摘要:

A theory is proposed for solving second-harmonic generation accompanying nonlinear reflection of shear (SH) waves. An analysis is presented for the resonant second-harmonic generation in a layered structure consisting of an isotropic layer and two semi-infinite isotropic solids. The result reveals that the effect of second-harmonic cumulative growth will occur once the component of incident SH-wave vector along the boundary equals the magnitude of the longitudinal wave vector of the elastic medium of the solid layer. Moreover, we have formally obtained the analytical expressions for the resonant second-harmonic generation in each region of the layered structure which yields physical insight into the process of the second-harmonic generation not previously available. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365866

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The propagation of surface acoustic waves has been investigated for a layered system (water-isotropic layer-isotropic substrate) where the layer is faster than the substrate. It has been found that when the velocity of the surface wave reaches the velocity of the shear wave of the substrate (cutoff) the behaviour of the attenuation has an anomalous character. Attenuation drops down towards zero below cutoff and increases abruptly beyond cutoff. Acoustic microscopy measurements on aluminum coated with oxalic oxide film were in coincidence with theory.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365867

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ion velocity distribution functions were measured using Doppler-shifted laser-induced fluorescence spectroscopy in an electron cyclotron resonance discharge in argon. The influence of the magnetic field configuration on the distributions was studied by making measurements with different magnetic field configurations. Results of a two-dimensional hybrid model of the discharge were used to help interpret the measured data. The results from the experiment and the simulation indicated that the magnetic field configuration had a strong influence on the ion velocity distribution functions. From the simulation it was concluded that the magnetic field configuration determined the axial distributions of plasma potential and electron density, and how these plasma parameters determined the ion velocity distribution function in the downstream region of the discharge.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365868

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article, a comprehensive treatment of the implantation-induced disordering (IID) ofCuPtB-ordered GaInP with regard to microstructuring is presented. Ion implantation reduces the thermal stability of the crystal, so that disordering occurs at temperatures smaller than 800 °C for which the ordered phase normally is stable. It is shown that IID is mediated by implantation defects and can be described quantitatively by a model based on defect annealing. From the temperature dependence of the disordering process an activation energy of 2.15 eV has been evaluated, which is supposed to be the migration enthalpy of group III vacancies. Lateral order/disorder structures were achieved by masked implantation using high resolution electron beam lithography for the definition of wire and dot implantation masks down to 35 nm width. These structures were examined using photoluminescence and transmission electron microscopy. Both methods show that the spatial resolution is determined by implantation straggling, whereas defect diffusion can be neglected. This is also confirmed by extracting the defect diffusion length from the disordering model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365869

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effects of post-H+implantation on electron traps that are induced byP+implantation (300 keV,1×109 cm−2) has been studied by deep-level transient spectroscopy.H+implantation is performed at room temperature to a dose of2×1010 cm−2in the range 30–120 keV. The post-H+implantation partly decreases the concentration of the electron traps induced byP+implantation, although it increases the concentrations around the projected range ofH+.The annealing effect is ascribed to the reaction of preexisting defects with point defects induced by postimplantation. Peaks are observed in the reduction ratio profiles of the preexisted trap concentrations versus the distance from the projected ranges of postimplantation. The highest values of the reduction ratios in each postimplantation tend to decrease with increasing distance between the projected ranges ofP+andH+.This is due to the decrease of the supply of point defects caused by postimplantation with increasing distance. We compare the reduction ratio profiles of the dominant three electron traps (Ec−0.12,0.15, and 0.39 eV). ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365870

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In the study of interfacial diffusion processes in polymer light-emitting diodes, the use of high-energy ion-scattering techniques can be of great value due to the possibility of quantitative elemental depth profiling. However, ion irradiation of polymers is known to cause various degradation effects, including the loss of hydrogen. Since the hydrogen loss determines the accuracy of depth profiling, it is an interesting subject for study in order to define experimental conditions in which the degradation is suppressed. The loss of hydrogen from porphyrins (organic solar cells) has been measured by means of elastic recoil detection analysis with 2, 4, and 7.6 MeVHe+beams. A theoretical model is proposed in which the hydrogen loss is described through the formation and recombination of free hydrogen radicals. A distinct difference is introduced between direct recombination processes and the diffusion of radicals out of the ion track. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365871

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ultraviolet-induced densification in fused silica is investigated using birefringence measurements to detect compaction-induced strain. This technique is capable of measuring compaction in the 10 parts per billion range in cm-sized specimens. A universal relation describing ultraviolet-induced compaction is discovered in which, using the total energy absorbed from two-photon absorption as the dose parameter, density changes equal a material dependent constant times the dose parameter to a power of about 0.65. This dose dependence is consistent with past compaction studies using electron beam and gamma radiation. Moreover, the density change per ionization “event” is found to be consistent for all radiation types. By comparing density measurements to refractive index change measurements found with interferometry, polarizability changes from ultraviolet-induced densification are extracted and compared with previous results using other radiation sources and inelastic densification methods. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365872

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Young’s modulusEand the modulus of rigidityGof zirconium hydridesZrHx(0.9⩽x⩽1.65)at 941 and 1001 K have been obtained as a function of hydrogen concentrationcby measuring resonance frequencies for bending and torsion vibrations of a polycrystalline wire. Ascincreases, observedEandGincrease in the bcc &bgr; phase, slightly increase linearly in the&bgr;+&dgr;phase, and then decrease in the fcc &dgr; phase. On the basis of a phenomenological free energy in terms of strain components taking account of space group symmetry, two types of Landau expansion of the free energies for the &bgr; phase in terms of the strain components which play an important role in the structural phase transition between the &bgr; and the &dgr; phases are examined. The observedEandGare assumed to be the same as the second-order coefficients of the free energy for the Bain distortions, which occur at the structural phase transition. The dependence of the third-order coefficients oncpermits the expanded free energies to describe the fact that the &bgr; phase is more stable than the &dgr; phase at lowc.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365873

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new technique is described, where picosecond laser pulses generate and probe 4.2 GPa nanoshocks in polymeric and polycrystalline solids at a high repetition rate of∼100/s.The term nanoshock refers to the short duration (a few ns) of the shock pulse and the very small shocked volume (a few ng). The nanoshock wave form is characterized by the shock front risetime, shock falltime, peak pressure, and velocity. Coherent Raman spectroscopy during nanoshock propagation in a 700-nm-thick layer of polycrystalline anthracene, called an optical nanogauge, is used to determine these quantities. A powerful method of analysis, singular value decomposition (SVD), is applied to Raman spectroscopy of shock waves for the first time. Using SVD analysis, the risetime of the nanoshock pulses is found to be less than 25 ps, and the velocity of the shock front in the nanogauge is monitored in real time. Some possible applications of nanoshock technology in the areas of shock-induced material transformation and shock-induced mechanical deformation processes, are discussed briefly. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365874

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A physically based crack softening damage model has been developed and used in a non-linear transient dynamic computer code (AUTODYN-2D). It is assumed that there is a finite number of orientated pre-existing flaws within the ceramic target. The mode I and mode II stress intensity factors are calculated in compression and tension and the strain energy release rate is then estimated and compared to a critical dynamic strain energy release rate. At initiation, a tension crack propagates at a velocity dependent on the mode I stress intensity factor and failure occurs in a computational cell when two neighbouring microcracks coalesce. The model was used to simulate two different plate impact experiments of alumina on alumina with encouraging results. The model was also used to analyze the impact of a steel sphere on alumina and shows strong correlation between experimental and predicted results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365875

出版商:AIP    

年代:1997

数据来源: AIP