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  • American Institute of Physics (AIP)  (8,513)
  • Berlin : Borntraeger
  • 1990-1994  (8,513)
  • 1930-1934
  • 1990  (8,513)
Collection
Publisher
Years
  • 1990-1994  (8,513)
  • 1930-1934
Year
  • 1
    Electronic Resource
    Electronic Resource
    A transmission electron microscopy study of the (Sm,Pr)5Co19 phase (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7510-7513 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission electron microscopy has been used to characterize the rhombohedral 5:19 phase (R3¯m) in a stoichiometric (Sm0.75Pr0.25)5Co19 alloy. In some regions, strain-induced contrast was observed in the 5:19 phase. By contrast analysis, this strain contrast was associated with a displacement vector of the type (1)/(3) [011¯0]. In other regions where the strain-induced contrast was significantly reduced, faults with the crystal structure of hexagonal (Sm,Pr)2Co7(2:7H) phase (P63/mmc) were observed. The formation of the faults is believed to release elastic energy within the 5:19 phase. In the interface regions between the 5:19 phase and the minor component hexagonal 2:7H phase, it was found by lattice imaging that the 5:19 and 2:7H plates are superimposed with a common c direction. The orientation relationship between the 5:19 and 2:7H phases is given by [0002]2:7H(parallel)[0003]5:19R and [112¯0]2:7H(parallel)[112¯0]5:19R.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345811
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  • 2
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    Detecting two magnetization components by the magneto-optical Kerr effect (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7520-7525 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel technique was detecting two orthogonal in-plane magnetization components is presented. This technique utilizes the magneto-optical Kerr effects to sense the two components. These components of magnetization are parallel and perpendicular to the plane of incidence of the light beam. The ability to sense two components, individually or simultaneously, is a result of the disparity in the longitudinal and transverse Kerr effects. Based on the Frensel reflection coefficients of these two effects, an anlysis is presented describing this dual component sensitivity. The physical conditions are given for simultaneous and individual detection of the two in-plane magnetization components. To substantiate this analysis, magneto-optical measurements are made on single-crystal Fe films. The results are discussed in the context of dual component sensitivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345813
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  • 3
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    CO2 laser treatment of As-S chalcogenide thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7536-7541 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The changes of the refractive index of As2 S3 and As2 S5 films deposited on glass substrates upon CO2 laser irradiation have been studied. The possibility of writing with the CO2 laser a waveguiding channel in As2 S3 is demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345816
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  • 4
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    Excitation of long-range surface polaritons in silver films by a finite-width light beam (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 555-557 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evanescent wave excitation of a long-range surface polariton in a silver film is treated including the effects of the finite width of the incident laser beam and the slow spatial variation of the amplitude of the surface polariton. The theoretical results of the antiresonance characteristics in the angular response of the reflectivity are compared with the available experimental observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345246
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  • 5
    Electronic Resource
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    Texture analysis of polycrystalline silicon films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 572-574 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method for the quantitative characterization of texture in thin films using x-ray diffraction is presented. The traditional technique, which makes use of a powder diffractometer, relies on peak intensity measurements at normal incidence. By using pole figure measurements and subsequent orientation distribution analysis we obtain the substantially improved coverage necessary to accurately characterize textures of thin silicon films which exhibit great variation and complexity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345196
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  • 6
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    Pulsed laser treatment of Fe2O3 film on Al2O3 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 569-571 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe2O3 film (∼110 A(ring)) on crystalline Al2O3 substrate is treated by ruby laser pulses at different energy densities up to a maximum of ∼7.5 J/cm2, and the transformations are examined by conversion electron Mössbauer spectroscopy and small-angle x-ray diffraction measurements. It is observed that transformations begin to appear in the sample at an energy density of ∼3.0 J/cm2 although significant modifications are observed only at energy densities higher than about 7.0 J/cm2. The values of hyperfine interaction parameters reveal that the laser treated samples contain FeAlO3 and FeAl2O4 phases, along with the residual α-Fe2O3 phase. The laser-mixed state undergoes structural modifications upon thermal annealing, leading to formation of the Fe3O4 phase and complete disappearance of the FeAlO3 phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345195
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  • 7
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    The effect of laser annealing of thin W(100) films on positron transmission reemission properties (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 575-577 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results on e+ transmission reemission properties are presented for three single-crystal W(100) films of thicknesses 1000, 2000, and 3100 A(ring) for incident e+ energies of 1.4–16 keV. The films were first cleaned with a 10-s laser pulse, then annealed in O2 (10−6 Torr), and finally heated in a vacuum (10−9 Torr). Thereafter the films showed good reemission properties. The maximum transmitted yields of slow e+ were 38% (1000 A(ring)), 27% (2000 A(ring)), and 17% (3100 A(ring)) at incident e+ energies of 4, 5.2, and 7.2 keV, respectively. The energy distributions of the reemitted e+ were characterized by a full width half maximum of 0.15–0.2 eV located at 2.8 eV containing 60%–70% of the e+ superimposed onto a nearly uniform distribution covering the energy interval 0–2.8 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345197
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  • 8
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    Limitations of the integrated sub-band-gap absorption for determining the density of defects in amorphous silicon (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 578-580 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss the procedure of calculating the density of states in the gap for amorphous silicon by integrating the excess sub-band-gap absorption. We show that in general the proportionality coefficient between the density of states and the integrated sub-band-gap absorption is not unique. The sum rule has been used improperly since integration of the excess subgap absorption is terminated either at a fixed energy or at an energy which does not include all optical transitions to the conduction band. We estimate the errors that can arise from this procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345198
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  • 9
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    Observation of quantum well polarization effects in the photocurrent of multilayer diodes (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 583-585 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Large electrical polarization effects in the time photoresponse of multilayer heterostructure diodes have been observed. This phenomenon manifests itself in a displacement current spike synchronous to a dark–light transition and in an opposite spike in the light–dark one. The effect is associated with the pileup and spatial separation of photogenerated electrons and holes in the wells in the space-charge region of the diode. At a particular forward bias voltage, the conduction photocurrent is eliminated, allowing accurate measurements of this phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345200
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  • 10
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    Effects of C+ implantation on the interdiffusion and resistivity of Cu/Ni/Au thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6189-6193 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of C+ implantation on the interdiffusion of Cu/Au and Cu/Ni/Au thin-film structures was investigated at temperatures ranging from 200 to 600 °C, and for different annealing times at 400 °C. For comparison, unimplanted Cu/Ni/Au and Cu/C/Ni/Au thin-film structures were also studied. The implantation of carbon ions has very little effect on the interdiffusion of Cu and Au at the temperatures investigated. For the Cu/C/Ni/Au structure, very little Cu-Au interdiffusion was observed within the temperature range studied. However, spontaneous delamination of C/Ni/Au from Cu occurred at ≥400 °C. This must be due to the poor adhesion of C to Cu which is made worse at these temperatures by the thermal expansion mismatch. X-ray diffraction analysis revealed the formation of intermetallic CuAu compounds after annealing of the implanted and unimplanted Cu/Au and Cu/Ni/Au structures. The mechanisms of diffusion are considered to be associated with this intermetallic alloying, which results in the generation of vacancies that form the diffusion paths. In the case where alloying does not occur, diffusion is therefore limited by solid solubility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345184
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  • 11
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    Excimer laser induced doping of phosphorus into silicon (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6197-6201 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Doping of single-crystal silicon in PF5 atmosphere by means of an ArF (193 nm) excimer laser has been investigated as a function of laser fluence, number of pulses, and PF5 gas pressure. We find that phosphorus atoms are only produced by pyrolysis of the PF5 molecules but not by photolysis. The doping experiments were performed in PF5 ambients or using an adsorbed PF5 layer. The results indicate that the incorporation process is external rate limited for doping in PF5 ambients and mainly diffusion limited when using the adsorbed layer. Moreover, the evolution of the incorporated dose with the PF5 pressure shows that at low pressures (〈0.5 Torr), the phosphorus atoms are supplied by a chemisorbed PF5 layer formed at the silicon surface, whereas at high pressures the main dopant source appears to be a layer of loosely bound PF5 molecules which has been physisorbed at the surface. It is also found that the surface quality is affected neither by the successive irradiation or by the heavy doping.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345186
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  • 12
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    Improved boundary conditions for the time-dependent Schrödinger equation (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 591-593 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improved boundary condition treatment for the time-dependent Schrödinger equation applied to resonant-tunneling diode simulation has been developed. This treatment is half-implicit, or centered in time, and allows larger time steps than the previous explicit treatment. The method does not complicate the time-dependent calculation since the resulting matrix is still tridiagonal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345203
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  • 13
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    The effect of interface roughness and island scattering on resonant tunneling time (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 593-595 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of interface roughness and island scattering on resonant tunneling time in double-barrier structures is investigated theoretically. The scattering process degrades the resonant tunneling peak current, broadens the resonance, and hence shortens the resonant tunneling time. For thin barrier structures, the tunneling time enhancement due to the scattering is relatively small, while the resonance width is dominated by the scattering for thick barrier samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345204
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  • 14
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    Measurements of twisted nematic cell gap by spectral and split-beam interferometric methods (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5-9 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transmissive Fabry–Perot interference peaks of a filled twisted nematic (TN) cell as a function of wavelength, from 400 to 600 nm and from 1100 to 2000 nm, have been used for the determination of the cell gap. Theoretical formulations have been developed to calculate the effective indices of refraction including the dispersive effect, as well as the twist geometry of the liquid-crystal medium for both the ordinary and extraordinary waves. When the light passes through the TN medium an even number of times caused by the interfacial reflections, the equations governing the effective indices of refraction are well behaved. For an odd number of passes, the validity of these equations is restricted to a region adjacent to the Mauguin limit. The cell gaps were derived from the measured effective optical paths and the calculated indices of refraction, which include the dispersive effect with or without the twisted deformation of the liquid-crystal medium. A general equation has also been obtained to derive the TN cell gap from the effective optical paths, which are measured by using the split-beam interferometric method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345205
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  • 15
