摘要:

The properties of a metal‐oxide‐metal (M‐O‐M) tunneling detector are presented and the parameters influencing its operation are discussed. The theory of operation and experimental results for small as well as large signals are presented. The polarity reversal at large‐signal levels is predicted theoretically and observed experimentally.

ISSN:0021-8979    

DOI:10.1063/1.1660062

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The photoelectric yield of evaporated KCl films was measured for photon energies from 7 to 14 eV. A gradual rise of photoelectron emission with time was observed under steady ultraviolet excitation of approximately 8 eV. In the presence of strong biasing radiation (visible light), the gradual rise of photomission did not appear. An attempt is made to explain the transient enhancement in terms of electron emission from newFcenters formed by excitons.

ISSN:0021-8979    

DOI:10.1063/1.1660063

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

On the basis of experimental evidence, it is suggested that the high secondary emission gain of Ag&sngbnd;O&sngbnd;Cs photocathodes is not associated with the photoemission of this material in the visible and near‐infrared region of the spectrum. Addition of Ag enhances photoemission but reduces secondary emission whereas superficial oxidation reduces photoemission but increases secondary emission. It is concluded that the Cs2O contained in the cathode, although by itself not sensitive to visible light, is responsible for the high secondary emission as well as for the high uv photoemission.

ISSN:0021-8979    

DOI:10.1063/1.1660064

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Chemical analyses and qualitative observations during the processing of S‐20 photocathodes indicate that the cesium produces a bulk as well as a surface effect. Quantitative confirmation for a bulk effect is provided by x‐ray studies of Na2KSb and (Cs)Na2KSb. It was found that addition of Cs increases the lattice constant from 7.727±0.003 to 7.745±0.004 Å. It is suggested that the larger lattice constant leads to a greater excess of Sb in the lattice and thereby to enhancedp‐type doping and band bending.

ISSN:0021-8979    

DOI:10.1063/1.1660065

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The voltage dependence of photoinjected currents in SiO2films for electric fields less than about 106V/cm exhibits anomalous behavior. It is shown that the physical mechanism responsible for this behavior is the scattering of photoinjected electrons in the SiO2image force potential well between the emitter and the potential maximum. A previously published model attributing the effect to electron trapping in SiO2is shown to be inconsistent with the experimental results. A theoretical model is presented and the voltage dependence of photocurrents is derived including the effects of scattering and barrier lowering. Experimental results from MIS structures using thermally grown SiO2are found to be in excellent agreement with theoretical predictions when a 34 Å mean free path for scattering in SiO2is used in the model.

ISSN:0021-8979    

DOI:10.1063/1.1660066

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Zinc‐doped InAsP liquid epitaxial layers with bandgaps between 0.4 and 1.34 eV were grown on InAs and InP substrates. The grown layers were 2–4‐&mgr; thick with mirror‐smooth as‐grown surfaces. Preliminary phase diagram calculations based on Darken's quadratic formalism to describe the ternary liquid in equilibrium with the pseudobinary solid are in good agreement with the bandgaps of the grown layers determined by photoluminescence. The InAsxP1−x&sngbnd;Cs2O heterojunction barrier height as a function of composition has been measured using photoemission. For InAs the barrier is at 1.24 eV, and it decreases with decreasing arsenic concentration to a value of 1.16 eV for InAsP with a 1.27‐eV bandgap. For InAsxP1−xsamples with bandgaps in the range 1.17–1.34 eV, high escape probabilities and efficient photoemission were observed. A typical cleaned (not cleaved) sample with a bandgap of 1.19 eV has a sensitivity of 600 &mgr;A/lm, 70 &mgr;A with a lumen source through a 2540 ir filter, a quantum efficiency of 1.5% at 1.06 &mgr;, and a &Ggr; escape probability of 0.08. This is the most sensitive infrared photocathode yet produced. All processing steps seem compatible with tube production. The effects of the heterojunction barrier are clearly visible with this material. The escape probability drops by an order‐of‐magnitude when the InAsxP1−xbandgap is reduced to 0.05 eV below the barrier.

