摘要:

Laser‐stimulated thermoluminescence emission is reported from a novel transparent glass phosphor exposed to &ggr;‐ray or ultraviolet radiation. Laser‐heated radiation dosimetry measurements, using this effect, are reported. A unique laser heating method permits the stimulation of the thermoluminescence without significantly raising the bulk temperature of the glass. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116742

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report photomodulated reflectance results on vertical cavity surface emitting laser structures. Photoreflectance spectra have been recorded under normal incidence at different temperatures between 9 and 300 K. The structure used is a &lgr; cavity grown in the AlGaAs‐based system emitting at a wavelength near 800 nm. We show that photoreflectance is a unique noninvasive tool to measure accurately the quantum well transition and the cavity mode alignment: both features can be distinguished very well. Furthermore, this technique offers the opportunity to determine the electric field within the undoped region from Franz–Keldysh oscillations, and gives the Al composition of the barrier material in the cavity. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116753

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The fabrication and modeling of novel, capacitive, ultrasonic air transducers is reported. Transmission experiments in air at 11.4, 9.2, and 3.1 MHz are shown to correspond with theory. The transducers are made using surface micromachining techniques, which enable the realization of center frequencies ranging from 1.8 to 11.6 MHz. The bandwidth of the transducers ranges from 5% to 20%, depending on processing parameters. Custom circuitry is able to detect 10 MHz capacitance fluctuations as small as 10−18F, which correspond to displacements on the order of 10−3A˚, in a bandwidth of 2 MHz with a signal to noise ratio of 20 dB. Such detection sensitivity is shown to yield air transducer systems capable of withstanding over 100 dB of signal attenuation, a figure of merit that has significant implications for ultrasonic imaging, nondestructive evaluation, gas flow and composition measurements, and range sensing. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116764

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The slowdown of the oxide etch rate with width of submicrometer structures is known as reactive ion etching (RIE) lag and has been explained by ion shadowing and differential charging of the sidewalls, among other effects [R. A. Gottscho and co‐workers, J. Vac. Sci. Technol. B10, 2133 (1992)]. Here we show for an inductively coupled high density plasma reactor working in the pressure regime from 6 to 20 mTorr that inverse RIE lag is primarily observed, i.e., the etch rates increase as the width of the microstructures decrease. Inverse RIE lag, which was first discussed by Vitkavageetal. [Tegal Plasma Proceedings Symposium, San Francisco, 1991 (unpublished)], may be explained by considering the neutral flux distribution at the structure bottom. The neutral flux has a stronger dependence on the aspect ratio than the ion flux due to its isotropic velocity distribution. The neutral flux distribution has been modeled and is consistent with etching profiles observed at high pressure. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116772

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The current–voltage characteristics of hollow cathode discharges and their predischarges in argon under dc and pulsed conditions were found to have a positive slope at pressures up to approximately 50 Torr, and currents up to 20 mA, at a hole diameter of 0.7 mm. In this range of pressure and current, parallel operation of hollow cathode discharges, without ballast, was demonstrated. Scaling to higher pressure is possible by reducing the hole diameter. Pulsed experiments with an array of cathode rings of 75 &mgr;m diameter allowed us to obtain parallel operation of more than 50 discharges at a pressure of 350 Torr in air. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116739

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The evolution of the cross‐hatch pattern (CHP) in InxGa1−xAs/GaAs heterostructures has been studied. It is found that stress is concentrated at the valleys of the CHP from the results of crack formation at the CHP valleys in the thick GaAs cap layer grown on an InGaAs layer. Residual strain in the InGaAs/GaAs epitaxial layer showing a CHP is confined along the valleys of the CHP with a nonuniform distribution throughout the epitaxial layer. The skeleton of the CHP is formed at the beginning of the rapid strain relaxation period and the depth of the CHP valleys increases after most of the strain has been released. We propose that the development of the CHP in the later stage of the growth takes place by the growth suppression at the CHP valleys due to the high level of stress concentration. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116740

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Using a Tersoff‐type empirical potential energy function, the free energy of formation for {113}‐type stacking faults in silicon has been calculated both as a function of stacking fault rod length and width at a variety of temperatures. A particular tetrahedral‐tetrahedral dimer has the lowest free energy of formation at 0 K and this type of stacking fault forms an assemblage of such dimers. The free energy of formation per interstitial in a ribbon fault decreases with ribbon width, ribbon length, and increase of temperature. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116741

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Polycrystalline diamond films were deposited in a MW‐PECVD reactor employing bias‐enhanced nucleation as pretreatment to promote the subsequent diamond nucleation. The substrate temperature during the bias‐enhanced nucleation was varied between 600° and 760 °C by external heating, while the other deposition parameters namely the microwave input power were kept constant. Likewise, the deposition parameters were not changed in the subsequent diamond growth period throughout the experiment. The films formed during the bias‐enhanced nucleation were analyzed employing electron energy loss spectroscopy (EELS) and scanning electron microscopy (SEM). The nuclei density (ND) obtained for good quality diamond crystals after the nucleation step and an additional growth period increases considerably from 1×106cm−2or less to 1×1010cm−2in a narrow temperature range between 670 and 700 °C. For temperatures exceeding 700 °C continuous films are formed. The structure of the pretreatment deposit also undergoes considerable changes: the intensity of the diamond plasmon increases with the substrate temperature, which is indicative of an increase in the concentration of diamond crystallites embedded in an otherwise amorphous carbon matrix. Our experiments suggest that diamond crystallites formed during the pretreatment serve as nucleation centers for the subsequent diamond growth. We can also conclude that the variation in the substrate temperature rather than the changes in the microwave input power or, respectively, plasma chemistry, drive the observed structural changes and increase inND. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116743

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

KTiOAsO4crystals grown from tungstate fluxes have been studied by white‐beam synchrotron radiation topography. It is shown that growth striations are primary planar defects. By anomalous scattering, ferroelectric domains in KTA are investigated and the ratio of ‖F(004)‖2to ‖F(004¯)‖2is calculated. The mechanisms of domain inversion via 2‐fold axis orn‐glide plane are also discussed in terms of the structural characteristics of KTA. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116744

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An irreversible light‐enhanced degradation has been observed in amorphous silicon solar cells exposed to intense illumination (50 suns) at elevated temperature (≳130 °C). Unlike the light‐induced degradation observed at lower temperatures, the light‐enhanced degradation observed at elevated temperatures is not reversed by annealing and it not suppressed by a strong reverse bias. An analysis of the time decay of the short‐wavelength spectral response at various temperatures indicates that the degradation mechanism is associated with the diffusion of hydrogen at elevated temperatures both in the dark and under intense illumination. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116745

出版商:AIP    

年代:1996

数据来源: AIP