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    Increase of electrical activation and mobility of Si-doped GaAs, grown at low substrate temperatures, by the migration-enhanced epitaxy method (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 589-591 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Si-doped GaAs layers were grown by the migration-enhanced epitaxy (MEE) method and by the conventional molecular-beam epitaxy (MBE) method, for the substrate temperatures between 220 and 670 °C. For the layers grown below 400 °C, the Si activation and mobility of the MEE layers are significantly higher than those of the MBE layers. For substrate temperatures above 400 °C, the MEE and MBE layers have roughly similar Si activation and mobility. The Raman and 4-K photoluminescence spectra of the layers are consistent with the measured electron concentrations. This work suggests that for Si doping in GaAs at low substrate temperatures (below 400 °C), the MEE method is a very desirable alternative to the conventional MBE method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345202
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  • 16
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    Optical heterodyne investigation of the ultrasonic properties of aqueous biomolecules, dimethyl sulfoxide, and 1,4-butanediol (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 68-75 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An optical heterodyne technique has been used to make new measurements of the ultrasonic properties of aqueous solutions of biomolecules, dimethyl sulfoxide, and 1,4-butanediol. A LiNbO3 transducer provided acoustic excitation from 0.2 to 1.5 GHz. Acoustic velocity and attenuation were measured using angularly resolved detection of Bragg-scattered light from the liquid sample. A thermodynamic theory based on the heat of mixing was used to explain the concentration dependence of the liquid mixture properties. This paper contributes new data at high frequencies, a calculation of measurement sensitivity for this technique, and a complete treatment of a little known thermodynamic theory that describes these results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345207
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  • 17
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    On the normal acceleration sensitivity of contoured quartz resonators rigidly supported along rectangular edges (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 60-67 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis of the normal acceleration sensitivity of contoured AT- and SC-cut quartz crystal resonators rigidly supported along rectangular edges is performed. The variational principle with all natural conditions for anisotropic static flexure is used in the calculation of the flexural biasing state. However, in this work the biasing shearing stresses with quadratic variation across the thickness of the plate are obtained a posteriori from the flexural solution in the conventional manner. The accompanying quadratically varying biasing shearing strains, which are very important in this work, are obtained from the constitutive equations along with all other quadratically varying strains resulting from the anisotropy. The calculated biasing deformation fields are employed in an existing perturbation equation along with the mode shapes of the contoured resonators to calculate the normal acceleration sensitivities. It is shown that the normal acceleration sensitivity vanishes for many cases and is less than a few parts in 1013 for all cases considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345206
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  • 18
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    Optical emission spectroscopy of rf discharge in SF6 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 97-107 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we present experimental results obtained for a rf discharge in SF6 and for SF6 with Ar and/or N2. The data for power dependence of some emission lines usually used in actinometry are acquired and their applicability and excitation kinetics discussed. We also present the spatial (time averaged) variations of some emission lines. From such data the spatial dependence of the high-energy tail of the electron energy distribution function may be obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345211
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  • 19
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    The role of hydrogen in diamond synthesis using a microwave plasma in a CO/H2 system (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6247-6254 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to clarify the role of hydrogen in diamond synthesis using a microwave plasma in a CO/H2 system, carbon films were grown by varying hydrogen mole fractions in a CO/H2/He microwave plasma. The correlation between film properties and plasma species was investigated through film characterization and plasma emission spectroscopy. C and C2 were formed in the gas phase of the CO/He system and only sootlike carbon was deposited. Hydrogen additions to the CO/He system were found to enhance diamond growth by suppressing the formation of C and C2, which inhibited diamond growth by blocking the nucleation sites. The complicated structure of amorphous hydrogenated carbon, diamond microcrystallites having a diameter of 100 A(ring), and graphitic carbon was formed in the CO(5%)/H2 (30%)/He system, while columnar polycrystallites were grown in the CO(5%)/H2 system. Almost the same amount of atomic hydrogen in the ground state was found to exist in both systems, whereas a larger amount of electronically excited atomic hydrogen existed in the CO/H2/He system than the CO/H2 system. The atomic hydrogen in the ground state enhanced diamond growth by removing the amorphous carbon deposits, while the electronically excited atomic hydrogen exhibited no contribution to diamond growth and reacted with the amorphous carbon deposits to form the amorphous hydrogenated carbon. Finally, oxygen-containing species and hydrocarbons were suggested to be important precursors for diamond crystallization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345191
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  • 20
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    A comparison of the reaction of titanium with amorphous and monocrystalline silicon (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6255-6264 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper describes investigations into the reactions occurring between Ti and monocrystalline Si (x-Si) or sputter-deposited amorphous Si (a-Si). Samples were structured so as to have the same Ti layer in contact with both crystalline and amorphous Si, and were thus ideally suited to compare the reactions in the same sample. Reactions were mainly investigated with cross-sectional transmission electron microscopy, but also with chemical characterization techniques such as Rutherford backscattering and Auger electron spectroscopy. We demonstrated that the reaction between Ti and x-Si or a-Si proceeded very similarly at low temperatures (≤450 °C). In both cases an amorphous silicide layer was observed to grow. Reaction rates were found to be nearly equal, even if some impurities were present on the x-Si surface prior to Ti deposition. One important difference was noted between the reactions, however. The reaction with a-Si was associated with Kirkendall void formation, while these voids were absent in the reaction with x-Si. We argued that the absence of voids in the case of the reaction with x-Si is due to a higher vacancy mobility in x-Si than in a-Si. At higher temperatures (500 °C), marked differences were observed in the reaction of Ti with crystalline or amorphous Si. These differences could be explained satisfactorily from thermodynamical considerations involving the heat of crystallization of a-Si. We postulated the existence of two kinetically competing pathways to go from the low-temperature configuration, where an amorphous silicide grows, to the stationary situation where diffusion-controlled growth of crystalline silicides occurs. The first one is crystallization of the amorphous silicide. The second one is the formation of a compositionally different crystalline silicide at the amorphous-silicide/x-Si interface. This postulate of kinetically competing pathways was used successfully to explain observations of amorphous and crystalline silicide growth in the Ni and Co/Si systems.
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    URL: http://dx.doi.org/10.1063/1.345141
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  • 21
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    Solid phase reaction of molybdenum-nickel alloy thin films with silicon (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6269-6273 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Solid phase reaction behavior of polycrystalline and amorphous alloys of MoNix (x=12, 20, and 88) with silicon in the temperature range 500–700 °C has been studied by glancing angle x-ray diffraction and Auger electron spectroscopy techniques. Two types of reaction mechanisms are observed in these alloy/silicon reactions and both are controlled by the composition of the refractory metal component. In molybdenum-rich polycrystalline alloy (Mo88Ni12) the reaction at 500 °C occurs due to out-diffusion of nickel from the alloy, while at 550 °C the reaction between the alloy and silicon mainly occurs due to in-diffusion of silicon. On the other hand, in nickel-rich alloy (Mo12Ni88), the reaction at 500 °C is dominated by nickel out-diffusion. The amorphous alloy (Mo80Ni20) was found to be stable on silicon up to 500 °C and a reaction at 550 °C occurs due to crystallization followed by out-diffusion of nickel and large amounts of silicon in-diffusion. In all these alloy/silicon reactions, a macroscopic phase separation between MoSi2 and NiSi or NiSi2 is observed and results in a two-layer structure consisting of [MoSi2+NiSi(or NiSi2)]/NiSi (or NiSi2)/Si(100).
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    URL: http://dx.doi.org/10.1063/1.345143
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  • 22
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    Electric-field-induced absorption changes in triangular quantum wells grown by pulsed-beam molecular-beam-epitaxy technique (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6461-6465 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present an observation of electric-field-induced excitonic quenching in GaAs/AlGaAs triangular quantum wells, grown by pulsed-beam molecular-beam-epitaxy technique. We have measured photocurrent spectra for both symmetric and asymmetric triangular quantum wells as a function of electric field. In both cases, at the ground-state exciton energy, we observed significant electroabsorption changes that were associated with the vanishing of sharp exciton resonances when the triangular quantum-well structures were electrically switched to systems with no quantum confinement for one or both types of carriers.
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    URL: http://dx.doi.org/10.1063/1.345120
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  • 23
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    Temperature dependence of the fundamental absorption edge of mercury cadmium telluride (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6454-6460 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the temperature dependence of the fundamental absorption edge of a series of Hg1−xCdxTe alloys (with composition x ranging from 0.5 to 1). Analyzing our data in the light of the three-dimensional theory of direct-allowed excitons, we find precise values for the fundamental Γ8-Γ6 interband transition energy in a temperature range extending from 0 to 300 K. All experimental results, including previous data for HgTe and mercury-rich Hg1−xCdxTe alloys, are well accounted for using a simple empirical formula: Eg (eV)=−0.303(1−x)+1.606x−0.132x(1−x)+[6.3(1−x) −3.25x −5.92x(1−x)]10−4T2/[11(1−x)+78.7x+T]. This expression, which is valid for all compositions 0≤x≤1 and temperatures 0≤T≤500 K, predicts an alloy composition such that the band-gap energy is temperature independent: We find x=0.505. Finally, it can be used for technological application purpose (far-infrared detection as well as optical-fiber communications performed at realistic values of the temperature) and gives accurate values for the temperature and composition dependence of the effective mass in the semiconducting range of alloys.
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    URL: http://dx.doi.org/10.1063/1.345119
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  • 24
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    Analysis of multilayer thin-film structures containing magneto-optic and anisotropic media at oblique incidence using 2×2 matrices (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6466-6475 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A complete analysis of multilayer structures containing an arbitrary number of dielectric, metal, magnetic, and birefringent/dichroic layers is presented. An algorithm, based on simple 2×2 matrices, is derived which allows reflection, transmission, absorption, magneto-optic conversion, birefringence, and dichroism of the structure to be computed on a personal computer. The incident beam is assumed to be plane monochromatic with arbitrary angle of incidence. There are no approximations involved, and the results are direct consequences of Maxwell's equations.
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    URL: http://dx.doi.org/10.1063/1.345121
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    Change in the optical-absorption coefficient induced by optical modulation of the internal electric field in doping-modulated amorphous silicon multilayers (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6476-6480 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical modulation of doping-modulated amorphous silicon multilayers (n-i-p-i multilayers) gives rise to an increase in optical transmission at around band-gap energy (∼1.8 eV). Results of the photoinduced transmission measurement for series of samples with different thicknesses of undoped or doped layers can be well explained by a model in which an internal electric field is screened under illumination by spatial separation of photoexcited electrons and holes, leading to a decrease in the optical-absorption coefficient as a result of photoinduced inverse electroabsorption. It can be confirmed through these optical measurements that spatial separation of photoexcited carriers takes place at room temperature in amorphous n-i-p-i multilayers based on hydrogenated amorphous silicon.
