摘要:

The time and spatial dependence of the temperature rise produced in ion‐implanted silicon subjected to pulsed electron beam bombardment has been numerically calculated. The temperature profiles generated were then used to calculate the thermoelastic stresses produced by the deposited energy. Experimental measurements of the incident energy density thresholds for fracture of the silicon have beem compared with damage threshold levels suggested by this analysis. The temperature calculations have been qualitatively verified by diffusion profile measurements as compared with calculated profiles based on dopant diffusion in liquid silicon. The shear forces produced by the large temperature gradients have been proposed as the primary cause of fracture which occurs at high beam fluences.

ISSN:0021-8979    

DOI:10.1063/1.328305

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The propagation of a laser beam through a two‐photon absorber (TPA) is discussed for the incident laser working at, above, and below its threshold of oscillation. It is shown that the fluctuation behavior characterized by the normalized moments ⟨I⟩/⟨I0⟩, ⟨I2⟩/⟨I0⟩2, and ⟨I2⟩/⟨I⟩2and the variances ⟨(&Dgr;I)2⟩ and ⟨(&Dgr;n)2⟩ change significantly throughout the absorption process. We also calculate the time‐dependent factorial moments of the laser field near threshold as it propagates inside the media and discuss this aspect of fluctuation behavior.

ISSN:0021-8979    

DOI:10.1063/1.328306

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Radiation‐induced defects and their annealing behavior inp‐ andn‐type CdTe irradiated with 2‐MeV electrons, neutrons, and60Co gamma rays have been investigated by means of photoluminescence, Hall, time‐of‐flight measurements, and the performance of CdTe gamma‐ray detectors. The 1.1‐eV emission band produced after electron irradiation at 77 K anneals at a stage centered around about 120 K and originates from a defect including Te vacancy. From the isothermal annealing experiment, an activation energy of about 0.2 eV is obtained for the annealing stage. The electron and gamma irradiation at 77 K with room‐temperature anneal, and neutron irradiation at 300 K enhance 1.53‐ and 1.55‐eV edge emission bands. It has been suggested that the 1.53‐eV band is attributed to a complex involving Cd vacancies. On the other hand, the 1.55‐eV band is attributed to a complex involving Te vacancies. An annealing stage centered at about 370 K is observed in electrical properties in relatively purep‐type crystals irradiated with electrons and gamma rays. It is found from the isothermal annealing that the annealing behavior of the stage obeys first‐order kinetics. The activation energy for the migration of the defects is estimated to be about 0.8 eV and the pre‐exponential factor is found to be about 108sec−1, suggesting long‐range migration of Cd vacancies. Electron‐trap levels lying at 0.058 and 0.5 eV below the conduction band are observed in crystals irradiated with gamma rays. The 0.058‐eV electron trap anneals at about 600 K and the origin is tentatively assigned to a complex involving Te vacancies as inferred from photoluminescence results. Electron‐drift mobility at room temperature is remarkably reduced after gamma irradiation, possibly due to the introduction of an electron‐trap level at about 0.5 eV below the conduction band. The 0.5‐eV electron‐trap level and the electron‐drift mobility anneal in the vicinity of about 600 K. The effects due to successive detector irradiations with60Co gamma rays markedly degraded the output pulse‐height spectra until ultimately the 59.5‐keV photopeak of the241Am gamma ray can not be discerned. Following annealing at 600 K, the pulse‐height spectrum recovers almost to the preirradiation value. This annealing behavior coincides with the recovery of the electron‐drift mobility of bulk crystals.

ISSN:0021-8979    

DOI:10.1063/1.328307

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The elastic constants of single‐crystal tungsten between 4.2 and 77 K have been measured utilizing a sampled continuous‐wave technique. The sensitivity of the present technique is such that the temperature dependenceCij(T) below 77 K is explicitly observed for the first time. A diffuse anomaly inCL(T), whereCL= 1/2 (C11+C12)+C44, is observed in the temperature range 15–22 K.

