摘要:

Unexpected periodic variations of the magnetic field were recently found along the axes of superconducting accelerator magnets. This modulation, which reduces the field quality of the magnets, shows a complex space and time dependence containing very long time constants. We show in this article that the variation of the field ratedB/dtalong the length of a superconducting cable induces superposed coupling currents which flow over a long length. The space and time dependence of these ‘‘supercurrents’’ for a two‐wire cable model is obtained by the solution of the diffusion equation with the diffusivity given by the cable parameters. The existence of supercurrents explains the observed effects in accelerator magnets. It is furthermore shown that supercurrents can lead to a highly inhomogeneous current distribution over the cable cross section and to additional coupling losses, even in sections of the magnet wheredB/dt=0. Both these effects can reduce the stability of magnets, which may explain the ramp rate limitation found in accelerator magnets as well as in large magnets for fusion research. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360694

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The current amplitudes of Shapiro steps in large‐area metallic‐barrier Josephson junctions, both with and without a ground plane, are investigated with the goal of optimizing junction parameters for programmable voltage standards. Using the resistively shunted junction model without capacitance, we calculate maximum step amplitudes as a function of reduced frequency and junction dimension for both one‐ and two‐dimensional junctions. For junctions without a ground plane, we conclude that step amplitudes of order 10 mA are practical, but significantly larger amplitudes require excessive microwave power.

ISSN:0021-8979    

DOI:10.1063/1.359644

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have observed oscillations in the differential conductance as a function of the width of the tunneling barrier formed between the tip of a scanning tunneling microscope and a clean cleaved InP(110) surface. The oscillations were analyzed in terms of a simple model for a field emitted tunneling current that experiences a finite reflectivity at the InP(110) surface due to the step in the potential at the sample side of the tunneling barrier. Oscillations were not found at high bias in accord with the energy dependence of the reflectivity, and quantitative agreement was found between the model‐implied value of the surface work function and reported data. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359645

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We investigate by photoacoustic spectroscopy the optical band‐gap energy of mercuric iodide, &agr;‐HgI2, grown by sublimation in a sealed ampoule. Due to its importance as a detector material operating at ambient temperature, the physical properties of &agr;‐HgI2have been recently studied. We found, by two different methods, the band‐gap energiesEG=2.32 and 2.39 eV, respectively. These results are in good agreement with recent measurements based on reflection and absorption spectra. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359646

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A process‐induced metastable defect inn‐type silicon is reported. The defect is found close to the wafer surface after combination of ambient gas‐flow annealing at ≊900 °C depending on subsequent cleaning procedure. The defect gives rise to a band‐gap levelEc−Et=0.25 eV observed by deep‐level transient spectroscopy after reverse‐bias cooling of the sample. Both annealing and generation of the defect proceed by 1st order processes. The activation enthalpies (&Dgr;E) and pre‐exponential factors (v) have been determined from Arrhenius analyses; the results are &Dgr;E=0.63 eV and &ngr;=1⋅1012s−1for annealing, and &Dgr;E=0.65 eV and &ngr;=6⋅1014s−1for generation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359647

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Transport measurements on large single crystals of Cd0.8Zn0.2Te:Cl indicate that Cl donors formDXcenters in CdZnTe. We have observed persistent photoconductivity (PPC) with an annealing temperatureTa≊130 K. Hall‐effect experiments indicate that the PPC arises from a persistent increase in the density of charge carriers; the saturation density isNsat=6×1016cm−3. The deep binding energy of theDXcenter isEd=0.22 eV. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359648

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The controlled placement of dopant atoms in all three dimensions of a host semiconductor would enable production of a variety of novel devices. We investigate the use of hydrogen adsorption and electron‐beam irradiation to achieve selective deposition of Sb on Si. The retention of Sb after annealing to 570 K on a hydrogen‐terminated Si(100) surface is enhanced in those areas that have been electron irradiated either before or after exposure to Sb4. The maximum contrast ratio is ≊2:1 for an electron dose of 0.05 C/cm−2. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359649

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report that organic electroluminescence devices with a hole transporting emitting layer composed of distyrylarylene derivatives realized highly efficient and bright emission in the blue‐green region. Luminous efficiency was obtained to be 2.1 lm/W in the low‐luminance region (135 cd/m2) using an indium tin oxide/emitting layer/electron transporting layer/Mg:Ag structure. The external quantum efficiency was estimated to be about 1.5%. The highest luminance was obtained to be 4000 cd/m2for the device. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359650

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

GaAs growth by atomic layer epitaxy (ALE) from tertiarybutylarsine (TBA) and triethylgallium (TEG) in a chemical beam epitaxy (CBE) system is reported. A stable 4×8 surface reconstruction has been observed after Ga deposition at low substrate temperatures in the absence of TBA flux. The TEG reaction rate at the sample surface has been found to be lower under ALE conditions than under CBE growth conditions. No decay in the reflection high‐energy electron diffraction intensity was observed after the ALE growth of 700 monolayers of GaAs at 550 °C. Grown samples exhibitp‐type doping in the range of 1015cm−3. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359651

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The formation of amorphous diamondlike films by deposition of energetic carbon atoms is modeled. Formation of diamondlike bonding is attributed to transient high pressure created by the ion impact. The relaxation to energetically favored graphitic state is assumed to proceed through succession of metastable states, taking place until the glass transition point is reached. The model illustrates from the new point of view the processes involved in the formation of diamondlike films. It predicts qualitatively similar dependence of film properties on the energy of the incoming carbon atoms as observed in experiments. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359652

出版商:AIP    

年代:1995

数据来源: AIP