摘要:

We have demonstrated the use of superconducting transition edge sensors for the wide-band detection of individual photons from the mid infrared (IR), through the optical, and into the far ultraviolet (UV). These tungsten transition edge sensors are squares about 18 &mgr;m on a side and detect single photon events above a threshold of 0.3 eV (4 &mgr;m wavelength), with an energy resolution of 0.15 eV full width at half maximum, and with a risetime (falltime) of .5 &mgr;s (60 &mgr;s). The calibration data extend up to the UV cutoff of the fiber optic feed at 3.5 eV (350 nm). ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121984

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The reason for the optical frequency doubling in the70Ga2S3–30La2S3glass is investigated. The tetragonalGa6La10/3S14phase due to crystallization of the glass is responsible for the frequency doubling. Dense and transparentGa6La10/3S14crystalline thin films have been prepared by means of the controlled surface treatment of the glass due to an ultrasonic surface treatment. The effective second-order nonlinear optical susceptibilities of the crystalline thin films are analyzed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121985

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Ultrasonic air transducers using leaky waves on thin membranes are analyzed using perturbation and normal mode approaches. The transducers utilize the efficient coupling of ultrasonic energy to air through radiation of these leaky wave modes when their phase velocity is close to the sound speed in air. Theoretical results on optimum transducer dimensions and bandwidth estimation show that a minimum conversion loss of 8.7 dB with a 78&percent; fractional bandwidth is possible. Common micromachining materials are shown to be suitable transducer materials and result in feasible devices. This is demonstrated by fabricating a 580 kHz transducer using a silicon membrane bonded to a ring of PZT-5H. With this configuration the transducer is self line focusing. Results of through transmission experiments on silicon and transmission images on paper are reported. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121986

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A Co-based amorphous phase with glass transition and supercooled liquid region before crystallization was formed inCo70−xFexZr10B20andCo72−xFexZr8B20alloys containing more than 14 at &percent; Fe. The crystallization temperature(Tx)is 899 K for the Co–Zr–B alloys and remains unchanged in the Fe concentration range up to 20&percent;. The glass transition temperature(Tg)decreases with increasing Fe content, and the&Dgr;Tx(=Tx−Tg)increases from 25 K at 14&percent; Fe to 34 K at 21&percent; Fe. The amorphous alloys with glass transition crystallize with a single stage precipitation of bcc Fe(Co) andCo3ZrB2phases. The Co-rich amorphous alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.58–0.83 T, low coercivity of 4.7–8.3 A/m, and high permeability of 5500–18 300 in the frequency range of1–103 kHzand low magnetostriction between−1.5×10−6and+10×10−6including zero. The success in synthesizing the soft magnetic amorphous alloys with high stability of supercooled liquid is promising for the future development of ferromagnetic Co-based bulk amorphous alloys. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121987

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Extended defect reduction in GaN grown by lateral epitaxial overgrowth (LEO) on large-areaSiO2/GaN/Al2O3wafers by low pressure metalorganic chemical vapor deposition is characterized using transmission electron microscopy and atomic force microscopy. The laterally overgrown GaN (LEO GaN) has a rectangular cross section with smooth (0001) and{112¯0}facets. The density of mixed-character and pure edge threading dislocations in the LEO GaN(<5×106 cm−2)is reduced by at least 3–4 orders of magnitude from that of bulk GaN(∼1010 cm−2).A small number of edge dislocations with line directions parallel to the basal plane are generated between the bulk-like overgrown GaN and the LEO GaN regions as well as at the intersection of adjacent merging LEO GaN stripes. The edge dislocations are most likely generated to accommodate the small misorientation between bulk-like GaN and LEO GaN regions as well as between adjacent single-crystal LEO GaN stripes. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121988

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

GraphoepitaxialNi50Ti50films were grown on Si substrates by sputter deposition of an alloy target. The microstructure evolution of the film was investigated by hot stage atomic force microscopy. The topological features of the martensitic graphoepitaxialNi50Ti50films are directly associated with etch pits on the surface of the silicon substrate and exhibit facets with well-defined preferential in-plane orientation. The highly ordered martensitic facets disappear as the film transforms to austenite at elevated temperatures. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121989

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A phenomenological mean-field theory is presented for the kinetics of strain relaxation due to misfit dislocation generation in the strained-layer growth of epitaxial semiconductor films on thin compliant substrates. The theory provides a generalized dislocation kinetic framework by coupling the mechanics of an epitaxial film on a compliant substrate with a well-known description of plastic deformation dynamics in semiconductor crystals. The theoretical results reproduce successfully recent experimental data for strain relaxation in the InAs/GaAs(110) heteroepitaxial system. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121990

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Local thermal conductivity inside grains of high-quality polycrystalline diamond grown by chemical vapor deposition is measured at room temperature with micrometer spatial resolution. An effective conductivity is determined by choosing experimental conditions where the measured heat flow extends over adjacent grains. It is found that the effective conductivity may vary by a factor of 2, depending on the averaged volume and position on the sample. These variations are attributed to different grain structures present at the investigated locations. Local conductivity within a single grain varies by ±30&percent; and a maximum value of 2350 W/mK is found. Local thermal conductivity data are related to the crystalline quality and impurity content determined by micro-Raman measurements. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121991

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

High-resolution transmission electron microscopy (HRTEM) shows that amorphous-tetrahedral diamondlike carbon(a-tC)films grown by pulsed-laser deposition on Si(100) consist of three-to-four layers, depending on the growth energetics. We estimate the density of each layer using both HRTEM image contrast and Rutherford backscattering spectrometry. The first carbon layer and final surface layer have relatively low density. The bulk of the film between these two layers has higher density. For films grown under the most energetic conditions, there exists a superdensea-tClayer between the interface and bulk layers. The density of all four layers, and the thickness of the surface and interfacial layers, correlate well with the energetics of the depositing carbon species. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121992

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This letter reports that electromigration lifetimes of Al–2Cu (wt. &percent;) thin-film conducting lines increase by more than three times when the lines are optimally aged to facilitate finely dispersedAl2Cuprecipitates in the interior of the grains. In contrast to other studies which did not report a beneficial aging effect for Al–Cu films, the present work substantiates the fact that proper control ofAl2Cuprecipitates improves resistance to electromigration failure. However, the benefit of aging the Al-2Cu lines investigated here was less pronounced and confined to a more narrow heat-treatment “window” than that previously found for the Al–2Cu–1Si lines. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121993

出版商:AIP    

年代:1998

数据来源: AIP