number are used to obtain quantities representing the power of modes as function of distance traveled and time spent in the material. The loss does not change significantly the real part of the wave number. When all ferrite layers have the same magnetization, then the loss experienced by a mode after it has spent a given period of time in the film is unique, independent of the order of the mode or the film thickness or the ground plane distances. When the magnetization differs from layer to layer then the loss experienced by a mode after it has spent a given period of time in the film depends on the order of the mode and the loss of each ferrite layers. The loss experienced by a mode after it has traveled a given distance in the ferrite depends on the order of the mode, the film thickness and the ground plane distances.
    Materialart: Digitale Medien
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  • 76
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4760-4762 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Cermet thin-film resistors consisting of roughly 50-A(ring) Pt or Mo particles in Al2O3 at compositions just below the percolation transition provide a number of useful features for thermometry. These include: continuous sensitivity from at least 50 mK to 300 K, adjustable temperature dependence, low heat capacity, small size, excellent stability, and a saturable magnetoresistance. The fabrication, microstructure, and temperature dependence of the resistance and magnetoresistance of these materials are described. We find poor agreement with existing theories of conduction in granular materials.
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  • 77
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4770-4771 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The formation range and thermal stability of vapor-deposited, amorphous Ni1−xZrx thin films is studied and compared with previous results for melt-spun ribbons and also with a thermodynamic prediction. Crystallization temperature and glass transition temperature for films and ribbons turn out to be nearly the same; the glass formation range for films is larger than that for ribbons and agrees very well with the thermodynamic prediction.
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  • 78
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4777-4780 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Photoemission spectroscopy is used to study chemistry and band bending at the Ca-GaAs(110) interface as a function of metal coverage. An intermediate position of the Fermi level (EF ) resulting from the formation of adsorbate-induced states and native defects is found at low coverage at 0.75–0.9 eV above the top of the valence-band maximum (VBM). An additional abrupt shift of EF leading to a final position 0.55 eV above VBM takes place when metallicity develops in the overlayer. The results for this interface supports Schottky-barrier models based on gap states induced or modified by the metal.
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  • 79
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4787-4789 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A mathematical model and experimental procedure for extraction of the local parameters of localized defects in mixed crystals from alloy fluctuations is proposed. The general procedure is illustrated using isothermal capacitance transient measurements.
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  • 80
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4219-4222 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Light-induced defects in intrinsic hydrogenated amorphous silicon (a-Si:H) are found to have a large effect on the short wavelength quantum efficiencies (SWQE) of a-Si:H solar cell structures. The dependence of SWQE on cell structure thickness, volume absorbed bias illumination, and externally applied voltage has been studied. The results on thick cell structures ((approximately-greater-than)0.5 μm) can be explained by a simple model which yields light-induced defects with hole capture cross sections of about 10−11 –10−12 cm2 and densities consistent with other measurements.
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  • 81
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4223-4228 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A ZnO-based varistor composition has been found whose I-V characteristic is essentially unaffected by temperature (4.2–300 K) or intense magnetic fields at 4.2 K (up to 10 T). Electrical measurements are reported at various temperatures for current densities in the range 10−11–10−3 A/cm2 . Specific-heat and thermal conductivity data are reported at 1.7–300 K. The specific heat below 10 K and above 100 K is dominated by defect modes, and the data can be understood based on simple defect models. The thermal conductivity displays a broad maximum at about 80 K (0.65 W cm−1 K−1 ), and it is concluded that the defect modes do not carry heat. The small temperature dependence of the prebreakdown conductivity is found to be in excellent agreement with a variable-range-hopping model, suggesting that this composition is just above the percolation threshold.
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  • 82
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4236-4238 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A simple equation of state for polymer liquids and solids, previously reported, is modified for simple liquids. Values of the parameters in the equation of state are given for 18 liquids. Comparison of the predictions of this equation with experimental data is made for all of the liquids.
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  • 83
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4233-4235 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Optical transitions in quantum-well heterostructures are very well revealed by photomodulated absorption spectroscopy. With respect to nonmodulated absorption spectroscopy, a strong increase in both room-temperature resolution and signal-to-noise ratio is observed. This new technique is most attractive for the investigation of multilayers grown on transparent substrates. The evolution of the spectral lineshapes of bulk and excitonic transitions as a function of temperature is shown.
