摘要:

The effect of a thermally grown silicon nitride(SiNx)film on end-of-range extrinsic dislocation loops in a silicon substrate was investigated by transmission electron microscopy. A layer of extrinsic dislocation loops was formed by annealing a Si wafer amorphized by aGe+ion implant. A nitride film was grown on the Si by further annealing in ammonia(NH3)at 810 and 910 °C for 30–180 min. Wafers with a loop layer were also annealed in argon (Ar) at the same conditions as theNH3-annealed wafers to determine loop behavior in an inert environment. Samples annealed inNH3had a significant decrease in the net number of interstitials bound by the loops, while those annealed in Ar showed no change. The results are explained by a supersaturation of vacancies caused by the presence of the nitride film, resulting in loop dissolution. By integrating the measured vacancy flux over the distance from the nitride/Si interface to the loop layer, we extract an estimate for the relative supersaturation of vacancies at 910 °C,CV/CV*∼4,whereCVis the concentration of vacancies and the asterisk denotes equilibrium. We rule out interstitial undersaturation-induced loop dissolution based on loop stability with temperature and oxidation-enhanced loop growth calculations. A comparison with estimatedCV/CV*values from a previous report using the same processing equipment and parameters but monitoring the change in Sb diffusivity with nitridation shows excellent agreement. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365316

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The damage produced in silicon carbide single crystals by ion implantation was investigated by Rutherford backscattering channeling and transmission electron microscopy techniques. Implantations were performed at liquid nitrogen and at room temperatures with several ions to examine the effect of the ion mass and of the substrate temperature on the damaging process. The damage accumulation is approximately linear with fluence until amorphization occurs when the elastic energy density deposited by the ions overcomes a critical value. The critical energy density for amorphization depends on the substrate temperature and is greatest at 300 K indicating that defects recombination occurs already at room temperature. Formation of extended defects never occurred and point defects and uncollapsed clusters of point defects were found before amorphization even in the case of light ion implantation. The atomic displacement energy has been estimated to be ∼12 eV/atom from the analysis of the damage process in dilute collision cascades. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365317

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Internal strains in cluster-compacted nanocrystalline Pd (crystallite size 10–20 nm) were studied by means of wide-angle x-ray scattering. The strain- and size-induced broadening of the Bragg diffraction peaks was determined by Hall or Warren–Averbach analyses. The Warren–Averbach analysis indicates a spatial confinement of internal strain fields. This result supports theoretical models according to which the sources of the stresses are located in the interfaces between the crystallites. Indirect further evidence for a stress localization is derived from recent findings on the variation of internal strains and atomic displacements with the crystallite size. In addition, an anisotropy of the line broadening was observed which cannot entirely be attributed to planar defects (maximum concentration 0.04) but indicates enhanced microstrains in the crystallographic⟨100⟩directions compared to the⟨111⟩directions. Based on this strain anisotropy, various distributions of microstresses are discussed taking into account the substantial elastic anisotropy of Pd. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365307

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fabry–Perot laser interferometry was used to obtain nanosecond time resolved particle velocity histories of the free surfaces of tantalum discs accelerated by detonating pentaerythritol tetranitrate (PETN) charges and of the interfaces between PETN detonation products and lithium fluoride crystals. The experimental records were compared to particle velocity histories calculated using very finely zoned meshes of the exact dimensions with theDYNA2Dhydrodynamic code. The duration of the PETN detonation reaction zone was demonstrated to be less than the 5 ns initial resolution of the Fabry–Perot technique, because the experimental records were accurately calculated using an instantaneous chemical reaction, the Chapman–Jouguet (C-J) model of detonation, and the reaction product Jones–Wilkins–Lee (JWL) equation of state for PETN detonation products previously determined by supracompression (overdriven detonation) studies. Some of the PETN charges were pressed to densities approaching the crystal density and exhibited the phenomenon of superdetonation. An ignition and growth Zeldovich–von Neumann–Doring (ZND) reactive flow model was developed to explain these experimental records and the results of previous PETN shock initiation experiments on single crystals of PETN. Good agreement was obtained for the induction time delays preceding chemical reaction, the run distances at which the initial shock waves were overtaken by the detonation waves in the compressed PETN, and the measured particle velocity histories produced by the overdriven detonation waves before they could relax to steady state C-J velocity and pressure. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365318

