摘要:

A novel shock tube reactor was used to pulse heat a gaseous mixture of He, FN3, and Bi(CH3)3along a 40 cm optical path between two highly reflective mirrors. Production of NF(a1&Dgr;) by dissociation of the azide was found to occur in a ‘‘delayed avalanche’’ approximately 50 &mgr;s after shock reflection, and weak lasing at 470 nm was observed that is assignable to electronic transitions in the BiF(A–X, &Dgr;v=3) band.

ISSN:0021-8979    

DOI:10.1063/1.354645

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The time‐varying charge buildup in the quantum well region of a resonant tunneling diode (RTD) and related capacitive effects are calculated using the scattering matrix method developed. The small signal analysis of admittance shows a prominent influence from the capacitive effect, due to the dynamic shifting of the resonant energy levels. The model developed is helpful for understanding the RTD’s high‐frequency behavior and device applications.

ISSN:0021-8979    

DOI:10.1063/1.355292

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The fields backscattered from arrays of electrically small copper and YBCO superconducting loops are measured and compared with moment method predictions to confirm the gain enhancements and changes inQfactors due to increasing the efficiencies of the antenna elements alone, without the influence of feed and matching networks. Measurements on coplanar and parallel loop arrays show only small increases in the backscattered fields of the YBCO scatterers, with the largest increase in efficiency being for the single loop. The mutual resistance between elements reduces the benefit of adding more elements to a YBCO loop, to a greater extent than when copper elements are added to a copper loop.

ISSN:0021-8979    

DOI:10.1063/1.354647

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The field‐effect conductance activation energyEaas a function of the gate voltageVgis investigated for polycrystalline silicon thin‐film transistors. An analytical expression forEais obtained for various models of the bulk and interface states. Using a computer minimization program to fit the experimentalEavsVgdata with the theory, the energy distribution of the bulk states and the interface states are separated for nonhydrogenated and hydrogenated polycrystalline silicon thin‐film transistors. In both cases, the bulk states have exponential band tails and a wide peak near the midgap and the interface states have an exponential distribution from the band edge.

ISSN:0021-8979    

DOI:10.1063/1.354648

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Conventional rf SQUIDs (superconducting quantum interference devices) consist of a superconducting loop interrupted by one weak link, and when read out via a tank circuit they produce output signals in the order of a few tens of microvolts. When the single weak link is replaced by a dc SQUID (a superconducting loop with two junctions) a so‐called double quantization loop SQUID is formed. In this paper it is shown theoretically, and supported experimentally with thin‐film devices of three different designs, that the general behaviour can be explained by a simplified picture of the fixed critical current of the single junction of the rf SQUID being replaced by an effective critical current of a dc SQUID loop that is varied by the applied magnetic flux (i.e., we have a rf SQUID with a variable &bgr; parameter). A more detailed analysis of the experimental data and the theory of this novel device reveals its interesting nonlinear character and shows the deviations from this simple picture. It is demonstrated experimentally that output signals in the order of ≥1 mV can be obtained with a suitable read‐out mode for the tank circuit, a clear advantage when compared to conventional rf SQUIDs. With respect to dc SQUIDs, the coupling to integrated planar input coils will be unproblematic since no microwave resonances should occur in the structures.

ISSN:0021-8979    

DOI:10.1063/1.354649

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A simple thermally controlled, thin‐film superconducting switch was developed for the purpose of multiplexing superconducting quantum interference device detection coils. Switching speeds of a few microseconds were achieved and multiplexing at low frequencies was demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.355321

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Epitaxial CeO2buffer layers and YBa2Cu3O7−&dgr;thin films have been growninsituon (11¯02) sapphire by electron beam evaporation. Buffer layers of only 20 nm thickness inhibit interdiffusion between YBa2Cu3O7−&dgr;and Al2O3as determined by depth profiling using x‐ray photoelectron spectroscopy. The layers show smooth surfaces and narrow interfaces. High lattice perfection of the CeO2layer has been shown by x‐ray diffraction. Laue oscillations up to ninth order have been observed in thin CeO2buffer layers on sapphire. We found only one epitaxial orientation with YBa2Cu3O7−&dgr;(001) ∥ CeO2(001) ∥ Al2O3(11¯02) and YBa2Cu3O7−&dgr;[110] ∥ CeO2[100] ∥ Al2O3[112¯0]. YBa2Cu3O7−&dgr;films grown on these buffer layers revealTc=88±0.5 K, &rgr;(300 K)=380 &mgr;&OHgr; cm, andjc(77 K, 0 T)=1.3×106A/cm2.

ISSN:0021-8979    

DOI:10.1063/1.354650

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The mechanical stresses of a pure Al film and a low‐thermal‐expansion Al‐3 at. % Ge thin film on (100) Si wafers are measured and compared in the temperature range of room temperature to 400 °C by the vibrating membrane method. The results are discussed including the comparison with those obtained by the popular wafer bending method. It was found that the chemical reaction between the Al and the Si substrate affects the mechanical stress. The relatively low stress in the Al(Ge) film is due to the interference of Ge precipitation. The relatively slow relaxation in the Al film during annealing may be caused by the dissolution of Si into Al.

ISSN:0021-8979    

DOI:10.1063/1.354623

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Indium phosphide solar cells are more radiation resistant than gallium arsenide and silicon solar cells and their growth by heteroepitaxy offers additional advantages leading to the development of lighter, mechanically strong and cost‐effective cells. Changes in heteroepitaxial InP cell efficiency under 0.5 and 3 MeV proton irradiations have been explained by the variation in the minority‐carrier diffusion length. The base diffusion length versus proton fluence has been calculated by simulating the cell performance. The diffusion length damage coefficientKLhas also been plotted as a function of proton fluence.  

ISSN:0021-8979    

DOI:10.1063/1.354600

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Theoretical treatment is given to the problem of a Coulomb center in thin wire with the dielectric constant æ≫1. The model describes adequately impurity centers and excitions in porous Si. The shape of Coulomb potential &fgr;(r) inside the wire disturbed drastically by image forces is analyzed. The exciton (or impurity) binding energy determined by the Schro¨dinger equation with &fgr;(r) demonstrates a manifold increase with the decrease of the wire radius.

ISSN:0021-8979    

DOI:10.1063/1.354601

出版商:AIP    

年代:1993

数据来源: AIP