摘要:

A method is described to optimally determine the elastic constants of anisotropic solids from wave‐speeds measurements in arbitrary nonprincipal planes. For such a problem, the characteristic equation is a degree‐three polynomial which generally does not factorize. By developing and rearranging this polynomial, a nonlinear system of equations is obtained. The elastic constants are then recovered by minimizing a functional derived from this overdetermined system of equations. Calculations of the functional are given for two specific cases, i.e., the orthorhombic and the hexagonal symmetries. Some numerical results showing the efficiency of the algorithm are presented. A numerical method is also described for the recovery of the orientation of the principal acoustical axes. This problem is solved through a double‐iterative numerical scheme. Numerical as well as experimental results are presented for a unidirectional composite material.

ISSN:0021-8979    

DOI:10.1063/1.345441

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A chamber experiment is conducted to study the propagation of high‐power microwave pulses through the air. Two mechanisms responsible for two different degrees of tail erosion have been identified experimentally. The optimum pulse amplitude for maximum energy transfer through the air has also been determined.

ISSN:0021-8979    

DOI:10.1063/1.345442

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Laser Raman spectroscopy was used to measure NF3dissociation and N2formation in the active volume of 13.56‐MHz NF3radio‐frequency (rf) discharges. Gating the rf discharge suppressed optical emission, allowing NF3and N2Raman measurements at rf powers where N2production was expected to be significant. Greater than 90% dissociation of the NF3was observed in a 750 mTorr discharge at rf power densities on the order of 1 W/cm2, yet less than 50 mTorr of N2was produced. NF was the only other nitrogen containing species detected in the active volume of the discharge.

ISSN:0021-8979    

DOI:10.1063/1.345443

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A one‐dimensional model is formulated for electron multiplication in the cathode fall of a glow discharge. The associated Boltzmann equation inzandvis converted to an integrodifferential equation in new variables that can be solved numerically using standard methods for ordinary differential equations in a single variable. The resulting distribution function in the (z,v) phase space is also the energy distribution of electron flux, which is used to find the current multiplication factor and the energy transport per unit electron current. Even in low‐voltage discharges with large current multiplication, the nonionizing collisions play a small role in determining the electron‐energy distribution and swarm behavior. Comparison with highly complex simulation, and with experiment, is very favorable.

ISSN:0021-8979    

DOI:10.1063/1.345444

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Two methods are examined for the measurement of the positive‐ion mobility in a positive cylindrical corona discharge. The first method employs the novel technique of monitoring the temporal decay of the cathode current following the cessation of the corona near threshold. A detailed analysis of the current decay is offered, and comparison with experimental results on coronas in nitrogen and dry air yield values of positive‐ion mobility that agree well with those found in the literature. The second technique for the measurement of the positive‐ion mobility is based upon the current‐voltage relationship of the discharge near threshold. The classical interpretation of the current‐voltage data is found to yield mobility values that are anomalously large. It is suggested that this classical interpretation is incomplete, as it does not consider the dependence of the anode electric field on corona current. One possible cause of such a current dependence is considered in detail: Joule heating of the gas near the anode may increase electron impact ionization, through a reduction in the gas density, in turn lowering the anode electric field. Analysis indicates that such a thermal feedback mechanism is of the correct magnitude to explain the overestimation of positive‐ion mobility from the classical interpretation of the current‐voltage relationships in the nitrogen and air coronas.

ISSN:0021-8979    

DOI:10.1063/1.345445

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Changes in gap state distribution due to defects induced by different doses of 10‐keV electrons in phosphorous‐dopeda‐Si:H are reported. These defects have been observed qualitatively by electron beam writing. Patterns thus generated were read by electron beam induced current (EBIC). The increased local recombination in the area results in the decrease of EBIC current due to the increased defect density. Shift in the Fermi level position after electron irradiation was observed from the measurement of conductivity with temperature. Deep level transient spectroscopy (DLTS) was used to study the changes in gap states for the different electron dose. It was observed that irradiation causes the generation of additional defects which alter the gap state distribution in then‐type material over a broad range of energies. Creation of defects having activation energies around 0.55 eV below the conduction band was prominent although the formation of dangling bonds which results in increase in states around 0.7 eV is observed. These defects act as nonradiative recombination centers as suggested from the photoluminescence results which show a decrease in the 0.85 photoluminescence peak intensity. The contrast produced in the electron beam writing could be annealed out at 150 °C, indicating the metastability of the defects, which was also confirmed by the DLTS, photoluminescence, and dark conductivity measurements.

ISSN:0021-8979    

DOI:10.1063/1.345446

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Different doses of iron ions were implanted in Czochralski grown single‐crystal silicon samples and subsequently annealed at 1000 °C for 2 h in a dry nitrogen atmosphere. The behavior of the implanted iron and of oxygen already present in the material was monitored. It was found that the existence of the remaining structural disorder after the annealing treatment plays a dominant role in iron and oxygen segregation into the disordered region. This confirms the theory which predicts that the structural disorder and related strain fields are dominant mechanisms for gettering of metallic ions.

ISSN:0021-8979    

DOI:10.1063/1.345447

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A Monte Carlo simulation is used to solve the ion‐implantation process with three‐dimensional boundaries. The projected range, standard deviation, skewness, kurtosis, and damage distributions after ion implanation for TiSi2heterostructures and the feasibility of the silicide doping process are simulated in this work.

ISSN:0021-8979    

DOI:10.1063/1.345448

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Silicon films damaged by ion implantation have been examined using the photothermal reflectance technique in the thermal wave regime (low‐modulation frequencies, large laser beam spot sizes). Data are presented on the sensitivity of this method to the implant dose and to the effects of thermal annealing. It has been shown that the technique provides information about the state of the implanted layer, and is a sensitive probe for monitoring the annihilation of the induced damage as a function of the annealing temperature. A model for the kinetics of damage annihilation has been presented to estimate the activation energy of thelocalannealing recovery mechanism, found to be 0.15 eV. The presence of negative annealing has been detected at about 500 °C, an advantage over the essentially insensitive Hall mobility method.

ISSN:0021-8979    

DOI:10.1063/1.345449

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Photothermal reflectance investigations as a function of temperature of various forms of silicon (crystalline, ion‐implanted, amorphous) are reported largely in the thermal wave regime (low‐modulation frequencies and large laser beam spot sizes). The observed results have been explained by a thermal wave model that has been extended to include the effect of lattice temperature. The influence of substrate on the observed signal has been examined in light of the temperature and frequency dependence of the thermal diffusion length. The possible application of the technique to depth‐profiling studies, and to the investigation of ion‐implanted semiconductors, is discussed.

ISSN:0021-8979    

DOI:10.1063/1.345450

出版商:AIP    

年代:1990

数据来源: AIP