摘要:

An optical technique based on confocal scanning optical microscopy (CSOM) is used to image the ferroelectric polarization ofBaxSr1−xTiO3(BST) thin films at room temperature with submicron spatial resolution. BST films were grown by pulsed laser deposition on (100)SrTiO3and MgO substrates at 750 °C in 300 mTorr of oxygen and postdeposition annealed in flowing oxygen at temperatures⩽1250 °C.Films of both paraelectric(x=0.5)and ferroelectric(x=0.8)compositions show a coexistence of both paraelectric and ferroelectric phases. The ferroelectric regions exhibit polarization switching and hysteresis at relatively low (1–2 kV/cm) applied fields. These results suggest that nonuniform stress is responsible for the strong inhomogeneous thermal broadening of the ferroelectric phase transition, and that dielectric loss in thin films may be dominated by a relatively small fraction of nanometer-sized regions. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120335

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A structural study is presented on proton exchangedLiNbO3waveguides prepared in benzoic acid vapor which, forz-cut substrates, were previously reported to simultaneously exhibit high index jump, very low losses, and undegraded nonlinear optical coefficients. X-ray rocking curves ofz-cut guides show a unique, intense peak with the same bandwidth as the substrate peak, located at the&kgr;2-phase position ofHxLi1−xNbO3, as well as a small &agr;-phase contribution. Forx-cut guides only the&bgr;1-phase peak is obtained, with a bandwidth about 60&percent; greater than the substrate peak. Distinctive features of&kgr;2and&bgr;1guides are also shown in micro-Raman spectra. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120336

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The electric field controlled bulk-like optical second-order susceptibility&khgr;(2)in thicker(Si5Ge5)100superlattices is reported. The relation between&khgr;(2)and the broken structural symmetry by applied external field was observed. The measured large value of&khgr;(2)for(Si5Ge5)100superlattices is evaluated to be∼5×10−6esu with the external field of 100 kV/cm, which indicates that(Si5Ge5)100superlattices have potential applications in optoelectronic devices. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120398

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Breakdown voltages of a capacitively coupled radio frequency nitrogen discharge at 13.56 MHz are measured using an insulated electrode system made from glass-covered aluminum disk plates. The breakdown voltages measured against the gas pressure exhibit typical V-shaped characteristics without peculiar sharp bend in the left branch of the minimum of the curve appearing in a low pressure region when metal electrodes are employed. The observed results are compared with the theoretical calculation based on the electron diffusion and mobility-controlled model, and a satisfactory agreement is found except for the precise prediction of the location of the minimum point. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120337

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This letter reports efficient treatment of NO emission with a transient, nonequilibrium plasma created by pulsed corona discharge. The transient plasma (≈50 ns) is found to reduce NO emission by 50&percent; in a flow of 2–25 l/s with energy cost ≈10–20 eV/molecule, corresponding to a fraction of source power of ≈5&percent;. The efficiency ofNOxreduction is a complex function of parameters that include pulse width, pulse polarity, current density, repetition rate, and reactor design. It was found that the best efficiencies are correlated with a low current density(0.2 A/cm2)and high repetition rate (1 kHz) under high flow rate. Careful optimization of all these parameters is required to reach cost effectiveNOxreduction. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120338

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The thermal stability of amorphous hard carbon films produced by cathodic arc deposition was studied by near edge x-ray absorption fine structure (NEXAFS) spectroscopy, Raman spectroscopy, and nanoindentation evaluation. Pure carbon films of up to 85&percent;sp3content were deposited using a pulsed biasing technique and annealed in ultrahigh vacuum up to 850 °C. NEXAFS spectra show no change in the film properties up to 700 °C, and a modification of the spectra for 800 and 850 °C, which indicate graphitization. Raman spectra show only a very slight change up to 850 °C. The nanoindentation data show no change in hardness and elastic modulus with annealing up to 850 °C. The study demonstrates the high thermal stability of the films. The difference in the NEXAFS and the Raman and nanoindentation results can be attributed to the surface sensitivity of NEXAFS in comparison to the more bulk sensitivity of Raman spectroscopy and nanoindentation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120339

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Highly luminescent ZnSe quantum dot arrays (QDAs) are spontaneously formed on cleavage-induced GaAs (110) surfaces. The QDAs are configured for their preferred growth on the step top. The confinement on carriers results from the difference in the band gaps of the strained ZnSe layer and the strain-relaxed ZnSe QDA. In contrast to other emissions from the ZnSe layer, the linewidth of the QDA emission is dependent neither on temperature nor on excitation intensity. Moreover, the energy position of the QDA emission is stable even at high excitations. These results reflect the &dgr; functionlike density of states of the QDAs. This letter suggests a novel approach to semiconductor QDs and QDAs. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120340

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have proposed an electro-optic effect in dichroic-dye-doped polymer ferroelectric liquid crystal thin films prepared by a spin-coating technique. A high-quality homeotropically aligned film has been realized. Guest-host type electro-optic switching is confirmed in the dye-doped film, and basic properties such as electric field dependence of the response time are studied. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120399

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Experimental results show that the background carrier concentrations in GaN films grown by metalorganic vapor phase epitaxy are related to defects. A thermal equilibrium method was used to calculate the background carrier concentration related to intrinsic defects in an ideal GaN crystal. The results show that the N vacancy concentration does not exceed2×1017 cm−3in GaN grown at temperatures ranging from 800 to 1500 K. It can be concluded that the N vacancy is one of the major sources of carriers when the carrier concentrationn<2×1017 cm−3,but the main sources should be other defects whenn>2×1017 cm−3;this conclusion may lead to ways for further improving the quality of GaN films. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120341

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present gating characteristics of submicron vertical resonant tunneling transistors in double quantum well heterostructures. Current–voltage characteristics at room temperature and 77 K for devices with minimum feature widths of 0.9 and 0.7&mgr;m are presented and discussed. The evolution of theI–Vcharacteristics with increasing negative gate biases is related to the change in the lateral confinement, with a transition from a large area 2D to a quasi-1D. Even gating of multiple wells and lateral confinement effects observable at 77 K make these devices ideally suited for applications in multi-valued logic systems and low-dimensional structures. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120342

出版商:AIP    

年代:1997

数据来源: AIP