摘要:

Optical modulation produced by acoustoelectric domains in semiconducting CdS is shown to be associated with the acoustic flux, rather than the accompanying high electric field in the domain. The optical modulation effect serves as a useful technique for exploring the origin and nature of the flux, and to understand the amplification process itself.

ISSN:0021-8979    

DOI:10.1063/1.1657274

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Elastic stiffness, acoustic absorption, and photoelastic constants of the crystal have been determined at room temperature using ultrasonic light diffraction and pulse‐echo methods. Two acoustic modes have been found to be particularly useful to acousto‐optical applications: One is the shear mode propagated in the [110] direction with displacement along [1¯10], which is characterized by a remarkably high acousto‐optical figure of merit,M(n6p2/&rgr;v3) = 793×10−18sec3/g; and the other is the longitudinal mode along [001] with high figure of merit defined taking account of frequency bandwidth,M′ (n7p2/&rgr;v) = 142×10−7cm2·sec/g, and low acoustic loss.

ISSN:0021-8979    

DOI:10.1063/1.1657275

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The formation of Cottrell atmospheres can change the scattering of phonons by dislocations and affect the lattice thermal resistivity due to dislocations. Since diffusion of solute atoms is required to form atmospheres, they are not formed instantaneously. Changes due to annealing are similarly time dependent. The diffusion equation is solved in its Fourier‐inverted form, and changes in phonon scattering and lattice thermal conductivity are obtained in a simple form. Changes in lattice thermal conductivity at higher temperatures occur faster, since diffusion through shorter distances is involved. Diffusion coefficients can be determined by studying the time dependence of the lattice thermal conductivity on annealing, and for slow diffusion this method may have advantages.

ISSN:0021-8979    

DOI:10.1063/1.1657276

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The dielectric constants, electrical conductivity, specific heat, and pyroelectric coefficients of ferro‐electric Sr1−xBaxNb2O6(SBN) are investigated as a function of temperature in the range 10°–500°K, and as a function of the Sr/Ba composition of the material. A simple technique for measuring absolute pyroelectric coefficients and spontaneous polarizations of ferroelectrics is described. The electric field and frequency dependence of the dielectric properties are also investigated. The theory of pyroelectric detection is discussed from a materials point of view, and the experimental data are considered in terms of the usefulness of SBN as a pyroelectric detector of electromagnetic radiation.

ISSN:0021-8979    

DOI:10.1063/1.1657277

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The Mo¨ssbauer spectra of the system (PbTiO3)0.95(BiFeO3)0.05have been studied from room temperature to 585°C. From the isomer‐shift of 0.491±0.02 mmsec−1at room temperature, the ionicity is found to be 60%±20%. A discontinuity in the plot of isomer‐shift versus temperature atTcis observed. The quadrupole splitting at room temperature is 0.295±0.02 mm/sec−1. A dip in the Mo¨ssbauer fraction is observed at the Curie temperature.

ISSN:0021-8979    

DOI:10.1063/1.1657278

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Dielectric loss measurements of a mixture consisting of a number of small single crystals of beta alumina suspended in alpha alumina have been made. The loss follows the Fuoss‐Kirkwood empirical formula &egr;″=&egr;″max[ln (fmax/f)&agr;]. Some speculations are made as to the cause of the width of the loss peaks. Substitution of other (K, Ag, Rb, NH4, Li, Tl) ions for sodium causes the loss curves to shift in a direction indicating higher resistivity of the substituted beta aluminas. A quantitative relation between the shift of the loss peaks and the known resistivity of the substituted beta aluminas as would be expected from the Maxwell‐Wagner relations was unable to be made.

ISSN:0021-8979    

DOI:10.1063/1.1657279

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Optimized lead stearate multilayer crystals have been built, using a modified Langmuir‐Blodgett technique, onto glass substrates of varying surface finish. The relative ultra‐soft x‐ray peak reflectivities of these crystals were measured. The results show that under normal conditions, where thick crystals are in use, a surface finish of very much better than 1 &mgr;in. CLA is required to achieve maximum peak reflectivity. Untreated float glass, highly polished steel, and selected mica were shown to provide suitable substrates.

ISSN:0021-8979    

DOI:10.1063/1.1657280

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An electromagnetic plane wave in eitherEorHpolarization is normally incident on a cylinder which is assumed to be an infinitely thin‐walled, perfectly conducting, circular tube of finite length with complete generality both in radius and length. For either polarization both axial and transverse currents are induced. The problem is transformed into determining an infinity of Fourier components by expanding each function of &thgr; into a Fourier series. For each Fourier component a pair of integral equations for the total currents is obtained. These are decoupled in a special sense permitting the transverse total current to be obtained first, followed by the axial total current. The diflerence current is then defined and expressed in terms of the total current, making possible the determination of the inside and the outside total current. These are experimentally measurab e quantities. The theoretical formulas for the scattered fields, the far field patterns, and the scattering cross sections are also derived in terms of the total current. Finally, sample results, both theoretical and experimental, are included.

ISSN:0021-8979    

DOI:10.1063/1.1657281

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Three methods of confining the angular dispersion of a field electron beam from ⟨100⟩ oriented tungsten emitters are investigated; they are (1) thermal‐field buildup, (2) selective work function reduction by zirconium adsorption, and (3) high‐temperature field evaporation. All three methods confine the emission to a beam half‐angle of less than 9° in the dc current range 0.1 to 100 &mgr;A. Method (1) results in a ∼50% reduction in beam voltage. Provided that the vacuum level is good (∼10−10Torr), long and short term current instabilities are negligible for dc current levels below 10 &mgr;A at 300°K for each of the emitter end forms investigated. The angular dispersion and beam voltage of a field ion beam can also be reduced by method (1) as described briefly in this paper.

ISSN:0021-8979    

DOI:10.1063/1.1657282

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The theory is presented for predicting the microwave breakdown characteristic of a rectangular aperture antenna, including the realistic near elastic fields. The theory is then compared with experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1657283

出版商:AIP    

年代:1969

数据来源: AIP