摘要:

The drift velocity of electrons in silicon at high electric fields is measured in the⟨111⟩direction over the range of lattice temperatures from 4.2° to 300°K. It is established that in this range a limiting drift velocity exists. Its temperature dependence is measured. The samples used and the method of measurement are briefly described.

ISSN:0021-8979    

DOI:10.1063/1.1657427

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Epitaxial layers of BaTiO3grow on Pt substrates when: (1) The Pt substrate has preferred orientation⟨111⟩; (2) BaTiO3powder is sintered on this substrate at 1400°C for 24 h in air. The epitaxial BaTiO3is single crystalline with an orientation of {111}BaTiO3//{111}Ptbut with a deformation in crystal structure. X‐ray diffraction data indicate that the spacingd111is larger by about 1% (0.023 Å) than that of original BaTiO3which is tetragonal phase at room temperature. The dielectric measurements show that the remanent polarization and the dielectric constant of this specimen are about ¼ and110values of those of polycrystalline BaTiO3, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1657428

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Dislocations, their origins, and their effects on photoluminescence efficiency have been studied in GaAs1−xPxsingle crystals grown by vapor phase epitaxy. Dislocations were observed using etch pit, optical‐transmission microscopy, and x‐ray topography techniques. Two types of dislocations are grown into GaAs1−xPxepitaxial crystals. Near the GaAs (substrate)‐GaAs1−xPxinterface a high density (>108cm−2) of pure edge dislocations with axes and Burgers vectors lying in the growth plane was observed. These originate from the lattice parameter mismatch between substrate and epitaxial layer. In the bulk GaAs1−xPx, a high density (∼106cm−2) of dislocations was observed with ⟨211⟩ and ⟨100⟩ directions and Burgers vectors parallel to those of the mismatch dislocations. These dislocations originate from the mismatch dislocations at the substrate‐epitaxial layer interface. The effect of dislocations on photoluminescence efficiency was studied by a novel technique. The photoluminescence was excited by focusing a He&sngbnd;Ne laser onto a 20‐micron spot on the polished sample surface. The photoluminescence was observed through a microscope at ×400 magnification. It was found that the dislocations grown into the GaAs1−xPxare not intrinsically deleterious to the photoluminescence efficiency; however, in impure material, impurities segregate at dislocations causing a lowering of the luminescence efficiency in a region within one micron of the dislocation core.

ISSN:0021-8979    

DOI:10.1063/1.1657429

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Results of optical and electrical measurements on Ni&sngbnd;P films are presented, in both as‐deposited and annealed films. The films range in thickness from 100 Å to 1 mm and vary in composition from 0%–16% P by weight. The results suggest a model for the structure of these films. For freshly deposited films, the model consists of a three‐dimensionally aggregated liquid‐like structure with nonmetallic properties. Heat treatment is shown to create a packing tendency followed by crystallization of the films at a relatively high temperature (around 350°C). This results in a nearly metallic film behavior.

ISSN:0021-8979    

DOI:10.1063/1.1657430

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A Nd‐glass laser system is described which emits a 4 GW diffraction‐limited laser pulse, at a radiance of 2×1017W/cm2‐sr. The device consists of a spatially mode‐selectedQ‐switched oscillator, operating in the lowest‐order HE11transverse mode, followed by a series of amplifiers that are coupled with appropriate beam‐expanding optics. A beam with a far‐field pattern corresponding to Fraunhofer diffraction, is approached through use of the proper gain distribution in the first amplifier and a 50% over‐expanded beam to allow uniform illumination of a physical aperture placed in front of the second amplifier. This system requires high optical‐quality laser rods capable of transmitting a diffraction‐limited beam. The induced optical distortions of the amplifiers during the pumping are minimized by appropriate Nd‐doping concentration, surface treatment, flashtube arrangement, and filtering of the pump light, yielding uniformity of pumping over almost the full cross section. Some experimental results on long‐path air breakdown, efficient second‐harmonic generation, and durability of laser glasses are described.