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  • 84
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4229-4232 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A composite varistor material containing silicon carbide, a conductor, and an insulator has been developed. The material has rubberlike flexibility and is easily formed. A higher leakage resistivity (∼1012 Ω cm) and greater nonlinearity (∼10) than for silicon carbide varistors permit the material to be used as a gapless surge suppressor. The breakdown voltage (1–10 kV/cm) and other properties of the material vary with composition. High current capability (〉200 A/cm2) and good energy absorption (〉40 J/cm3) are obtained. Also, the material exhibits a low-temperature coefficient (∼4×10−3/K) and a low dielectric constant (∼10) with no observed loss peak.
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  • 85
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3205-3209 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The residual donor species in undoped GaAs epilayers grown by metalorganic chemical vapor deposition have been characterized by magnetophotoluminescence (MPL) measurements at high magnetic fields (7 T). Most samples were grown using trimethylgallium and arsine, but samples grown using the liquid group-V source t-butylarsine were also studied. The results show good agreement with identifications previously made in high-purity samples (NA+ND≤5×1014 cm−3) at zero magnetic field, but with greatly improved spectral resolution and signal levels. With the MPL technique, residual donor species were resolved even in relatively impure samples (NA+ND=1×1016) for which no information was obtained at zero magnetic field. For the samples grown with arsine, Ge donors were observed to predominate in the high-purity samples, but Si was the dominant donor in the lower-purity samples. The Si impurity was traced to contamination from a quartz baffle in the growth chamber. Lower levels of sulfur donors were observed in many samples. Sulfur was found to be the second most predominant donor after Ge in samples grown with t-butylarsine.
    Materialart: Digitale Medien
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  • 86
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3229-3232 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Fluorine redistribution during heat treatment of chemical vapor deposited tungsten/polycrystalline silicon gate structures was analyzed by the nuclear resonance broadening technique. The tungsten layer was deposited from a hydrogen/tungsten hexafluoride gas mixture. Upon heat treatment in the temperature range 1020–1325-K tungsten disilicide formation was observed using Rutherford backscattering spectrometry. In the as-deposited sample, the fluorine was accumulated at the tungsten/polycrystalline silicon interface. After silicide formation the fluorine was observed at the tungsten disilicide/polycrystalline silicon interface. At temperatures above 1120 K fluorine starts to diffuse through the polycrystalline silicon layer. A variation in the total fluorine content between the samples was also observed. The origin of the fluorine redistribution as well as the variation in the total fluorine content is discussed in connection to conceivable mechanisms.
    Materialart: Digitale Medien
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  • 87
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3820-3824 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Transient, combined conduction and radiation is solved in an absorbing, emitting, and isotropically scattering solid cylinder initially at uniform temperature and for times t〉0 subjected to a constant temperature at the black cylindrical surface. The collocation method is used to solve the radiation part of the problem and the implicit finite difference scheme is used to solve the conduction part. The effects of the conduction to radiation parameter, the single scattering albedo, the optical thickness of the medium on the temperature distribution, and the heat flux are examined.
    Materialart: Digitale Medien
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  • 88
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3825-3830 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using an arbitrary initial unipolar space-charge distribution consisting of two species of charge carriers of different but constant mobilities in a medium, relations for the electric fields and charge-carrier densities are derived as functions of positions and time. The highly nonlinear, one-dimensional equations, which are derived for swarms of charge carriers between parallel plane electrodes with a fixed potential difference, include the effects of the space-charge fields. A general method is outlined which, in principle, can be used to generate a second order differential equation whose solution predicts the time-dependent current caused by the drifting space-charge swarm. The general equations are applied to the special case where the initial space-charge distributions are uniform in a solid or fluid medium. Although the resulting differential equation is complicated, the equation is in a form such that its solutions could be computer generated.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 89
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3851-3854 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Time profiles of underwater shock wave pressure, current, and voltage were measured for exploding aluminum, aluminum-lithium alloy, and copper wire in water when an inductive energy store was discharged through the wire. A linear relationship existed between the peak voltage across exploding wire and the underwater shock wave pressure generated by the wire. The aluminum-lithium alloy reached a highly resistive state more quickly than pure aluminum wire at the same heating rate. The chemical reaction between the exploding wire material and the surrounding water plays a small role in the generation of detonation wave.