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    URL: http://dx.doi.org/10.1063/1.345122
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    Photoluminescence from ultrashort-period AlAs-GaAs atomic-layer superlattices (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6481-6485 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence for (AlAs)n(GaAs)n (n=1, 2, 3, and 4) ultrashort-period superlattices grown by flow-rate modulation epitaxy is analyzed at various temperatures between 4.6 and 300 K. An excitonic intense emission line caused by an indirect transition is observed at low temperatures. Another emission band, caused by a direct transition, appears at elevated temperatures. The results of photoluminescence excitation spectroscopy reveal that the superlattices have an indirect minimum band gap. The direct and indirect band-gap energies of these superlattices, with periods of up to 1 monolayer, are presented. A simple Kronig–Penney calculation shows relatively good agreement with the experimental results for direct transitions.
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    Spatially resolved space-charge density in the hydrogenated amorphous silicon Schottky barrier from surface photovoltage measurements (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6486-6489 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A procedure is developed to derive the differential capacitance of the hydrogenated amorphous silicon (a-Si:H) Schottky barrier from surface photovoltage measurements. An algorithm for deducing the spatial variation of the space-charge density, and of the band-gap density of states, from the frequency-dependent capacitance spectrum, is proposed and implemented for undoped a-Si:H. The space-charge density and the density of states near the Fermi level are found to span three orders of magnitude, falling below 1015 cm−3 and 1016 cm−3 eV−1, respectively, into the bulk of the Pt/a-Si:H Schottky barrier.
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    Growth and properties of thin GaAs epitaxial layers on Al2O3 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6497-6506 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The metalorganic vapor-phase epitaxy of GaAs on Al2O3 substrates was carried out over a growth temperature range of 600–800 °C. Several physical characterization techniques were used to obtain information on the initial stages of epitaxial growth and its influence on the physical properties of the epitaxial layer. The initial GaAs growth proceeds by island formation and coalescence, and the initial density of GaAs islands is a strong determinant of the epitaxial layer crystalline quality. An incommensurate growth model is presented to explain the dependence of the film properties on the growth parameters. The presence of defects in even very thick layers limits the applicability of these materials in device structures.
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    Particulates in aluminum sputtering discharges (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6490-6496 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma-generated particulates are receiving increasing attention as a possible source of device yield reduction in plasma-assisted etching and deposition processes. We have investigated aluminum sputtering in argon discharges between parallel-plate aluminum electrodes under both direct current and radio frequency excitation. Pulsed laser-induced fluorescence experiments indicate that particulates containing aluminum form in these discharges under conditions in which aluminum sputtering takes place. Under sufficiently powerful laser excitation, the laser acts to dissociate the particles, resulting in an enhanced aluminum-atom laser-induced fluorescence signal. Spatial regions of atomic aluminum fluorescence enhancement coincide exactly with nonresonant light scattering profiles from a low-power helium-neon laser. The pulsed laser was observed to locally deplete particulates on a time scale of seconds. Particle profiles appear to evolve in the discharge on a time scale of tens of minutes to hours. The spatial profile of the particles depends in a sensitive manner on the applied voltage, as well as other discharge variables. At a sufficiently negative dc voltage applied to the cathode, particles were observed to be excluded from the interelectrode region.
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    URL: http://dx.doi.org/10.1063/1.346081
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    Controlled doping of GaAs films grown with tertiarybutylarsine (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6507-6512 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To assess the suitability of alternative arsenic compounds for device applications, development of growth procedures for controlled n and p doping are required. In this paper we report the first studies of the doping characteristics of sulfur, silicon, and carbon species in GaAs films grown with tertiarybutylarsine, t-BuAsH2. Hydrogen sulfide, H2S, and hexamethyldisilane, (CH3)6Si2, were used as dopant sources. The effects of growth temperature, dopant source concentration, V/III ratio and substrate crystallographic orientation on dopant incorporation were investigated. We demonstrate the capability of controllably doping GaAs films grown with t-BuAsH2, and report the first fabrication of active devices (n+-n metal-semiconductor field effect transistors) from t-BuAsH2-grown material. These devices exhibited dc and microwave performance comparable to that achieved with arsine-grown devices.
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    URL: http://dx.doi.org/10.1063/1.345126
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    Some properties of the circular waveguide with azimuthally magnetized ferrite (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6529-6537 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comprehensive analysis of normal rotationally symmetric TE modes in a circular waveguide, filled with ferrite, magnetized azimuthally to remanence by a coaxial switching conductor of finite radius, is presented. The characteristic equation of the structure, derived in terms of Kummer and Tricomi confluent hypergeometric functions of complex parameter and variable, is solved numerically, using specially compiled tables of wave functions. Families of theoretically calculated nonreciprocal phase characteristics of the gyrotropic waveguide are shown in normalized form for the two latched states of remanent magnetization, a variety of ferrite parameters, and different values of switching conductor to waveguide radius ratio. The influence of structure geometry and parameters of anisotropic ferrite on normalized differential phase shift and cutoff frequency spectrum of the TE01 mode is discussed.
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    URL: http://dx.doi.org/10.1063/1.345130
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    A new type of high efficiency with a low-cost solar cell having the structure of a μc-SiC/polycrystalline silicon heterojunction (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6538-6543 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new type of high-efficiency solar cell has been developed by a simple production process only with electron cyclotron resonance plasma-assisted chemical vapor deposition of highly conductive microcrystalline silicon carbide (μ c -SiC) on polycrystalline silicon (poly-Si). The device consists of a p -type μ c -SiC/ n -type poly-Si heterojunction where the window material is a specially made wide-band gap and highly conductive μ c -SiC. At the present stage, a conversion efficiency of 15.4% with V oc=556 mV, J sc=35.7 mA/cm2, and F. F.=77.4% has been achieved. Also employing this device as a bottom cell in a four-terminal amorphous silicon ( a -Si) tandem-type solar cell, 16.8% efficiency has been obtained. A series of technical data on the fabrication technology and device performance is presented and discussed.
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    Extended Goodman model for series resistance masking on bulky semiconductor junction capacitance (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6544-6547 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of series resistance on the apparent semiconductor junction capacitance C' has been studied after Goodman [J. Appl. Phys. 34, 329 (1963)] in an attempt to explain the occurrence of minima in the apparent C'−2 vs voltage characteristics at high frequencies and for a large series resistance. A correction scheme has been formulated to convert C'−2 into the actual C−2 at any bias and frequency. The present model is consistent with the apparent capacitance behavior of a commercial Si Zener diode in series with a discrete resistor.
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    A temperature-independent capacitance in semiconductor-insulator-semiconductor capacitors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6548-6551 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Both measurements of capacitance-voltage (C-V) curves of n− GaAs-undoped Al xGa1− xAs- n+ GaAs (AlGaAs) capacitors at different temperatures, and calculations of C-V curves of semiconductor-insulator-semiconductor (SIS) capacitors at different temperatures, show that there is a temperature-invariant capacitance CC and voltage VC at which C-V curves at different temperatures intersect. We show that this is a general property of SIS capacitors having a degenerate gate and nondegenerate substrate of the same doping type, and that qVC, where q is the electron charge, is approximately equal to the Fermi energy of the degenerate GaAs gate. VC provides a good estimate for the voltage required to establish an accumulation layer on n− GaAs at low temperatures, which is determined from magnetotunneling measurements on AlGaAs capacitors.
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    The influence of the pregroove on the shape of thermomagnetically written domains (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6552-6559 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to clarify the influence of pregrooved substrates on the shape of thermomagnetically written domains, the difference between the shape of the domains written on a pregrooved area and that written on a mirror area have been examined. Trilayered magneto-optical media, which had rare-earth- (RE-) rich TbFeCo films, transition-metal-rich TbFeCo films, and RE-rich GdTbFeCo films as a recording layer, were sputtered on disk substrates. The substrates had both a pregrooved area and a mirror area in a recording track. The domains were written in each medium by varying the recording power and the external field, and were observed by an Ar+ -laser scanning polarized microscope. In the case of TbFeCo media which were written with lower recording power condition, the shape of the domains on a pregrooved area were almost the same as those written on a mirror area. On the other hand, the widths of the domains written on a mirror area became larger than those of domains written on a pregrooved area when the recording power was increased. In the case of a GdTbFeCo medium, the widths of the domains written on a mirror area were much larger than those of domains written on a pregrooved area independent of the recording conditions. The lengths of the domains written on both areas were almost the same for all cases. It is believed that the reason for the experimental results is that thermal diffusion in the film plane is suppressed at the step of a pregroove. The different result between TbFeCo and GdTbFeCo films is believed to come from the differences in the contracting forces on the domain walls during the writing process.
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    Crystallinity and Schottky diode characteristics of GaAs grown on Si by metalorganic chemical vapor deposition (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6908-6913 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The crystallinity of GaAs grown on Si with various intermediate layers by metalorganic chemical vapor deposition and characteristics of Schottky diodes fabricated on the grown GaAs/Si have been studied. The GaAs/Si with an Al0.55Ga0.45P intermediate layer has both good crystallinity, x-ray full width at half maximum of 188 arc sec, and a smooth surface. The Schottky diode fabricated on the GaAs/Si with an Al0.55Ga0.45P intermediate layer also shows good forward and reverse current-voltage characteristics with an ideality factor of 1.06, as good as for an n-type GaAs substrate. However, a relatively large leakage current is observed under reverse and small forward bias. This leakage current is caused by generation and recombination through the centers related to dislocations in the GaAs/Si.
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    Schottky barrier height enhancement of n-In0.53Ga0.47As by a novel chemical passivation technique (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6571-6573 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel method of enhancing Schottky barrier height, while reducing the surface-state density on n-type In0.53Ga0.47 As surfaces using P2S5/(NH4)2S and (NH4)2Sx passivation is described in this communication. The current-voltage and capacitance-voltage characteristics show that passivated diodes have lower reverse leakage current and higher effective barrier height than that of the unpassivated diodes. The electrical characteristics of passivated diodes have not changed after one month of exposure to the air.
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    URL: http://dx.doi.org/10.1063/1.345138
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    Some observations of the effects of high pressures and temperatures on the stability of YBa2Cu3O7−x (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6934-6939 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hot isostatic pressing and heat treatments in high-pressure oxygen were used to study the effect of pressure on the stability of YBa2Cu3O7−x. At 875 °C the compound decomposes at an oxygen pressure of about 7 bars. The decomposition involves formation of Y2BaCu3O5 and a Ba-Cu oxide phase. Formation of the latter phase involves additional oxidation because this phase can contain as many as 1.5 oxygen atoms per barium atom. The decomposition can most simply be visualized by considering the chemical reaction 2(YBa2Cu3O7−x)+( (1)/(4) +x−y/2)O2→Y2BaCuO5+Ba3Cu5O9.5−y. Encapsulated samples also decompose during hot isostatic pressing, but the process appears to be more complex. The compound YBa2Cu4O8 was detected in addition to the two products observed in oxygen-treated samples. The reaction above, with YBa2Cu3O7−x serving as an oxygen source, aids in understanding the microstructural observations for encapsulated samples. Decomposition can be completely reversed by annealing in air for 20 h at 875 °C.