ISSN:0021-8979    

DOI:10.1063/1.1660067

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The present investigation is concerned with the conditions associated with the development of an anode spot for metal‐vapor (vacuum) arcs. Chief among the aims of the investigation is the determination of the threshold current density for anode‐spot formation for a variety of electrode materials spanning a wide range of thermal and electrical properties. Electrodes of Sn, Al, Ag, Cu, Mo, and W were chosen for study in a plane‐parallel electrode geometry. Arcing was over one‐half cycle of a 60‐Hz current wave. The onset of anode‐spot formation was determined from high‐speed streak photographs of the discharge. An oscillographic record of the arc voltage was obtained simultaneously with the streak picture. From the data obtained particular interest attaches to the threshold current for anode‐spot formation, the threshold current density derived from it, and the arc voltage‐current characteristic. The threshold current densities (peak values) range from a low of 0.9×102A/cm2for tin to a high of 5.4×102A/cm2for tungsten, copper having the value 4.0×102A/cm2. In general, high‐current metal‐vapor arcs have positive volt‐ampere characteristics and exhibit an hysteresis effect. Rapid changes in arc voltage, noise voltage, and in the magnitude of the hysteresis effect are associated with the formation of an anode spot. The noise voltage and arc drop decrease as the spot develops. In addition a marked increase in luminosity appears in the plasma at the site of the spot. There is a strong correlation between the threshold current for anode‐spot formation and the thermal characteristicTm(k&rgr;c)1/2of the electrode material.

ISSN:0021-8979    

DOI:10.1063/1.1660068

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A method for computing the approximate photocount statistics for Gaussian light is presented. This method may be used for the superposition of coherent radiation with chaotic radiation of arbitrary spectral shape. Data is presented for Gaussian‐, triangular‐, and square‐shaped spectra as well as for Lorentzian‐shaped spectra. The results show that the photocount statistics are significantly dependent upon spectral shape for intermediate time‐bandwidth products. The results also show that the Bedard, Chang, and Mandel approximation gives a better fit to a Gaussian‐shaped spectrum then to a Lorentzian‐shaped spectrum. Significant differences between the photocount statistics for a time‐bandwidth product of 10 and Poisson statistics were also obtained; even for a signal‐to‐noise ratio of 40:1.

ISSN:0021-8979    

DOI:10.1063/1.1660069

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

For the case of stress relaxation at constant strain, the Green‐Rivlin theory for nonlinear materials with memory predicts that the stress is a power series in the strain where the coefficients, called kernels, characterize the material. This prediction of the theory has been tested using data obtained on the polycarbonate of bisphenol A in the timescale range 10–1000 sec and temperature range 23°–130°C. At each temperature level of this study, the two leading terms of the power series account for actual behavior within the standard deviation of the experimental data (3%) up to the level of tensile strain where instability (cold‐drawing) occurs. The first (``linear'') kernel decreases monotonously with temperature asTgis approached, but the second and higher kernels each vary with temperature in a complex manner. The utility of summarizing the nonlinear behavior of polymers by kernel functions is appraised and discussed in the light of recent findings on the range of validity of linear viscoelasticity theory. It is concluded that the second and higher kernels of the theory do not have any obvious physical significance. It is also suggested that the first and the second kernels might represent adequately by themselves the nonlinear viscoelastic behavior of glassy, amorphous polymers up to about 5% strain, whereas the third and higher kernels appear in addition to be necessary for semicrystalline polymers.

ISSN:0021-8979    

DOI:10.1063/1.1660070

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Powder samples of high‐density polyethylene and nickel of particle sizesRpandRm, respectively, were mixed and compacted at room temperature under a pressure of 1000 kg/cm2. Microscopic examination of polished sections of the compact, by reflected light, showed that the metallic particles did not penetrate the polymeric particles and that this resulted in a segregated distribution of metallic particles at high ratios ofRp/Rm. The electrical resistivity of the compacts had a value of 1016&OHgr; cm unless the composition of metal reached a critical value, beyond which the resistivity decreased markedly by as much as twenty orders‐of‐magnitude. This critical composition was found to decrease with an increase in the ratioRp/Rmthroughout the range studied of from 1 to 16. The general features of the dependence of electrical resistivity on composition of metal could be rationalized by reference to a model according to which small particles of nickel form a monolayer on the large particles of polymer in the mixture of powders. This arrangement was supposed to be but little changed during compaction and to result in a segregated distribution of metal which can be visualized as approximating to the accommodation of metallic particles on three mutually perpendicular sets of lattice planes. The critical composition for a sudden decrease in electrical resistivity was assumed to correspond to the first nonzero probability for infinitely long chains of contiguously occupied lattice sites.

ISSN:0021-8979    

DOI:10.1063/1.1660071

出版商:AIP    

年代:1971

数据来源: AIP