摘要:

The dielectric breakdown of pressurized water and salt solutions subjected to high amplitude electric fields of submicrosecond duration has been investigated. Well‐defined pulses (80 kV, 3 ns rise time, 100 ns duration) have been applied to a gap (0.04–0.21 cm), between Rogowski profile electrodes, containing de‐ionized, nondistilled water; de‐ionized, distilled water; sodium chloride solutions (0.001–1.0 M); or magnesium sulfate solutions (0.01–0.1 M). Breakdown in these liquids has been studied at pressures up to 400 atm. Calibrated voltage dividers situated on the source and load sides of the test gap permitted measurement of the interelectrode potential and the current response. From these measurements, the time lag to breakdown, breakdown voltage, power input to the liquid, and temporal characteristics of the breakdown process have been determined. The breakdown time lag increases with increasing pressure and gap width, and decreases with increasing field. Moreover, it is weakly dependent on the conductivity of the liquid. A dynamical model has been developed to explain these results. In this model, field emission currents heat the liquid and create a region with density below the critical density for the formation of electron avalanches. An ionizing wave front subsequently develops and propagates via a sequence of processes occurring in the region ahead of the front; namely, heating by electron injection, lowering of the liquid density, and avalanche growth and retardation. The time for nucleation of the low density region has been experimentally determined and is in good agreement with theory. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359002

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present results of an experimental study on the effect of the inclusion of ferroelectric thiourea particles in paraelectric amorphous KBr on the ferroelectric phase transition. The phase transition as a function of temperature has been observed with optical second‐harmonic generation (SHG) of infrared light. The Curie temperatureTcshows a minimum as a function of the volume fractionxof thiourea in the composites atx=0.4. We describe the experimentally observed density dependence of the Curie temperature in a phenomenological mean‐field model. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359003

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A series of five short‐period (InAs)6/(AlSb)6superlattices, grown either with AlAs‐like, InSb‐like, or alternating interfaces, were studied by means of x‐ray diffraction, high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, photoluminescence and ellipsometry. The combination of these techniques allows us to explain the pronounced differences in the optical and structural properties of both types of interfaces. In samples with an AlAs‐like bottom interface x‐ray, HRTEM and Raman results demonstrate the differing structural quality to be related to inhomogeneous strain relaxation and As intermixing. The energies of the critical points E0, E1and E1+&Dgr;1of the samples with pure AlAs‐like interfaces are shifted by more than 100 meV to higher energies with respect to those of the samples with InSb‐like interfaces. These differences can be understood on the basis of the different interfacial atomic structure and strain in the samples. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359004

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

GaInAsP quantum‐well lasers are usually built by keeping constant the anion (CYlasers) or the cation (CXlasers) concentration into wells and barriers. We interpret the higher performances ofCY‐laser structures comparatively withCXstructures by the significant increase of the effective nonradiative lifetime coming from the reduced overlap between the electron and hole gases. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359005

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An investigation of the structural properties of hydrogenated amorphous silicon carbide (a‐Si1−xCx:H) films prepared by the plasma‐enhanced chemical vapor deposition of silane and acetylene has been undertaken using a combination of infrared (IR), Raman, and x‐ray photoelectron spectroscopy (XPS) measurements. The compositions of the silicon, carbon, and hydrogen in the films were found to be dependent on the preparation conditions. From the IR results, it is found that the Si—H bond decreases and the C—H bond increases as the film’s carbon increases. The Raman spectra showed that while the Si—Si and C—C bonds can be detected in silicon‐rich and carbon‐rich samples, respectively, the Si—C band can only be observed ina‐Si0.7C0.3:H anda‐Si0.5C0.5:H. The XPS results showed that the stoichiometry calculation from the flow rates of the reacting gases was good fora‐Si0.7C0.3:H but not fora‐Si0.3C0.7:H. Reactive ion etching of thea‐Si1−xCx:H films showed that the etch rate was dependent on the films’ carbon concentration and films prepared with acetylene as source gas were more resistive to etching compared to that prepared by butadiene. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359006

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Stability of the electro‐optic coefficient of a poled and cross‐linked nonlinear optical polymer is reported at 85, 100, and 110 °C. The observed decay, which is due to orientational relaxation of the nonlinear optical dyes in the films, is discussed in terms of several proposed models. The introduction of a continuously varying relaxation time, which occurs when considering physical agingduringthe stability tests, is observed to account for orientational relaxation over a long time period. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359007

