摘要:

Pressures in diamond‐anvil high‐pressure cells often are determined by measuring ruby emission spectra because theR1luminescence has high quantum efficiency and frequency of theR1band shifts almost linearly with pressure, independent of temperature. To more than 600 K, pressures can be precisely determined by measuring luminescence spectra at ambient and high pressures at the same temperature. The temperature dependence of the frequency of theR1line is not simple, and empirical approximations have been developed so that a pressure at a known temperature might be estimated from measurements of spectra at thatPandTand at ambient pressure and one temperature; that is, without measuring theR1line at ambient pressure at each temperature. Measurements reported here show that, between 100 and 260 K, pressures computed by using empirical approximations calibrated near ambient temperature may be in error from 0.1 to several GPa. The temperature dependence of theR1line is accurately described by the function suggested by McCumber and Sturge [J. Appl. Phys.34, 1682 (1963)]. Measurements at several temperatures between 100 and at least 400 K are needed to evaluate the precise parameters of this function appropriate for a particular spectrometer and ruby. Therefore, it is often practical for studies at pressures to a few GPa simply to determine the wavelength of theR1line at a given temperature and ambient pressure by measuring it.

ISSN:0021-8979    

DOI:10.1063/1.351950

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Recent work by Gupta and Shen [Appl. Phys Lett.58, 583 (1991)] has shown that in a nonhydrostatic environment, the frequency of the rubyR2line provides a reliable measure of the mean stress or pressure. When using the frequency of either theR1orR2line to measure pressure at nonambient temperature, it is necessary to know the temperature dependence of the line shift. Unfortunately, the shift of theR2line with temperature has not been reported. The rubyR1andR2fluorescence shifts have been determined as a function of temperature from 15 to 600 K. Both can be fitted very well to the simple cubic formsR1(T) =14 423+4.49×10−2T−4.81×10−4T2+3.71×10−7T3cm−1andR2(T)=14 452 +3.00×10−2T−3.88×10−4T2+2.55×10−7T3cm−1. From 300 to 600 K the shifts fit well to linear functions of temperature. In addition, it is found that theR1‐R2splitting changes by about 3 cm−1over the 600 K temperature range. Linewidths were found to vary both with temperature and from sample to sample.

ISSN:0021-8979    

DOI:10.1063/1.351951

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Laser action from barium vapor has been investigated using small‐scale (20–40 cm−3) high‐repetition‐rate discharge‐heated and low‐repetition‐rate externally‐heated devices. Strongest output occurs at 1.13, 1.50, and 2.55 &mgr;m, with weaker emission at 2.92 and 4.72 &mgr;m. The range of discharge conditions for which laser action occurs at these wavelengths is described and the temporal occurrence of laser output is presented. The implications of this study to the future development of barium lasers are considered.

ISSN:0021-8979    

DOI:10.1063/1.351952

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Dual wavelength electro‐optical bistability in resistor‐biased and symmetric self electro‐optic effect devices and their input power dependence are investigated using InGaAs/AlGaAs multiple quantum wells. A new principle to drive the devices using two widely separated wavelengths for signal and control light is proposed and demonstrated to obtain optical transmission bistability between two stable states of the signal light at &lgr;1by varying the control beam power at &lgr;2. Detailed experimental results of signal power dependencies of the optical responses are presented and rigorously explained based on the voltage switching mechanism of the signal diode by the second control light using a simple load line analysis. Advantages of this new device configuration are discussed taking full merit of the transparency of the GaAs substrate to the signal wavelength.

ISSN:0021-8979    

DOI:10.1063/1.351953

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Surface acoustic waves (SAWS) directional couplers have long been known in both microwave and integrated acoustic applications. Such couplers, when both channels are of different widths and different dispersion characteristics, may also be used as electronic filters. SAW directional couplers are ideal for inclusion in acoustical signal processing devices, as modulators or switches. This article represents formulation and physical properties of advanced high transfer efficiency SAW directional couplers, using the coupled mode theory. One kind of directional coupler is especially considered and discussed in detail. The obtained coupling parameters are applicable to any guided modes in parallel waveguides of the same cross section, similar to 1/vindex of refractive and identical shapes. Coupling constants and physical parameters for the coupled acoustic modes, computed according to this theory, are shown and seem to agree very well with experimental data.

