摘要:

We have investigated the electrical and metallurgical behavior of the InP/Au/Ni contact system. We show that when a layer of Au, 100 A˚ or more in thickness, is introduced betweenn‐InP and Ni contact metallization, specific contact resistivityRcvalues in the low 10−8&OHgr; cm2range are achieved after sintering. It is suggested that these ultralow values ofRcare due to the presence, at the metal‐InP interface, of a Ni3P layer combined with a stoichiometry change in the InP surface. We show, in addition, that it is possible to achieve very lowRcvalues with this system without incurring device destroying sinter‐induced metallurgical interdiffusion.

ISSN:0021-8979    

DOI:10.1063/1.355071

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A theoretical investigation on the quantum field effect directional coupler is presented. The behavior of electrons in the device is studied by solving the Schro¨dinger equation directly. The complete transfer effect is revealed to be an intrinsic property of the parity symmetry of the system. Transfer length is precisely calculated by using the transfer matrix method. Two model transverse confinements have been used in the calculation. One is a symmetric double rectangular well; and the other is a symmetric double finite‐parabolic potential. Conductance of the device is investigated by applying the Landauer formula. Conductance oscillations with Fermi energy and barrier height are obtained. One method of determining the transfer length from the curve of conductance vs barrier height is proposed. Special attention is paid to the multimodedness of the device. Correlation among the different modes is demonstrated to reduce the transfer effect of the device. Reflection at the interfaces between uncoupled and coupled waveguides is proved to be negligible.

ISSN:0021-8979    

DOI:10.1063/1.355072

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We describe here the application of photoconductive frequency resolved spectroscopy to determine excess carrier lifetime distributions and carrier kinetics in SIMOX (separation by implanting oxygen) material. In order to evaluate the influence of the implant and anneal processes on the quality of the silicon overlayer we have also analyzed unprocessed bulk silicon, high temperature annealed bulk silicon and as‐implanted SIMOX material. Our photoconductive frequency resolved spectroscopy results reveal that the SIMOX layers have a higher density of defects than standard device quality silicon substrates. Characteristic parameters of the dominant traps in these materials have been obtained from Arrhenius plots of the lifetime distributions. The defects found in these SIMOX layers are shown to be formed during the high temperature anneal stage of the material production.

ISSN:0021-8979    

DOI:10.1063/1.355073

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We attempted to measure the critical current densityJcof ceramic superconductors with pulsed magnetic fields. Using a pair of search coils coaxially mounted just below a ring sample, we measured induced signals that were considered to be proportional to the time derivative of the sample magnetization. Four samples were used: YBa2Cu3Oy, YBa2Cu4Oy, Bi2Sr2CaCu2Oy, and Bi1.6Pb0.4Sr2Ca2Cu3Oy. These were all synthesized by the polymerized complex method. It was found that the induced signals from the paired search coils are typically of two types. One shows a monotonic decrease to zero as a function of time. The other has a minimum at a certain time and then approaches zero. The observed signals were simulated in the framework of the Bean model and the Kim–Anderson model for critical current density. Theoretical profiles by these two models reproduce the observed results well and suggest that the two types of induced signals are the same in appropriate limits. We discuss how to evaluateJcfrom the observed signals.

ISSN:0021-8979    

DOI:10.1063/1.355074

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The phase formation in BiSrCaCuO (BSCCO) films grown byinsitulaser ablation has been studied as a function of excess concentrations of Ca and Cu in the target with oxidation gases such as O2and N2O, gas pressures ranging from 0.02 to 10 Torr, and substrate temperatures ranging from 490 to 750 °C. A set of phase diagrams has been plotted illustrating O2or N2O partial pressures vs substrate temperature, marking the stability fields and transitions among different phases of Bi2Sr2CuOx(2201), Bi2Sr2CaCu2Ox(2212), Bi2Sr2Ca2Cu3Ox(2223), and Bi2Sr2Ca3Cu4Ox(2234), amorphous products, and decomposition of the BSCCO films. In O2and N2O, the first appearance of the 2212 phase is located at 510 °C/20 mTorr and 490 °C/100 mTorr, respectively. The BSCCO film decomposes at a high temperature that increases with increasing gas pressure. Higher gas pressures enhance the growth of the 2201 phase that may also be formed by cooling from partial film melting. Higher substrate temperature and gas pressure as well as the surplus of Ca and Cu in the target facilitate the growth of the 2223 and 2234 phases. The decomposition curve of the Ca and Cu enhanced BSCCO films is shown to be found at lower temperatures in comparison to the stability lines of the 2212 and 2223 phases; furthermore, its slope deviation occurs at 650–690 °C which is lower by as much as about 130 °C compared to that of stoichiometric superconductors. Nearly pure 2212, 2223, or 2234 films or a mixture of them can be grown within a temperature range of 575–690 °C at a pressure as high as 10 Torr, irrespective of the kind of oxidation gas.