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    The effective microwave surface impedance of high Tc thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6940-6945 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of the effective surface impedance Zeff=Reff+iXeff of superconducting thin films on the film thickness d, on the magnetic field penetration depth λ, and on the dielectric properties of the substrate material is investigated theoretically by means of impedance transformations. It was found that the effective surface resistance Reff can be expressed by RSf(d/λ)+Rtrans where RS is the intrinsic surface resistance of the superconductor. The function f(d/λ) describes the altered current density distribution in the film. Rtrans arises from power transmission through the film. It depends on d and λ as well as on the dielectric properties of the substrate material and is significantly altered in the case of a resonant background. The effective surface reactance Xeff of a superconducting thin film can be expressed by XS cosh(d/λ) where XS=ωμ0λ is the intrinsic surface reactance. Measurements of Zeff at 87 GHz have been performed for YBa2Cu3O7−δ thin films grown epitaxially by laser ablation on SrTiO3, MgO, and LaAlO3. With the best films, Reff (77 K) values of 21 mΩ and RS (77 K) values of 8 mΩ were achieved. The temperature dependence of λ was found to be in good agreement to both weak-coupling BCS theory in the clean limit and the empirical two-fluid model relation with λ (0 K) values ranging from 140 to 170 nm and 205 to 250 nm, respectively.
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    The properties of Y1Ba2Cu3O7−δ thin films with silver doping prepared by spray pyrolysis (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6946-6952 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting, silver-doped films of Y1Ba2Cu3O7−δ have been deposited by spray pyrolysis of aqueous nitrate solutions onto MgO substrates. The superconducting transport properties, microstructure, and microwave losses have been characterized for various amounts of AgNO3 added to the spraying solution. These films had resistive transition temperatures between 79 and 85 K with widths from 3 to 7 K. The room-temperature resistivity was a strong function of the silver doping, dropping by a factor of 50 for the heavily doped films. Critical current densities at 4 K were typically several 103 A/cm2 with little correlation to the silver doping. Lattice constants also were not significantly affected by the silver doping level, however, lightly doped films were denser, had the strongest c axis preferred orientation, and a smoother surface. Rf surface resistance was measured at 18 GHz, and for the best films dropped a factor of 10 below copper by 40 K. The London penetration depth was estimated to be approximately 1 μm for the best films.
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    Structure and superconducting properties of YBa2Cu3O7−x films prepared by nitrogen laser evaporation and CO2 laser annealing in oxygen (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6953-6957 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting YBa2Cu3O7−x thin films were obtained under high vacuum (10−5 Torr) on substrates of polycrystalline Al2O3 sapphire, SrTiO3, and Si, having zero resistance at 81, 85, 87, and 79 K, respectively. A N2 laser of 3.5 J cm−2 energy density was used for the evaporation. The substrates were heated by a cw single-mode CO2 laser and the annealing was performed by the same laser in O2 atmosphere. Local planar superconducting regions were obtained by focusing the radiation of the cw CO2 laser upon the films. The films were investigated by scanning electron microscope, x-ray microanalysis, and x-ray diffraction.
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    Magnetization reversal in cobalt-aluminum fine-particle ferromagnets: Microstructure and coercivity (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6958-6967 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic age hardening produced by decomposition of a β-CoAl(B2) alloy has been studied by correlating the microstructure with the changes in magnetic properties during aging. A model based on coherent rotation has been developed to describe quantitatively the intrinsic coercivity of these fine-particle ferromagnets as well as the temperature dependence of the coercivity over the temperature range from 77 to 757 K. The model incorporates both magnetocrystalline anisotropy constants K1 and K2 in addition to the shape anisotropy of the elongated single-domain particles of metastable HCP cobalt which precipitate from solid solution during heat treatment. The magnetic properties of the particles are shown to depend critically on the crystallography of the solid-state transformation and particle morphology which were determined by transmission electron microscopy and diffraction.
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    Lorentz electron microscopy of iron-rare-earth-boron sintered permanent magnets (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6968-6975 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of domain walls with microstructural features in sintered Fe-Nd-B magnets has been investigated by Lorentz microscopy using a high-voltage transmission electron microscope. Grain boundaries that are normal to the wall do not affect the progress of a moving wall, while those that are parallel to the wall interact strongly. The effect of the grain boundary Nd-rich fcc phase on the movement of the wall appears to depend upon the thickness of the fcc phase. Inclusions inside the matrix phase that are within 1000 A(ring) interact with the walls to pin them, while larger inclusions do not. It is suggested that a uniform distribution of inclusions with magnetic properties very different from that of the 2-14-1 phase be used to pin domain walls in order to improve the temperature dependence of the intrinsic coercivity and remanence.
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    Particular behavior of the initial susceptibility in weakly stressed polycrystalline soft magnetic materials (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6976-6980 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of perpendicular compression on initial susceptibility of polycrystalline soft magnetic materials is investigated. In particular, it is shown that susceptibility magnitude does not decrease immediately with the stress applied. Consequently, a threshold is pointed out below which the domain-wall susceptibility keeps constant and equal to the initial value. Investigations of this threshold, between room temperature and the Curie temperature (550 K), has allowed a tight connection with intrinsic parameters of the spontaneous domain-wall arrangement to be established. In order to demonstrate this result, two types of materials have been prepared: perfect materials with domain-wall configuration approaching ideal orientation and defective materials with randomly dispersed domain-wall arrangement.
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    Crystal structure and magnetic softness of Fe-Si polycrystalline films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6981-6990 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic softness of polycrystalline Fe-based alloy films is investigated. From calculation of magnetocrystalline anisotropy and magnetostriction assuming the magnetization is confined in a certain crystal plane of bcc Fe or Fe-Si alloy, Fe alloy films with (111) orientation parallel to the film plane are expected to have good magnetic softness. Fe-6.9 wt. % Si polycrystalline films with various crystallographic orientations such as (100), (110), or (111) oriented parallel to the film plane plane are deposited on underlayers such as MgO, ZnO, and ZnSe by a high-rate sputtering system. Fe-Si films on ZnSe underlayers with (111) orientation exhibit smaller Hc and better thermal stability than those of films with other orientations. Magnetic softness and thermal stability are improved for the double-layered films with those orientations. For multilayered Fe-6.9 wt. % Si films on ZnSe underlayers, the Hc of deposited films is about 0.5 Oe, and is stable against annealing up to 500 °C.
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    Phase modulation in GaAs/AlGaAs double heterostructures. I. Theory (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6998-7005 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work aims at a systematic study of phase modulation in GaAs/AlGaAs double-heterostructure waveguides with different doping profiles. Both theoretical (part I) and experimental (part II) aspects are investigated, leading to interesting new results. Phase modulation is the sum of a linear electro-optic term, a quadratic electro-optic term, and a free-carrier term. The carrier term is shown to be the sum of a plasma term, an intervalence-band term (for holes only), a band-filling term, and a band-shrinkage term, the latter being due to many-body effects. A new analytic expression for the band-filling term is derived which shows that the band-filling effect does not depend on the carrier effective mass. We prove that the band-shrinkage term is approximately half of the band-filling term, but has opposite sign. The phase modulation is computed using an overlap integral between the optical intensity and the local refractive-index difference. We also report an analytic expression for the modulation efficiency of a p-i-n junction double-heterostructure modulator. This expression is very accurate and only requires knowledge of the depletion width and the guiding parameters.
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    URL: http://dx.doi.org/10.1063/1.345045
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    Phase modulation in GaAs/AlGaAs double heterostructures. II. Experiment (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7006-7012 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Phase modulation in GaAs/AlxGa1−xAs double heterostructures with different doping profiles is systematically investigated. Very good agreement between the experimental measurements and the theory developed in Part I of this paper is reported. By measuring the phase modulation for both transverse electric and transverse magnetic modes along the [110] and [11¯0] crystallographic directions, we are able to deduce accurate values for the linear electro-optic coefficient. Values of r41=−1.68×10−10 cm/V at λ=1.15 μm and r41=−1.72×10−10 at λ=1.09 μm are obtained with an estimated accuracy of ±5%. An accurate estimation of the carrier effect permits us to deduce the quadratic electro-optic coefficient for GaAs. The values are R11=−2.0×10−16 cm2/V2, R12=−1.7×10−16 cm2/V2 at λ=1.15 μm, and R11=−2.9×10−16 cm2/V2, R12=−2.4×10−16 cm2/V2 at λ=1.09 μm with an estimated uncertainty of ±25% for all values. Contrast measurement of Fabry–Perot fringes enables us to evaluate the modulator losses. A value of 4.8 cm−1 is reported for a P-n doped modulator (n=6×1017 cm−3). Free-carrier absorption is shown to be the dominant loss process in high-quality structures.
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    URL: http://dx.doi.org/10.1063/1.345046
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    Influence of mechanical grinding and polishing operations of brittle polycrystalline alumina on the pulsed surface flashover performance (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6991-6997 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The degradation of the pulsed surface flashover performance of 99.9% pure polycrystalline alumina in an insulator-bridged vacuum gap, due to the mechanical grinding and finishing of the insulator is reported. The flashover characteristics of three different surface finishes—as-fired (0.8 μm), a ground surface (0.25 μm), and a polished surface (0.05 μm)—were studied using time-coordinated voltage, current, and luminosity diagnostics with a temporal resolution of ∼1.5 ns, for 0.5/15-μs pulsed voltage excitations. The flashover strengths of the ground samples are lower than the as-fired sample by about 50% while the strengths of the polished surfaces are intermediate between the two. These results contradict earlier reports which attribute the lower holdoff of smooth finishes to the enhanced secondary emission yield as compared to the rougher surface finishes. The lower flashover strengths for the ground surface as compared to the as-fired surface are attributed by us to the surface defects consisting of intergranular and transgranular fracture features induced by the mechanical grinding operation. The improved performance of the polished surface over the ground surface is proposed to be due to the partial removal of the damage created during the grinding operations. The suggested increase in the defect density in the surface layers of ground and polished surfaces relative to the as-fired finish is substantiated by characteristic defect-dominated signatures in the luminosity-current profiles. These results are in agreement with an earlier report describing the role of trapped carriers in the flashover process. It is concluded that the insulating properties of the surface as influenced by the microstructural features are strongly dependent on the precise mode of material removal during grinding and polishing operations and hence cannot simply be correlated to the gross surface topography in terms of surface roughness, particularly for hard and brittle ceramic materials.