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoluminescence (PL) has been used to study defects introduced by 1‐MeV‐electron irradiation in cubic silicon carbide (3C‐SiC) films epitaxially grown on Si substrates by means of chemical vapor deposition. A dominant PL line of 1.913 eV observed in 3C‐SiC irradiated with electrons was found to disappear at annealing stages of ≊100 and 700 °C. The annealing stages of the 1.913 eV PL center and its fraction annealed at each annealing stage were in good agreement with those obtained for theT1 electron spin resonance center, which is attributed to isolated vacancies at silicon sublattice sites [H. Itoh, M. Yoshikawa, I. Nashiyama, S. Misawa, H. Okumura, and S. Yoshida, IEEE Trans. Nucl. Sci.NS‐37, 1732 (1990)]. This result indicates that the 1.913 eV PL line arises from silicon vacancies in 3C‐SiC. The characteristics of other PL lines induced in 3C‐SiC epilayers by irradiation are also discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359008

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The photoluminescence characteristics of pseudomorphic In0.19Ga0.81As/GaAs quantum well structures grown on both the conventional (001) and the unconventional (112)B GaAs substrate are investigated. It is found that the emission spectra of the structures grown on the (112)B surface exhibit some spectral characteristics not observed on similar structures grown on the (001) surface. A spectral blue shift of thee→hh1 transition with increasing optical pump intensity is observed for the quantum wells on the (112) surface. This shift is interpreted to be evidence of a strain‐induced piezoelectric field. A second spectral feature located within the band gap of the In0.19Ga0.81As layer is also observed for the (112) structure; this feature is thought to be an impurity‐related emission. The expected transition energies of the quantum well structures are calculated using the effective mass theory based on the 4×4 Luttinger valence band Hamiltonian, and a related strain Hamiltonian. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359009

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This work characterizes the laser sputtering of gold by 248 nm laser pulses at near‐threshold fluences (material removal rates ≤10 A˚/pulse) using time‐of‐flight plume diagnostics, scanning electron microscope analysis of the surface topography, and thermal analysis of the transient near surface conditions. Pulsed laser irradiation leads to development of surface topography characterized by droplet and ridge formations, and to the liberation of micrometer‐sized droplets into the plume. The development of surface topography has been identified with a hydrodynamic response to phase change occurring at the surface of the target. Drawing upon a Rayleigh–Taylor instability description of the melt surface, the readily observable ∼5 &mgr;m periodicity in topography formation can be theoretically predicted. Additionally, the preferential formation and liberation of ∼1 &mgr;m diameter droplets at the target surface is observed. Nevertheless, the majority of sputtered mass flux is not comprised of droplets, but of neutral gold atoms with almost perfect Boltzmann translational energy distribution. The mean translational energy of the gold atoms, however, is much too high to reconcile with a simple thermal vaporization model. The yield, translational energy, and angular characteristics of the plume are strongly influenced by the surface topography. Local variations in the light absorption and heat transfer explain the qualitative trends in the experimental results. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359010

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Adhesion between thin Te‐based alloy films and fluorocarbon polymer sublayers, prepared by sputtering or plasma polymerization, was investigated by observing the 1 &mgr;m‐sized ablative hole opening process with a focused laser beam. Interpretations of the mechanisms for the change in energy required for the hole opening and pit geometry were based on the framework of studies of the ablative hole opening process for optical recording. Observations suggest that the molten material flow during the hole opening includes a ductile fracture and a viscous flow of the molten sublayer material as well as of active layer material. Adhesion acts as an energy barrier against the above mentioned flow of molten material during the hole opening process. Since the fluorocarbon films used in the present work had highly cross‐linked structures, the adhesion was mainly dominated by the dynamic force of adhesion. Therefore, the hole opening process was mainly affected by the dynamic force of adhesion rather than the static force, which is dominated by the surface energy of the sublayer. There was a good correlation between the dynamic force of adhesion estimated by the peel‐off strength and the concentrations of the ‐CF‐ and ‐C‐CF‐ structures estimated from C1sspectra obtained by x‐ray photoelectron spectroscopy. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359011

出版商:AIP    

年代:1995

数据来源: AIP