    Materialart: Digitale Medien
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  • 90
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3874-3879 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The flow and temperature fields in a tandem radio-frequency (rf) plasma torch were calculated. The method employed here is based on our previous rf plasma model. The flow and temperature fields of this tandem plasma show similar features to those of a dc-rf hybrid plasma, and the carrier gas can be injected into the high-temperature region (∼9000 °C) of the second plasma by regulating the linear velocity of the sheath gas. As might be expected, the derived results suggest that the tandem plasma has a possibility to give higher efficiencies for practical processing than conventional rf plasmas. A new type of tandem rf plasma torch was designed based on the results of the calculations. The stability of this plasma was examined under various conditions. Thus, a stable plasma could be maintained even when carrier gas of high flow rate (∼5 l/min of H2) was injected into the top of the second plasma. These theoretical and experimental investigations showed that the tandem plasma torch is an effective reactor for the preparation of refractory compounds by plasma chemical vapor deposition processes.
    Materialart: Digitale Medien
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  • 91
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3863-3873 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A fundamental study of the formation of negative hydrogen ions via surface conversion is presented. Employed is a novel type of converter, namely a pure barium metal surface. In spite of the high work function of barium compared to more conventional cesiated converters, considerable yields of negative ions were produced. Conversion efficiencies up of 4% are obtained, which is of the same order as for cesiated converters. The high negative-ion yield is probably related to the electron density of barium, which is almost twice that of cesiuim. This is confirmed by model calculations and by UHV scattering experiments under well-defined conditions. Furthermore, calculations showed that the hydrogen coverage of the converter increases with increasing flux of positive hydrogen ions to the surface. This behavior is confirmed experimentally. Seeding the hydrogen plasma with argon has no significant effect on the conversion efficiency. This is believed to be related to the competition between the lowering of the surface hydrogen coverage and the increase of the hydrogen desorption rate, both due to the higher sputter coefficient of argon compared to hydrogen.
    Materialart: Digitale Medien
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  • 92
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3885-3889 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The production of luminescence quenching localized defects by moving dislocations in GaAs plastically deformed at 350 °C has been established by low-temperature (80 K) band-edge cathodoluminescence (CL) and chemical etch-pit studies. Specimens were deformed to two levels, (1) measurable macroscopic plastic deformation, and (2) 20% of the stress applied in (1). It was established by CL and chemical etching that numerous dislocations were generated on the four {111} stressed slip planes of the macroscopically deformed specimen. Uniform bands of reduced CL signal were correlated to bands of enhanced etching in the lightly deformed samples. It was established from the etching and CL images that these bands are not produced by deformation-induced dislocations but must consist of numerous localized luminescence quenching (Refs. 1–3) defects (e.g., point defects and small dislocation loops) created by the passage of dislocations.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3890-3900 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A model is proposed for crack initiation on a pristine surface. In this model failure starts from a flat surface and the crack develops during the strength or lifetime experiment. Both energy and kinetic arguments are used. The model is applied to lifetime calculations of pristine optical fibers. Surface energy and bulk elastic energy are calculated for a fiber with a flat and a slightly distorted surface. When a small amount of elastic energy is removed locally from the fiber, e.g., by dissolution, the distorted state is more stable. Like cracks in brittle materials, the stable distortions for pristine optical fibers have local radii of curvature at atomic dimensions. In this model the lifetime of a pristine fiber is mainly determined by the time needed to pass from a flat surface to a relatively small surface distortion. From the derived expression for the lifetime, the exponent n in the empirical power law expression for subcritical crack growth can be interpreted. It is shown that n is stress dependent. The discrepancy in n value observed for silica glass fibers (n(approximately-equal-to)20) and bulk fused silica (n(approximately-equal-to)40) is removed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3915-3917 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The oxygen lattice diffusion in YBa2Cu3O7−y was studied with 18O as a tracer. For the composition of y=0.07, the oxygen lattice diffusion coefficient is represented by Dl,O =2.87×10−1 exp[−173(kJ/mol)/RT] cm2/s in the temperature range 250–400 °C. The oxygen lattice diffusion coefficient decreases with the increasing value of y.
    Materialart: Digitale Medien
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  • 95
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3934-3937 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The direct growth of GaAs by molecular-beam epitaxy on nominally (100)-oriented silicon with a buried implanted oxide is demonstrated. Nomarski interference contrast optical microscopy, transmission electron microscopy, and Rutherford backscattering techniques have been employed to characterize these layers. The formation of hillocks and a uniform layer of GaAs in the intervening regions between hillocks have been observed. Microtwins and threading dislocations are the predominant defects in these layers. Furthermore, we report the absence of antiphase domain boundaries within the GaAs hillocks.