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Cadmium sulfide crystals were shocked along the crystalcaxis to peak stresses ranging between 18 and 75 kbar. Stress-time profiles were measured both at the impact surface and after transmission through 1 to 2-mm-thick samples. Detailed analysis of the present data in combination with published static results makes a persuasive case for the completion of the wurtzite to rocksalt phase change in less than 0.2 &mgr;s under shock loading. The main findings are: the transition stress is measured to be32.5±1 kbar;transformation to the final state is a two step process with the first step being too rapid (less than 10 ns) to be observed in our experiments and the second step occurring in 0.1 to 0.2 &mgr;s; the transition occurs directly from the elastic state prior to any plastic deformation. The calculated mean stress for the transition is 22.9 kbar in good agreement with the 23 kbar pressure reported in static high pressure studies; the presence of large shear stress has no effect on the transition pressure. Our results suggest that the onset of the phase transition results in plastic deformation and, subsequently, the phase transition and plasticity are coupled under shock loading. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365319

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new concept of dynamic potential (macrostress potential or macrostrain-rate potential), which has two components, i.e., deformation and kinetic potentials for heterogeneous materials under intense dynamic loading, is proposed using a micromechanical approach. In particular, for voided nonlinear materials, the approximate expression of the macrostress potential is derived through an upper bound approach. Simplified physical models for ductile porous materials (aggregates of voids and ductile matrix) are employed with the matrix material taken as power-law thermal viscoplastic and incompressible. Approximate velocity fields for the matrix are adopted to derive the dynamic loading criterion and an approximate functional form of the dynamic loading criterion is developed. The inertial, rate sensitivity, and thermal effects are directly included in the expressions of the macrostress potential and the dynamic loading function. Various features of the loading function are numerically investigated in detail. Numerical analysis reveals that both the dynamic growth of voids and the loading surface have strong rate dependence and temperature dependence. Experimental data, theoretical analysis, and numerical modeling indicate that the inertial and thermal effects play a very important role in the dynamic behavior of the voided nonlinear materials. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365320

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A thermodynamic description of metals in the range of high pressures and temperatures is obtained and applied to the problem of the stability of strong shock waves under spontaneous emission of sound. A three-term form of the equation of state is employed to describe the contributions of the cold elastic pressure, the thermal atomic pressure, and the thermal pressure of the free electrons to the total pressure. The full determination of the equation of state is performed from the experimental Hugoniot data and from a model (such as the Slater–Landau model) connecting the atomic Gru¨neisen parameter and the atomic cold pressure. From the equation of state, the behavior of the Mach number, the temperature, and the entropy along the Hugoniot adiabatic is obtained and analyzed. The calculation of the sound velocity behind the shock enables the application of the Kontorovich criterion for the spontaneous emission of sound from the shock’s front. It is shown that metals with a relatively low slope of the shock velocity versus the particle-velocity straight line exhibit such an unstable behavior for high enough shock intensities. The effects of the electrons’ thermal pressure on both the thermodynamic properties of the metals and the stability of shocks are analyzed and discussed. In particular, it is shown that the electronic contribution to the total pressure has a stabilizing effect. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365321

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The dispersion relations of oscillation modes in a piezoelectric slab with hexagonal symmetry are given, considering the slab infinite with respect to the axesx1andx2with the six-order symmetry axis perpendicular to thex1–x2plane. Four types of modes are identified: two of them are transversal horizontal and the other two are associated to electrostatic potential waves which determine the longitudinal and flexural modes. The secular equations for these modes are given and numerical results for the piezoelectric transducer ceramic slab are obtained and compared to experimental results with a very good agreement. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365358

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of enhanced atomic mobility on the growth of hard carbon films was examined. Tetrahedrally bonded amorphous carbon films were deposited by condensing energetic carbon ions using an arc-discharge deposition method. The deposition temperature varied between 50 and 400 °C. The dependence of elastic properties on deposition temperature was examined by determining the frequency-dependent propagation velocity of ultrasonic surface acoustic waves induced by a laser. A remarkable decrease in elastic coefficient was revealed above the deposition temperature of 300 °C and complete relaxation was obtained at 400 °C. This observation was analyzed by using a simple model which was in turn supported by molecular dynamics simulations. The relaxation turns out to be a thermally activated, dynamic process with an activation energy of 0.57 eV. Possible relaxation mechanisms associated with the migration of atoms or defects on a growing surface are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365322

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Highly carbon doped (001) oriented GaAs layers were grown by metalorganic vapor phase epitaxy using the precursor trimethylgallium with either arsine or trimethylarsenic. Postgrowth infrared measurements using polarized light demonstrate that proposed grown-in planar carbon–hydrogen[H–(CAs)2]complexes, giving vibrational absorption at2688 cm−1,have the twoCAsatoms aligned along the [110] direction. A previously unreported absorption peak at576 cm−1exhibits polarization dependent absorption orthogonal to that of the2688 cm−1line. Investigation of a sample containing the[D–(CAs)2]complex indicates that the576 cm−1line would have to be a transverse mode of the unpairedCAsatom. Polarization difference spectra show the presence of other aligned carbon related complexes giving absorption close to the line(582 cm−1)due to isolatedCAsatoms. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365352

出版商:AIP    

年代:1997

数据来源: AIP