摘要:

Small defects in edge‐to‐edge weldings of thin pieces of stainless steel have been detected by the mirage effect. A simple 1D theoretical model shows the physical parameters influencing the experimental results. Using the phase of both the transverse and normal deviations at various frequencies allows for the separation of optical and thermal effects, of surface and subsurface defects, and for the determination of the depths and widths of the subsurface defects.

ISSN:0021-8979    

DOI:10.1063/1.334540

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Reverse‐bias pulsed deep‐level transient spectroscopy (RDLTS) has recently been used for studies of electric field‐enhanced emission from a deep‐level defect. The sensitivity, spatial, and temperature resolutions of this technique are investigated and compared with those of DLTS. The electric field strength in a narrow region, where the transient capacitance signal comes from, can be accurately controlled by using RDLTS. The calculated results indicate that there is an optimal operating condition given by a range of emission pulse widths and heights. This operating condition is given for the best compromise of the temperature and spatial resolutions.

ISSN:0021-8979    

DOI:10.1063/1.334541

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Infrared reflection and transmission measurements were used to study the thermally induced regrowth of (100) oriented, Be‐implanted GaAs samples. The samples used in this study were implanted at low temperature (−100 °C) with 250‐keV Be ions to a fluence of 6×1015cm−2. The samples were postannealed at temperatures ranging from 100 to 550 °C. Isochronal and isothermal annealing at a series of temperatures between 180 and 240 °C were performed. Infrared reflection spectra were analyzed by using a three or four layer dielectric model. Analysis of the annealing data suggests that an amorphous layer first anneals to a second metastable amorphous state and then becomes a damaged crystalline layer after annealing at 220 °C for 12 h. The observed regrowth is not by a simple epitaxial process. After annealing at 400 °C for 1 h, the damage in the layer is reduced sufficiently for the refractive index to recover almost to the preimplantation value. On annealing at 450 °C free carriers are observed. From the measured average regrowth rate for the amorphous layer at various anneal temperature, an effective activation energy is estimated to be about 1.45 eV. This compares with activation energies of 2.3 eV for Si and 2.0 eV for Ge.

ISSN:0021-8979    

DOI:10.1063/1.334542

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We report on Cr, Mn, Fe, and Zn redistributions either in undoped and unimplanted, or in doped and implanted indium phosphide substrates. Depth profiles, obtained by secondary ion mass spectrometry, demonstrate that residual impurities, as well as dopants, redistribute during thermal processing and that several parameters govern simultaneously the observed phenomena. Results are interpreted in terms of implantation‐related damage and thermally generated defects, solubility modifications induced by the position of the Fermi level,p‐njunction‐related electric fields, and pure diffusion mechanisms.

ISSN:0021-8979    

DOI:10.1063/1.334543

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Optical absorption, electron spin resonance (ESR), thermoluminescence, and x‐ray‐induced luminescence techniques have been used to characterize point defects in LiNbO3. A series of crystals with different magnesium‐doping levels and Li/Nb ratios were investigated, and the defects were introduced either by x‐ray irradiation at low temperatures (10–85 K) or by reduction at high temperature in a vacuum. The samples may be classified into two groups, according to their response to radiation and reduction. A threshold (i.e., a sharp change in behavior due to a small change in composition) marks the change from one type of response to the other. The concentrations of both magnesium and lithium affect the threshold level. An electron trap, represented by an optical absorption band peaking at 1200 nm and a broad ESR spectrum centered atgc=1.82, is observed in several of the heavily‐doped crystals after irradiation. A corresponding hole trap produced during the same irradiation has an optical absorption peak near 500 nm and an ESR line atgc=2.03. An intense thermoluminescence peak, obtained after x‐ray irradiation at 15 K, occurs at 70 K in this latter group of crystals and correlates with the thermal decay of the electron and hole traps just described. Following vacuum reduction at 1000 °C, these heavily‐doped crystals exhibit an optical absorption spectrum that can be decomposed into two bands peaking near 760 and 1200 nm, and a broad ESR spectrum withgc=1.82. The 1200‐nm band and ESR signal are associated with an electron trap (identical to the one produced during the irradiations). This electron trap is suggested to be a Mg+complex.