ISSN:0021-8979    

DOI:10.1063/1.1657431

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The electromagnetic field as a function of time in a conducting, infinitely long cylindrical tank into which a helical current is injected is considered. The longitudinal component of the magnetic field is treated in complete detail, and a plot of magnetic field vs time is given for the circularly symmetric case with parameters closely approximating the Astron configuration.

ISSN:0021-8979    

DOI:10.1063/1.1657432

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The propagation of microwave magnetoelastic waves in a ferromagnet subjected to pulsed magnetic fields is investigated. In the first part of the theoretical analysis, which is restricted to spatially uniform bias fields, the interaction between the magnetic and elastic systems is neglected. Using a coupled‐mode approach, it is found that plane spin waves propagate in magnetic field transients with negligible reflections, constant momentum and wavenumber, but variable frequency and power flow. These results are further elucidated by the study of a simple step transient case. In the presence of magnetoelastic interaction, the theory indicates that besides changes in frequency and in power flow, the field gradient causes group velocity modulation and changes in the time duration of wave packets. In addition there is an exchange of momentum between the different branches of the dispersion relation; this exchange is calculated in terms of critical field gradients, The analysis reveals that negligible coupling occurs for field gradients much smaller than the critical values, resulting in efficient magnon/phonon conversion. The critical gradients are given for both shear and longitudinal waves propagating along certain crystallographic directions.

ISSN:0021-8979    

DOI:10.1063/1.1657433

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Experiments which confirm the theoretical predictions on the propagation of magnetoelastic waves in time varying magnetic fields are described. Frequency shifts of spin waves as high as 1 GHz have been observed at L‐band microwave frequencies, in axially magnetized rods of yttrium iron garnet (YIG). Experiments with magnetoelastic pulses were performed in cases where the signal is injected either as a phonon (piezoelectric excitation) or as a magnon (fine‐wire excitation). The first demonstrates frequency conversion and group velocity modulation. The latter scheme is suitable to observe pulse compression and expansion due to frequency modulation and time changes of the group velocity. It is also used to ``trap'' magnetoelastic pulses in the phonon state, by removal of the crossover point.

ISSN:0021-8979    

DOI:10.1063/1.1657434

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A theoretical discussion is given of infrared detection systems employing an optically nonlinear crystal, a laser in the visible, and photomultiplier to detect the light produced at the sum or difference frequency. Three optical mixing systems are considered in detail and compared with direct detection: (a) cinnabar (HgS) in a single‐pass optical system with the He&sngbnd;Ne 0.6328 &mgr;m cw laser, (b) the same crystal and laser with a ring resonator and narrow‐band output filter, and (c) an ideal resonant system with a crystal as nonlinear as HgS but without absorption or double refraction. The noise output consisting of up‐converted thermal noise and (in the case of the difference frequency) optical parametric noise is computed quantitatively. These systems have too small a quantum efficiency to compete with a heterodyne system employing an ir laser and a detector of high quantum efficiency such as a Ge:Cu‐cooled photoconductor. The Ge:Cu detector has however a large dark noise compared to a good photomultiplier, and consequently optical mixing can surpass nonheterodyne direct detection if the required value ofB≡(S/N)&Dgr;fis sufficiently small. The range of superiority of optical mixing over nonheterodyne direct detection extends high enough inBfor Morse code for system (a) (if sum frequency is used), nearly high enough for a telephone channel for (b) and up to the television level for (c).

ISSN:0021-8979    

DOI:10.1063/1.1657435

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Probability density distributions of the interval spacings between zero‐crossings of band‐limited Nyquist and 1/fnoise signals are examined using an interval‐to‐pulseheight converter and a multichannel pulse‐height analyzer. The Nyquist noise distributions follow a simple exponential law, as expected. In the case of 1/fnoise, the distributions are approximately proportional to the inverse square of the spacing interval. The probability density is statistically stationary, that is, independent of sample length and independent of the sample selected. For signals in a 1 Hz to 5 kHz band the most probable spacing interval is 1.2×10−4sec, which occurs with a maximum probability density of 2.2×103sec−1. The most probable value is inversely proportional to the highest signal frequency present and the peak probability density is proportional to this frequency.

ISSN:0021-8979    

DOI:10.1063/1.1657436

出版商:AIP    

年代:1969

数据来源: AIP