摘要:

We have investigated the efficiency and the thermal stability of Pt gettering at different sites in crystalline Si. In particular, we compared the gettering performances of heavilyn‐type doped regions formed by P diffusion, cavities formed after high‐temperature annealings of He implanted Si, and damage induced by ion implantation of B, C, or Si. These sites were introduced on one side of wafers containing a uniform Pt concentration in the range 1×1013–5×1014atoms/cm3. The uniform concentration of Pt was attained by means of Pt implantation followed by a high‐temperature thermal process. The gettering efficiency of the different sites was monitored during thermal processes at 700 °C for times ranging from 1 to 48 h. Thermal stability of gettering was investigated with a subsequent thermal process in the temperature range 750–900 °C during which part of the gettered Pt is released in the bulk of the wafer. The kinetics of Pt gettering at the different sites is found to be similar since it is fully dominated by the kick‐out diffusion mechanism of the metal impurity. The thermal stability is instead site‐dependent and can be described in terms of an effective binding enthalpy of 1.9, 2.6, and 3.0 eV between Pt atoms and cavities, P‐doped region, and ion‐implantation damage, respectively. The physical meaning of the binding enthalpy is investigated and discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363381

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

One of the outstanding questions concerning the compressive behavior of brittle materials concerns the failure wave observed in glasses. While much work has centered around relatively open structure, low density glasses such as borosilicate (pyrex) and soda‐lime (float, which is partially filled), none has addressed the response of highly filled lead glasses. This work presents the results of a series of plate impact experiments carried out on the lead glass DEDF.TMThis material was shocked in uniaxial strain and the longitudinal and lateral components of stress and strain were measured. The failure wave, observed in lower density glasses, was observed in this material but its velocity reached that of the shock at less than twice the Hugoniot elastic limit (HEL). ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363382

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A molecular dynamics method is used to analyze the dynamic propagation of an atomistic crack tip. The simulation shows that the crack propagates at a relatively constant global velocity which is well below the Rayleigh wave velocity. However the local propagation velocity oscillates violently, and it is limited by the longitudinal wave velocity. The crack velocity oscillation is caused by a repeated process of crack tip blunting and sharpening. When the crack tip opening displacement exceeds a certain critical value, a lattice instability takes place and results in dislocation emissions from the crack tip. Based on this concept, a criterion for dislocation emission from a moving crack tip is proposed. The simulation also identifies the emitted dislocation as a source for microcrack nucleation. A simple method is used to examine this nucleation process. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363383

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Examination was made of ultrasonic attenuation &agr;44and elastic constantC44of vanadium single crystals with hydrogen between 4.2 and 220 K, as a function of temperature, hydrogen concentration, frequency, and rates of cooling and heating. Attenuation in the V–H &agr; phase at 210 K increased in proportion to the square of hydrogen concentration, whileC44was linear. At a cooling rate of 3.0 K/min, attenuation of the specimen with 1000 at. ppm H increased below the critical solution temperature and showed a peak. At 0.1 K/min, discontinuous decrease was observed at the temperature. During isothermal annealing below this temperature, attenuation at the higher cooling rate decreased with time in two stages and approached the value for the lower cooling rate. The results are discussed based on ultrasonic double refraction due to the volume array of hydrogens and hydride particles formed under the influence ofC44‐mode ultrasonic waves. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363390

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A thermodynamic equation of state (EOS) is derived which is appropriate for investigating the thermodynamic variations along isobaric paths. By using this EOS, a Hugoniot EOS model with a unified theoretical basis is proposed for predicting the shock compression behavior of porous materials. The model is tested on 2024 aluminum, copper, and tungsten which are the typical materials with low, intermediate, and high shock impedance, respectively, and commonly used as standards. The calculated Hugoniots for these three materials with different initial densities are in good agreement with the corresponding experimental data published previously. It shows that this Hugoniot EOS model can satisfactorily predict the Hugoniot of porous materials over a wide pressure range. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363391

