摘要:

A novel optical technique based on the observation of time‐dependent changes in the intensity of light scattered from particles during their motion in a liquid containing contrasting medium is outlined. Principles of the method and theoretical models are presented for sweepout and transit experiments which permit determination of particle sizes, mobilities, charges, particle‐substrate interaction forces, and also the removal times of particles from the substrates. Average values and at least the second moments of these quantities are determined. The method was tested on several nonaqueous dispersions with particular attention being paid to titanium dioxide particles in a hydrocarbon fluid. Particle mobilities were measured over a wide range of electric fields and found to increase with field. Particle charges were found roughly proportional to particle size and the average particle‐substrate interaction forces were found to be ∼1.4×10−10N in reasonable agreement with a theoretical estimate of the electrostatic interaction forces. Dynamics of charged particles subject to high‐frequency fields was also investigated.

ISSN:0021-8979    

DOI:10.1063/1.325663

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In this paper we present a theoretical model for the linear and nonlinear coupling between surface acoustic waves and a semiconductor diode array separated from the piezoelectric medium by a thin airgap. We account for the periodic nature of the diode sensor and we discuss the various approximations made. This model yields the convolution efficiency as a function of diode bias, diode charge, or incoming illumination. Two modes of light detection are considered: the photovoltage mode where shining light is equivalent to forward biasing the diodes, and the precharge mode where the photon flux controls the discharge of initially charged up diodes and the remaining charge is read out after the so called photon integration time. Experimental devices have been measured which usepndiode matrices of the vidicon type laid down in close vicinity to a LiNbO3delay line. We show that the measured data very well compare with the theoretical predictions. In addition we note that light sensitivity thresholds of some 10−2&mgr;W/cm2have been demonstrated. The light dynamic range reaches 50 dB. In the precharge mode, a higher contrast is obtained over a 10–20‐dB range which can be shifted by changing the integration time.

ISSN:0021-8979    

DOI:10.1063/1.325664

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Analytic functions are derived for the spectral noise voltage density between two circular sensor electrodes on a two‐dimensional isotropic conductor, placed either transversely or longitudinally to a homogeneous electric field. The sensor electrodes are far removed from both the bias electrodes and the boundaries. The relations have been checked experimentally for 1/fconductivity fluctuations. Both the transverse and longitudinal noise are proportional toI−2Fs(J⋅J˜)2dswhere J⋅J˜ represents the dot (scalar) product of the homogeneous current density J and the adjoint current density J˜, and the current through the bias electrodes isI. It is found that the transverse noise is somewhat smaller than the longitudinal noise.

ISSN:0021-8979    

DOI:10.1063/1.325665

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The photoinduced charge‐transfer process in PLZT ceramics is studied by measuring the refractive‐index changes during hologram recording at &lgr;=488 nm. From the measured values of the photoinduced space‐charge fields, it is concluded that the photocarrier drift lengths are comparable with the fringe spacing (a few &mgr;m); the photorefractive sensitivity is limited by the low photoexcitation quantum efficiency (10−4) and is not influenced by oxidoreduction treatments.

ISSN:0021-8979    

DOI:10.1063/1.325666

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The threshold electric field required to initiate current oscillations inn‐InSb has been measured as a function of temperature from 77 to 135 °K. The results are explained under the assumption that a critical constant value for the amplified phonon flux is required for current oscillations within the temperature range covered. Good agreement is found with the theoretical method.

ISSN:0021-8979    

DOI:10.1063/1.325667

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Variations versus temperature of the electrical properties (conductivity, Hall and drift mobilities) in semi‐insulating GaAs are explained by a model which accounts for the spatial fluctuation of impurity densities. A discussion of this model is also presented.

ISSN:0021-8979    

DOI:10.1063/1.325668

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The Hall coefficient, dc conductivity, and thermopower have been measured in three single crystals of zinc selenide heavily doped with indium to various degrees. It has been found that the excessive doping with indium leads to an increase of compensation with the increase of doping. The galvanomagnetic as well as thermopower measurements suggest impurity‐band conduction in the entire temperature region investigated (77–300 °K) in this material.

ISSN:0021-8979    

DOI:10.1063/1.325669

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The low‐frequency parallel and transverse diffusion coefficients for electrons in InP are calculated using Monte Carlo methods for lattice temperatures of 200, 300, and 500 K. The sensitivity of the computed values to the duration of the flight sampling time is investigated, and this is shown to be a consequence of the frequency dependence of the diffusion coefficient. To test this hypothesis the variation of the parallel diffusion coefficient with both frequency and field at 300 K is determined. For fields above threshold the parallel diffusion coefficient first rises from its low‐frequency value to a maximum and thereafter decreases with increasing frequency; for fields substantially below threshold a slow monotonic decrease is observed.

ISSN:0021-8979    

DOI:10.1063/1.325670

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Electrical noise measurments have been made on thin films of PS, PE, and PET, over the frequency range 10−4–1 Hz, the temperature range 20–80 °C, and under applied fields up to destructive breakdown. The noise power is found to be less than the measurable limit of 10−29A2/Hz until near‐breakdown fields are applied, at which time a rapid increase in noise is observed with noise‐power spectra varying with frequency as 1/f&agr;, with 1.3<&agr;<1.7, and proportional to the square of the steady current. Very similar characteristics were observed in all three polymers. We give a tentative explanation for this high‐field phenomenon in terms of the activation of sensitive spots, thermal runaway, and subsequent annealing.

ISSN:0021-8979    

DOI:10.1063/1.325671

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Polycrystalline sintered pellets of &agr;‐Fe2O3have been studied by capacitance and photoelectrochemical techniques. The pellets exhibit (i) photocurrent saturation at a given wavelength with increasing applied voltage, (ii) large dark currents at low applied voltage (0.76 &mgr;A cm−2at +0.2 V SCE), (iii) cathodic and anodic photocurrent transients at low levels of monochromatic irradiation, (iv) photocurrent onset at photon energies greater than 2.1 eV, and (v) flat‐band potentials of −0.67 V SCE andpH=4. Capacitance measurements followed a Mott‐Schottky relationship indicating a predominance of the semiconductor space‐charge layer over surface states and electrolyte effects. No degradation of the semiconductor properties could be observed atpH=4.

ISSN:0021-8979    

DOI:10.1063/1.325672

出版商:AIP    

年代:1979

数据来源: AIP