摘要:

The pressure of the barium I‐II transition has been determined in a modified single‐stage piston‐cylinder apparatus to be 55.0±0.5 kbar at 22°C. Three barium samples of different purity were used and no significant variation of the transition pressure found. The temperature coefficient of the transition pressure is 0–0.015 kbar/°C near room temperature. The effect of the presence of dissolved hydrogen on the transition pressure is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1709184

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

If absorption in the reflector is low, ultrasoft x rays exhibit a well‐defined critical angle of total reflection. Experiments with simple apparatus verify critical angles calculated for paraffin of &thgr;c≈4° for carbon radiation (&lgr;=44.7 Å) and &thgr;c≈6° for boron radiation (&lgr;=67.7 Å). Utilization of this concept in a low‐resolution (10<&lgr;/&Dgr;&lgr;<20) instrument for the chemical analysis of carbon and boron by a paraffin reflector and of nitrogen, oxygen, and fluorine by a lithium fluoride mirror is suggested.

ISSN:0021-8979    

DOI:10.1063/1.1709185

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Experimental data on the heat generated during torsional oscillations of polymethylmethacrylate tubes are presented. Various factors which affect the internal heat generation, including the amplitude and frequency of oscillation and the ambient temperature are investigated. A comparison of the mechanical energy added to a specimen during a cycle of deformation and the resulting heat indicates that some energy is ``stored'' during the process. In addition to the detail of the response during a single cycle of deformation, the longtime response of the material to constant strain‐amplitude oscillations is investigated. The data demonstrate that thermomechanical coupling effects can be extremely important.

ISSN:0021-8979    

DOI:10.1063/1.1709186

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The anharmonic decay of a high‐frequency longitudinal elastic wave at low temperatures, such thatℏ&ohgr;>KT, is calculated by perturbation theory, using a Gru¨neisen parameter as measure of the anharmonicity. The attenuation at very low temperatures varies as the fifth power of frequency, and is small at frequencies below 1012Hz.

ISSN:0021-8979    

DOI:10.1063/1.1709187

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Acceleration of a microwave‐energized plasma by expansion in a diverging magnetic field is studied. Results of a theoretical collisionless particle analysis are reviewed. An experimental accelerator is described and its pertinent conditions are considered. Measurements of plasma beam shape and potential are compared with the theoretical predictions. The conclusions are that, while some experimental characteristics (beam shape and potential profile) agree with theory, collisions in the experimental device prevent it from attaining operating conditions predicted by collisionless theory.

ISSN:0021-8979    

DOI:10.1063/1.1709188

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Avalanche generation of minority carriers was studied under pulsed‐field conditions in thermally oxidized silicon surfaces. In the doping range between 5×1016and 1×1018cm−3avalanche breakdown voltages and fields are in agreement with step‐junction results. For lower doping, breakdown voltages are below the expected values. Avalanche light‐emission observations revealed this effect to be due to field concentration at the contact edges. In the higher doping range between 1018and 1019cm−3minority carriers are produced by Zener tunneling. Band bending for tunneling is 1.1 V, independent of doping.

ISSN:0021-8979    

DOI:10.1063/1.1709189

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

When a field greater than that required to produce Gunn instabilities is applied to gallium arsenide containing free electrons in concentrations of 1017cm−3or more, excess current rather than current saturation is seen. Impact ionization due to high‐field domains causes a substantial increase in carrier density. The processes involved in the generation and recombination of these excess carriers are analyzed here. Recombination occurs by competing radiative and nonradiative mechanisms, with long‐term trapping also playing a role. Measurements of the time dependence of excess conductivity and recombination radiation, the spectral distribution of the radiation, and its intensity as a function of excess carrier concentration, allow the generation rate and recombination cross sections to be deduced. The generation rate is consistent with that expected from flat‐topped domains. Cross sections for the capture of both holes and electrons by the recombination centers dominant under these conditions are of the order 10−17cm2. The emitted radiation is strongly self‐absorbed; correction for this factor shows that most of the original emission has energy greater than the bandgap. The direct recombination cross section is deduced to be near 5×10−18cm2, which is in reasonable agreement with that derived from the van Roosbroeck‐Shockley theory.

ISSN:0021-8979    

DOI:10.1063/1.1709190

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The theory of hot electron diffusion is developed for the case of space‐charge‐limited current flow in insulators or weakly doped semiconductors. To compare the results of the calculation with experiments on siliconn+‐&pgr;‐n+structures by Denda and Nicolet, a crude theory of the uniform‐field hot‐electron effect inn‐type silicon is developed.

ISSN:0021-8979    

DOI:10.1063/1.1709191

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A consistent electronic theory of adhesion is developed relating to the contact of bodies of different nature.The strength (as well as energy) of adhesion is calculated for the contact of crystal bodies (semiconductors, metals) as well as for the contact of amorphous bodies whose surface is saturated by donor and acceptor functional groups. The theory developed allows us to calculate the electrostatic component, when certain (experimentally determined) physiochemical characteristics of studied objects are known. The theory also determines the temperature dependence of the adhesion strength. The main inference is that cases of electrostatic component reading values of the order of 108−109(dyn/cm2) are fairly realistic. There follows from the theory the role of surface conditions as the chief factor of high adhesion. The theory suggests the ways for conditioning the adhesion via chemical modification of the surfaces (sometimes also of the bulk) of contacting bodies, and indicates which characteristics of solid bodies are to be studied when investigating the adhesion.

ISSN:0021-8979    

DOI:10.1063/1.1709192

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The reflectance spectra of the cubic fluoride perovskites KMgF3, KMnF3, KCoF3, KNiF3, RbMnF3, and mixed crystals of K (Mg0.8:Ni0.2) F3and K (Mg0.5:Ni0.5) F3have been measured from 4000−40 cm−1at 300° and 85°K. The spectra of all crystals at both temperatures have been fitted by means of a classical dispersion analysis to yield the frequencies, oscillator strengths, and damping constants of the three ir active lattice vibrations. An assignment of the normal mode frequencies to particular vibrations has been made. The high‐ and low‐frequency dielectric constants of these materials have been determined from the reflectance measurements. The isotropic polarizabilities of Mg2+, Mn2+, Co2+, Ni2+, and Rb+have been calculated. The transverse effective charge at 300°K has been obtained in order to determine the strength of second‐order dipole moments due to charge deformation during lattice vibrations.

ISSN:0021-8979    

DOI:10.1063/1.1709193

出版商:AIP    

年代:1967

数据来源: AIP