摘要:

A convenient critical current method for observing the salient features of flux trapping in superconductors is used to study a variety of lead and lead‐alloy samples. The critical fieldsHt,Ha, Hcfor type I and Hc2for type II superconductors are obtained and found to be in accord with the results of other investigators employing different techniques. Because of self‐fields due to current asymmetries, the full critical currents of some samples are observed in nonzero applied fieldsHpI. The critical current versus applied‐magnetic‐field characteristics of lead pressure contacts and their application to a simple magnetic null detector are discussed. It is found that trapping flux in certain solid specimens can cause a fourfold enhancement of the peak critical current.

ISSN:0021-8979    

DOI:10.1063/1.1659492

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Single crystals of lithium fluoride from various sources were investigated by optical absorption in the visible and in the vacuum ultraviolet, irradiation with x rays or with ultraviolet from a microwave discharge source, measurement of total luminescence output and of luminescence emission spectra as a function of temperature, optical and thermal bleaching of absorption centers, and thermally stimulated luminescence. In addition to obtaining specific quantitative data on the parameters of theFcenter, hole traps and luminescence centers in lithium fluoride, it is concluded that the dominant luminescence and trapping centers are associated with specific impurities in the lithium fluoride, and that theFcenters are not involved in the production of visible x‐ray‐induced or thermally stimulated luminescence.

ISSN:0021-8979    

DOI:10.1063/1.1659493

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

To understand the kinetics of the radiative emission in (Zn, O)‐doped GaP, primarily at room temperature, we have measured luminescence lifetimes using pulsed photoexcitation from argon and He&sngbnd;Ne lasers. Measurements of time decay and temperature dependences of the radiative emission have enabled us to identify the emission in the near infrared as resulting from transitions involving a bound electron at an oxygen site to a free hole in the valence band. Measurements of the temperature dependence of the decay times and the luminescence intensities of the exciton (red) and bound‐electron to free‐hole (infrared) emissions also substantiate the conclusions that nonradiative recombination paths exist out of the Zn&sngbnd;O complex and provide evidence for the existence of a nonradiative ``shunt path'' out of the conduction band. The bound electron to free‐hole recombination out of oxygen is believed to be primarily radiative. For an annealed sample, the decay times of the exciton and bound‐to‐free transitions are measured to be 170 nsec and 11.2 &mgr;sec at 300°K. From the relative variation of the excitonic and bound electron to free‐hole intensities and their decay times in annealed and quenched samples it is reaffirmed that on annealing the quantum efficiency of the exciton emission increases and, furthermore, concluded that on annealing the quantum efficiency of bound‐electron to free‐hole emission also increases. A study of these effects increases our understanding of the process of annealing. Finally a weak correlation between the external quantum efficiency of excitonic (red) emission and its decay times is established for optimally doped, solution‐grown GaP.

ISSN:0021-8979    

DOI:10.1063/1.1659494

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The effect of the varying permeability of the pole faces of an electromagnet with applied field on the signal detected by the pickup coils of a vibrating sample magnetometer has been analyzed by using the technique of magnetic images. It is shown that such an effect can significantly alter the signal detected by the pickup coils and, as a result, the calibration of the instrument.

ISSN:0021-8979    

DOI:10.1063/1.1659495

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Experimental measurements of the antiferromagnetic resonance in MnF2at 4.2°K have been made as a function of microwave frequency and sample size and shape. Measurement frequencies ranged from 100 to 305 GHz. The experimental data have been analyzed with the aid of a newly derived electrodynamic treatment of the experimental arrangement combined with a molecular field theoretic calculation of the rf permeability tensor for MnF2. Agreement between experiment and theory is good using only a one‐parameter fit. It was found that the linewidth is not strongly frequency dependent in very good samples except at frequencies very near to or very far from the zero‐field resonance frequency. The effect of sample size on observed linewidth is very significant. A value of 90 Oe is given for the residual size‐independent linewidth. Experimental aspects are emphasized due to the extremely high frequencies employed.

ISSN:0021-8979    

DOI:10.1063/1.1659496

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Strains in thin epitaxially grown films resulting mainly from the difference in the coefficients of thermal expansion between film and substrate have been measured using an x‐ray double‐crystal diffractometer. The measured strains are in agreement with those predicted from known thermal expansion data. Tensile stresses of about 6.5×109dyn/cm2parallel to the surface have been found at room temperature in a film deposited at 1225°C.

ISSN:0021-8979    

DOI:10.1063/1.1659497

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Several methods are advanced to represent the directional dependence of elastic coefficients for cubic materials which are then illustrated using silicon, copper, and molybdenum. The extensively displayed coefficient is the shear stiffness. Also presented are some rarely shown coefficients such asC1123′ andC1312′ whose on‐axes values are zero. Polar plots are made of the shear stiffness coefficientC1313′ for silicon, for some planes that have a common zone axis. A method particularly suitable for illustrating anisotropy in transverse coefficients is presented in which a family of polar plots is superimposed on the standard triangle.

ISSN:0021-8979    

DOI:10.1063/1.1659498

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The effect of impurities on the critical resolved shear stress (CRSS) of magnesium oxide single crystals has been determined using compression testing in crystals containing up to 40 mole ppm Fe3+and up to 500 mole ppm of Ni+2impurities. In pure crystals containing small amounts of Fe2+, the value of 0.73±0.07 kg/mm2is determined as the CRSS, and two distinguishable strain hardening regions are identified. The effect on CRSS on Fe3+content and of isochronal and isothermal aging is also studied; precipitation hardening is observed on aging even for very low concentrations of Fe3+. Heat treatments have very little effect on Ni+2‐doped crystals, and yielding studies show that Fe3+is much more significant than Ni2+in hardening MgO.

ISSN:0021-8979    

DOI:10.1063/1.1659499

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The photovoltaic properties of Cu2S&sngbnd;CdS heterojunctions have been compared before and after short heat treatment, using measuredI‐Vcharacteristics, junction capacitance, and spectral response. After heat treatment slow transients in the photoresponse and effects of secondary illumination were investigated. Optical quenching of the photocurrent was observed in two ir bands corresponding to transitions at 0.8 and 1.1 eV, and enhancement of the photocurrent was seen forhv>1.5 eV. Long persistence of the enhancement effect was observed, which thermally quenched with an activation energy of 0.95 eV. A model for the heterojunction is proposed in which hole trapping in deep imperfection centers in the CdS near the junction is the key mechanism. A conduction band spike is assumed to exist at the Cu2S&sngbnd;CdS interface. The transparency of this spike to photoexcited electrons diffusing from the Cu2S is modulated by variations in the CdS depletion width caused by the deep trapping.

ISSN:0021-8979    

DOI:10.1063/1.1659500

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A theoretical study is presented on the characteristics and electromagnetic fields, in vacuum, of a widely used slow‐wave line. The main interest of such a structure is connected with its performances as a plasma producing, heating, and ejecting device.

ISSN:0021-8979    

DOI:10.1063/1.1659501

出版商:AIP    

年代:1970

数据来源: AIP