ISSN:0021-8979    

DOI:10.1063/1.328308

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Previous experiments have suggested that tungsten undergoes a significant loss of shear strength when shock loaded to stresses greater than 7 GPa. In order to investigate this effect in more detail, a series of experiments was conducted in which polycrystalline tungsten was first shock loaded to approximately 10 GPa and then either unloaded or reloaded from the shocked state. Analysis of measured time‐resolved wave profiles indicates that during initial compression to 9.7 GPa, the shear stress in polycrystalline tungsten increases to a maximum value of 1.1 GPA near a longitudinal stress of 5 GPa, but decreases to a final value of 0.8 GPa for stresses approaching 10 GPa. During reloading from a longitudinal stress of 9.7 GPa to a final value of ∼14 GPa, the shear stress increases to a peak value of 1.2 GPa and softens to 1.0 GPa in the final state. During unloading from the shocked state, the initial response is elastic with a strong Baushinger effect. Examination of a recovered sample shows evidence for both deformation slipping and twinning, which may be responsible for the observed softening.

ISSN:0021-8979    

DOI:10.1063/1.328309

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The present work on depleted uranium alloyed with 0.78% titanium by weight (i.e., U‐0.8 Ti) describes the nature of deformation it undergoes when subjected to shock compression at room temperature. The principal results emerging out of the present work are: (1) The stress limits of elastic deformation are dependent on the thickness of U‐0.8Ti. The stress limit decreases from over 3.0 GPa at the impact surface to 1.2 GPa at a depth of 9 mm in U‐0.8 Ti; (2) The lower limit of the stress agrees with the static yield stress in U‐0.8 Ti; (3) Above the elastic stress limit, the deformation of U‐0.8 Ti proceeds in a manner of the ideal plastic solid; and (4) The pressure derivative of Lame’s parameter of U‐0.8 Ti is estimated to be 3.8.

ISSN:0021-8979    

DOI:10.1063/1.328310

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A method for direct measurement of strain in plane impact experiments is presented. The method is based on recording resistance changes of a longitudinal resistance gauge placed in the target specimen. To demonstrate the validity of the method we conducted a series of plane impact experiments in which manganin and constantan resistance gauges were placed in targets made of different materials. From the experimental results we conclude that the uniaxial strain in the target material can be determined to within an error of &Dgr;&egr;=±0.2%.

ISSN:0021-8979    

DOI:10.1063/1.328311

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An experimental technique is described which uses anisotropic crystals to generate dynamic pressure‐shear loading in materials. The coupled longitudinal and shear motion generated upon planar impact of the anisotropic crystal can be transmitted into a specimen bonded to the rear surface of the crystal, and monitored using velocity interferometer techniques. Test results usingy‐cut quartz generators andx‐cut quartz andy‐cut quartz samples indicate that shear stresses up to 0.35 GPa can be transmitted across epoxy‐bonded interfaces. The technique has been successfully used to detect a 0.2 GPa shear wave in 6061‐T6 aluminum at 0.7 GPa longitudinal stress. The shear wave velocity profiles have an accuracy of ±12%. The use of longer delay legs in the interferometer is suggested to improve the accuracy. Results obtained in this investigation are compared with numerical solutions obtained using the finite‐difference wave propagation code TOODY.

ISSN:0021-8979    

DOI:10.1063/1.328312

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Specular x‐ray reflections originating at grazing incidence at the boundary planes of thin laminated structures interfere to give the known Kiessig fringes. The change of this interference pattern during diffusion in thin multilayers is used for the study of phase formation in Au‐Al thin film couples. Layered growth of Au2Al obeying a parabolic growth relation was observed in the temperature range from 50 to 80 °C. The activation energy of the process was found to be 1.05 eV.

ISSN:0021-8979    

DOI:10.1063/1.328313

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Although the literature contains many measurements of the diffusivity of carbon in Fe and steels, recent progress in plasma carburizing has made this regime around 1050 °C and over 1% carbon concentration of great interest. We have measured the diffusivity of carbon in steel from 975 to 1075 °C up to 1.3% carbon concentration by the steady‐state method. Our results are in agreement with previous measurements of Smith and Wells, Batz, and Mehl in the regime of low temperatures and carbon concentrations. Using activation energies determined over a wider temperature range by the latter authors, we derive as an empirical expression forDthroughout the range of temperatures and concentrations investigated,D=0.47 exp (−1.6 C) ×exp[−(37 000−6600 C)/RT] cm2/sec. Here,Cis expressed in weight percent carbon and the energies are in cal/mole.

ISSN:0021-8979    

DOI:10.1063/1.328314

出版商:AIP    

年代:1980

数据来源: AIP