ISSN:0021-8979    

DOI:10.1063/1.351954

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The frequency dependence of the scattering contribution of ultrasonic attenuation and sound velocity of longitudinal waves was measured in a frequency range from 2 to 50 MHz. For model systems we used gelatine samples with 20 wt % glass beads of 315–400 &mgr;m and 180–250 &mgr;m diameter and with 10 wt % glass beads of 42–174 &mgr;m diameter. The application of a recently developed Fourier transform technique allowed us to observe both ultrasonic attenuation and velocity with sufficiently high accuracy for quantitative comparison with sound scattering theory. The frequency dependence of sound attenuation shows multiple maxima, whereas in the frequency dependence of the velocity difference a sharp minimum on the order of 1% of the absolute velocity occurs. For the simulation of ultrasonic attenuation and sound velocity we combined a multiple scattering approach from Waterman and Truell [J. Math. Phys.2, 512 (1961)] with a acoustic resonance scattering theory for a viscoelastic sphere developed by Ayres and Gaunaurd [J. Acoust. Soc. Am.81, 301 (1986)]. Supplementary in the computations, the attenuation of the matrix and the particle size distribution were taken into account. Comparison of the simulated data to the experimental results shows good agreement.

ISSN:0021-8979    

DOI:10.1063/1.351955

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A variational theory of the radiant emittance of the mercury‐argon discharge is developed and applied to an investigation of the effects of alterations of the isotopic composition of the mercury. The theory includes the effects of transport of resonance radiation, elastic and inelastic collisions, resonant exchange of excitation, diffusion of the mercury atoms, the isotope‐ and hyperfine‐shifted structure of the resonance line, and the surfaces of the discharge on the emittance. Two sensitive parameters—the branching ratio for radiative decay of the resonance state and the rate constant for resonant exchange of excitation—are fitted to data on natural mercury. The remaining insensitive parameters are given values based on microscopic estimates. The resulting theory reproduces the experimentally observed results for mercury—196 enhanced mixtures. We predict small effects for mixtures with other isotopes enhanced. The crucial role played by resonant exchange of excitation is emphasized.  

ISSN:0021-8979    

DOI:10.1063/1.351956

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The time dependent as well as amplitude modulation frequency dependent ion flux from parallel plate radio frequency discharges have been measured by mass spectrometry and modeled using the fluid equations. The negative ion flux to the grounded electrode becomes large after the rf excitation is turned off and has complex temporal features which depend upon the ion, gas mixture, applied dc bias voltage and other externally controlled parameters. Some of these features can be explained with the assistance of the fluid equation model. In short, negative ions can be formed during the active glow as well as after the glow excitation has been turned off. The resulting negative ion flux to the grounded electrode during the afterglow is determined in part by when the negative ion is formed. For example, if the amplitude modulation frequency at which the flux of a negative ion goes to zero is larger than 100 kHz, it indicates that ion is formed in the afterglow. (Of course, it may exist during the active glow as well.) Conversely, ions with signal only at small modulation frequencies are unlikely to have been produced by attachment in the afterglow. The experimental results are from CF4and Cl2‐He discharges. One finding was that the temporal and modulation frequency dependencies of F−and SiF5−ions from CF4discharges indicate that SiF5−exists only in a thin layer above the grounded electrode.

ISSN:0021-8979    

DOI:10.1063/1.351957

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In an effort to attain a better understanding of the nature of the defects introduced in GaAs by irradiating it with energetic light ions; electron or proton irradiatedn‐type GaAs samples, cut from the same layer grown by molecular‐beam epitaxy, have been studied by deep level transient spectroscopy. By comparing the spectra, including the effects of high electric fields, and by using results for annealed samples, it is possible to determine which of the traps reported in electron irradiated GaAs, most of which are believed to be arsenic interstitial‐vacancy pairs, are present in the proton irradiated material. The traps identified in proton irradiated GaAs include most of those found in electron irradiated material, either after irradiation or after irradiation and annealing. The results indicate that two of these traps are associated with defects which are more complex than simple interstitial‐vacancy pairs. Two traps were found in proton irradiated material which have not been observed in electron irradiated GaAs. One of these is nearly as abundant as the prominentE3 center observed in electron irradiated GaAs and is probably also not a simple pair. The deep level transient spectroscopy peak for this trap is not clearly separated from that ofE3 in proton irradiated GaAs. The other trap is probably associated with a particular impurity present in the MBE grown sample layers.

ISSN:0021-8979    

DOI:10.1063/1.351958

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Bonding of a 1360‐nm‐thick single crystalline silicon membrane onto an oxidized wafer was enhanced by ion mixing using 1250 keV14N+ion implantation. The oxidized wafer was covered by a thin, thermally grown oxide (134 nm) and implantation was performed either in random or in channeling directions through the membrane. Ion doses were in the range of 0.5×1016to 5×1016atoms/cm2. Implantation was followed by an annealing at 1000 °C for 0.5 h in nitrogen gas to remove the radiation defects. Due to the effect of implantation, the bonding quality was very good in all cases. In addition, results of Rutherford backscattering spectroscopy and transmission electron microscopy showed that using channeled implantation with a dose of 0.5×1016atoms/cm2, the adherent silicon layer was of high quality (∼1.5×103dislocations/cm2) and the interface remained sharp.

ISSN:0021-8979    

DOI:10.1063/1.351959

出版商:AIP    

年代:1992

数据来源: AIP