摘要:

The analysis is based on the Khokhlov–Zabolotskaya–Kuznetsov wave equation. Analytical and approximate solutions are derived for the second harmonic component in the Bessel nondiffracting beam. The theoretical results indicate that the second harmonic beam is nearly nondiffracting in the radial direction and the pressure amplitude is proportional to the square root of propagation distance in the quasilinear approximation, and that the beamwidth of the second harmonic is just 1/2 times that of the fundamental component in the Bessel field, not as 1/&sqrt;2 times in the fields radiated by other sources. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116483

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Porous silicon superlattice was fabricated and its Raman spectra were examined. The clear zone‐folded doublets from longitudinal acoustic phonons were obtained up to fourth order. A similar phenomenon was not observed in ordinary porous silicon. Using the elastic continuum model, we calculated the frequencies of these folded doublets and the obtained results were in excellent agreement with the experimental ones. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116484

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We quantify a model which incorporates observed features of contaminant particle growth in plasma processing reactors. According to the model, large ‘‘predator’’ particles grow by adsorbing smaller, typically neutral, ‘‘prey’’ protoparticles. The latter are supplied by an assumed constant mass injection of contaminant material. Scaling laws and quantitative predictions compare favorably with published experimental results. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116485

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ferroelectric layered‐oxides SrBi2Ta2O9thin films were prepared on Pt coated Si wafers and single‐crystal sapphire by metalorganic chemical vapor deposition (MOCVD). The films were specular and crack‐free and showed complete crystallization at temperatures between 650 and 700 °C. Good ferroelectric properties were obtained for a 200 nm thick film with Pt electrodes: 2PrandEcwere about 8.3 &mgr;C/cm2and 60 kV/cm, respectively. The leakage currents were as low as 8×10−9A/cm2at 150 kV/cm. The films also showed fatigue‐free characteristics: no fatigue was observed up to 1.4×1010switching cycles. These high quality MOCVD films make high‐intensity (≳1 Mbit) nonvolatile memory devices possible. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116486

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this letter, we demonstrate that the strong reverse saturation which has been observed at high intensity in a C60solution, is also manifest at a low intensity. The behavior fits well to a rate equation model based on a six level system with known photophysical parameters. Furthermore, we demonstrate that it can be utilized to generate optical switching and bistability. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116487

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Boron nitride (BN) thin films (containing mixed cBN/hBN phase) have been deposited on Si(100) substrates using neutralized nitrogen beam and electron beam evaporation of boron. All as‐deposited BN films wereptype with a room‐temperature carrier concentration in the range of 5×1016to 1×1017cm−3. The Mg‐doped BN films showed carrier concentrations in the range of 1.2×1018cm−3to 5.2×1018cm−3when the Mg cell temperature was varied from 250 to 500 °C. The films were analyzed for both majority elements (B and N) and dopant/impurity (Si, Mg, Fe, etc.) incorporation using secondary ion mass spectroscopy and mass spectroscopy of recoiled ions (MRSI). MRSI is shown to be superior for dopant characterization of boron nitride thin films. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116488

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a first‐principles investigation of the structural properties of two models for the Si(001)–SiO2interface. The models derive from attaching tridymite, a crystalline form of SiO2, to Si(001), and then allowing for full relaxation. These models do not show electronic states in the silicon gap, as required by electrical experiments. They contain the three intermediate oxidation states of silicon, consistent with photoemission experiments. We study bond length and bond angle distributions and measures of local strain. The strain is localized to a transition region at the interface. Strain does not persist in the full oxide. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116489

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Reflection high energy electron diffraction (RHEED) intensity measurements reveal that the strain in a Si1−xGexlayer on a vicinal Si(001) surface converts a (1×2) domain dominated step configuration to a (2×1) domain dominated one. The dependence of the effect on the Ge content is similar to the dependence of the critical thickness of the pseudomorphic growth of Si1−xGexlayers on Ge content. No conversion effect has been observed on exact Si(001) substrates. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116490

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The Si(111)‐7×7 area surrounded by the Si(111)‐&sqrt;3×&sqrt;3R30°‐Ga region has been observed by scanning tunneling microscopy during the thermal desorption of Ga atoms at ∼600 °C and after the desorption. The 7×7 area exhibits triangular and strip patterns on the nanometer scale for the Si(111) substrates tilting toward the [112¯] and [1¯1¯2] directions, respectively. This is because faulted halves of the 7×7 reconstruction are adjacent to the &sqrt;3×&sqrt;3‐Ga area on the boundary between the 7×7 and &sqrt;3×&sqrt;3‐Ga areas during Ga desorption. It has been found that strip patterns with nanometer‐scale precision are formed on the Si(111) substrates tilting toward the [1¯1¯2] direction. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116491

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Crystalline carbon nitride films have been synthesized in a rf plasma assisted hot filament chemical vapor deposition system. Large crystalline grains up to ∼10 &mgr;m in size as well as film‐like regions are observed in the morphology of the films. &bgr;‐C3N4with two groups of lattice parameters (one is consistent with the theoretical value and the other is ∼3% smaller) in the deposited films on polycrystalline Ni substrate has been revealed by x‐ray diffraction spectrum (XRD). No Raman shift peaks have been found by Raman scattering measurement, but some presently unknown diffraction peaks appeared in the XRD spectrum. It is proposed that there are possible unknown structures of crystalline C‐N in the films. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116492

出版商:AIP    

年代:1996

数据来源: AIP