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    URL: http://dx.doi.org/10.1063/1.345044
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    Investigation of different Si-related photoluminescence emissions involved in a deep broadband in Al0.3Ga0.7As (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7013-7018 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed photoluminescence study of a deep broadband emission as a function of the dopant concentration is conducted in molecular-beam epitaxy-grown silicon-doped Al0.3Ga0.7As single layers. The deep broadband which is correlated to the Si concentration consists of several emissions among which three are suggested to be due to different Si complexes. The effects of annealing the samples contributed immensely to this investigation. A model to explain the direct and indirect participations of SiAs in the formation of Si complexes during heat treatment is proposed. The photoluminescence is complemented by the Hall-effect, capacitance, and secondary-ion-mass spectroscopy measurements.
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    Infrared absorption analysis of films deposited by glow-discharge of silane/helium mixtures (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7031-7033 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using infrared (IR) absorption measurements, it is proposed that amorphous hydrogenated silicon films obtained from plasma-enhanced chemical vapor deposition of Silane (SiH4 ) highly diluted in helium at high rf-power densities, consist of an amorphous tissue in which a columnar microstructure is embedded. The evolution of the IR spectrum with dilution evidences a remarkable tendency to the substitution of monohydrides by dihydrides. The films show high transparency and good conductivity. These properties make them suitable to be used as window layers for thin-film solar cells when conveniently doped.
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    URL: http://dx.doi.org/10.1063/1.346078
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    Cryogenic cathodoluminescence of plasma-deposited polycrystalline diamond coatings (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7019-7025 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The cathodoluminescence spectra of microwave plasma-deposited polycrystalline diamond films have been measured at liquid-nitrogen temperatures over the spectral region of 230–800 nm. The diamond coatings had been deposited under several different deposition temperatures and reactant compositions. Measurements on natural type-IIB diamond crystals were made for comparison. The intrinsic exciton emission bands which fall in the UV just below the band edge were observed, as well as several defect and impurity bands which extend throughout the visible part of the spectrum. SEM micrographs and Raman spectra were obtained for the same set of samples used for the cathodoluminescence measurements. It was found that the diamond-related cathodoluminescence features were most intense in samples whose Raman spectra exhibited the most intense cubic diamond line at 1332 cm−1 and the least intense graphitic band at about 1500 cm−1.
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    Ge redistribution in solid-phase Ge/Pd/GaAs ohmic contact formation (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 334-339 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A backside secondary ion mass spectrometry technique is employed to examine elemental redistribution in the Ge/Pd/GaAs ohmic contact as a function of annealing conditions. Dilute Al containing marker layers (Ga1−x Alx As) in the GaAs permit precise calibration and alignment of the elemental depth profiles. Double etch-stop thinning yields high depth resolution. The onset of ohmic behavior is found to occur when Ge is detected at the GaAs surface. Good ohmic behavior is observed when an interfacial layer of reacted Pd4GaAs is dispersed and complete coverage of Ge occurs. The Ge/GaAs interface is abrupt with the Ge concentration dropping by over three orders of magnitude within 100 A(ring). About 40 A(ring) of GaAs is found to be consumed during the ohmic contact formation. Degradation of the ohmic contacts, as a result of further heat treatment, was found to correlate with Ge in-diffusion into the GaAs. The results place strict limitations on doping and heterointerface models of ohmic behavior for this contact.
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    A single hybrid interferometer for infrared and visible testing (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7059-7064 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An infrared (10 μm) wave front is recorded holographically on a dynamic recording medium consisting of a thin oil film on a glass substrate. The phase hologram obtained is used to restore the information of the infrared wave front or alternatively as a diffraction grating for a visible reconstruction beam. This property is applied to implement a single hybrid interferometer (Michelson or Mach–Zehnder) for the simultaneous testing of infrared and/or visible optical components. Experimental results for both visible and infrared components (parallel plate, lens) confirm the usefulness of this interferometer.
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    Properties and device applications of hydrogenated amorphous silicon carbide films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7065-7070 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogenated amorphous silicon carbide (a-SiC:H) films were deposited with a radio-frequency plasma-enhanced chemical vapor deposition system which utilizes a dc electric field applied independently of the inductively coupled rf field. The source gases were SiH4 and CH4. It was found that application of an electric field directed out of the substrate surface enhances the growth rate and yields some improvements in photoconductivity. The compositions of the films were evaluated by x-ray photoelectron spectroscopy for a range of source gas mixtures. In order to assess the applicability of a-SiC:H thin films, heterojunction a-SiC:H/crystalline Si (c-Si) diodes were fabricated and their electrical characteristics evaluated. The diode capacitance-voltage results confirmed a step junction, which was consistent with the abruptness of the interface demonstrated by high-resolution transmission electron microscopy. The heterojunction diodes also showed good rectifying properties, suggesting promise for a-SiC@B:H in device applications.
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    Growth of Al oxide layers on GaAs (100) by reaction with condensed molecular oxygen (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7148-7151 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An Al oxide-GaAs (100) interface fabricated by the reactive deposition of Al into a molecular oxygen overlayer on a gallium terminated GaAs (100) surface at T=49 K is studied by synchrotron radiation photoemission. Al forms a stable oxide layer by reaction with O2 until all the oxygen is consumed. Limited oxidation of surface As atoms (≈20%) is observed during the initial deposition of Al, but further Al deposition reduces the AsO bond. The well-known exchange reaction between Al and Ga when Al is directly deposited on GaAs (100) is not observed.
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    Interaction of a permanent magnet with a superconducting hollow cylinder (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7154-7156 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Meissner-effect interaction of a small permanent magnet with a superconducting hollow cylinder has been investigated by solving the Laplace equation numerically using a finite-difference method. The calculations reveal the existence of stable equilibrium configurations for a range of shapes and sizes of the cylinder. The computed magnitude of the Hooke's law force constant is close to those measured for small magnets levitated above superconducting disks.
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    Sequential power transfer between stripes of a diode laser array via photorefractive two-wave mixing in BaTiO3 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7160-7162 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the transfer of 48% of the incident power from a semiconductor laser array into a diffraction-limited beam by means of photorefractive coherent beam combination in BaTiO3, using a progressive two-wave mixing geometry. A single-element, photorefractive beam combiner is described which should allow the transfer of 88% of the power of a suitable array into a single diffraction-limited beam.
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    Characterization of high-purity InP by photoluminescence (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7165-7168 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InP polycrystals grown by the HB technique and InP single crystals grown by the liquid-encapsulated Czochralski technique have been evaluated by photoluminescence. It was found that as the carrier concentration is decreased, the photoluminescence spectrum shows finer structures. When the carrier concentration is less than 9×1014 cm−3, a strong free-exciton peak could be observed.
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    Titanium silicide as a diffusion source for arsenic (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7174-7176 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The matter transport of arsenic ions implanted into titanium silicide layers has been investigated after thermal diffusion treatment in the 800 °C–1100 °C temperature range. The arsenic atoms redistribute between TiSi2 and Si with a segregation coefficient depending on temperature. The diffused amount increases linearly with the square root of annealing time at 1100 °C. The n-doped shallow Si layer has a quite good electrical activity with a mean resistivity of about 1.2 MΩ cm. The leakage current of the reverse-biased n+/p junction is instead quite high. Stacking faults are observed in the diffused layer.
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    Theoretical model of gravitational perturbation of current collector axisymmetric flow field (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6099-6108 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Some designs of liquid-metal current collectors in homopolar motors and generators are essentially rotating liquid-metal fluids in cylindrical channels with free surfaces and will, at critical rotational speeds, become unstable. An investigation at David Taylor Research Center is being performed to understand the role of gravity in modifying this ejection instability. Some gravitational effects can be theoretically treated by perturbation techniques on the axisymmetric base flow of the liquid metal. This leads to a modification of previously calculated critical-current-collector ejection values neglecting gravity effects. The purpose of this paper is to document the derivation of the mathematical model which determines the perturbation of the liquid-metal base flow due to gravitational effects. Since gravity is a small force compared with the centrifugal effects, the base flow solutions can be expanded in inverse powers of the Froude number and modified liquid-flow profiles can be determined as a function of the azimuthal angle. This model will be used in later work to theoretically study the effects of gravity on the ejection point of the current collector.
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    URL: http://dx.doi.org/10.1063/1.345170
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    Control of plasma parameters and electric fields in a microwave-rf hybrid plasma (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6114-6117 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Control of electron energy and electric field in a low-pressure argon plasma produced by a hybrid (2.45 GHz microwave and 13.56 MHz rf) discharge was studied for thin-film preparation. The hybrid plasma was found to be useful over a wide range of magnetic field strengths, unlike conventional microwave plasma. A novel probe measurement revealed that the electron temperature and density were effectively controllable by the microwave power and the magnetic field strength, rather than the rf power, and the potential profile describing the electric field was controllable by the magnetic field strength. The control of an ion beam injected from the microwave into the rf plasma is described.
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    A theory of weak transient electrical discharges on dielectric surfaces (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6118-6124 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear evolution of transient electrical discharges initiated from a small charge spot on dielectric surfaces is analyzed with a transmission line model. The relation between the resistance per unit length, Rˆ, and the current, I, is assumed to be given by a local Arc Welder's Ansatz: Rˆ||I||=E*, where E* is a positive constant. Comparison is made with a similar study of discharges initiated from a large charge spot. While both studies predict conditions under which charge is, or is not, transported to a dielectric edge, significant differences in the two cases are revealed. For example, if charge is not transported to an edge, current reversal is possible if the charge spot is small, but can only be unidirectional if the spot is large.
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    Role of recoil implanted oxygen in determining boron diffusion in silicon (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6135-6140 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Annealing of silicon implanted with boron through a surface oxide results in an enhanced diffusion of boron. This enhanced diffusion is suppressed during an initial incubation period. An activation energy of 2 eV is associated with the enhanced diffusion, indicating excess silicon interstitials may be involved. On the other hand, the process leading to the onset of enhanced diffusion possesses an apparent activation energy of 3.7 eV. Two-step annealing reduces the latter value to 2.6 eV, the activation energy for interstitial oxygen diffusion. The different activation energies evaluated for the saturation process will be discussed. Transmission electron microscopy shows that the coalescence of dislocations, as well as the growth of faulted loops, proceeds rapidly after the incubation period for enhance diffusion. Precipitates along small dislocation loops are also observed after the incubation period. It is proposed that oxygen precipitation, with emission of silicon interstitials, predominates for annealing beyond the incubation period and is therefore responsible for the enhanced diffusion of boron. The enhanced diffusion sequence is initially incubated by trapping oxygen at dislocations. The real onset of the enhanced diffusion occurs when the dislocations are saturated and the oxide precipitation at the dislocations commences.
