摘要:

Acoustoelectric amplification, in the linear approximation, is considered for a system containing several types of carriers in the two limiting cases of fast and slow carrier equilibration. The pertinent expressions are first derived for a piezoelectric semiconductor and then expanded to the more practical case of a layered system containing one or more semiconducting layers coupled to a piezoelectric element. An experimental example is given in the form of a guided elastic plate wave in lead zirconate titanate coupled to a plate of near‐intrinsic Ge.

ISSN:0021-8979    

DOI:10.1063/1.1659053

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The Raman spectrum of ZnTe has been investigated. The fundamental frequencies have been found to bev¯LO=208.3±0.5 cm−1andv¯TO= 177.5±0.5 cm−1. The temperature variation ofv¯LOhas been examined between room temperature and 4°K. The zone boundary frequencies at the critical pointsX, L, andWhave been estimated from the second‐order Raman spectrum. In determining these frequencies a theoretical model was used to assist in the assignment of the frequencies and as a check on the consistency of the results. The values obtained were further checked using regularities previously observed in the phonon spectra of zinc‐blende semiconductors.

ISSN:0021-8979    

DOI:10.1063/1.1659054

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Specimens of hcp4He used for thermal conductivity measurements have been examined by an x‐ray method. This method is described and several Laue photographs are shown. These photographs are an excellent test of specimen quality. The number of reflections observed for high‐quality crystals is sufficient for orientation determinations.

ISSN:0021-8979    

DOI:10.1063/1.1659055

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

As discovered by Price and Walker, small uniform pores may be created in muscovite by etching in HF thin samples that have been subjected to fission particle irradiation. The process of pore growth is followed by monitoring the conductance across a thin sample as the etching proceeds. For irradiation with252Cf the tracks quickly etch to a radius of 33 Å‐the region of primary damage. Further radial etching in the undamaged material is slow but increases to a fixed rate as the radius increases. This radius dependence of etching is interpreted by a kinetic analog of the Kelvin equation for vapor pressure over curved surfaces. With suitable assumptions on the mechanism of attack, the surface energy of the muscovite‐solution interface is calculated to be about 300 ergs/cm2.

ISSN:0021-8979    

DOI:10.1063/1.1659056

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Starting with the traditional time‐invariant paraboloidal model to represent the diffusion‐controlled growth of a needle‐shaped crystal in a pure supercooled melt, the effect of thermal imbalance at the solid‐liquid interface is calculated. In particular, the diffusion field equations are solved for the initial excess velocity distribution at the interface, on the assumption that the shape constraint is suddenly replaced by the constraint of heat conservation. The computed results show that the hypothetical paraboloid tends to bulge everywhere behind the tip, with a pronounced circumferential peak bulge at one radius from the tip of the needle. The analytical result correlates well with the observed shape of dendritic needle crystals whose side branches protrude from (rather than oscillate about) the paraboloidal root shape. The paper concludes with the suggestion that the formation of side branches may be usefully regarded as the self‐induced oscillation of a nonlinear system. To minimize deviations from the law of heat conservation, the analytic model should include traveling interface waves.

ISSN:0021-8979    

DOI:10.1063/1.1659057

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The basic objective is the presentation of a description of rate‐sensitive plastic materials which agrees with events on the microscopic level and with macroscopic experiments and which is internally consistent. We utilize the framework of the thermodynamics with internal state variables formulated recently by Coleman and Gurtin. The internal state variables in the present theory are considered to be average quantities related to properties of the crystal defects in the material. Rate‐dependent phenomena, (e.g., a time‐dependent stress‐strain relation, creep, etc.) are studied in detail. The theory is illustrated with a simple example.

ISSN:0021-8979    

DOI:10.1063/1.1659058

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The solute diffusion of cobalt in beta‐uranium was measured using the thin‐layer sectioning technique. The results can be expressed byD= 1.54×10−2exp(−27 450/RT) cm2/sec. The diffusivities of cobalt are higher by about three orders of magnitude than the self‐diffusion coefficients in beta‐uranium. The possibility of cobalt diffusing by means of the combined substitutional‐interstitial mechanism has been examined.

ISSN:0021-8979    

DOI:10.1063/1.1659059

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A theoretical model has been developed to explain the movement of ap‐njunction in PbSe by the interdiffusion process. This model, which is a modification of an interdiffusion theory due to Brebrick, has one value for the diffusion coefficient inp‐type material and another value inn‐type material. Solutions to the diffusion equation for this model are obtained and compared to experimental interdiffusion data for PbSe at 400°C obtained by thep‐n junction method. The significance of the results to device fabrication and annealing is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659060

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The mechanism of field‐enhanced secondary emission has been studied experimentally in detail for KCl low‐density transmission dynodes transferred in a dry nitrogen atmosphere. By means of a Kelvin probe located at the center of a collector, dynode surface potentials and their relationship with collector potential, secondary yield, primary energy, and current density have been studied. A unique relationship between yield and surface potential has been found, independent of all other parameters for current densities between 1 and 10 nA/cm2. This study clearly shows that an avalanche process, together with an increase in escape length, is responsible for the high yields obtainable. A study of transient effects reveals that the high surface potential needed for high yield decays rapidly after the primary beam is turned off. A smaller surface potential, with a long decay time constant, can be expected to provide slight field enhancement for single particle bombardment at low rates. The statistical distributions of the number of emitted secondary electrons per primary incident at high (1‐MeV) and low (9.5‐keV) energies have been measured for low‐density films of CsI and KCl at low count rates. The results do not differ very much from those obtained previously from normal density films except that the yields are somewhat higher, particularly after the film has been charged with a dense primary beam. The distributions obtained are non‐Poissonian in nature (more nearly exponential), and this is explained by their similarity to normal density films.

ISSN:0021-8979    

DOI:10.1063/1.1659061

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An electron impact ion source suitable for use with a quadrupole mass filter is described. Ion formation occurs throughout a relatively large volume since no magnetic field collimation of the ionization electron stream is used. A sensitivity of 8 Torr−1was obtained for an ion energy of 50 eV rising to a constant sensitivity of 12 Torr−1for ion energies in excess of 250 eV. Trajectory tracing has been used to give some insight into the efficient operation of the ion source.

ISSN:0021-8979    

DOI:10.1063/1.1659062

出版商:AIP    

年代:1970

数据来源: AIP