摘要:

An x‐ray diffraction technique recently developed by Houska and co‐workers was applied to the problem of measuring interdiffusion at 600°C in 11.2 &mgr; Ag/Cu bimetallic thin films prepared by vapor deposition on mica. The technique consists in matching experimental intensity bands to those calculated from assumed concentration profiles. The profiles which gave best fit in the Ag‐rich layer were analyzed by means of a linear diffusion equation solved in a finite region with fixed interface. The value of 1.45×10−12cm2/sec was obtained for the interdiffusion coefficient in the Ag‐rich phase.

ISSN:0021-8979    

DOI:10.1063/1.323061

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The change in length of 1‐m‐long LiF single crystal has been determined as a function of hydrostatic pressure up to 7 kbar over the temperature range 28–41°C. The length change has been measured to an accuracy of less than 500 A by using a Fabry‐Perot type He‐Ne laser interferometer, and under a temperature‐controlled environment with temperature variations less than 0.002°C. Several isothermal equations of state, together with those derived from the Born model of ionic solids, have been used in analyzing the pressure‐volume data. The isothermal bulk modulusBoand its pressure derivativeB′oat atmospheric pressure and 28.83±0.05 °C obtained from the two‐parameter (BoandB′o) equations of state areBo=664.5±0.5 kbar andB′o=5.40±0.18, respectively. The present results differ considerably from the static measurements of Bridgman and also of Vaidya and Kennedy, but are in excellent agreement with the values obtained by ultrasonic measurements. Using the two‐parameter equations of state, the pressure volume data is extrapolated to ∼5 Mbar in order to compare with the shock wave data and to examine the differences between the various equations of state, which are hardly distinguishable in the low‐pressure region. Although the presentV/Vomeasurements are sufficiently accurate to obtain accurate values ofB″o, the present pressure measurements are not (although we believe they are as accurate as is possible at the present time).

ISSN:0021-8979    

DOI:10.1063/1.323062

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A closed‐form thermal model is presented which describes heat transfer in thin‐film photoconductors under laser irradiation. Previously published thermal models for laser damage are not valid for thin‐film detectors fabricated with thick protective layers. In these detectors it is necessary to take into account heat diffusion from the absorbing film into the protective layer as well as the substrate. The thermal model was validated by measuring the damage thresholds of PbS and PbSe photoconductors and comparing theoretical and experimental results. The model was then used to analyze the thermal response of thin‐film detectors fabricated with different substrates and thermal coupling parameters. It is shown that considerable improvement in the performance of thin‐film photoconductors under high thermal loading can be achieved.

ISSN:0021-8979    

DOI:10.1063/1.323063

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Four previously published models for laser damage in infrared detectors, based on closed‐form solutions to the heat diffusion equation, are reviewed and their limitations discussed. A generalized two‐dimensional numerical model based on a finite element technique is presented. This model can be used to calculate damage thresholds whenever the closed‐form solutions are not appropriate, and is sufficiently general that it can treat most cases expected to be of interest in laser detector damage. The numerical model is used to calculate thresholds for HgCdTe photovoltaic detectors. Experimentally measured laser damage thresholds are reported for Hg0.8Cd0.2Te crystals whose size and thermal configurations are similar to those of photovoltaic detectors. These thresholds are found to be in good agreement with theoretical values.

ISSN:0021-8979    

DOI:10.1063/1.323064

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Interfacial deformed layers existing in GaAs epitaxial wafers are conveniently observed on a {110} cleavage face by means of a room‐temperature photoetching technique with a slightly modified Abrahams‐Buiocchi etchant. Examination is mainly confined to vapor‐grown GaAs samples composed of an 0.4‐&mgr;‐thick Sn‐doped epitaxial layer [n? (6–10) ×1016cm−3] and a Cr‐doped semi‐insulating substrate. It is established that the deformed layer results from thermal stress imposed on the arsenic depletion layer generated at the substrate surface in the preheating stage prior to growth. The strain field is found to extend more than 10 &mgr; into the substrate side and even into the epitaxial layer side. Electron mobility in the submicron epitaxial layer is lowered by the presence of this strain field. However, this can be improved from 10 to 30% by annealing. It is also found that dislocations are generated in the deformed layer when the imposed stress is increased by coating the back side of the substrate with a SiO2film. The dislocation density increases rapidly, but the deformed‐layer thickness gradually decreases as the SiO2film thickness increases. Slip dislocations are generated from the periphery of the epitaxial wafer during the cooling process. This is due to stress concentration at the periphery.

ISSN:0021-8979    

DOI:10.1063/1.323065

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A new technique is presented to study surface absorption properties by utilizing the interaction of a radiatively heated surface region with an acoustic‐surface‐wave probe. Surface‐wave phase changes are induced by the absorption of 10.6‐&mgr;m laser radiation. A detailed theory is presented to describe the thermal‐acoustic interaction under the condition that the laser‐induced temperature change is uniform within the acoustic‐wave penetration depth. Where the theory is applicable, calculations in which there are no free parameters agree with quantitative phase‐change measurements onyx&agr;‐quartz andyzlithium niobate. Phase‐change dispersion measurements are shown which indicate a sensitivity to the depth dependence of the absorbed radiation and the resulting temperature distribution.

ISSN:0021-8979    

DOI:10.1063/1.323066

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Measurements of the scattering of He‐Ne laser light from nematic liquid crystals during transient time induced by an electric field have been made both on a simple homogeneously aligned cell and a 90° twisted cell. The nematic liquid crystal used in this experiment is a mixture of pentyl‐cyano‐biphenyl and hexyloxy‐cyano‐biphenyl of 4 : 1 by weight. The response waveforms of the scattered light intensity are dependent on the scattering angles and on the polarization of both the incident and the outgoing light. Moreover, the scattering distribution pattern depends strongly on the polarization of the light. These results can be partially explained by orientation fluctuations and relaxation of directors.

ISSN:0021-8979    

DOI:10.1063/1.323067

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Thin films of Bi12PbO19, one of the &ggr;‐Bi2O3family, were prepared on glass and Si substrates by rf sputtering. Films of &ggr;‐phase Bi12PbO19were obtained at the substrate temperature of 450–600 °C. The films were found to be highly oriented with the ⟨310⟩ axis normal to the substrate surface and exhibited piezoelectricity. The electromechanical coupling factors for the longitudinal mode measured were 0.16–0.22 with the phase velocities of 3600–3800 m/sec.

ISSN:0021-8979    

DOI:10.1063/1.323068

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The goal is to estimate the feasibility of using electrostatically plugged cusps and mirrors to confine thermonuclear plasmas. Assuming the density of ’’trapped electrons’’ to be small, the present work describes a set of equations for determining equilibrium particle densities, temperatures, and potential barrier heights. The equations are solved for specific cases involving neutral beam injection, and the ratioQof fusion power output to injection power input is determined. FavorableQvalues are found for applied voltages exceeding 250 kV.

ISSN:0021-8979    

DOI:10.1063/1.323069

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The spectra and angular distributions of high‐energy electrons emitted from laser‐produced plasmas have been measured. The plasmas were produced using short pulses from both CO2and Nd : glass lasers to irradiate polyethylene slabs. For a CO2laser intensity of approximately 3×1014W/cm2we find at least an order of magnitude greater energy conversion to high‐energy electrons than with a Nd : glass laser intensity of approximately 5×1015W/cm2. The angular distribution of electron emission is strongly peaked along the target normal (i.e., density gradient) and fine angular structure is observed.

ISSN:0021-8979    

DOI:10.1063/1.323070

出版商:AIP    

年代:1976

数据来源: AIP