摘要:

Measurements of the temperature dependence of surface acoustic wave velocity were performed for propagation onX, Y, AC, AT, and along thexaxis of several other rotatedYcuts of quartz over the temperature range −25° to +75°C. A pulsed rf technique was employed. To facilitate the measurement of angular dependence of the temperature coefficient of velocity, surface wave delay lines were constructed in which the waves were excited on the quartz by means of an interdigital electrode structure on a glass substrate which was brought into contact with the quartz. Calculations of the temperature coefficients of velocity and delay time were performed using an iterative computer program based on the work of Coquin and Tiersten. The measurements and calculations are in good agreement in most cases, the largest discrepancy being approximately five percent. It is concluded that the orientation which best combines low‐temperature dependence of delay time, high coupling constant, and a minimum of deleterious side effects is 42½° rotatedY‐cut quartz with propagation along thexaxis.

ISSN:0021-8979    

DOI:10.1063/1.1659311

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The acousto‐optic properties of crystalline germanium have been measured, including a complete and accurate characterization of the photoelastic tensor. The results of this work indicate that germanium has a substantially larger acousto‐optic figure of merit, (n6p2/&rgr;V3), than other known infrared materials, with the exception of crystalline tellurium. Because germanium has superior optical and mechanical properties, it should be preferred to tellurium for many infrared modulation and deflection applications. In addition, we propose that germanium be used as a standard for future infrared acousto‐optic material studies in the same way that fused silica has been used in the visible and near visible portion of the spectrum.

ISSN:0021-8979    

DOI:10.1063/1.1659312

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Although the theory of Giordmaine and Wang adequately predicts the centerline intensity of a molecular beam from a channel source, it is less successful in describing the angular distribution. This deficiency has been ascribed to a nonzero number density at the tube exit. The end conditions chosen by previous workers lead to angular distributions which fail to satisfy total flow and average cosine restrictions. A method of choosing the parameters of the linear density profile which satisfies these integral constraints is described. The computed angular distributions according to the theories utilizing different end conditions differ very little from each other, but represent a clear improvement over Giordmaine and Wang's angular distribution.

ISSN:0021-8979    

DOI:10.1063/1.1659313

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A statistical mechanical model of gas solubility in glass is presented. For equilibrium, the Gibbs free energy of the free gas is equated to that of the gas in solution. Expressions for the Gibbs energies are obtained from assumptions of the atomic motion in the free gas and dissolved states. The resulting solubility equations express the solubility (in atoms per cubic centimeter of glass) as a function of gas pressure, temperature, fundamental constants, and material parameters. An initial evaluation of the model is made by comparison with literature data for helium and neon in fused silica.

ISSN:0021-8979    

DOI:10.1063/1.1659314

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Homoepitaxial growth of GaAs was studiedin situin an ultrahigh‐vacuum high‐energy electron diffraction (HEED) system. Two surface structures,GaAs(1¯1¯1¯)−(19)1/2andGaAs(1¯1¯1¯)−2, were observed during growth. The transition from one surface structure to the other was found to be a function of the deposition rate and the substrate temperature, with the high‐temperature structure being the(1¯1¯1¯)−(19)1/2. The film growth morphology was studied by the carbon replication technique. Growth by a step mechanism was observed on a bromine‐methanol etched surface while three‐dimensional nuclei were observed on a polished or contaminated surface.

ISSN:0021-8979    

DOI:10.1063/1.1659315

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Precipitation and dissolution potentials for KCl, NaCl, BaCl2, and NH4Cl have been measured with a Lindemann electrometer both in air as well as in nitrogen. The values in the latter case are lower. The electrode on which precipitation and dissolution takes place is found to be negative. The available evidence shows that static potential is developed. In order to assess the relative contributions of (i) diffusion potential, (ii) thermodiffusion potential, and (iii) zeta potential to the overall precipitation and dissolution potential, suitable experiments have been performed. Zeta potential was estimated from measurements of streaming potentials. Phase potentials have also been measured. It appears that the major contribution to the observed precipitation and dissolution potential arises due to unequal mobilities of the two ions being incorporated into or detached from the crystal lattice. The temperature, concentration, and time dependence of the various potentials have also been investigated.

ISSN:0021-8979    

DOI:10.1063/1.1659316

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The propagation of surface waves on free and metallized surfaces of cubic and hexagonal crystals is investigated numerically. Surface wave velocity curves and relative differential velocity curves are presented for propagation on typical surfaces of four selected crystals (gallium arsenide, bismuth germanium oxide, zinc oxide, and cadmium sulfide). Special attention is paid to degenerate modes wherein decoupling among the various components of mechanical displacement and the electric field occurs.

ISSN:0021-8979    

DOI:10.1063/1.1659317

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Measurements of the electrical resistivity of thin silver films prepared by evaporation on amorphous substrates in ultrahigh vacuum indicate partial specular reflection of the conduction electrons at the films' surfaces. Some correlation between the electrical resistivity and the structure of the deposited films was observed, and the influence of residual gases during the evaporation process on structure and properties of the films was investigated.

ISSN:0021-8979    

DOI:10.1063/1.1659318

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The stress fields &sgr;ijand the dilatation field &Dgr; have been obtained in contour plots for a straight dislocation situated perpendicular to a reflection plane in an anisotropic crystal. A common characteristic feature of the results obtained for various metals at room temperature is that no twofold symmetry exists in any of &sgr;ijor in &Dgr; with respect to any axis normal to the dislocation line. For certain values of the modified elastic compliancesS16andS26, anomalous patterns have been found in the elastic fields that each of the &sgr;11, &sgr;33, and &Dgr; fields is divided into six sectors as compared to the usual cases of two sectors, and either of &sgr;12and &sgr;22fields is divided into two sectors in contrast to the normal pattern of six sectors. Some direct effects of the asymmetries and certain anomalies of these elastic fields on deformation processes are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659319

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Dislocation motion in crystals is usually measured on loops generated from a deliberately introduced nucleating center such as a scratch. In germanium crystals it has been noticed that motion of an individual loop is usually asymmetric as observed by etch‐pit techniques. The asymmetry has been assumed to arise from motion of dislocations having different character. The validity of this assumption was tested directly by x‐ray topographic contrast experiments on crystals of germanium and silicon. From appropriate reflections that give either a strong or vanishing contrast it is possible to determine the Burgers vector of the dislocation loop. For both bending and compression tests, dislocation loops generated from a scratch and subsequently moved have a Burgers vector in the maximum resolved shear stress direction. Thus, for the specimen orientation ⟨123⟩ commonly used in velocity experiments both ends of the dislocation loops intersecting the surface of observation have the same character. In some cases the asymmetry may be due to the shape of the loop. The x‐ray evidence refutes the conclusions reached by previous workers that asymmetrical motion is due to dislocations of different character.

ISSN:0021-8979    

DOI:10.1063/1.1659320

出版商:AIP    

年代:1970

数据来源: AIP