摘要:

New insulating Bi14(Sr0.33Ca0.67)5O26layered single crystals have been grown by a flux method and their crystallographic properties have been characterized. The crystals exhibited a smooth cleaved surface perpendicular to [001] orientation. The x‐ray precession camera analysis indicated the crystals have rhombohedral symmetry, belonging to a Laue group of 3¯m. Furthermore, some kinds of rare‐earth elements have been successfully substituted for lattice sites of the crystal. The variation of thec‐axis length reflected ionic radii of the rare‐earth elements substituted. Radiant luminescence has been observed in visible and infrared regions in the Er‐doped crystals, which was assigned to electron transition between spin‐orbit levels of trivalent Er ions in the crystal.

ISSN:0021-8979    

DOI:10.1063/1.348361

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A set of resistivity‐temperature (R‐T) curves measured under various applied fields in a high‐TcBi‐Pb‐Sr‐Ca‐Cu‐O thin film which has a zero‐resistance temperatureTc0of 110 K is reported. The remarkable broadening of the transition width is discussed under the flux‐creep model, considering the very short coherence length of this oxide superconductor. The resistivity is thermally activated, which is consistent with the Arrhenius law with a magnetic field and orientation‐dependent activation energyU0(H,&THgr;). TheU0(H,&THgr;) has a very high value of 381.6 meV under a field of 0.1 T parallel to thecaxis. The upper critical fieldHc2determined from theseR‐Tcurves shows high values and the effect of flux creep to theHc2(0) is examined by the irreversible behavior with the ‘‘giant’’ flux‐creep model.

ISSN:0021-8979    

DOI:10.1063/1.348362

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Measurements of the magnetic anisotropy of a series of Pd/Co multilayers grown by magnetically enhanced dc triode sputter deposition revealed an interface contribution of 0.53 erg/cm2and a net volume anisotropy of −13.2×108erg/cm3. A characteristic reduction of perpendicular anisotropy for ultrathin Co layers (<4 A˚) is explained by using a pair interaction model to evaluate a thickness dependence of the interface anisotropy. For Pd‐Co interfaces with perfectly sharp composition modulation an interface anisotropy of 0.79 erg/cm2is predicted. By modeling the magnetization behavior a domain‐wall energy density of 2±0.5 erg/cm2is obtained for Pd/Co (2 A˚) multilayers with Pd thicknesses in the range of 4–20 A˚. For perpendicular Pd75Co25alloy thin films the same model gives domain‐wall energy densities in the range of 1–2 erg/cm2. For ultrathin Co layers the interlayer Co–Co coupling range is ∼20 A˚. Temperature dependence of saturation magnetization of a Pd(11 A˚)/Co(7.8 A˚) multilayer demonstrates complete mixing of Pd and Co by 380 °C.

ISSN:0021-8979    

DOI:10.1063/1.348363

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

TheJ‐aggregates with variation of size of 3,3’‐disulfopropyl‐5,5’‐dichloro‐9‐ethyl‐thiacarbocyanine (Dye 1) were formed on the surface of octahedral AgBr microcrystals in a photographic emulsion, and their size was evaluated by a spectroscopic method. Light‐induced electron transfer from the aggregates to the microcrystals left positive holes in the aggregates, which gave rise to an electron‐spin resonance (ESR) signal. The intensity of the ESR signal increased, and the rate of its decay decreased, as the aggregate size increased. The decay of the signal was caused by the recombination of positive holes with photolytic silver clusters after repetition of detrapping and trapping of positive holes by the aggregates. The enthalpy of activation of the decay, for which the detrapping of positive holes was responsible, was independent of the aggregate size. The analysis of the saturation of the signal intensity with increasing the power of microwave has indicated that the increase in the aggregate size could enhance the migration and thus increase the entropy of positive holes in the aggregates. It is therefore considered that the decrease in the rate of the decay of positive holes with increasing the aggregate size resulted from the change, not in the enthalpy, but in the entropy of positive holes in the aggregates. The above‐stated behavior of positive holes in the aggregates gave an explanation for the insufficiency in photographic sensitivity caused by the growth ofJ‐aggregates of Dye 1.

