摘要:

The elasto‐plastic properties of piezoresistance gauges influence their response as stress transducers in shock‐wave experiments. In the present article, we discuss these relations for lateral stress gauges upon shock loading and unloading. It is shown that piezoresistance response in the elastic range of the gauge material depends on the properties of the matrix material. On the other hand, these gauges have a unique calibration curve, both for loading and unloading, within their plastic range. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358891

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The unstable structural responses of a model intermetallic lattice to hydrostatic and uniaxial loadings have been determined by elastic stability analysis and molecular‐dynamics simulations. Two crystalline phases of Ni3Al, the naturally occurringL12and a hypotheticalD022, are analyzed to correlate the effects of structural symmetry with stress‐induced lattice deformations. Under isotropic expansion, the former fcc lattice develops extensive cavitation and amorphization at critical isotropic tensile loading, whereas the latter, a tetragonal lattice, shows cleavage behavior. These qualitative differences do not appear in the elastic stability analysis. Both phases show similar responses to uniaxial tension. In all cases critical strains for lattice instability predicted on the basis of elastic stiffness coefficients are found to be in good agreement with direct simulations. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359577

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Hydrogenated defects in microwave plasma chemical‐vapor‐deposited (CVD) diamond films have been examined by proton nuclear magnetic resonance and infrared spectroscopy and correlated with the thermal conductivity of these samples. The measured thermal conductivities of 1–22 W cm−1 K−1are consistent with an upper limit predicted based on the assumption that the scattering rate from hydrogenated defects is proportional to the as‐deposited hydrogen contents of ≤0.5 at. % H. This hydrogen is predominantly clustered, consistent with hydrogen passivated diamond surfaces. Thus, the as‐deposited hydrogen content may be a measure of the internal surface area of the polycrystalline diamond film which is hydrogen passivated. Part of this surface area may be due to elongated voids, several microns in dimension, which are observed by scanning electron microscopy of polished diamond film cross sections. These voids may arise from the columnar film growth process and thus be a common feature of CVD diamond films. Phonon scattering from these voids which are oriented along the film growth direction could account for film‐to‐film variation in and the anisotropy of the thermal conductivity of CVD diamond films. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358892

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The thermal interdiffusion on the group‐V sublattice in InxGa1−xAs‐InxGa1−xAsyP1−yquantum‐well structures has been characterized for samples annealed either with silicon nitride encapsulation or under a phosphine overpressure in two different metalorganic vapor‐phase‐epitaxy reactors under different phosphine overpressures. Under all conditions the interdiffusion lengths were found to be comparable, with only small effects due to the phosphine overpressure. This suggests that interdiffusion results obtained from silicon nitride capped samples can be applied to the interdiffusion that occurs during growth conditions. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358893

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

X‐ray diffraction has been used to measure the residual strain in In1−xAlxSb (x=0.15–0.64) layers of thicknessh=0.1 &mgr;m, grown epitaxially on (100) InSb substrates. The results for this tensile‐strained system are compared with a well‐studied compressive‐strain system, viz., InGaAs/GaAs. Experimental evidence is presented which suggests that the strain relaxation mechanism in this system is different from that in InGaAs/GaAs. This includes an observed critical layer thickness (hc) which is about five times thehcgiven by the Matthews and Blakeslee [J. Cryst. Growth27, 118 (1974)] type models and a measured relaxation coefficient which is quasilinear inh/hcfor 5<h/hc<35. The results have also been compared with predictions of the Dodson–Tsao (DT) model [Appl. Phys. Lett.51, 1710 (1987)] which fits well the quasilinear behavior of the relaxation coefficient. In addition, it is argued that the DT equation provides a generic model that is not restricted to dislocation‐mediated strain relief. Other possible mechanisms of strain relaxation in InAlSb/InSb are discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358894

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Excess As is incorporated in GaAs grown at low substrate temperatures by molecular beam epitaxy. Excess As is distributed in the epilayer as defects and the material exhibits considerable strain. When annealed to moderate temperatures, the strain is seen to disappear and the excess As is now in the form of semimetallic clusters. It has been proposed that these As clusters form buried Schottky barriers with the GaAs matrix and are surrounded by spherical depletion regions. In this article, we examine the effects of doping on the material properties and compare our results to the buried Schottky barrier mode. Si‐doped GaAs epilayers grown at 250 °C, with doping densities between 5×1017and 5×1018cm−3, were annealed to temperatures between 700 and 1000 °C for 30 s. Be‐doped GaAs epilayers grown at 250 °C, with doping densities between 5×1017and 5×1019cm−3, were annealed to temperatures between 700 and 900 °C for 30 s. Using extensive Hall measurements and transmission electron microscopy, we observe that the As precipitates deplete the surrounding GaAs matrix. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358895

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A model based on space‐charge assisted diffusion of O−is proposed to describe the rapid thermal oxidation kinetics of silicon in dry oxygen ambient. The space‐charge region within the growing oxide layer is assumed to have a constant planar charge density which results in a characteristics length, &lgr;c, the extend of the space‐charge region. The diffusion of O−and therefore the oxide growth rate will be driven by two components, the concentration gradient and space‐charge drift. The discrepancy in the calculated values of diffusion activation energies for O−is explained by comparing the strength of the space‐charge regions. The strength of space charge depends on the range of photon energies irradiated by the heating lamps used in different rapid thermal processors. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358896

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The structure of laser‐deposited and sputtered Fe/Nb and Fe/Ag multilayers was investigated by x‐ray diffraction. Significant differences in the textures, sharpness of the interfaces, and critical bilayer thicknesses for alloys are obtained for these two deposition processes. For small bilayer thicknesses, the measured x‐ray‐diffraction patterns were analyzed by computer simulations using a one‐dimensional model, which includes the occurrence of amorphous or disordered interlayers between the crystalline layers and takes layer thickness fluctuations into account. These simulations indicate that already in as‐prepared Fe/Nb multilayers thin amorphous interlayers exist and describe the thickness increase during an interdiffusion reaction already in the early stages of the transformation. In the case of Fe/Ag multilayers, the interfaces are disordered after deposition and first sharpen during annealing at about 250 °C, before grain coarsening occurs. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358897

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The transient reflecting grating (TRG) technique was applied to evaluate both nitrogen‐ion‐implanted and nonimplanted thin‐film coatings (thickness: 40 nm) of diamondlike carbon (DLC) on metallic multilayered substrates. Different TRG responses corresponding to the different nitrogen ion doses were observed. Hypersonic surface wave velocities as well as the thermal diffusivities were obtained with a variety of grating spacings. Effective elastic moduli (Young’s moduli) for the DLC coatings were given by using a theoretical treatment with a model. Nitrogen ion implantation hardened the DLC coating. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358898

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

InGaAs/InP short‐period superlattices (SPSLs) grown by gas source molecular beam epitaxy (GSMBE) and by gas source migration enhanced epitaxy (GSMEE) on (001)InP substrates were investigated by x‐ray diffraction (XRD) and Raman scattering. XRD and Raman scattering results show that, although the average lattice mismatch relative to the InP substrate in GSMBE‐grown SPSL is close to zero, there may be some lattice parameter relaxation and substrate‐layer tilting caused by asymmetrical ordering of atomic layers and/or interchange between As and P atoms at interfaces. In GSMEE‐grown SPSLs, layer‐by‐layer growth is achieved and strained interface layers are formed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358899

出版商:AIP    

年代:1995

数据来源: AIP