摘要:

The fraction of hydrogen dissociated in the plume of a dc arcjet used for diamond deposition is determined by calorimetry to be0.33±0.12.A dc arc is struck in a mixture of argon and hydrogen at 90 psi and the effluent is expanded through a converging/diverging nozzle into a reactor maintained at 25 Torr. Methane(<1&percent;)is added to the luminous gas plume in the diverging nozzle. This supersonic jet impinges on a water cooled molybdenum substrate, and diamond thin film grows from the reactive mixture. The electrical power input of the arcjet (1.6 kW) is balanced by the power losses due to cooling of the nozzle, enthalpy change in the gas, ionization of the gas, dissociation ofH2,and the directed velocity of the gas phase. The gas temperature is determined by linear laser-induced fluorescence (LIF) measurements of several rotational lines of NO seeded to the gas plume. The velocity of the gas plume is obtained via the Doppler shift between LIF signals measured simultaneously in a stationary reference cell and in the arcjet. The atomic hydrogen fraction increases as a function of the feedstockH2/Arratio and with increasing input power to the arcjet. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365411

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A method was developed for the frequency dependence of the electrorheological (ER) response of suspensions of highly conducting particles with a low conducting surface film. At dc or low frequency ac field, the shear yield stress of the ER fluids considered is determined by the conductivity ratio&sgr;I/&sgr;fof the film to the host oil; at high frequency ac field it is determined by the permittivity ratio&egr;I/&egr;f.The critical frequency separating the conduction domain from the dielectric domain is proportional to&sgr;f/&egr;f,the ratio of the conductivity to the permittivity of the host oil. To obtain a high shear yield stress at high frequency ac field, a high ratio of the permittivity of the surface film to the oil is desired and a reasonably thin surface film. Too thin a film increases the possibility of electrical breakdown in the film especially at a small ratio of&egr;I/&egr;f.An effective method for overcoming electrical breakdown in the surface film is to increase the permittivity of the film. Good agreement exists between the measured shear yield stress, current density, and the applied breakdown field for oxidized aluminum particles suspended in silicone oil and those predicted by the present model. Recommendations are given for the design of ER fluids with high yield strength and reasonable current density. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365412

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We theoretically investigate a gated resonant tunneling diode as a potential new quantum resonant tunneling transistor. The resonant tunneling transistor is dimensionally controllable in the active channel using a lateral depletion region. Under bias conditions in which the resonant tunneling transistor reaches zero dimensionality in the well region, we consider the attractive and repulsive perturbation potentials(Vpe)of impurity or defect scattering in source and well regions. A transfer matrix formalism is employed to calculate the transmission probabilities and current densities through the double barrier, and we describe the scattering matrices using the presence of evanescent modes in various lateral confinement configurations. We discuss the effect of scattering and subband mixing on the current-voltage characteristics of resonant tunneling transistors. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365413

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The capacitance associated with free-carrier charge storage in the quasineutral region is a primary factor in limiting the switching speed ofp/njunction devices. This capacitance has been conventionally modeled using assumptions such as low-level injection, nondegeneracy, complete impurity ionization, and no space-charge region thickness modulation. These assumptions can give rise to a large error in device modeling, particularly for modern devices with very small geometry and high bias conditions. In this article, a comprehensive quasineutral region capacitance model including relevant device physics is developed. Comparisons between the present and conventional models are made, and the effects of using these two different models on the total capacitance of junction diode are also investigated. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365414

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Heterostructure Si/Ge/Sip-metal–oxide–semiconductor field effect transistors (MOSFETs) with 1-nm-thick pure Ge channels grown pseudomorphically on Si substrates have been fabricated and characterized. Simultaneous solution of Schrodinger and Poisson’s equations reveals that the 1-nm-thick Ge region can effectively confine holes in a subsurface channel. This result is confirmed through the fabrication of test MOS capacitors and MOSFETs using a process with plasma enhanced chemical vapor deposition gate oxide and a peak thermal budget of just 5 s at 600 °C. (Raman spectroscopy shows that this thermal treatment does not significantly relax the strain in the Ge layer). However, transconductance measurements on the MOSFETs indicate that the mobility of holes in the buried channel is substantiallylessthan at the Si surface. It is speculated that this poor mobility may result from hole scattering at the abrupt Si/Ge interface. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365415

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the origins of the leakage current in polycrystalline silicon (poly-Si) thin film transistors. Temperature dependent transfer characteristics were measured as a function of drain voltage. Three kinds of leakage current were introduced to explain the experimental results. The leakage current may arise from the generation current at very low drain voltage, and may result in the same activation energy between leakage current and conductivity of undoped poly-Si. The leakage current may be due to the thermionic field emission via grain boundary defects in the intermediate drain voltage region. At high drain voltage and high negative gate voltage, the leakage current may result from the field enhanced tunneling of electrons in the valence band to the conduction band via grain boundary traps. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365416

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A parametric resonance due to temperature oscillations in superconducting micron-scale waveguides is considered. Oscillations of superconductor temperature are assumed to be induced by the irradiation of the waveguide with a laser beam. The laser power and parameters of the waveguide providing a possibility of parametric excitation have been calculated. It is shown that for a waveguide made of aYBa2Cu3O7microstrip with resonant frequency of 10 GHz a laser with a power of about 70W/cm2is needed to excite oscillations. The effect can be used for the creation of high-sensitivity tuneable filters and optoelectric transformers on superconducting microstrips in the GHz range. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365417

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on electroluminescence from two-layer organic diodes made of poly(3-methyl-4-octylthiophene) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,2,4-oxadiazole films between electrodes of indium tin oxide and Ca/Al. The diodes emitted light in the green-blue range; the electroluminescence spectra varied between diodes with different thicknesses of the polymer and molecular layers. The optical phenomena were simulated with a model accounting for interference effects; simulated results showed that the electroluminescence from the organic diode can be due neither to luminescence of the polymer nor of the molecular layer. These model simulations, together with electrochemical measurements, can be interpreted as evidence for an indirect optical transition at the polymer/molecule interface that only occurs in a strong electric field. We label this transition an electroplex. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365418

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new type of active device composed of metals is fabricated based on the galvanomagnetic electromotive force effect, which is at the origin of the magnetoresistance effect and of the so-called planar Hall effect. A power gain (the ratio of the signal output to a signal input) of 2.5 is experimentally obtained for this active device. This experimental result shows the feasibility of active devices based on quite a different principle from existing ones. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365419

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The diffusion of defects during the thermal growth ofSiO2film on Si(100) in dryO2was investigated using sequential treatments in natural oxygen(16O2)and in heavy oxygen(18O2)in a Joule effect furnace. The18Odepth profiles were measured with a depth resolution better than 1 nm, using the nuclear reaction narrow resonance18O(p,&agr;)15N(ER=151 keV,&Ggr;R=100 eV). From these profiles, we confirmed that just below the surface an exchange between the oxygen atoms from the gas phase and those from the silica occurs, even for silica films thicker than 20 nm. This fact is not predicted by the Deal and Grove model. A diffusion of oxygen related defects takes place in the near surface region, with an apparent diffusion coefficientD*=4.33×10−19 cm2/sfor an oxidation temperature ofT=930 °Cand for an oxygen pressure ofP=100 mbar.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365420

出版商:AIP    

年代:1997

数据来源: AIP