摘要:

The semiempirical scaling law for flux pinning,Fp=ABnc2bl(1−b)mhas been tested for bronze process Nb3Sn conductors under uniaxial tension. The dependences of the bulk pinning forceFpon the upper critical fieldBc2 and the reduced field,b=B/Bc2, were weakly affected by strain. However, the factorA, which depends on the number and strength of the pinning centers, and on the Ginzburg‐Landau parameter &kgr; decreased by more than a factor of 20 when the compressive prestrain on the Nb3Sn was removed by application of external stress. The variations ofTcandBc2with strain suggest that the change in &kgr; is not sufficient to account for the change inA. Therefore, it is probable that strain induces microstructural changes which affect the number and/or strength of the pinning centers.

ISSN:0021-8979    

DOI:10.1063/1.327893

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Electron spin resonance (ESR), electron‐nuclear double resonance (ENDOR), and optical absorption have been used to investigate radiation effects in synthetic crystals of berlinite (AlPO4). Crystals from seeded and unseeded growth were included in the study and impurities in both types of samples were determined by emission spectrographic techniques. The presence of significant concentrations of Fe3+ions was verified by ESR measurements. When the berlinite samples were irradiated at 300 K with 1.7‐MeV electrons, six distinct hole‐like centers were created. Thermal anneal studies revealed that four of these centers decay near 425 K and the other two decay at 550 K. All six centers exhibited a hyperfine interaction with a 100% abundantI=1/2 nucleus. The irradiation induced a light orange coloration in the crystals and optical absorption spectra revealed a band at 520 nm along with additional absorption in the ultraviolet region. When the samples were irradiated at 77 K, two additional defects were produced which are not stable at room temperature. One of these latter centers is identified as atomic hydrogen.

ISSN:0021-8979    

DOI:10.1063/1.327894

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We report on the optical properties ofa‐Si : H prepared by cathodic sputtering of a Si target in an 80% argon/20% hydrogen reactive gas at ∼9×10−3Torr. The deposition rate &fgr; (by means of the rf voltage) and the substrate temperature were varied. The total hydrogen content [H] and the concentration of hydrogen involved in SiH bonds [H1] or in SiH2bonds [H2] were measured. We find [H]≳[H1]+[H2], two times higher in some preparation ranges (&ngr;?15 A˚/min or &ngr;=100 A˚/min), which implies the occurrence of hydrogen atoms H′ not bonded in the usual SiH or SiH2forms. The optical absorption coefficient, the optical energy gapE0, and the refractive indexnswere measured.E0decreases asvincreases, is independent ofTsfor &fgr;≳30 A˚/min, and decreases asTsincreases forv≳30 A˚/min.nsincreases toward the crystalline value as &fgr; increases andTsdecreases. The similarity of the properties of the layers obtained by sputtering and glow discharge is emphasized. We suggest equilibrium between hydrogen bonds as SiH and SiH2and the other form(s) and that the optical gap is controlled by the deformation of the silicon matrix by the various hydrogen species.

ISSN:0021-8979    

DOI:10.1063/1.327895

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Photoinduced charge carrier generation and trapping in an organic material, viz., Michler’s ketone (tetramethyldiaminodiphenyl ketone), in the form of a binder layer, has been studied. The material forms fairly good photoelectrets, stored charge being of the order of 10−9Coul. Photoelectret charge shows saturation effects for different polarizing parameters, viz., time of photopolarization, intensity of illumination, and applied voltage. An exponentially rising photoinduced voltage has been observed which persists even in the dark, i.e., the material forms an autophotoelectret state as well.

ISSN:0021-8979    

DOI:10.1063/1.327896

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The physical processes in photoacoustic microscopy are described with an emphasis on the unique capability for microscopic thermal wave visualization of the sample.

ISSN:0021-8979    

DOI:10.1063/1.327924

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The low‐temperature (2 K) photoluminescence (PL) of AlxGa1−xAs (0<x<0.25 was studied in an effort to characterize shallow acceptors in material grown by organometallic vapor phase epitaxy and liquid phase epitaxy techniques. The dominant shallow acceptor in nominally undoped AlxGa1−xAs specimens grown by both techniques was identified as Carbon, withEA=26 meV forx=0.EAwas observed to increase with increasingxto ∼36 meV atx∼0.20, as expected for an effective mass like center whereEA∝[m*(x)/&egr;(x)2]. The PL peak due to the conduction band to acceptor transition was found to become progressively broader with increasingx, which is attributed to increasing donor plus acceptor concentration. The acceptor Ge was studied in intentionally doped LPE specimens. It also behaves as a simple effective masslike center, withEGe∼40 meV for GaAs and 55 meV for Al0.2Ga0.8As, contrary to earlier reports of anomalous behavior.

