摘要:

We have used a two-dimensional charge transport model to study edge effects in photorefractive thin films. Our result shows the presence of a large surface charge layer that causes saturation of trap-limited-field in the large fringe spacing limit. Quadratic electro-optic materials were used as an example to quantitatively study the contribution of the surface-charge-layer field to the total photorefractive grating. We clearly demonstrate that the device performance can be dominated by either surface charge or bulk trap charges. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364197

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new approach to measure the optical second-order nonlinear coefficient tensor of material which is difficult to prepare as a large single crystal is demonstrated. In such a case, due to the limitation of the crystal direction the Maker fringe measurement cannot provide each tensor component but instead yields an effective value. A technique using the second-harmonic generation with evanescent wave (SHEW) makes up for the Maker fringe result. We have applied the measurements to the organic material 4-nitro-2-ethoxyamide-4′benzyloxytolane (NEBT). The combined results from different measurements clarify the nonlinear optical character of NEBT molecules and the largest component of the optical second-order coefficient tensor was obtained to be 39±8 pm/V. The combination of the Maker fringe and the SHEW technique can be a powerful tool. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364218

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A two-dimensional model of the hollow cathode and the high-voltage segmented hollow cathode sputtering discharges at high current densities is presented. The main plasma parameters (e.g., complete electron distribution function, spatial distributions of particle densities, gas temperature, etc.) are determined self-consistently. The most important mechanisms contributing to the operating characteristics of these hollow cathode discharges are identified and described quantitatively. The most representative hollow cathode configurations are analyzed and the results are compared to existing experimental data for the helium-argon-copper system, e.g., voltage-current characteristics, density of copper atoms as a function of the discharge current, and percentage argon. Good agreement is found between model predictions and experimental results. The model can be adapted to other high-voltage variants of the hollow cathode discharges. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364198

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In high plasma density ([e]>1011–1012cm−3) reactors for materials processing, the sheath thickness is often <100 s &mgr;m while the reactor dimensions are 10 s cm. Resolving the sheath in computer models of these devices using reasonable grid resolution is therefore problematic. If the sheath is not resolved, the plasma potential and stochastic electron heating produced by the substrate bias may not be well represented. In this article, we describe a semianalytic model for radio frequency (rf) biased sheaths which has been integrated into a two-dimensional model for plasma etching reactors. The basis of the sheath model is to track the charging and discharging of the sheath in time, and use a one-dimensional analytical model to obtain the instantaneous sheath voltage drop based on the sheath charge and the plasma conditions at the sheath edge. Results from the integrated model for an inductively coupled plasma etching reactor with powers of 200–800 W and rf bias powers from 50 to 400 W in Ar and Ar/Cl2will be discussed. We found that the sheath voltage wave form remains nearly sinusoidal, and that the plasma density, and consequently the ion flux to the surface, scale primarily with inductively coupled power. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364199

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Atomic chlorine is an important chemical species in plasma processing of silicon and III–V compound semiconductors. Two-photon laser-induced fluorescence (LIF) has been used to measure the relative atomic chlorine density in an inductively driven, rf discharge in chlorine gas. The Cl density in the center of the discharge was independent of rf power in the range of 150–400 W and increased a factor of 2 when the pressure was increased from 15 to 50 mTorr. LIF measurements performed on both levels of the chlorine spin-split ground state indicate similar trends for both energy levels in the inductive plasma mode. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364192

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

When a XeCl excimer laser beam was focused in a high-pressure argon gas up to 150 atm, a hot and dense plasma was produced at the focal spot. The plasma developed not only backward but also forward, which differed from one produced by a visible laser. The radius of the forward plasma became smaller beyond the focal spot. There had been no explanation for the development mechanism of the forward plasma. A new model for the forward development mechanism called a forward breakdown wave was proposed. The forward plasma was calculated assuming that the laser beam transmitted through the plasma was further focused by the plasma. This model could predict the forward development behavior considerably well. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364200