ISSN:0021-8979    

DOI:10.1063/1.348364

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thin films of lead zirconate titanate (PZT) have been prepared by the sol‐gel processing method using metal alkoxides. The crystallographic and morphological properties of the films have been analyzed by x‐ray diffraction and scanning electron microscopy. The elemental composition of the films was determined by Rutherford backscattering, electron microprobe, and Auger electron spectroscopy, and was compared to that of the precursor solution characterized by inductively coupled plasma spectrophotometry. Results are presented which illustrate the relationships between the properties and the observed structure of the thin films, with the processing conditions. The electrical properties, dielectric constant, and ferroelectric hysterisis response were tested to determine the quality of the films. The experimental observations suggest two competing mechanisms during the PZT formation: lead loss out of the film, and nucleation of the PZT phase with its subsequent crystallization.

ISSN:0021-8979    

DOI:10.1063/1.348365

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have explored the effects of various processing parameters on the dielectric and electronic integrity of sol‐gel‐derived silicate thin films and have identified several factors that strongly affect the thin‐film electronic properties. We find that sol‐gel dielectrics can exhibit excellent dielectric integrity: viz., low interface trap densities and fairly good insulating properties approaching those of a thermally grown silicon dioxide film on silicon.

ISSN:0021-8979    

DOI:10.1063/1.348366

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The removal of SO2from simulated gas streams (N2/O2/H2O/SO2) is experimentally investigated using a dielectric barrier discharge, and by computer modeling. Conversion of SO2to primarily H2SO4is found to be limited by the generation of OH radicals. Increasing the concentrations of O2and H2O increases the generation of OH radicals and results in more removal of SO2from gas streams. Removal efficiencies of ≳80% were experimentally achieved. Results from the model suggest that more efficient removal is obtained with a series of short, highE/Ncurrent pulses rather than a single, lowE/Ncurrent pulse. Results from the model also suggest that uv illumination of the plasma to photolyze O3will improve the removal of SO2from the gas stream. Photolysis of O3produces O(1D) atoms which generate OH radicals by H abstraction from H2O, thereby increasing the removal of SO2.

ISSN:0021-8979    

DOI:10.1063/1.348367

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

High values of the ideality factorn, in the range 1–6, have been found at low temperatures in highly dopedn++p+junctions with phosphorous and gallium or boron diffusion profiles. By studying the thermal activation of the forward current it has been possible to establish that tunneling related to charge carrier transport plays a decisive role for the generation of the highnfactors. The tunneling component can be explained by the presence of local electric fields, much higher than the average field in the space‐charge region, and the tunneling becomes more evident forp‐njunctions with higher concentration of shallow dopants at the interception point between thep+and then++concentration profiles. The use of a specially designed method based on deep‐level transient spectroscopy has made it possible to conclude that the recombination centers, contributing to the recombination current, are positioned in then++phosphorous emitter and have the same properties for gallium and boronpbase profiles. The concentration of isolated recombination centers decreases with increasing phosphorous concentrations due to clustering or precipitation, and increases the electric field constrictions.

ISSN:0021-8979    

DOI:10.1063/1.348368

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

This paper discusses selected design issues important to the operation of high‐speed AlInAs/GaInAs heterojunction bipolar transistors (HBTs). Simulation results reveal that velocity overshoot is an important effect in AlInAs/GaInAs HBTs. It is found to first order that the electron average speed through the base and base/collector depletion region is near 5×107cm/s. Introduction of a built‐in electric field in the base region improves theft. However, the resultant improvement of the cutoff frequency in the AlInAs/GaInAs HBT is not as significant as in the AlGaAs/GaAs HBT because of the already larger electron velocity in the GaInAs base. Compositional grading in the emitter is not suggested in AlInAs/GaInAs HBTs because it degrades the dc and ac characteristics. The effects of a base setback layer at the emitter/base junction on dc current gain and cutoff frequency have also been studied. It is found that both the doping density and the thickness of the setback layer affect the cutoff frequency, and that the setback layer always degrades the intrinsic performance. The intrinsic setback layer has the lowest cutoff frequency whilep‐doped setback layer has the highest one.

ISSN:0021-8979    

DOI:10.1063/1.348369

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thin bilayer films of copper metal on titanium were sputter deposited on oxidized silicon wafers and annealed in vacuum and hydrogen ambients. Annealing in vacuum caused the bilayers to fail in tension, while the hydrogen annealed films did not fail. This observation is explained as stress generated due to crystal lattice volume changes and thermal expansion coefficients.

ISSN:0021-8979    

DOI:10.1063/1.348370

出版商:AIP    

年代:1991

数据来源: AIP