摘要:

Samples of undoped GaAs‐ and Si‐doped GaAs were oxidized at different oxidation temperatures, for different durations. Three different experimental techniques that complete each other were used: Raman scattering, Auger electron spectroscopy, and the ellipsometry technique. The growth of crystalline arsenic layer takes place after oxidation during 10 h, 45 min, and 5 min at temperatures of 400, 500, and 600 °C, respectively. The oxide layer is formed as a result of three competing processes: diffusion in accordance with Fick’s law, diffusion with larger diffusion coefficient through the oxide layer, and stopping of diffusion by the crystalline arsenic layer that grows at the GaAs/oxide interface. The effect of Si doping on the oxidation process of GaAs is to impede the crystallization of the arsenic layer, to diminish the diffusion coefficient in the course of the initial stages of the reaction between the oxygen and GaAs, and to cause a small rise in the activation energy.

ISSN:0021-8979    

DOI:10.1063/1.354884

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The structural ordering development during mechanical alloying of the Al50Ti50alloy was investigated by using molecular‐dynamics computer simulations. Random external forces with both random orientations and magnitudes were used to simulate the mechanical alloying processes and pseudopotential was used as a model for the interaction between the atoms. The results indicate that the final nonequilibrium phase obtained through simulation of mechanical alloying is an amorphous state which can be formed experimentally in the laboratory. The transformation from crystals to amorphous state may locally be a first‐order‐like phase transition, but statistically it is a gradual phase transition due to the characteristics of random external forces which help atoms to overcome their energetic barrier during the mechanical alloying. This means that the transformation occurs in random sites and is discontinuous.

ISSN:0021-8979    

DOI:10.1063/1.354885

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The sequential, layering techniques used to prepare multilayer materials result in significant structural incoherence due to deviations from the intended thicknesses within an elemental layer and local deviations from the average due to islanding of the depositing elements during deposition. We demonstrate that if the domain size of the structural incoherence is large compared with the wavelength of the scattering radiation, the structural incoherence manifests itself in the low‐angle diffraction pattern by attenuating the intensity of the subsidiary maxima relative to the Bragg maxima. We also show that the subsidiary maxima in the low‐angle diffraction pattern of a multilayer result from incomplete destructive interference from all of the interfaces, not just from the top and bottom surface of the film. A technique for incorporating structural incoherence when modeling the diffraction pattern of a multilayer structure is presented. The ability of this model to simulate the experimental diffraction pattern of an iron‐silicon multilayer is demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.354857

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We reported enhanced oxygen precipitation in quenched Czochralski silicon crystals after solution annealing at 1270 °C in nitrogen or in dry oxygen [J. Appl. Phys.66, 3958 (1989)]. We attributed this phenomena to intrinsic point defects. However, hydrogen was introduced into samples during solution annealing at 1270 °C and aggregates of hydrogen were formed during quenching. This article examines hydrogen aggregates by Secco etching and transmission electron microscope. Hydrogen‐related aggregates are found to be related to enhanced oxygen precipitation.

ISSN:0021-8979    

DOI:10.1063/1.354858

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The dynamic behavior of &agr;, &bgr;, and screw dislocations in both undoped and doped InP is investigated. The generation of dislocations from a surface scratch is suppressed in doped InP. This effect is attributed to the immobilization of dislocations due to locking by impurities similar as observed in GaAs. Isovalent Ga and As dopants are found not to affect the dislocation velocity. Zn acceptors strongly reduce the dislocation velocities of all type of dislocations while S donors enhance the velocity of &agr; dislocations and reduce the velocity of &bgr; and screw dislocations. Such impurity effects are in contrast with those observed in GaAs. The measured dislocation velocities are expressed with a simple empirical equation as a function of stress and temperature. The mechanical strength of InP reflects the above dynamic behavior of individual dislocations. An increase in the yield strength results from a decrease in the dislocation velocity in Zn‐doped InP. On the other hand, an increase in the strength at high temperatures results from dislocation immobilization in Zn‐ or S‐doped InP.  

ISSN:0021-8979    

DOI:10.1063/1.354859

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The nucleation of misfit dislocations through the extension of dissociated dislocations in the strained interface is considered theoretically. The predicted critical thickness of misfit dislocation nucleation by a dissociated dislocation is compared with that predicted for a perfect dislocation. It is shown that the model of misfit dislocation nucleation by the movement of a dissociated dislocation is more likely.  

ISSN:0021-8979    

DOI:10.1063/1.354860

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Semiconducting oxides such as Bi4Sr3Ca3CuyOx(y=0–5) and Bi4Sr3Ca3−zLizCu4Ox(z=0.1, 0.5, and 1.0), many of which become superconductors in their glass‐ceramic phases, have been studied over the wide temperature (77–450 K) and frequency (100–104Hz) ranges. The universal power‐law behavior [exponents≤1 in &sgr;(&ohgr;)=&sgr;0+A&ohgr;s] is found to be valid for most of these glasses. Little deviation from this limiting behavior is also observed for some glass compositions in the low‐temperature and high‐frequency regions. The correlated barrier hopping model based on the pair approximation is found to be more appropriate for explaining the frequency and temperature‐dependent ac conductivity data. The random walk type of model, on the other hand, is found to be valid for a limited range of temperature.

ISSN:0021-8979    

DOI:10.1063/1.355328

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have calculated the static yield stress of electrorheological fluid directly introducing cubic particle chains arranged in a triangular lattice to elucidate the influence of the many‐body effect. The shape of the stress‐strain curve at a high concentration of particles is much different from that at a low concentration, and the static yield stress saturates at a high concentration (&fgr;=0.4), the same as is the case of spherical particle chains arranged in a rectangular lattice. In both cases of low and high volume fractions, the yield stress increases in proportion to the permittivity ratio of particles and dispersion fluid.

ISSN:0021-8979    

DOI:10.1063/1.354834

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The simplest of all structures in an electrorheological fluid is a single chain of dielectric particles. The shape of a chain deformed by flow in a square tube is observed and is found to be reasonably consistent with a model of chain force based on point‐dipole nearest‐neighbor interactions.

ISSN:0021-8979    

DOI:10.1063/1.354835

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The anomalies of the second‐, third‐, and fourth‐order elastic constants have been derived for barium titanate and related compounds for the phase transition from cubic to tetragonal and from the tetragonal to the orthorhombic phases. The equilibrium values of the three components of the order parameter and the strain variables in the two phases have been obtained from the stability conditions. The fluctuations in the order parameter in the two phases have been derived from the Landau–Khalatnikov equations. Expressions have been given for the shift in the zero point energy in the tetragonal and orthorhombic phases, and these are shown to be proportional to (T−Tc)2. The anomalies for all the second‐order elastic constants have been derived for both phases, and relations among them have been reported. It is shown that the elastic anomalies suffer a discontinuity at the transition temperature for both the phases. Our expressions give the temperature variation of the third‐order elastic and fourth‐order elastic constants for the phase transition from the tetragonal to the orthorhombic phase.

ISSN:0021-8979    

DOI:10.1063/1.354836

出版商:AIP    

年代:1993

数据来源: AIP