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this article we present a detailed numerical analysis of the problem of diffusion‐controlled growth of a solid intermediate phase from two saturated solutions (solid solute and solid or liquid solvent). Spherical geometry is considered and the quasi‐steady‐state approximation used in earlier analytical models is eliminated. Comparison between our results and those from Larson’s model allows us to conclude that the use of a numerical scheme may lead to a significant gain in accuracy except when a solute‐rich sphere is converting into a dilute phase. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363392

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The depth distribution of sulphur near the Si/GaAs(110) interface has been measured using particle induced x‐ray emission (PIXE) in conjunction with Rutherford backscattering spectrometry (RBS); ozone oxidation and a hydrofluoric acid step‐etching technique were used for sequential removal of Si/GaAs atomic layers. The depth resolution was also calibrated via16O(d,p)17O nuclear reaction analysis and x‐ray photoemission spectroscopy. PIXE/RBS measurements found a half monolayer of sulphur on the H2Sxpassivated GaAs(110) surface. Upon deposition of 15 A˚ silicon on the S‐passivated GaAs(110), the total amount of sulphur remained constant as compared to that before Si deposition. However, no orientated S–Ga bonds were detected via the x‐ray absorption measurement and the depth profile revealed that the sulphur atoms diffused into both the GaAs substrate and the Si heterolayer. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363393

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An ac calorimetric method is applied to the direct measurement of thermal diffusivity of single fibers. Theoretical analysis is presented, taking into account the two‐dimensional ac thermal wave for cylindrical systems and the effect of time delay at the temperature detecting system. Experimental tests are performed using nickel and stainless steel wires about 20 &mgr;m in diameter. The thermal conductivity of fibers about 10 &mgr;m in diameter of the advanced materials, polyacrylonitrile‐based carbon, TORAYCA, and aramide, Kevlar, is determined. The relationship between the thermal conductivity and electric conductivity and the crystalline size of these fibers is discussed. For composite materials made of carbon fibers, the observed thermal conductivity agrees with the thermal conductivity estimated using the values determined by the present method. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363394

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

To determine the influence of interface type on the accumulation of damage and ion mixing in GaAs/AlxGa1−xAs heterostructures, the damage produced by ion implantation at 77 K in single‐layer (GaAs/AlxGa1−xAs/GaAs) and double‐layer (GaAs/AlxGa1−xAs/GaAs/ AlxGa1−xAs/GaAs) heterostructures has been investigated by using a combination of Rutherford backscattering spectrometry and transmission electron microscopy. In the single‐layer geometry, the degree of disorder increases with depth and the mixing is greater at the AlxGa1−xAs on GaAs interface than at the GaAs on AlxGa1−xAs one. The damage distribution in the sample with the double‐layer geometry was different in the two layers, but overall it was similar to that in the single‐layer geometry. These trends were observed in samples withx=0.6 and 0.2. These results indicate that migration of charged defects due to the presence of an implantation‐induced electric field is not responsible for the asymmetry in the damage accumulation across the layer, the interface disorder and ion mixing, and the initiation of amorphization at interfaces. Instead, these effects can be better understood in terms of the depth dependence of the density of cascade events. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363395

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Various x‐ray techniques have been applied to a study of semiconductor superlattices consisting of 100‐period of InxGa1−xAs (15 A˚)/GaAs (100 A˚) grown on GaAs(100) substrates by molecular beam epitaxy. Structural parameters pertaining to the morphology of interfaces and thickness variations were obtained. The interfaces in these superlattices are found to be highly correlated, and the layers all show a high degree of crystallinity. Splittings in the x‐ray reflectivity and diffraction patterns in one of the samples provide clear evidence for pronounced thickness modulation, and direct comparison of the diffraction satellite peaks with results of high resolution transmission electron microscopy indicates that there exists a lateral structural ordering in the [110] direction during epitaxial growth. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363421

出版商:AIP    

年代:1996

数据来源: AIP