摘要:

In this paper, we analyze the generation of hypersonic waves via piezoelectric surface excitation in cavity resonators and derive formulas enabling one to calculate the electromechanical conversion factor and the electric field direction for optimal excitation of any pure acoustic mode, provided the relevant material constants and cavity parameters are known. Quantitative results are given for certain acoustic modes in quartz, CdS, and LiNbO3crystals.

ISSN:0021-8979    

DOI:10.1063/1.1662222

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The pyroelectric response and theD*of thin pyroelectric films on, a substrate are calculated as a function of the substrate and film thickness. It is found that for low‐frequency applications the pyroelectric layer should not be made too thin, preferably several micrometers thick, that the substrate should be as thin as possible, and that the product of its specific heat, density, and heat conductivity should be as small as possible. For thick substrates there is an intermediate frequency region where the value ofD*is practically independent of frequency. This intermediate frequency region extends to higher frequencies if the pyroelectric layer is made thinner, butD*decreases with decreasing film thickness in that region.

ISSN:0021-8979    

DOI:10.1063/1.1662223

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Dynamic yield strengths, compression data under uniaxial shock‐wave loading, and sonic velocities at 1 bar are reported for polycrystalline TiB2, SiC, Be4B, Be4B+8 wt% BeO, Be2B, AlB12, TiBe12, and ZrBe13. Hugoniot elastic limits were measured as 86, 80, 74, 77, 65, 87, 53, and 71 kbar, respectively. Evidence of phase transitions was seen for the Be4B materials at 500 kbar and for SiC at 240 and 960 kbar.

ISSN:0021-8979    

DOI:10.1063/1.1662224

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A technique is presented for the measurement of the Gru¨neisen parameter &Ggr; of a solid from the free surface velocity induced by pulsed energy deposition. The technique is applied to both energy ‐(internal energy density) dependent and energy‐independent Gru¨neisen data. The measurements employ a velocity interferometer to determine the free surface velocity of solids exposed to a pulsed electron beam. For the cases where &Ggr; is independent of temperature, or energy density, the &Ggr; values are obtained from the maximum free surface velocity as a function of incident fluence. Energy‐dependent Gru¨neisen data are extracted by an analysis based on the differentiation of the free surface velocity with respect to the initial energy density of the solid. The analysis takes into account the effects of both the finite exposure time of the electron pulses and the delay time of the interferometer. Results are presented for Al, Cu, Ge, and Si in a temperature range where &Ggr; is constant. In addition, for silicon &Ggr; is measured as a function of energy over the temperature range 50–300°K, where &Ggr; is strongly energy dependent. In all cases the results are in excellent agreement with the thermodynamic values.

ISSN:0021-8979    

DOI:10.1063/1.1662225

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Variation in the elastic constants of lead, barium, and strontium nitrates in the range 4–300 K has been investigated with great accuracy using resonance and pulse‐echo ultrasonic methods. The thermoelastic behavior of the three nitrates are compared. Strontium nitrate and lead nitrate especially appear to be much more anharmonic than barium nitrate.

ISSN:0021-8979    

DOI:10.1063/1.1662226

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The dependence of dielectric breakdown in shock‐loaded ferroelectric ceramics on both the shock amplitude and the electric field strength was investigated by employing shock reverberation techniques. In these experiments thick projectile disks were impacted on relatively thin specimens of hot‐pressed PZT 65/35 [Pb0.99Nb0.02(Zr0.65Ti0.35)0.98O3] poled to 10, 20, and 30 &mgr;C/cm2. The principal results of this investigation are: (i) dielectric breakdown is not explicitly a function of stress for stress values in the region of this study (<23 kbar), (ii) breakdown is not instantaneous, (iii) for fields greater than the breakdown threshold (≈5 kV/mm) the time between introduction of the shock into the ferroelectric and onset of breakdown decreases rapidly with increasing electric field, (iv) electric fields generated by 10‐kbar shocks in specimens poled to 30 &mgr;C/cm2are sufficient to cause breakdown, and (v) axial release waves can travel at a velocity as much as 15% faster than the initial stress wave.

ISSN:0021-8979    

DOI:10.1063/1.1662227

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Infrared‐absorption measurements on carbon‐implanted silicon are reported. A localized vibrational mode for substitutional carbon has been observed in annealed samples and in samples implanted at 500°C. The results suggest that between 40 and 60% of the implanted ions occupy substitutional sites. A broad absorption band which shifts to shorter wavelength on annealing has been observed and is attributed to the formation of SiC microcrystals. Absorption bands at 1097, 750, 640, and 625 cm−1have been observed in pulled crystals. It is suggested that these bands arise due to the presence of carbon‐oxygen complexes formed during implantation.

ISSN:0021-8979    

DOI:10.1063/1.1662228

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Ion channeling and backscattering of 450‐ to 1340‐keV protons were used to study the crystalline perfection of heteroepitaxial Si layers of thicknesses between 1 and 3 &mgr;m. An approximate calculation of the dechanneling background was used to obtain the depth profiles of crystalline imperfections in the epitaxial layers. Both the plural scattering theories of Meyer and Keilet al.were used in the calculation and are shown to give similar profiles. Channeling measurements as a function of sample temperature, beam energy, and layer removal were used to check the self‐consistency of the analysis. Analysis of these measurements for a given sample gave the same depth profile (±20%) confirming the validity of the technique. The technique provides a convenient evaluation of epitaxial layers containing large numbers of crystalline imperfections.

ISSN:0021-8979    

DOI:10.1063/1.1662229

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The crystalline quality of heteroepitaxial (100) and (111) Si layers on spinel or sapphire substrates has been investigated using ion channeling and electron microscopy. Ion channeling and backscattering give the depth profile of the density of imperfections, and electron microscopy is used to determine the nature of the imperfections as well as give an additional determination of their density. Transmission electron microscopy indicates that stacking faults and microtwins are the dominant types of imperfections in the layers, and these defects are interpreted to be the primary source of scattering centers for the channeled ions. Both channeling and scanning electron microscopy measurements indicate that the density of imperfections decreases with increasing distance from the interface. At equal distances from the interface a lower density of imperfections was observed in the Si layer for (111) Si/spinel and (100) Si/sapphire as compared to (100) Si/spinel. Large differences in the rate of decrease of the density of imperfections were observed for (100) Si/sapphire from different suppliers. The interpretation of the influence of the fault planes on channeling has been achieved by modeling the scattering by these defects. Semiquantitative correlations of scattering center densities from electron microscopy and channeling measurements indicate higher absolute densities for the channeling results, while relative densities determined at various depths by these two techniques are in agreement.

ISSN:0021-8979    

DOI:10.1063/1.1662230

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

As an approach to correlate atomistic and mechanical properties of metallic materials, work has recently been performed in order to understand the surface energy for brittle fracture in terms also of frequencies of the normal modes of vibration of the metal itself. In the same frame, the interpretation of the glide systems in fcc and bcc metals has been attempted and is presented here. The one‐dimensional model developed by Frenkel and Kontorova for an edge dislocation is reformulated in order to take advantage of the knowledge of interplanar force constants experimentally accessible by neutron inelastic scattering. The numerical solution is given following the procedure proposed by Hobart. Peierls energies and critical shear stresses have been thus evaluated on an atomistic level for some glide systems in fcc (Al, Cu, Ni) and bcc (Fe, W, Ta, Nb) metals.

ISSN:0021-8979    

DOI:10.1063/1.1662231

出版商:AIP    

年代:1973

数据来源: AIP