摘要:

Infrared absorption forp‐type degenerate GaAs is studied at room temperature for various hole concentrations. At high absorption coefficients, a Burstein‐like shift is observed for samples doped above 1019/cm3; this shift is interpreted as a decrease in the valence band electron population. A direct transition analysis was made on 1017/cm3material, yielding an energy gap of 1.39±0.02 ev. The free carrier absorption was extrapolated to shorter wavelengths and subtracted from the data. The resulting absorption edges extend to energies beyond the fundamental edge and reveal the presence of an added absorption mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1777165

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Attempts were made to observe a work function variation with thickness of thin gold, platinum, and silver films. The films were vacuum deposited onto fused silica substrates at pressures of about 10−8torr. The vibrating capacitor method was used to measure the contact potential difference between the films and a platinum reference surface as a function of film resistance. The measurements were carried out at pressures of 10−8−10−10torr. The contact potential difference was found to be independent of film resistance in the range of 5 ohms/sq to 108ohms/sq.

ISSN:0021-8979    

DOI:10.1063/1.1777166

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A new technique using ``amorphous'' boron as a pressure vessel yields satisfactory Debye—Scherrer patterns for substances subjected to quasi‐hydrostatic pressures ranging up to at least 150 kbar. The pressure attained depends on sample size and its compressibility. In general, the pressure attained is higher for the more incompressible substances. The following substances have been used to test the apparatus: Fe, NaCl, KCl, AgCl, CaCO3, and NaNO3. Evidence for polymorphic transitions was found for all substances except NaCl. The changes in lattice spacings and the observed transformations are consistent with the transition pressures and volume decrements determined by Bridgman or by shock‐wave experiments in the case of Fe. The high‐pressure structures are tentatively identified.

ISSN:0021-8979    

DOI:10.1063/1.1777167

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The theory of damping due to dislocations developed by Granato and Lu¨cke concerning a model of a dislocation line pinned by major (unbreakable) and minor (breakable) pins, the latter distributed at random along its length, is extended in two ways: the hysteretic breakaway loss is calculated for higher amplitudes; and the frequency dependent or dynamic loss is shown to be, also, amplitude dependent. The presence in a crystal of two dislocation systems of different average loop lengths is considered as an explanation of the discrepancy between some of the experimental results and the G and L theory. The configuration of the combined dynamic and breakaway loss for the long loop system for variousLN/Lcratios andLNvalues is described, whereLN, Lcare the average loop lengths between major and minor pins, respectively. An interesting feature is the prediction of a low amplitude maximum in the decrement. The theory does not extend to the high frequency region and like the G and L theory is unreliable forLN/Lcless than 5.

ISSN:0021-8979    

DOI:10.1063/1.1777168

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Measurements of 40‐kc acoustic damping in well‐annealed polycrystalline, 99.996% pure aluminum at temperatures between 4.2° and 273°K are compared with theories of dislocation damping by Granato and Lu¨cke and by Rogers. Two dislocation systems are indicated, both pinned by impurity atoms, with the average loop length of the one greater than that of the other. An amplitude‐dependent dynamic loss and an amplitude‐dependent breakaway loss for the long‐loop system, and the usual amplitude‐dependent breakaway loss for the short‐loop system are observed. The temperature dependence of various parameters important to the several types of damping is discussed and limits to the values of the types deduced for different temperatures. Electron‐lattice damping is observed at temperatures below 60°K and is found to be larger than theory predicts.

ISSN:0021-8979    

DOI:10.1063/1.1777169

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Investigations have been made of plasma oscillations by studying space‐charge waves in velocity‐modulated electron beams. The convection current in a velocity‐modulated slowly‐drifting electron beam was measured as a function of distance from the modulating cavity. The experiments indicate that in the presence of an appreciable velocity spread, the fast space‐charge wave is damped while the slow space‐charge wave remains unattenuated. The measurements were made under conditions where the velocity spread is dominated by lens effects in the electron‐optical system. The results confirm qualitatively the theory of Berghammer and thus demonstrate the existence of the much disputed Landau damping.

ISSN:0021-8979    

DOI:10.1063/1.1777170

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

General kinetic models are established for the climb of edge and screw dislocations. The climb of a straight unconstrained edge dislocation is considered in terms of the diffusion of nonequilibrium point defects to (or from) the line and their absorption (emission) and destruction (creation) at the line. The climb is nucleated by the formation of short rows of defects which are attached to the edge of the extra plane and are bounded by jog pairs. Climb occurs by the growth of these aggregates until they destroy each other by mutual collisions. Noa prioriassumptions are made about the ability of either the dislocation or the jogs to maintain local point defect equilibrium during climb, and account is taken of rapid defect diffusion along the core. Effects of nonequilibrium defects in perturbing the jog population are also included. Equations describing this edge dislocation climb are developed but are left in a general form. Complete solutions are worked out in a following paper (Part II). Complications which arise when geometrical constraints and line curvature are present are discussed, and a description of the relationships between curvature, macroscopic line tension, and jog density is given. It is concluded that the results for the unconstrained climb model can be used in many such cases over a considerable range of conditions. The treatment of screw dislocation climb focuses attention on the climb of an initially straight dislocation into a multi‐turned helix. The detailed mechanisms are found to depend strongly upon the geometry and mobility of point defects and point defect aggregates on the core, and therefore only a qualitative theory is given. It is suggested that in many crystals vacancies largely dissociate into kinks when they enter the core, and that the helical turns build up rather uniformly along the line by the aggregation of ordered arrangements of these kinks.

ISSN:0021-8979    

DOI:10.1063/1.1777171

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Quantitative expressions for the steady state climb rate of a straight unconstrained edge dislocation are obtained. The results represent specific solutions to a general kinetic model of climb developed in preceding work (Part I). Solutions are obtained for the case where interstitials in the lattice can be neglected compared to vacancies, where the dominant point defects responsible for fast diffusion along dislocation cores are vacancies, and where unlike jogs attract one another. Noa prioriassumptions are made about the ability of the dislocation or its jogs to maintain local point defect equilibrium. A wide range of conditions is treated including positive and negative climb where the vacancy concentrations may be either near or far from equilibrium. Positive and negative climb are shown to be inherently different processes, and it is found that dislocations tend to get joggy in crystals far from equilibrium. Several brief applications to problems of current interest are given. A need for critical experiments is emphasized.

ISSN:0021-8979    

DOI:10.1063/1.1777172

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Alumina whiskers have been grown on single‐crystal alumina substrates by heating aluminum filings, located near the crystals, to 1400°C in a stream of wet hydrogen. The whiskers grew crystallographically coherent with the substrate, and had their axes either parallel to thecaxis or in one of 12 equally spaced directions in the basal plane. These 12 directions divide into two distinct sets, a ⟨112¯0⟩ set and a ⟨11¯00⟩ set, each having sixfold symmetry, and with the directions of one set midway between the directions of the other. These growth directions are the screw‐dislocation directions in alumina, hence it seems plausible that the whiskers grew coherently with the substrate at the site of emergent screw dislocations.

ISSN:0021-8979    

DOI:10.1063/1.1777173

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Giant pulses of optical maser radiation have been produced which are several orders of magnitude larger than the commonly observed spontaneous pulses. The pulses were produced by varying the effective reflectivity of the reflecting surfaces at the ends of the ruby rod through a Kerr‐cell switching technique. The measured pulse characteristics are found to be in agreement with theoretical predictions.

ISSN:0021-8979    

DOI:10.1063/1.1777174

出版商:AIP    

年代:1962

数据来源: AIP