摘要:

Under conditions of continuous acoustic generation, light scattered from oppositely directed surface acoustic waves ony‐cutz‐propagating lithium niobate was frequency analyzed with a high‐resolution Fabry‐Perot interferometer. The following parameters were measured at 105 MHz: acoustic power standing‐wave ratio, reflection coefficient for both sending and receiving transducers, low‐power acoustic damping coefficients, surface wave propagation velocity, and nonlinear harmonic growth. We note that the method used has an advantage over other methods since it is to a large extent independent of the optical quality of the propagation surface.

ISSN:0021-8979    

DOI:10.1063/1.1661841

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The velocities of microwave ultrasonic waves at 9.2 GHz have been measured using pulse‐echo techniques in X‐cut and Z‐cut quartz rods. In the X‐cut quartz, the longitudinal mode velocity was (5.71±0.05)×105cm/sec and the transverse mode velocities were (5.20±0.05)×105cm/sec. The longitudinal velocity for the Z‐cut quartz was (6.33±0.03)×105cm/sec. In contrast with the measurements of Ogawa and Sakamoto these results agree with the low—frequency velocities reported by McSkimin [J. Acoust. Soc. Am. 34, 1271 (1962)].

ISSN:0021-8979    

DOI:10.1063/1.1661916

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A single integral solution is presented for displacements arising from a concentrated force in an infinite medium with cubic elastic anisotropy. The integrand is an explicit algebraic expression of the three elastic constants and the spherical coordinates of the point at which the displacements are required. The integral gives the displacement components referred to the cubic axes. Although the concentrated force is along a cubic axis, a force in an arbitrary direction can be constructed by the superposition of the solutions for its components along the axes. Applications are suggested that use distributions of point forces to model defects in cubic crystals. Elastic displacement fields are presented for crystals of Na, Cu, Rb I, Nb and W.

ISSN:0021-8979    

DOI:10.1063/1.1661942

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Microwave ultrasonic attentuation measurements have been made on single crystals of topaz, beryl, and tourmaline, and all are found to exhibit very low losses. The room‐temperature attenuation coefficients are consistent with the Akhiezer mechanism which arises from interactions between the ultrasonic wave and the thermal‐phonon assembly.

ISSN:0021-8979    

DOI:10.1063/1.1661842

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The crystallographic structure and orientation of Ge films formed by sputter deposition onto Ge (111) substrates have been investigated as a function of various deposition parameters. Important parameters affecting the film structure include growth rate, substrate temperature, substrate‐surface cleanliness, and sputtering‐gas purity. The structure of the sputter‐deposited films was examined by HEED, while the substrate surface was characterized by HEED, LEED, and Auger electron spectroscopy. Results show that epitaxy of Ge can be obtained by sputter deposition at substrate temperatures as low as 100 °C, provided the deposition conditions are properly optimized. A plot of the film structure as a function of substrate temperature and growth rate defines the three regions of crystallinity (amorphous, polycrystalline, and single crystalline), indicating the existence of a triple point. The amorphous‐polycrystalline and epitaxial transitions occur at temperatures considerably lower than those reported by previous investigations. Thermal regeneration of the substrate surface results in a considerable reduction of the transition temperatures. Oxygen in the sputtering atmosphere plays a significant role in determining the epitaxial temperature.

ISSN:0021-8979    

DOI:10.1063/1.1661849

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Cu single‐crystal cubes have been &ggr; irradiated in the [001] and[11¯0]directions, and the ultrasonic attenuation due to dislocation damping has been determined in the [110] direction after the various irradiation treatments. Fricke dosimetry indicates that about 10% less secondary electron energy exits the crystal in the[11¯0]irradiation than in the [001] irradiation. The fact that more energy is absorbed in the[11¯0]irradiation is consistent with the dislocation damping studies which indicate that more dislocation‐pinning point defects are created in this case. The damping data obey the Granato‐Lu¨cke damping theory, and quantitative predictions as to the dislocation loop length and number of pinners created during irradiation are made on the basis of the theory. The anisotropy in radiation damage is consistent with theoretical predictions of anisotropy of replacement energy and focusing energy in Cu.

ISSN:0021-8979    

DOI:10.1063/1.1661861

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The radiation blistering of polycrystalline niobium surfaces at room temperature has been investigated for different doses of helium ions implanted at 0.5 MeV and for different amounts of initial defect structure in the samples. The cold‐worked samples show large blisters (up to 500 &mgr;m in diameter), many of which are ruptured. In samples annealed before irradiation, the blistering at low doses (0.1 C/cm2) was lower than in the cold‐worked sample, but at a higher dose (1.0 C/cm2) the blistering was even greater. The observation of interconnecting bubbles offers a possible explanation for the formation of such large blisters at low temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1661870

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Internal friction and modulus measurements were made between 13 and 38 kHz as a function of temperature on several copper crystals into which a low density (∼ 105–106cm−2) of dislocations had been introduced by deformation in compression. The dislocation contributions to damping and modulus defect were determined by comparison with duplicate measurements made after the dislocations had been immobilized by irradiation. Dislocation densities were evaluated by etch‐pit counting, and as a result enough information was obtained to determine absolute values for the loop length and drag coefficient in the vibrating‐string (Koehler/Granato‐Lu¨cke) model of dislocation damping. The loop length was found to have appreciable temperature dependence and the drag coefficient was found to be higher by a factor of ∼ 15–∼65 than values obtained for copper by MHz damping and dislocation velocity measurements. Similar results were obtained in several samples and it is noted that the measured damping and modulus values are not greatly different from those obtained by other experiments. It thus appears that for the kHz frequency range in pure copper crystals basic elements of the string model require revision.

ISSN:0021-8979    

DOI:10.1063/1.1661880

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Limited beams of low MHz ultrasound are directed at plane interfaces between water and different solids. Reradiated energy is observed by means of schlieren visualization outside the region predicted by Schoch for incidence at the Rayleigh angle. Some of the solids have properties that would cause prediction of a beam displacement many times that for aluminum. Previous thoery would predict the reflected beam to emerge totally separated from the incident beam for several of the materials used, but no such separation is observed. It is concluded that the reradiated field is composed of specular reflection and Rayleigh‐wave radiation at and near the Rayleigh angle. These two radiations are out of phase at low MHz frequencies, and where they coexist and are of equal amplitude, which occurs within the specular region, a null strip occurs. This strip is sharply defined at exactly the Rayleigh angle. Surface waves (sometimes called pseudosurface waves) are also generated at the longitudinal and shear critical angles. These are also shown to radiate into the fluid but are generated to a much lesser degree and are difficult to demonstrate by schlieren visualization.

ISSN:0021-8979    

DOI:10.1063/1.1661909

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Propagation characteristics and the equivalent circuit model of delay lines using Lamb waves excited by interdigital transducers on unpolarized PZT ceramic plates have been studied. Dispersive characteristics of phase velocities of Lamb waves excited by the interdigital transducers are in good agreement with the numerical solution from the dispersive equation of phase velocities developed by Worlton. When the product of frequency times plate thickness is below 1.3×106Hz mm, the zeroth symmetric Lamb wave is strongly excited. The Lamb waves are excited most effectively when the half‐period of interdigital electrode is equal to the wavelength of the Lamb wave. Also, the values of the attenuation coefficient and the reflection coefficient from the edge of the specimen are given. It is shown that the generation of symmetrical‐mode Lamb waves by our transducer is equivalently represented by a thickness mode transducer of half‐wavelength inserted perpendicular to the plate.

ISSN:0021-8979    

DOI:10.1063/1.1661939

出版商:AIP    

年代:1973

数据来源: AIP