摘要:

The theory of acceleration waves is applied in the analysis of the formation and propagation of acoustoelectric domains in piezoelectric semiconductors. A one‐dimensional version of the general nonlinear electroelastic equations for deformable semiconductors recently presented is employed in the analysis. Consequently, the mechanical and dielectric nonlinearities are included in the analysis as well as the semiconduction nonlinearity. Equations are derived for both the propagation velocity and the amplitude of the growing disturbance as a function of the state of the material immediately ahead of the wave front. These rather general results are specialized to the case of a homogeneous steady state ahead of the wave and the condition for the threshold field is determined. In this latter case the wave front propagates with constant velocity and the amplitude equation indicates the formation of a shock in a finite time for conditions conductive to domain formation. When the electrical conduction equation, which can be quite general in this treatment, is specialized to the form usually employed for semiconductors, the aforementioned more general condition for the threshold field reduces to the known result.

ISSN:0021-8979    

DOI:10.1063/1.323198

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Conventional measurement techniques for the investigation of the behavior of corona‐charged polymer foil electrets allow one to determine the equivalent surface charge and the surface potential decayaftertermination of the charging process. This paper describes a technique which determines charges, currents, and potentialsduringthe charging process. The application of this technique to Teflon and polyethylene foils show the usefullness of the method. The values of transit times and of the trap‐modulated mobility for polyethylene are obtained.

ISSN:0021-8979    

DOI:10.1063/1.323199

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A perturbation formula is developed to provide a systematic way of analyzing the nonlinear interaction of waves in piezoelectric media. From this perturbation formula, a set of coupled‐amplitude equations is obtained for surface acoustic waves coupled with the charge carriers in an adjacent semiconductor. The nonlinear coupling coefficients associated with semiconductive nonlinearities are expressed explicitly in terms of material constants of the piezoelectric substrate and the semiconductor layer, wave vectors, and polarizations of interacting beams. Making use of the coupled‐amplitude equations, the generation of second harmonic Bleustein‐Gulyaev waves is studied. The dependence of the second harmonic signal on the thickness and resistivity of the semiconductor sample is investigated and compared with the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.323200

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Spallation induced in thin specimens of tantalum by rapid in‐depth energy deposition has been studied in a series of electron‐beam experiments in which peak deposition levels were varied from ∼130 to ∼700 J/g. Incipient spall was observed at ∼225 J/g. Analysis of the experiments with a one‐dimensional wave‐propagation code indicated that the tensile stress at the incipient spall level was ∼26 kbar, which is considerably lower than the ∼70−kbar tensile stress previously found to produce comparable damage in room‐temperature plate‐impact experiments. The analysis further indicated that strains induced in the samples at the incipient spall level were about the same (0.035) for both types of experiments after accounting for the thermal‐expansion component of strain in the electron‐beam experiments. This observation supports a contention that induced mechanical strain would be a suitable criterion for use in describing the spallation phenomenon in uniaxial‐strain situations.

ISSN:0021-8979    

DOI:10.1063/1.323201

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The Rutherford backscattering technique using 1‐MeV protons has been employed to analyze pure and doped lead azide thin films of various thicknessess which had been prepared by vacuum evaporation followed by vapor conversion. The films were found to be approximately homogeneous in composition with depth within the limits of the depth resolution of the experiment. The energy rate lossdE/dxof the films was found to be about 60 keV/&mgr;m. The Tl‐doped films showed a somewhat different backscattering spectrum from the undoped films.

ISSN:0021-8979    

DOI:10.1063/1.323149

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The optical absorption edge for chemical‐vapor‐deposited silicon nitride films on sapphire substrates has been measured for different deposition conditions, and as a function of ion bombardment and subsequent annealing. An exponential form for the absorption edge, consistent with a disorder‐limited edge, is observed for all films. While the slope of the absorption edge is independent of the measurement temperature, the energy for the edge decreases with increasing temperature by (2–4) ×10−4eV/°C. The energy and slope of the absorption edge are lower for films deposited at 760 °C than for films deposited at 1000 °C, and displacement damage introduced by ion bombardment causes a decrease in both the slope and energy for the edge. Ion‐bombardment‐induced changes saturate when the energy deposition into damage processes is ∼10 eV/atom. The effects of a lower deposition temperature and of ion bombardment upon the absorption edge are attributed to a degradation of short‐range order. Annealing of the bombardment‐induced effects occurs over a broad temperature range, and the prebombardment absorption edge is essentially recovered by annealing at the deposition temperature.

ISSN:0021-8979    

DOI:10.1063/1.323177

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The elastic constants of a single crystal of the double hcp allotrope of neodymium have been measured over the temperature range 4.2–300 °K. The magnetic orderings which occur in neodymium near 7.5 and 19 °K are readily evident as cusps in the temperature dependences of some of the directly measured ultrasonic wave velocities, as well as in the associated elastic constants, and the character of the magnetic interactions is reflected in the differing effects on the various elastic constants. Comparison of the elastic constants of neodymium with those of seven other rare earths shows a trend with atomic number which is similar to trends which have been observed in other physical properties.

ISSN:0021-8979    

DOI:10.1063/1.323178

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The rate at which rare‐earth intermetallic compounds absorb and desorb hydrogen can be controlled by ’’poisoning’’ the catalytic reaction, H2=2H. Specimens treated with SO2, a well‐known catalytic ’’poison’’, are prevented from absorbing hydrogen for extended periods. More surprisingly, SO2treatment after hydriding prevents hydrogen desorption by specimens for weeks. The applications of this process to energy storage are numerous.

ISSN:0021-8979    

DOI:10.1063/1.323179

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

We have measured the transverse voltage from slant‐angle‐deposited metal films due to laser illumination as a function of film geometry. For a fixed laser spot size, the voltage is found to vary inversely with film widthdfordsmall compared to contact separationa. Ford/a⩾∼1 the voltage approaches a constant. The experimental results are in good agreement with the open‐circuit voltage from a finite‐current dipole and consistent with the thermoelectric model previously proposed. Useful design parameters for transverse thermoelectric optical detectors are implied by the data.

ISSN:0021-8979    

DOI:10.1063/1.323180

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Contact pairs of Ag, W, and Ag‐W were operated 6000 times in a 20‐A 110‐V ac circuit. The effect of contact‐resistance change was observed by measuring the temperature rise (TR) at the fixed contact while passing the steady‐state 20 A. TheTRwas measured before the switching had begun and after each 1000 operations. A large number of contact pairs were used in order to ensure a good statistical interpretation of the data. The chemical composition of the contact surfaces was measured using a Debye‐Scherer x‐ray analysis. The distribution of contact resistance for Ag contacts remained the same throughout the experiment. For W contacts, the distribution was initially higher than that for Ag: the result of conductivity and hardness differences. During the switching experiments, the formation of tungsten oxides on the contact surface resulted in high contact‐resistance values. For Ag‐W, the distribution was initially closer to that for Ag contacts: the result of a thin surface layer of Ag on the Ag‐W. During the switching, the Ag‐W contact‐resistance distribution gradually increased in dispersion and had higher values than those measured for W contacts. The x‐ray data showed that not only were tungsten oxides formed, but also there was a high probability that some of the free Ag on the contact surface formed an insulating silver tungstate.

ISSN:0021-8979    

DOI:10.1063/1.323181

出版商:AIP    

年代:1976

数据来源: AIP