ISSN:0021-8979    

DOI:10.1063/1.327844

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We have calculated the total emittance &egr;tofn‐type GaAs as a function of doping level and thickness in the temperature range between 300 and 1500 °K. &egr;tis related to the spectral emittance &egr;&lgr;, which in turn depends on the index of refraction, thickness, and absorption coefficient &agr;. To obtain a theoretical representation of &agr;, a model is constructed which includes contributions by the fundamental edge, interconduction band, and free carriers (acoustic and optical phonons and ionized impurities). Since this two‐parameter model offers a good description of assorted &agr; measurements with respect to wavelength, impurity level, and temperature, the evaluation of &egr;&lgr;is relatively straightforward. At each temperature, &egr;tis computed by the numerical integration of &egr;&lgr;over a wide wavelength range followed by normalization to &sgr;T4. The calculations show that &egr;tincreases with temperature and doping level. At 1300 °K, for a 1‐cm‐thick sample, as the carrier concentration rises from 1016to 1017cm−3, &egr;tincreases from 0.28 to 0.68, respectively. These results are compared with those for Ge and general comments are made on the &egr;tofp‐type and semi‐insulating GaAs. Finally, employing &egr;tas one of the parameters in the quasi‐steady state heat transfer/thermal stress model for dislocation generation in the Czochralski growth of GaAs, we explain the inherent difficulty encountered in pulling sizable defect‐free crystals in terms of the severe thermal strss generation in excess of the critical resolved shear stress. One realistic set of conditions that would lead to a dislocation‐free GaAs is small diameter (∼1 cm), light doping concentration (∼1016cm−3), and shallow ambient temperature gradient (<100 °K).

ISSN:0021-8979    

DOI:10.1063/1.327845

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Cathodoluminescence spectra from thin films of silicon dioxide on silicon dioxide were investigated. Four luminescence bands are observed in silicon dioxide in a conventional semiconductor device. Band A at 290 nm (4.27 eV) and band C at 560 nm (2.21 eV) increase substantially with increasing electron irradiation and originate from the electron beam induced defects. Band B at 415 nm (2.99 eV) is not intrinsic in pure silicon dioxide, but is observed in carbon implanted silicon dioxide. The depth‐dependent concentration of the luminescence centers for band B from carbon implanted oxide was close to the distribution of the implanted carbon and the luminescence center of band B was attributed to carbon in the silicon dioxide. Band D at 650 nm (1.91 eV) may originate from residual and/or adsorbed H2O. The technique of cathodoluminescence presented in this paper will be able to provide useful information on the defects and impurities in silicon dioxide.

ISSN:0021-8979    

DOI:10.1063/1.327846

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The stimulated emission from CdSe at 80 °K under nitrogen or dye laser excitation has been studied. Its dependence on the pumping laser wavelength, on the excitation intensity, and on the excited length of the sample has been investigated. Optical gain spectrum measurements confirm the attribution of the light amplification process to two different radiative mechanisms involving, respectively, the exciton‐exciton interaction and the electron‐hole plasma recombination, for a photoinjected electron‐hole densitync?1017pairs/cm3.

ISSN:0021-8979    

DOI:10.1063/1.327847

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Variation of &bgr;‐ray backscattering with the atomic number of target material has been studied using thick targets of polythene, aluminum, iron, copper, zinc, tin, silver, tungsten, and lead for five &bgr; emitters, viz.,35S,147Pm,204Tl,32P, and90Sr‐90Y. Effects of geometry and &bgr;‐ray end‐point energy have been investigated using a reflection geometry in which the geometry factors were varied by more than 40 and &bgr;‐ray energy varied over a range 0.167–2.27 MeV. It is found that the mean value of the index ofZdependence of &bgr;‐ray backscattering is 1.840.05 over these regions of geometry and energy. Deviations for soft &bgr; emitters have been confirmed as due to air absorption. The importance of these results in studies of two‐component systems is emphasized.

ISSN:0021-8979    

DOI:10.1063/1.327848

出版商:AIP    

年代:1980

数据来源: AIP