    Materialart: Digitale Medien
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  • 96
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3938-3944 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The incorporation and electrical activation of As, implanted in situ during molecular-beam epitaxial growth of epilayers on Si(100), is reported. Parameters varied included growth temperature (460–700 °C), implantation energy (500–1000 eV), and concentration (1017→〉1020/cm3 ). In general, the material was excellent with 100% activation and bulk mobilities for concentrations up to the equilibrium solid solubility limit and carrier densities in excess of five times this limit in highly doped samples.
    Materialart: Digitale Medien
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  • 97
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3949-3957 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Silicon-rich silicon nitride (designated SiNx:H) films, prepared by the plasma-enhanced chemical vapor deposition technique, have been studied. The films studied contain a wide range of Si contents, which are controlled by the SiH4/NH3 flowrate ratio during the deposition process. Using transmission electron microscopy, coupled with the electron diffraction technique, we have found that the as-deposited films are amorphous. Upon high-temperature (〉900 °C) annealing, however, we observe silicon microcrystals in the Si-rich films. The temperature at which the microcrystals start to form decreases with increasing Si richness. Reactions of the SiNx:H film with the gate aluminum as a result of post-metallization annealing treatment (at 400 °C) have been observed, and these reactions cause a drastic reduction of the temperature required for crystallization. Charge separation and current conduction studies made on Al/SiNx:H/Si structures have revealed that electrons are the dominant current carriers for either polarity, and the conduction mechanism in the SiNx:H layer is consistent with the Poole–Frankel type of transport process for moderately Si-rich films.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3965-3971 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Auger electron spectroscopy, x-ray photoelectron spectroscopy, and secondary-ion mass spectrometry have been used to elucidate the role of surface segregation and preferential sputtering of bismuth in rf-magnetron-sputtered bismuth–iron-garnet films. It turns out that bismuth is enriched by a factor of up to 2.4, as compared to the bulk content, within the first 1–1.5 nm beneath the advancing film surface during growth. Furthermore, Ar+-ion bombardment at projectile energies as low as 50 eV gives rise to a rather complete depletion of bismuth in the garnet surface. As neither surface segregation nor preferential sputtering of bismuth can be observed in as-polished single-crystalline Bi12SiO20 used as our reference, we conclude that the bond strength between bismuth and oxygen is weaker than that of the other garnet constituents. This is confirmed by comparing the calculated sputter yield of the element oxide. Thus, bismuth-rich crystallographically perfect epitaxial iron-garnet films can only be grown by sputtering if the growing film is protected against energetic particle bombardment.
    Materialart: Digitale Medien
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  • 99
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3975-3979 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: p-type GaAs with doping levels of up to 5.8×1020 cm−3 has been grown by metalorganic molecular-beam epitaxy (MOMBE) using carbon (C) as a dopant. The mobility and minority-carrier diffusion length of the C-doped MOMBE layers were comparable to those of Be-doped MBE layers. The diffusion coefficient of C at 900 °C was estimated to be 6×10−15 cm2 /s which is about two orders of magnitude less than that of Be (1×10−12 cm2 /s). In addition, the lattice constant of C-doped GaAs was found to be 5.6533 A(ring) which completely matches that of the substrate, while the lattice constant of Be-doped GaAs decreases to 5.6467 A(ring) at a doping level of 2×1020 cm−3 as reported by Lievin et al. [Inst. Phys. Conf. Ser. No. 79, 595 (1985)].
    Materialart: Digitale Medien
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  • 100
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3994-3998 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Small amounts of In2O3 and Li2O were added to the ZnO-Bi2O3-MnO2 ternary primitive varistor system. Considering Schottky disorder and Frenkel disorder, oxygen vacancy or zinc interstitial density was expected to decrease with In2O3 doping and to increase with Li2O doping. Using admittance spectroscopy, a 0.32-eV electron trap, which is suggested to be an ionized oxygen vacancy, was observed regardless of the doping conditions. Changes in the peak height, for the 0.32-eV trap, in the admittance spectra are correlated with In2O3 and Li2O doping. Doping with In2O3 reduces the conductance contribution due to the trap, while doping with Li2O enhances it. However, calculations show that small amounts of dopants, less than 100 ppm, do not greatly influence the trap density. The trap density remains within experimental error approximately 1.0×1017 cm−3.
    Materialart: Digitale Medien
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