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    Vacancy-type defects in Si+ -implanted GaAs and its effects on electrical activation by rapid thermal annealing (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6153-6158 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The depth distributions of vacancy-type defects in Si+ -implanted and thermally activated GaAs were studied by a slow positron beam technique and were compared with the results observed with a transmission electron microscope. In as-implanted GaAs, the concentration of vacancy-type defects decreased monotonically with increasing depth below the surface and the generation of point defects was demonstrated by the lattice image of transmission electron microscopy. The vacancy concentration is not dependent upon activation conditions; however, the electrical activation coefficiency obtained from Hall measurements is enhanced with increasing activation annealing time. This indicates that the electrical activation of Si+ -implanted GaAs is proceeding by the exchange of interstitial Si with substitutional Ga rather than the recombination of interstitial Si into Ga-related vacancies. The maximum number of extrinsic-type stacking faults was observed at 70–80 nm below the surface after the activation annealing, which is compared with that of vacancy-type defects, at 25–35 nm, obtained by the slow positron beam technique. This discrepancy in both of the damage distributions could originate in different types of defects existing along the depth below the surface, which was discussed with the high-energy recoil theory.
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    MeV Be implantation in GaAs (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6165-6170 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-energy Be implantation was performed at 1, 2, and 3 MeV for a dose of 1×1013 cm−2 and at 2 MeV in the dose range of 4×1012–1×1014 cm−2. Range statistics from as-implanted secondary ion mass spectrometry profiles were calculated. The implanted wafers were activated by either conventional furnace or rapid thermal annealing. For the same implant dose, 1×1013 cm−2, the dopant electrical activation decreased with increasing ion energy. For the 2-MeV implants, the dopant electrical activation increased with the implant dose, in the range used in this study. An activation as high as 98% was measured for the 2-MeV/1×1014-cm−2 Be implant.
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    Cleavage energies in semiconductors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6175-6178 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a method for the calculation of the surface and cleavage energies, Eγ, for semiconductors, based on a tight-binding Green's function approach and a difference-equation solution for the layered structure. Energies are calculated for a representative group of semiconductors, and cleavage energies are found to agree well with the available experimental data. We find ESiγ(111)=1360 ergs/cm2, and Eγ(110)=1000, 180, and 120 ergs/cm2 for GaAs, CdTe, and HgTe, respectively.
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    Effects of etching with a mixture of HCl gas and H2 on the GaAs surface cleaning in molecular-beam epitaxy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6274-6280 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ cleaning of GaAs substrates with a HCl gas and hydrogen mixture prior to molecular-beam epitaxy has been investigated. The chemical reaction during etching was monitored using a quadrupole mass spectrometer. After etching, reflection high-energy electron diffraction patterns revealed (2×4) arsenic-stabilized surfaces and (4×2) gallium-stabilized surfaces as reconstructed structures in the gas-etched substrate surface. These structures suggest that the gas-etched substrate surface is atomically flat, resembling an epitaxial layer surface. To study the effect of gas etching, the carrier depletion layer and the residual carbon impurity around the substrate epitaxial interface were measured by capacitance-voltage carrier profiling and secondary-ion mass spectroscopy. After gas etching, the carrier depletion was greatly reduced, from 1.2×1012 to 1×1010 cm−2. The carbon impurity around the interface also decreased by one order of magnitude. We discussed the surface-cleaning mechanism using the atomic hydrogen terminating model of the GaAs surface during etching. We then applied this etching technique to in situ cleaning of semi-insulating GaAs substrates prior to the growth of selectively doped GaAs/N-AlGaAs heterostructures with very thin GaAs buffer layers.
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    Hydrogen incorporation scheme in hydrogenated amorphous silicon/silicon carbon multilayers (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6301-6305 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using infrared absorption spectroscopy, we investigated the scheme of hydrogen incorporation into the well layer (a-Si:H) of a-Si:H/a-Si1−xCx :H (x=0.2, 0.5, and 0.8) multilayers fabricated by a glow discharge method. Hydrogen atoms are incorporated into the well layer in the form of the 2090-cm−1 mode, i.e., SiH monohydride bonds on internal microvoid surfaces or SiH2 dihydride bonds up to a well-layer thickness of 40 A(ring), and then SiH monohydride bonds of the 2000-cm−1 mode are formed. Even up to 100 A(ring), hydrogen atoms of the 2090-cm−1 mode are dominant rather than SiH monohydride bonds of the 2000-cm−1 mode. The optical energy gap of the multilayer is also discussed in connection with the scheme of hydrogen incorporation.
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    Characterization of the EL2 center in GaAs by optical admittance spectroscopy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6309-6314 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the electron optical capture cross section, σ0n(hν), of EL2 (the most important native center in GaAs) using a new technique which we have recently developed: optical admittance spectroscopy. This is a spectroscopic technique based on the measurement of the capacitance and conductance of a junction under monochromatic light of energy hν. This technique allows the measurement of the spectrum σ0n(hν) of each center located in the band gap. We have measured the electron photoionization cross section of the EL2 center, σ0n(hν), at three different temperatures within a range limited at high temperature by thermal emission and at low temperature by photoquenching (a feature characteristic of EL2 below 140 K). The study of the experimental data reveals that this center has a more complex nature than that of a simple defect. It seems to behave like a family of very close levels corresponding to similar atomic structures and located near the midgap. These results also reveal the existence of a shallow level close to the valence band and associated with EL2.
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    URL: http://dx.doi.org/10.1063/1.345149
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    Trap emission rates in GaAs in the presence of surface acoustic waves (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6315-6322 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental and theoretical analyses of the effects of surface acoustic waves (SAW) on trap emission rates in GaAs are presented. Measurements of electron trap emission rates using deep level transient spectroscopy measurements performed in the presence of SAW are discussed. For the three trapping levels investigated, the observed increases in the trap emission rates can be described by trap activation energies which decrease in direct proportion to the SAW power. A theoretical analysis of the effects of the acoustic strain, electric field, and heating associated with the SAW is also presented. This analysis is used to predict the magnitude and functional dependence of the emission rate enhancement. The theoretical predictions follow the same functional dependence as the experimental data but the predicted magnitudes of the shifts in trap energies are about a factor of 2 lower than the measured values.
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    URL: http://dx.doi.org/10.1063/1.345150
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    Identification and ionization energies of the shallow donor metastable states in GaAs:Si (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6323-6328 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transitions from the 1s0 ground state to the shallow donor metastable states in n-GaAs have been investigated at a temperature of T=4.2 K, magnetic fields up to 6 T, and for far-infrared transition energies between 50 and 300 cm−1. The final states of these transitions have been identified and characterized by high-field quantum numbers. The magnetic-field dependence of the ionization energies of some of these metastable states have been determined.
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    URL: http://dx.doi.org/10.1063/1.345151
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    The theory of the photoconductance under the presence of a small photocarrier grating (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6329-6333 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently, responding to the need for the determination of the minority-carrier diffusion length in noncrystalline materials and devices, Ritter, Zeldov, and Weiser suggested a new photocarrier grating technique that became very popular among researchers of these materials. In this paper we present the first closed-form solutions for the photoconductance of the corresponding physical system. This system consists of a photoconductor that is subjected to both a uniform illumination and a periodically varying illumination of much lower intensity. The present analysis, which considers the effect of trapping, enables the evaluation of the conditions under which the experimental results can be uniquely translated into the value of the ambipolar diffusion length and thus into the mobility-lifetime (μτ) product of the minority carriers. In particular it is shown that the larger the shallow trapping the more justified the above translation.
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    URL: http://dx.doi.org/10.1063/1.345152
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    Effects of substrate temperature on the electrical and physical properties of silicon dioxide films deposited from electron cyclotron resonant microwave plasmas (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6347-6352 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Silicon dioxide films have been fabricated at growth temperatures ranging from 25 to 330 °C from an electron cyclotron resonant microwave plasma. Films were deposited from a SiH4/Ar/N2O reactant gas mixture. The minimum temperature required to fabricate high-electrical-quality silicon dioxide films is between 255 and 290 °C. In metal-oxide-semiconductor devices, electron injection field strengths and breakdown field strengths were as high as 5 and 8 MV/cm, respectively, for oxides grown above this temperature range. Films grown at temperatures slightly below the 255–290 °C range have much poorer electrical integrity. A concomitant increase in the refractive index was observed with the improvement in the electrical integrity of these films. The refractive index increased with increasing growth temperature and was in the range of 1.44–1.47. In the 255–290 °C temperature range, the refractive index of the silicon dioxide films reached approximately 1.46–1.47, and saturates thereafter. Infrared spectroscopy indicated a hydrogen content in these films of approximately 4 at. %. The hydrogen was bonded as SiOH, while no SiH impurity groups were detected. The dependence of the deposition rate on the substrate temperature was dependent on the location of the substrate. For films grown on substrates in contact with the plasma, the deposition rate was found to decrease with increasing substrate temperature. In contrast, for films grown on substrates located in the plasma afterglow, the deposition rate increased with increasing substrate temperature.
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    Theoretical and experimental study of the longitudinal uniaxial stress dependence of I-V characteristics in GaAs-AlxGa1−xAs-GaAs heterojunction barriers (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6360-6367 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tunneling and thermionic emission through n+-GaAs–i-AlxGa1−xAs–n-GaAs heterojunction barriers are studied as a function of temperature from 77 to 200 K and as a function of externally applied uniaxial stress up to 10 kbar. A procedure to extract parameters for theoretical calculations is also proposed. The parameters extracted from the I-V characteristics of these heterostructures grown on (100) GaAs substrates with different aluminum mole fractions from 0.3 to 0.8 and thicknesses from 300 to 400 A(ring) agree well with those of previous reports. The dependence of the I-V characteristics on uniaxial stress in the 〈100〉 direction perpendicular to the heterojunction plane has also been measured. The experimental results show good agreement with theoretical calculations assuming there is a linear stress-dependent decrease of the energy-band edges of the longitudinal X valleys (Xl) in AlGaAs with respect to the Γ valley in GaAs. The slope of the decrease is found to be 14±2 meV/kbar. This results in an X-valley shear deformation potential of 9.6±1.8 eV, which is believed to be the most accurate measured value to date.
