摘要:

A simple acoustic scanning device has been devised in which a chirped SAW beam is converted into a focused scanning bulk wave beam by coherent scattering from a grating of parallel grooves. The device can operate in both transmitting and receiving modes, and is applicable to the acoustic imaging of objects in real time.

ISSN:0003-6951    

DOI:10.1063/1.88780

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Evidence is provided showing that incomplete melt removal, or wipe‐off, at the conclusion of liquid phase epitaxial (LPE) In1−xGaxP1−zAszgrowth results in strained pitted dark layers because of the loss in composition match between the melt and substrate. Similarly, a small amount of drag‐over of one quaternary melt under a different composition melt is sufficient to cause attack of the underlying substrate (or LPE layer) and to cause local changes in the second melt destroying the composition match with the substrate. Single‐layer and multilayer In1−xGaxP1−zAszstructures are shown in which incomplete melt removal causes the growth of pitted ragged nonuniform layers side by side with uniform planar layers.

ISSN:0003-6951    

DOI:10.1063/1.88781

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

Thin epitaxial films of silicon have been grown at 600 °C on (111) silicon surfaces by vacuum deposition. The silicon deposition and growth was performed subsequent to a hot deposition (125 °C) of 300‐A˚ gold film on the substrate.

ISSN:0003-6951    

DOI:10.1063/1.88782

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

New measurements now permit a comparison to be made with various theories for the propagation characteristics of the strip acoustic surface waveguide in order to determine which theory is the most accurate. These new measurements are presented in the framework of all previously available measurements and theories for the strip waveguide. The ways in which the theories differ are indicated, and recommendations are made as to which theory should be used in which parameter range.

ISSN:0003-6951    

DOI:10.1063/1.88783

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A novel selective solar absorber, consisting of a dispersion of semiconductor grains in a low‐dielectric‐constant insulator is proposed. Calculations based on Maxwell‐Garnett theory show that because of its lower reflectivity for &lgr;<1.5 &mgr;m this material is about 60% more efficient than silicon in converting solar energy to heat. Reflectivity measurements for Ge‐Al2O3films on aluminum agree with the predictions of the Maxwell‐Garnett theory. The problems associated with the reduction to practice are discussed.

ISSN:0003-6951    

DOI:10.1063/1.88784

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

We have observed enrichments of N15as large as 21±1% in the mixed nitrogenous products (NO, N2O, NO2) of the reaction of N2and O2driven by a pulsed glow discharge at 77 °K. A typical energy expenditure per atom separated was 0.22 MeV. Enrichments increased but yields decreased as the electrical energy deposited per reactant molecule was reduced. Under similar conditions enrichment of 15% was observed for N15from the reaction N2+3D2→2ND3.

ISSN:0003-6951    

DOI:10.1063/1.88785

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The decay time of the photoluminescence due to the recombination of excitons bound to nitrogen in GaPxAs1−xalloys (x≳0.55) at 4.2 °K has been studied by uv laser time‐resolved spectroscopy. Using hydrogen implantation in order to reduce greatly the nonradiative lifetime of the samples, we show that the measured decay time is the radiative lifetime &tgr;xRof the bound excitons. Its variation with alloy composition is in good qualitative agreement with theoretical predictions. The observed decrease of &tgr;xRwhen the alloy becomes richer in GaAs is due to the modification of the recombination transition rate when the &Ggr; band gets closer to theXband (band‐structure effect).

ISSN:0003-6951    

DOI:10.1063/1.88786

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

An enhancement of conductivity was observed in ann‐type tin oxide semiconductor when coated with a highly polarizable insulating dye. The enhanced conductivity is thought to be a result of conduction electron–exciton interactions. The relationship between the observed photoresistivity and the excited states of the dye molecules is discussed.

ISSN:0003-6951    

DOI:10.1063/1.88787

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

A method of growing single‐crystal low‐resistivity (∼103&OHgr; cm)n‐type AlN is described in which dc ultraviolet electroluminescence is observed for the first time. The emission is in a broad band extending from 215 nm into the blue end of the visible spectrum. AlN grown on tungsten and sapphire substrates is contacted with Al and Nb. Light emission occurs in small spots near the negatively biased contact for currents of a few mA at voltages as low as 17 V, but typically in the range between 30 and 150 V. The external quantum efficiency is 6×10−6, and at constant current the light output is nearly independent of temperature up to several hundred degrees centigrade.

ISSN:0003-6951    

DOI:10.1063/1.88788

出版商:AIP    

年代:1976

数据来源: AIP

摘要:

The wavelength dependence of the group delay in a multimode silica fiber was determined from the wavelength‐dependent phase shift of the sinusoidally modulated light transmitted by the fiber. When the lower‐order modes were dominant in the modal power distribution, the measured dispersion at a wavelength of 830 nm was 0.90 ns/10 nm/km. When the launching conditions were changed to excite more of the higher‐order modes, the measured dispersion decreased to 0.60 ns/10 nm/km, indicating that the material dispersion was compensated partially by the waveguide dispersion.

ISSN:0003-6951    

DOI:10.1063/1.88767

出版商:AIP    

年代:1976

数据来源: AIP