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The ion beam-induced crystalline-to-amorphous transition has been investigated for crystalline phases in the Al2O3–SiO2system: Al2O3, SiO2(quartz), Al2SiO5(kyanite, andalusite, sillimanite), and 3Al2O3⋅2SiO2(mullite). Xe+1.5 MeV was used to irradiate samples at temperatures from 15 to 1023 Kin situin a transmission electron microscope to determine the critical amorphization doses. The susceptibility to amorphization is (highest to lowest): quartz, sillimanite, kyanite, andalusite, mullite, and alumina. These data are compared to viscosities and activation energies for viscous flow of melts in this system. The doses required for amorphization by ion irradiation are related to the viscosities of the melts. The activation energies for irradiation-enhanced annealing are qualitatively correlated with the activation energies of viscous flow. These results suggest a parallel between ion beam irradiation-induced amorphization and glass formation. Glass-forming “ability’’ correlates with susceptibility to radiation-induced amorphization. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364219

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The orientation distribution of a textured polycrystalline material has been traditionally determined from a few individual pole figures of lattice planeshkl, measured by x-ray or neutron diffraction. A new method is demonstrated that uses the whole diffraction spectrum, rather than extracted peak intensities, by combining the orientation distribution calculation with the crystallographic Rietveld method. The feasibility of the method is illustrated with time-of-flight neutron diffraction data of experimentally deformed polycrystalline calcite. It is possible to obtain quantitative information on texture, crystal structure, microstructure, and residual stress from highly incomplete pole figures and from regions of the diffraction spectrum containing many overlapping peaks. The approach provides a key for quantitative texture analysis of low symmetry compounds and of composites with complicated diffraction spectra. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364220

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The anomalous, low-stress, shock initiation of detonation observed in earlier studies of pentaerythritol tetranitrate single crystals was examined in more detail experimentally. Time-resolved particle-velocity histories were obtained for [110], [001] and [100] orientations of single-crystal pentaerythritol tetranitrate explosive for shock input stresses of 4–7 GPa using laser interferometry instrumentation. At about 4.2 GPa an elastic-plastic, two-wave structure was noted in [110] and [001] orientations, and a single shock wave for [100] orientation. The two-wave structure provides an explanation for the anomalous shock initiation sensitivity and intermediate velocity transition previously observed in [110] orientation at this stress level. It also explains details of fluorescent emission histories from [110] and [001] crystals previously measured. The orientation-dependent results are consistent with the model of steric hindrance to shear at the molecular level. Fits to the elastic Hugoniot data in [110] and [001] orientations are given as well as a revised fit for the bulk Hugoniot. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364201

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ion-beam mixing of the immiscible Ag–Cu alloy system was investigated using 1.0 MeV Kr ion irradiation at temperatures ranging from 80 to 473 K. Mixing of binary (80 nm Cu/55 nm Ag) and multilayer [(8.5 nm Cu/12.2 nm Ag)×11] samples was characterized by backscattering spectrometry, electrical resistivity, and x-ray diffraction. Below room temperature, the Ag–Cu system is rendered completely miscible by Kr irradiation with the formation of a simple homogeneous phase. For irradiation at 473 K, the system again becomes immiscible, but with enhanced solubilities in the two terminal phases. At intermediate temperatures, two or three phases are formed, a nearly equiatomic phase, and one, and sometimes two, terminal phases. Irradiation at elevated temperatures of samples completely mixed at low temperature led to the decomposition of the near equiatomic phase; the new steady states were nearly the same as those obtained by direct irradiation of an as-deposited sample. Phase formation depended only weakly on the ion flux, although at the higher temperatures the decomposition reaction was favored by lower ion fluxes. The experimental results are explained using a diffusion model based on a competition between cascade mixing and thermally activated demixing. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364202

出版商:AIP    

年代:1997

数据来源: AIP