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    URL: http://dx.doi.org/10.1063/1.345157
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    Hall measurements as a function of temperature on monocrystalline SiC thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6375-6381 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hall measurements were conducted at temperatures up to 1000 K on unintentionally doped n-type β(3C)- and α(6H)-SiC thin films epitaxially grown on both on-axis and vicinal Si (100) and α(6H)-SiC (0001) by chemical vapor deposition. The carrier concentration versus temperature data were analyzed using a compensation model. The β-SiC films grown on Si were highly compensated (NA/ND=0.73–0.98). The compensation ratio was not as large in the SiC films grown on α-SiC (NA/ND=0.36, for β-SiC on α-SiC, and 0.02, for α-SiC on α-SiC). The donor ionization energy for β-SiC on Si was calculated to be 14–21 meV. Analogous values for β- and α-SiC films on α-SiC were 33 and 84 meV, respectively. These values are smaller than those for N determined from photoluminescence studies.
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    Phase coherent length measurements in single-crystal NiSi2 films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6368-6374 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The phase coherent length lφ of conduction electrons in single-crystal NiSi2 films has been measured using weak localization phenomena. Logarithmic temperature dependence and logarithmic magnetic-field dependence of the conductivity observed in epitaxially grown NiSi2 single-crystal films with thicknesses from 6 to 40 nm are interpreted in terms of the two-dimensional weak localization with strong spin-orbit interaction. Considerably long-phase coherent lengths are obtained by fitting analyses using magnetoconductance data; lφ=0.8 μm at 4.2 K and 1.5 μm at 2 K. This is due to a very low concentration of magnetic scatterers in NiSi2. Because of its long-phase coherent length, the single-crystal NiSi2 film can be applied to novel quantum interference devices.
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    URL: http://dx.doi.org/10.1063/1.345158
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    Rapid thermal processing of YBa2Cu3O7 spun wires (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6382-6388 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rapid thermal processing has been utilized to sinter and anneal phase-pure and CuO-rich YBa2Cu3O7 fibers and woven fibers formed by melt spinning a powder/polymer composite. The optimum temperature for sintering the powders varies for the stoichiometric (1025 °C) and 5% CuO-rich fibers (1000 °C), but in both cases the temperature window is extremely narrow (±25 °C). Typical processing consists of a rapid heating (250 °C/s) of the fibers to the sintering temperature in 1 atm of pure oxygen, holding at temperature for 1 s and cooling over a period of 2–3 min. The resulting fibers are orthorhombic YBa2Cu3O7 with large Meissner and shielding fractions, have zero resistance up to 92 K, critical-current densities in zero applied field to 1100 A/cm2 at 76 K, and show clean grain boundaries by transmission electron microscopy. Despite the short processing times, microstructural analysis shows considerable grain growth and evidence of metastable congruent melting of oxygen-rich YBa2Cu3O7.
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    URL: http://dx.doi.org/10.1063/1.345160
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    Ion beam sputtering of in situ superconducting Y-Ba-Cu-O films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6389-6393 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Oriented superconducting YBa2Cu3O7 thin films were deposited on yttria stabilized zirconia and SrTiO3 substrates by ion-beam sputtering of a nonstoichiometric oxide target. The films exhibited zero-resistance critical temperatures as high as 83.5 K without post-deposition anneals. Both the deposition rate and the c-lattice parameter data displayed two distinct regimes of dependence on the beam power of the ion source. Low-power sputtering yielded films with large c-dimensions and low Tc's. Higher-power sputtering produced a continuous decrease in the c-lattice parameter and increase in critical temperature. Films having the smaller c-lattice parameters were Cu rich. The Cu content of films deposited at beam voltages of 800 V and above increased with increasing beam power.
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    Effect of third-element additions on properties of Co-Cr-based films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6394-6398 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fundamental effects of adding several elements to the Co-Cr system on the properties of Co-Cr-based films were extensively investigated. Tantalum, molybdenum, vanadium, and rhenium were chosen as the additives. A large amount of each element was added to a Co–17-at. % Cr film. Ta addition improved the squareness and suppressed the in-plane coercive force without lowering the perpendicular coercive force for the films with perpendicular magnetization. All the additives were effective in suppressing the grain growth. The ternary alloy films were likely to have finer grains than Co-Cr films. Ta was found to be the most advantageous in a wide range of the content, from the total balance of squareness, coercive force, and grain size. The recording characteristics of Co-Cr-Ta films were also examined in comparison with those of Co-Cr films. The recording density and the signal-to-noise ratio of Co-Cr-Ta films were appreciably higher than those of Co-Cr films.
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    Dielectric relaxation functions and models (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6399-6404 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric relaxation function is defined as the transient current generated by the application of a unit voltage. In analogy with viscoelasticity, a second relaxation function can be defined as the transient voltage generated by the application of a unit current. Each of these functions generates its own distribution function of relaxation times. If one of the distribution functions is truncated, the other has been found to contain single lines apparently devoid of physical significance. Using a particular test function derived from the Curie–von Schweidler law1,2 [Ann. Chim. Phys. 18, 20 (1899); Handbuch der Elektrizitaet und des Magnetisms (Barth, Leipzig, 1918), p. 286] it is shown here that such lines do not appear in all instances. On the other hand, the relaxation function, as a monotonously decreasing function, frequently is believed to contain only two types of parameters, one energy dissipative and another energy storing. However, using the same test function as above, one can prove that a relaxation function can contain all three types of parameters, one dissipative and two energy-storing ones. Therefore, a relaxation system cannot, in general, be defined as a two-parameter system. An energy-dissipative parameter represents resistive elements, while energy-storing parameters represent capacitive and inductive elements.
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    URL: http://dx.doi.org/10.1063/1.345163
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    Structural properties of (100) BaF2 on (100) InP grown by in situ rapid isothermal processing (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6411-6414 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
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    URL: http://dx.doi.org/10.1063/1.345165
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    Dielectric and pyroelectric properties of the morphotropic phase boundary lead barium niobate (PBN) single crystals at low temperature (10–300 K) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6405-6410 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature (10–300 K) dielectric and pyroelectric properties of morphotropic-phase-boundary lead-barium-niobate tungsten-bronze ferroelectric single crystals have been investigated. Strong "Debye-like'' dielectric dispersion, along a nonpolar direction (perpendicular to the polarization direction), has been observed and characterized by dielectric spectrum techniques. A direct charge measurement method has been used to study the low-temperature pyroelectric properties in polar and nonpolar directions. A "frozen-in'' polarization component in a nonpolar direction is also reported. The low-temperature relaxation effects are explained by the internal reorientation polarization perturbation and a thermally agitated local dipole fluctuation model.
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    Voltage ramp breakdown analysis of thick plasma-deposited Si3N4 metal-insulator-metal capacitors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6415-6426 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thick (570 nm) plasma-enhanced chemical-vapor-deposited Si3N4 films are analyzed by voltage breakdown and I-V measurements. Exponentials of the form exp(const/E) are shown to fit the log of the reliability function of such films. An expression for dielectric lifetime that is proportional to exp[(B+H)/(3E)] and that also is a function of the cumulative fraction of failed capacitors, F, is derived. B and H are, respectively, the tunneling-current and hole-generation exponential constants. For these films, B=339 MV/cm and H=120 MV/cm. Voltage breakdown is observed to occur either while the dominant current-transport mechanism is tunneling or during a higher-current mode. In the latter case, both B and a value for H can be determined from voltage breakdown measurements.
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    Optical dispersion relations for AlSb from E=0 to 6.0 eV (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6427-6431 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A complete set of the model dielectric functions, ε(ω), for calculation of the optical dispersion relations of semiconductors are presented. The model is based on the Kramers–Kronig transformation and includes the E0, E0+Δ0, E1, E1+Δ1, E'0 (E0+Δ'0), E2, E1, and Eidg (indirect-band-gap) transitions as the main dispersion mechanisms. Detailed analyses are presented for AlSb, and results are in satisfactory agreement with the experimental data over the entire range of photon energies (0–6.0 eV). Dielectric-related optical data of AlSb, such as the refractive index, the extinction coefficient, and the absorption coefficient, are also presented as an example of the ability of our model.
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    URL: http://dx.doi.org/10.1063/1.345115
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    Separation of optical thin-film and substrate absorption by means of photothermal surface deformation technique (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6575-6578 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photothermal surface deformation (PTD) technique is shown to be feasible to separate absorption losses of single-layer film and substrate absorption from each other by a completely contactless detection of the thermoelastic sample response only appropriately varying the focus radius of the heating beam. This offers a method for a depth-resolved distinction of absorptive regions within a layered structure by the help of lateral resolved PTD absorption measurements. Additionally, both the sensitivity and feasibility of the apparatus is demonstrated by selected results at 10.6 μm.
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    Deep level spectroscopy in p-GaSe single crystals (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6581-6582 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Deep levels have been examined in nonintentionally doped p-type gallium selenide single crystals using photoinduced current transient spectroscopy measurements. Two hole trapping levels at 0.20 and 0.80 eV above the valence band have been observed and the corresponding thermal capture cross section evaluated. The possible origin and nature of these centers are also discussed.
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    Gain enhancement in a free electron laser by two-stream instability (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6583-6585 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The gain of an electromagnetic wave in a free electron laser is calculated. It is demonstrated that when the electron beam develops instabilities, this gain can be enhanced. Calculations for the case of the two-stream instability show that the growth rate is more than seven times larger and the gain per pass can be increased by more than two orders of magnitudes.
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    URL: http://dx.doi.org/10.1063/1.345091
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    Fractal-like Si crystallization during interfacial reactions in thin Al/amorphous SiC layers (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6586-6588 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Interfacial reactions between thin films of Al and amorphous (a-) SiC annealed with tungsten-halogen lamps lead to the formation of Si fractal-like structures at temperatures as low as 275 °C in less than 100 s. By using a-SiC/Al/a-SiC sandwiches with different SiC/Al thickness ratios, it is shown that the nucleation of Si crystals is faster on smaller-grained Al. This is attributed to the higher Al surface energy and the increased density of high-energy multiple grain junctions in thinner (smaller grained) Al layers. When the Al layer is very thin (≤50 A(ring)) a solid-state amorphization reaction occurs between Al and a-SiC without subsequent Si crystallization. Formation of Al4C3 follows Si crystallization, or in the very thin Al layer, the amorphization reaction.
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    Nitrogen ion dynamics in low-pressure nitrogen plasma and plasma sheath (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 146-153 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser-induced fluorescence (LIF) excitation and time-resolved LIF spectroscopy have been used to explore the interaction of a nitrogen plasma with a metal surface. The rotational temperature, the concentration of N+2, and the lifetime of N+2(B2Σ+u)υ=0 were measured as a function of distance from the metal surface. It was observed that the lifetime of the excited ion decreases sharply in the plasma sheath which is created in front of the metal surface. The concentration of N+2(X 2Σ+g), which was measured simultaneously with the lifetime of excited N+2, indicates a quasilinear decrease from the cathode to the grounded surface. Trot undergoes a gradual reduction from the bulk plasma up to the surface where its value is a good approximation of the surface temperature. An interpretation of these phenomena including a numerical simulation of the lifetime decrease is proposed here. The calculated values are in good agreement with experimental results. The dependence of lifetime decrease on the sheath potential as well as on other important parameters (cross section, profile of the electric field) is further discussed.
