摘要:

The positron lifetime spectra and ionic conductivity have been measured for poly(ether urethane)‐LiClO4polymeric electrolyte as a function of temperature. The glass transition temperatureTg, free‐volumeVf, and fractional free‐volumefwere derived from the positron annihilation parameters. A correlation between fractional free‐volumef(T) and conductivity &sgr; aboveTg, log[&sgr;/&sgr;(Tg)]=C1[f(T)−f(Tg)]/f[T], was first experimentally confirmed using measured positron annihilation results. The comparison of the value of the obtained constantC1with the universal values for the segmental diffusion of amorphous polymers indicated that the critical free volume required for the ion transport is much smaller than that required for polymer chain segment mobility. Carrier transport and the segmental motion are discussed in terms of the free‐volume theory. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359326

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have investigated the optical properties of GaAs/AlAs superlattices grown by molecular beam epitaxy (MBE) and atomic layer MBE (ALMBE) on {113}A‐oriented GaAs substrates. The corrugation which appears in the samples obtained by MBE does not exhibit any periodicity. Phonon‐associated replicas are only observed on the photoluminescence excitation spectra of ALMBE superlattices. It was found that the observed differences can be attributed to the growth techniques employed in the synthesis of the samples: MBE superlattices have rougher interfaces than the ALMBE ones, but a lower number of nonradiative recombination centers. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359523

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Surface analysis of bismuth‐based high‐Tcsuperconductors, like Bi2Sr2CaCu2O8+&dgr;(Bi‐2212) and Bi2Sr2Ca2Cu3O10+&dgr;(Bi‐2223) has been carried out by secondary ion mass spectrometry and x‐ray photoelectron spectroscopy techniques. The results have been compared with that of similar measurements on Bi2O3, CuO, and CaCO3samples so as to have detailed information about the surface binding energy as well as the chemical nature of the various individual components that exist inside these high‐Tccompounds. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359327

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Replicas of a mask are etched in Si wafers with a micrometer lateral resolution and typical depths of 200 nm by irradiation with filtered synchrotron radiation using cutoff wavelengths of 105, 122, and 150 nm. An excellent selectivity and anisotropy is obtained by suppressing the spontaneous etching of the XeF2etch gas (typical 10−2mbar) with O2or Ar buffer gas (typical 1 mbar). The efficiency of etching increases by more than two orders of magnitude by reducing the wavelength from longer than 150 nm to the spectral range of 105–122 nm. The number of removed Si atoms per incident photon reaches a value above unity for the short wavelengths. This very high quantum efficiency, which exceeds that in the visible spectral range by more than four orders of magnitude, is attributed to selective electronic excitation of a thin fluorosilyl layer on top of the Si wafer. The low probability of absorption in this layer implies a reaction efficiency far above unity. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359329

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Undoped polycrystalline Si (poly‐Si) films were deposited as a function of the rf power (0–30 W) and deposition temperatureTd(600–750 °C) using disilane by a plasma‐enhanced chemical vapor deposition (PECVD) method. For comparison, poly‐Si films were also deposited using monosilane. The preferential orientation to a random, (100), or (110) texture was able to be selected by changing some of these deposition conditions. It was suggested that the change in the texture is caused by a change in the surface‐diffusion coefficient of SiHnadsorbates and by effects of an ion bombardment, rather than by a change in the deposition rate. For PECVD poly‐Si films, both the x‐ray relative intensity and the crystallinity rapidly decreased with decreasing the film thickness thinner than 0.4 &mgr;m. The value ofgin the electron spin resonance spectra and that of stress strongly depended on the rf power and the thickness. Further, when a film was annealed in H2plasma, the value ofgshifted from 2.0054 to 2.0043. These results are examined in terms of formation of different types of grain boundary which can be associated with a lattice deformation around the dangling bonds. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359330

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Easy to make, patterned, Schottky barriers are investigated. In particular, the following aspects have been considered: the patterning technique, the electrical barrier height, and potential usage as solar cells. Patterning of the Si surfaces was achieved by photoablation process using an UV excimer laser in a presence of various solutions. Using a 5 mW red HeNe laser launched at various angles on the Si surface we have found that patterned solar cells ablated with 2:3:100 of HF:HNO3:H2O were as much as 23% more efficient than nonpatterned cells. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359331

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Edge‐defined film‐fed growth (EFG) Si grown with carbon monoxide (CO) added to the Ar ambient during crystal growth yields solar cells with higher efficiencies than when grown without CO. This increase in cell efficiency is not fully understood. Surface photovoltage, deep‐level transient spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to determine the minority carrier diffusion lengths, impurity distributions, and defect structures in uncontaminated, Cr contaminated, and V contaminated EFG material grown with and without CO added to the Ar ambient. We conclude that ‘‘SiC‐like’’ complexes in the near‐surface region of the CO ambient material act as gettering sites during crystal growth, and that this gettering action results in lower bulk impurity levels and higher solar cell efficiencies. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359332

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have measured the current‐voltage, flux‐voltage, and noise characteristics of 77 K superconducting quantum interference devices made with step edge junctions and multilevel edge junctions on SrTiO3substrates and with step edge junctions on LaAlO3. We find in each case that theI‐Vcurves can have excess currents of up to 50%–80%, that the responsivity, ∂V/∂&Fgr;, can be substantially smaller than expected from the resistively shunted junction (RSJ) model, but that the white noise voltage spectral density is about as expected. We discuss the extent to which the reduction of the responsivity is correlated with the excess current. We note that the observed unchanged magnitude of the voltage noise and the reduced responsivity would both be expected if we based the RSJ predictions on a model in which the excess current is not considered part of the Josephson current. Finally and perhaps fundamentally, we find that simulations made assuming a nonsinusoidal current‐phase relationship give rise to an excess current, a reduction of the responsivity, and little change in the voltage noise spectral density, at least qualitatively as is observed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359333

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report measurements on current‐voltage (I‐V) characteristics of externally shunted Josephson tunnel junctions where the external shunts have nonzero inductance. At low temperatures (T<6.6 K), we observe standardI‐Vcurves, but as temperature is increased above 6.6 K we observe an anomaly in theI‐Vcurves. We attribute this anomaly to the nonzero inductance in the shunt loop. Numerical simulations which properly take into account the effect of inductance show that the dynamics in the anomalous region of theI‐Vcurve are dominated by subharmonic relaxation oscillations. We use a load‐line analysis model to study the transition between the relaxation oscillations and the Josephson oscillations. The analysis is in good agreement with our data. Our analysis further predicts, and our data confirms, that in order for the relaxation oscillations to occur it is necessary to have &bgr;C=2&pgr;IcR2sC/&Fgr;0<(4/&pgr;)2, regardless of the value of the inductance. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359334

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the formation of Schottky contacts, with a barrier height as large as 0.9 eV, on epitaxial InGaP grown on GaAs wafers. The contacts are formed by removing surface oxide layers. Thermal reactions between Ti and InGaP and/or surface treatment with buffered hydrogen fluoride solution are effective for selective removal of surface oxide. These methods do not decrease the InGaP film thickness. They are promising for fabricating GaAs metal‐semiconductor field‐effect transistors with a thin InGaP film for increased barrier height. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359335

出版商:AIP    

年代:1995

数据来源: AIP