ISSN:0021-8979    

DOI:10.1063/1.334544

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The crystal structure of low cristobalite (SiO2) was refined at 10, 293, and 473 K from time‐of‐flight neutron powder diffraction data. One of the Si‐O distances and one Si‐O‐Si angle change considerably: 10 K, 1.602(1) and 1.617(1) A˚, 144.7(1)°; 473 K, 1.605(2) and 1.590(2) A˚, 148.4(1)°. The angular distortion of the SiO4tetrahedron is greater at 473 K than at the lower temperatures. Root‐mean‐square displacements of Si and O are greater for cristobalite than for quartz and coesite at room temperature. The negative correlation between Si‐O distance and Si‐O‐Si angle for cristobalite is similar to that for quartz held at a higher temperature (∼350 K). Any adjustment of the Si‐O distance for riding motion between Si and O atoms would reduce the variation of Si‐O distance with temperature and with Si‐O‐Si angle. Furthermore, adjustment of the Si‐O‐Si angle for rocking of the oxygen atom out of the Si‐O‐Si plane could improve the correlation between secant (Si‐O‐Si) and the isotropic chemical shift for29Si nuclear magnetic resonance in silica polymorphs. The temperature variation of the crystal structure of low cristobalite cannot be modeled by simple tilting of rigid tetrahedra.

ISSN:0021-8979    

DOI:10.1063/1.334545

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An ion‐irradiation‐induced phase transformation from Ni2Al3to NiAl has been investigated by transmission electron diffraction. Compound samples of Ni2Al3were irradiated at liquid nitrogen, room temperature, and 100 °C with 300‐keV Xe and 60‐keV Ne ions. Transformation to NiAl was observed in all cases. Detailed examination of the closely related equilibrium NiAl and Ni2Al3structures permits explanation of this transformation based on the structural similarity of the two phases and using a model built around radiation disordering of vacancies.

ISSN:0021-8979    

DOI:10.1063/1.334546

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The thermal characteristics of matrix‐addressed smectic liquid‐crystal cells are studied using the temperature dependence of the resistance of the heater and detector lines and compared to analytic solutions. The cell behavior is most strongly affected by the thermal properties of the substrate near the liquid crystal if the heater is at that interface. Cell features further away from the heater have a smaller influence. The cell power efficiency improves if the thermal flow through the substrate is reduced relative to the liquid crystal. The cell addressing speed can be increased if the substrate has two layers composed of a thin insulator on a conducting layer. Increasing the insulator thickness improves efficiency but reduces speed.

ISSN:0021-8979    

DOI:10.1063/1.334547

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The present study reports the experimental results and a theoretical model, based on short‐range order and electronic charge transfer from Ti to Fe, to explain the dependence of the isomer shift on the iron content in  &bgr;‐Ti(Fe) solid solution. The theoretical expression reported here for the isomer shift depends on three different fitting parameters which take into account the electronic‐charge transfer, and has been fitted with the experimental data for samples containing 3–18 at. % Fe.

ISSN:0021-8979    

DOI:10.1063/1.335457

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

In processes such as thermal oxidation and phosphorus diffusion, where self‐interstitials are generated in excess, what happens to the vacancy concentration may significantly affect many diffusion processes which occur via dual mechanisms. Most authors in diffusion modelling have assumed as self‐evident that, for a very long time or in steady state, the product of the vacancy and the interstitial concentrations should be a constant. It is shown here that this assumption is generally invalid. The fallacy in the analogy between this case and the solubility product is pointed out. A correct relationship is first derived on a uniform defect concentration approximation. Then rigorous expressions for both the vacancy and the interstitial concentrations are given from an exact solution of simultaneous vacancy and interstitial continuity equations that include diffusion, recombination, and generation terms, under appropriate boundary conditions. The errors in the results from previous speculations are especially severe in the surface region.

ISSN:0021-8979    

DOI:10.1063/1.334548

出版商:AIP    

年代:1985

数据来源: AIP