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    A model of dc glow discharges with abnormal cathode fall (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 154-162 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model for an abnormal glow discharge, including a self-consistent analysis of the cathode fall, was developed. It combines microscopic particle simulation by means of Monte Carlo methods with a fluid model of the gas discharge. The model allows calculations of the steady-state electrical field distribution, the charged-particle densities, and the current densities along the axis of the discharge. The model was used to simulate a glow discharge in 80% He and 20% SF6 at a pressure of 8 Torr with a current density of 1 A/cm2. The computed discharge voltage agrees well with measured values. The computer code can easily be modified to describe the charged-particle densities and energies not only in the cathode fall region, but in any plasma boundary layer.
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    Dynamical response of cholesteric liquid crystals under dilative stresses (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 169-172 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a theoretical treatment and experimental data for the dynamical behavior of a cholesteric liquid crystal submitted to uniaxial dilative strains applied along the helical axis. The results show the importance of the permeative contribution in the transient regime before a new equilibrium state is found where the apparent pitch is varied.
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    Isotopic exchange in hard amorphous carbonized layers (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 163-168 
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    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hard amorphous films of a-C:H and a-C:D were deposited by a rf glow discharge in either CH4 or CD4 . By ion bombardment with protons and deuterons, the H/D exchange process was studied as function of the bombardment fluence by means of depth profile measurements. The local hydrogen and deuterium contents are not adding up to a constant "saturation'' value: the local mixing model is not valid. Instead of that an initial depletion appears, which depends on the incident energy of the ions. At higher fluences, the total (H+D):C ratio tends to increase again, due to an increasing influence of the deposition process. This demonstrates a structural difference between a-C:H films and hydrogen-saturated layers of implanted carbon.
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    URL: http://dx.doi.org/10.1063/1.345296
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    Neutron and proton irradiation of shallow channel GaAs direct-coupled field-effect-transistor logic devices and circuits (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 173-179 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron and proton irradiations have been performed on self-aligned GaAs metal-semiconductor field-effect transistors (MESFETs) and resistors utilizing shallow ion-implanted channels. FET threshold voltage shifts during irradiation were lower than reported elsewhere (less than 115 mV for a −0.85 V threshold FET irradiated by 4.3×1014 neutron cm−2). This is shown to be explained by the shallow active layers used. A neutron carrier removal rate between 20 and 25 cm−1 is necessary to fit the FET data. Carrier removal rates derived from resistor damage were 150 cm−1 for peak doping levels of 4×1017 cm−3, greatly in excess of those derived from epitaxial or bulk GaAs resistors, and inconsistent with values obtained from threshold shifts of FETs with identical active layers. Resistor and FET threshold voltage changes for 52 MeV proton irradiation were nearly an order of magnitude greater than for an equivalent dose of 1 MeV (Si) neutrons. The extrapolated worst-case failure dose of direct-coupled FET logic inverters was better than 1.8×1015 neutron cm−2 despite the limited noise margins of this logic scheme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345277
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  • 94
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    Compositional and magnetic properties of iron nitride thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7514-7519 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The compositional and magnetic properties of iron-nitride thin films deposited by dc reactive magnetron sputtering under various nitrogen partial pressure conditions have been investigated by x-ray diffraction, Mössbauer and Auger electron spectroscopy as well as magnetic measurements. The x-ray diffraction patterns indicate a mixed phase composition. 57Fe Mössbauer spectroscopy shows that part of the nitrogen atoms are randomly distributed on interstitial sites with the formation of nonstoichiometric compounds. The excessive width of the Mössbauer lines indicates the degree of disorder of the different iron nitride precipitates. The nitrogen concentration as a function of depth is obtained by sputter-etched Auger electron spectroscopy. Furthermore, the ferromagnetic films show moderate saturation magnetization and coercivities at room temperature as compared with pure iron thin films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345812
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  • 95
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    The effect of electron irradiation on YBa2Cu3Ox with gold bead contacts (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7478-7482 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the effect of 1-MeV electron irradiation up to a total dose of 5.7×1017 electrons/cm2 at room temperature on YBa2Cu3Ox with gold bead contacts made by the melting technique. We measured the superconducting transition temperature Tc, the critical current density Jc at 77 K, the normal-state resistivity, and the contact resistance for gold bead contacts as a function of fluence on the same samples without disturbing the contacts. Tc remained constant at 91 K, and Jc at 77 K remained constant around 90 A/cm2. The normal-state resistivity increased systematically by about 15% for the total dose. Finally, the surface contact resistance at 77 K remained less than 4.2 μΩ cm2 throughout the radiations. These studies took place over an 8-month period, and subsequent measurements indicate that the results are definitely due to radiation effects and not aging effects. Since the total dose represents 120 years of electron exposure in geosynchronous orbit, we conclude that the superconductor YBa2Cu3Ox with gold bead contacts would perform well in a space environment of electron irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345833
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  • 96
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    Physical and electromagnetic properties of Y-Ba-Cu-O superconductors synthesized with peroxides (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7488-7492 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The physical and electromagnetic properties of Y-Ba-Cu-O superconductors synthesized with BaO2 (barium peroxide) have been studied. A comparison of reactions with BaCO3 and BaO indicates that the peroxide promotes formation and strong alignment of platelet grains in planes normal to the c axis, yields material with larger grain sizes and aspect ratios, reduces the synthesis reaction time by over half, increases the volume fraction of material that goes superconducting (Meissner effect), and facilitates metallic conduction in the normal state. Critical current densities of 1.1×104 A/cm2 at 77 K have been observed in peroxide-synthesized material. These beneficial effects may be due to the low melting temperature of BaO2 (450 °C), and the elimination of residual unreacted BaCO3, BaO, and/or C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345835
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  • 97
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    Surface layers on superconducting Y-Ba-Cu-O films studied with x-ray photoelectron spectroscopy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 7483-7487 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray photoelectron spectroscopy (XPS) examines only a thin surface layer (〈5 nm) that may not be representative of the bulk. We separated the information from the surface and bulk by using laser-deposited superconducting films that have nearly atomically flat surfaces for which quantitative analysis formalisms exist. The chemical compositions of high Tc (90 K) and high Jc (〉106 A/cm2) Y-Ba-Cu-O films on SrTiO3 (001) substrates were examined. From the relative intensities of the surface and bulk components of the Ba(3d) and Ba(4d) spectra taken at different take-off angles and different escape depths [using Al Kα (1486.6 eV) and Mg Kα (1253.6 eV) excitations], we have determined the nonsuperconducting surface layer thickness to be 1 nm and the layer composition to be BaCuO2. The surface layer thickness for a superconducting film only 8 nm thick was also 1 nm. By detecting the substrate Ti signal through this film, and ruling out a high density pinholes, we provide evidence that the XPS data contain information from the superconducting phase. A polycrystalline pellet scraped in vacuum had a surface layer only 0.4 nm thick. Since typical photoelectron escape depths are about 2 nm, about 80% of the detected signal originates in the bulk. The surface layer contains Cu2+ and oxygen with a photoelectron binding energy of 531 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345834
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  • 98
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    On the effect of asymmetries on the jet from a linear shaped charge (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6701-6704 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The jet from a linear-shaped charge is formed by the collapse of the wedge-shaped liner brought about by the passage of the detonation wave through the surrounding explosive. There is a variety of possible sources of asymmetry which can affect this process. The thickness distributions along each face of the liner may vary. The detonation wave may traverse the liner asymmetrically. The quantity or other properties of the explosive adjoining the liner arms may differ. In such situations the velocities imparted to opposite liner elements at equal distances from the intersection of the arms will in general be different. Thus a pair of liner elements which do meet will in general have started from different distances down their respective liner arms, and will not meet on the axis of symmetry of the charge. This effect causes the process of formation of the jet at the meeting point to occur asymmetrically. This paper presents an investigation of this phenomenon. We generalize the classical analysis of the symmetric steady-state collapse of a liner to include the asymmetries we have described. We present an extension of the classical jet formation theory to the asymmetric case by making several simple physical assumptions. We consider an example of a typical asymmetry in liner thickness and recover values for the off-axis velocity of the jet of the order observed in experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345107
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  • 99
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    Theory of multistage intense ion-beam acceleration (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6705-6717 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present an analytic theory for magnetically insulated, multistage acceleration of high-intensity ion beams, where the diamagnetic effect due to electron flow is important. Our theory is an extension of the single-stage diode theory developed by Desjarlais [Phys. Rev. Lett. 59, 2295 (1987)], based on a self-consistent calculation of the virtual cathode position, which has been successful in modeling Applied-B ion diode experiments on several accelerators. The new theory incorporates a finite injection energy qW for the beam ions. We have found a critical voltage V1(W) that corresponds to V* of the single-stage theory. As the voltage approaches V1, unlimited beam-current density can penetrate the gap without the formation of a virtual anode because the dynamic gap goes to zero. At voltages lower than V1, a sufficiently large injection current will cause the formation of a virtual anode in response to the large beam space charge. Furthermore, we have found that unlimited beam current can penetrate an accelerating gap operated above a second critical voltage V2(W). At voltages below V2, there is a maximum steady-state current that can be transmitted through the gap. The critical voltage V2 is smaller than V1 and is unique to the multistage theory. If fluctuations allow electron transport across magnetic field lines so that any virtual anode is neutralized, V2 goes to zero for all beam injection energies. This effect can be used to test the importance of field fluctuations on the electron dynamics in magnetically insulated ion acceleration gaps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345108
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  • 100
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    Copper emissions from pulsed discharges in CF4/O2 and Ar (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6728-6733 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Emission from atomic copper and CuF is characterized in a pulsed dc discharge in CF4/O2/Ar with a copper electrode. Similar emission is seen from neat Ar discharges, provided that a F- (or H2O-) containing plasma has been operated first. Near the electrode surface emissions from CuF and lower-energy states of Cu are observed. In the bulk of the plasma, additional emission is seen from more energetic states of Cu at the end of the pulse. Lifetime and energy considerations suggest that much of the Cu emission seen in Ar plasmas may arise from collisions between argon metastables and some molecular species, such as CuF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345110
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