ISSN:0021-8979    

DOI:10.1063/1.355075

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Current research into x‐ray detection using superconducting tunnel junctions indicates that the poor spectral resolution obtained so far, in comparison with theoretical expectations, is partly due to the excellent acoustic coupling of the junction and substrate. The substrate acts both as a source of noise and as a heat sink for the nonequilibrium junction, thus masking the intrinsic response of the superconducting electrodes to photoexcitation. A new design for a superconducting tunnel junction based on an x‐ray detector is presented. The design effectively decouples the substrate and junction and should therefore eliminate many causes of spectral degradation, bringing resolution closer to that predicted theoretically, and thus allowing experimental investigation of the intrinsic superconducting film response to x‐ray photoexcitation. An outline of the way in which the design can be optimized geometrically to achieve the decoupling is given. Further optimization of the intrinsic film response to x‐ray photons is achieved through the introduction of specific absorbing and trapping regions to improve both the quantum efficiency and charge output of the new design. The use of ‘‘pairing potential barriers’’ within the electrode leads will also improve the intrinsic resolution of this device.

ISSN:0021-8979    

DOI:10.1063/1.355076

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

YBa2Cu3O7−xfilms have been deposited on MgO by reactive, off‐axis magnetron sputtering in an argon, oxygen, and hydrogen gas mixture. The material and electrical properties of the films were studied for deposition temperatures from 600 to 760 °C. The films, all approximately 300 nm thick, were predominantlya‐axis oriented when deposited at or below 620 °C but werec‐axis oriented when deposited at temperatures above 640 °C. The surfaces of films deposited between 640 and 710 °C were partially covered witha‐axis grains. Surface roughness measurements indicated the smoothest films occurred for deposition temperatures below 680 °C. Resistance ratios as great as 3.1 were observed for some films. Transition temperatures exceeded 89 K and resistivities at 100 K were less than 150 &mgr;&OHgr; cm for the best films. Low‐temperature critical current densities exceeded 107A/cm2for films deposited from 640 to 720 °C. The temperature dependence of the critical current density near the transition temperature had a power law dependence of nearly 3/2 for deposition temperatures below 690 °C. The power law dependence decreased for increasing deposition temperatures, dropping to nearly 1.1 in the film deposited at 750 °C.

ISSN:0021-8979    

DOI:10.1063/1.355077

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The magnetic anisotropy of a nanocrystalline soft magnetic Fe73.5Cu1Nb3Si13.5B9alloy has been determined by studying the magnetization process. The experimental results on the approach to magnetic saturation have been used to determine its effective magnetic anisotropy constant ⟨K⟩. This is about one tenth of the magnetocrystalline anisotropy constantK1of individual &agr;‐Fe (Si) grains.

ISSN:0021-8979    

DOI:10.1063/1.355078

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Sm‐Fe‐N permanent magnets have been prepared by mechanical alloying of Sm and Fe powder and subsequently treating the material in a two‐step process. Measurements of the minor hysteresis loops and of the initial magnetization curve were performed at room temperature. The reversible susceptibility (&khgr;rev), the total susceptibility (&khgr;tot) of the initial magnetization curve and of the demagnetization curve, and the temperature dependence of the coercive field (Hc) of a magnetically isotropic nanocrystalline Sm‐Fe‐N magnet have been measured up to a field strength of 6.4 MA/m. The anisotropy constants,K1andK2, of Sm2Fe17Nxwere deduced from the crystalline electric field calculation in the temperature range from 0 to 500 K. The critical diameter of single domain Sm‐Fe‐N particles was calculated to be 320 nm at room temperature. This leads to the conclusion that mechanically alloyed Sm‐Fe‐N is composed of single‐domain particles. The temperature dependence of the coercive field of Sm‐Fe‐N has been analyzed within the framework of the micromagnetic models. It is concluded from these results that the nucleation process controls the coercivity mechanism of mechanically alloyed Sm‐Fe‐N material. The thermostability of the Sm‐Fe‐N magnet has also been tested.

ISSN:0021-8979    

DOI:10.1063/1.355079

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A neutron‐diffraction study of Nd2Fe14−xSixB has shown that silicon preferentially occupies the 4csite in the transition‐metal sublattice in Nd2Fe14B. Silicon also exhibits a moderate preference for the 8j1site, is almost excluded from the 16k2site, and avoids the 16k1, 8j2, and 4esites. The silicon site occupancy is correlated with a preference for a silicon atom to have rare‐earth atoms in its coordination environment. The Mo¨ssbauer spectra of Nd2Fe14−xSixB have been fit with a model which takes into account the distribution of near‐neighbor environments of an iron atom due to the presence of silicon. These fits show that the substitution of silicon in the near‐neighbor environment of an iron atom primarily influences the long‐range contributions to the hyperfine field experienced by the iron. The mechanism for the increase in the Curie temperature when silicon is added to Nd2Fe14B‐type magnets is more subtle than previously believed, but can be explained by the relative decrease in the proportion of short iron‐iron bonds when silicon is substituted for iron.

ISSN:0021-8979    

DOI:10.1063/1.355080

出版商:AIP    

年代:1993

数据来源: AIP