摘要:

An alignment method for materials with cholesteric to smecticC* phase transitions is described. Ordering of the molecules, confined between glass plates which have been coated with a polymer and buffed, is achieved using an electric field. While the buffing direction defines the orientation of the long axis of the molecules, the electric field defines the direction of the layer tilt. In cells with only one buffed surface, polar surface interactions are thought to be responsible for producing monodomain specimens.

ISSN:0021-8979    

DOI:10.1063/1.336333

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An improved light‐beam‐induced current apparatus was used to evaluate grain‐boundary activity in a polycrystalline solar cell. The grain‐boundary recombination velocity and the diffusion length in the neighboring grains were obtained by processing of the grain‐boundary profiles. The technique was applied using various wavelengths in the 550–950 nm range to check the consistency of the method and to examine the depth profile of the parameters measured. The results show that the diffusion length measurement is independent of the wavelength, and that the measured grain‐boundary recombination velocity increases with the wavelength. The method was also used to evaluate hydrogen passivation of the grain boundary examined.

ISSN:0021-8979    

DOI:10.1063/1.336334

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report on the glass‐forming ability and crystallization products of Cu‐, Ni‐, Co‐, and Fe‐Zr around the composition M90Zr10. Cu‐Zr cannot be made glassy by metal spinning in this composition range and Ni‐Zr only with difficulty at Ni90Zr10. Two new metastable phases are observed: Co5Zr and a bcc form of Ni.

ISSN:0021-8979    

DOI:10.1063/1.336335

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The multiple scattering theory has been a powerful tool in estimating the effective elastic properties of polycrystalline substances and different types of composite materials in terms of the component elastic properties. Both perturbative and self‐consistent solutions within the framework of multiple scattering theory have been developed for cubic polycrystals by R. Zeller and P. H. Dederichs [Phys. Status. Solidi B55, 831 (1973)]. Recently we have suggested [T. R. Middya, Mala Paul, and A. N. Basu, J. Appl. Phys.58, 4095 (1985)] a perturbative method of calculation for all the noncubic polycrystals up to orthorhombic symmetry. Although the method has been quite successful in dealing with noncubic polycrystals with low anisotropy factors, it becomes too complex to handle the high anisotropy cases. Moreover, the results for many crystals for such cases with perturbation carried up to second order are inconsistent as they fall outside the well‐known Hashin–Shtrikman (H–S) bounds. In order to overcome this difficulty, in this work we discuss a self‐consistentT‐matrix solution for the effective elastic properties of hexagonal, tetragonal, trigonal, and orthorhombic polycrystals. Within the approximation of multiple scattering of all orders from a single grain, we have obtained the self‐consistent solution by exploiting the symmetry of each class. Next we have employed the formulas thus obtained to calculate the effective bulk and shear moduli of hexagonal, tetragonal, trigonal, and orthorhombic polycrystals. Finally the results are compared with our previous perturbative calculations, the H–S bounds and experiment. Unlike the previous calculations, all the self‐consistent results fall within the H–S bounds. In addition to providing simple analytical formulas which can tackle polycrystals with arbitrary values of anisotropy factors, these formulas may also be used for evaluation of mechanical properties of composites having components belonging to different symmetries.

ISSN:0021-8979    

DOI:10.1063/1.336336

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In the present investigation we have generalized the result obtained in the preceding paper [J. Appl. Phys.59, 2368 (1985)] to treat composites containing crystallites of different crystal symmetries and arbitrary values of the elastic constants. This result has been used to discuss the existing theories intended to solve the same problem. An interesting finding of this analysis is that the present approach provides a single framework to discuss all the previous results which are particular cases of the general formulas derived here. Earlier all these cases were treated separately employing different approaches. Next we apply our results to six different binary composites and we find that our predictions compare quite favorably with experiment. For comparison we also calculate the same quantities by simulating the composite on a computer by the dynamic method originally developed by [T. R. Middya, A. N. Basu, and S. Sengupta [J. Appl. Phys. 57, 1844 (1985)] to discuss monocomponent polycrystal elastic properties. The two sets of results agree with each other for small differences in elastic properties of the components of a composite. But for larger differences, they diverge. Since the two approaches are based on widely different assumptions and the overall agreement of the effective‐medium theory is distinctly superior, it appears that the existing experiments are consistent with the assumptions of the multiple scattering theory.

ISSN:0021-8979    

DOI:10.1063/1.336337

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The first‐order Raman scattering from heavily doped and highly compensated GaAs:Si has been measured with a constant impurity concentration of 1.1 × 1019cm−3. The dampedq=0L− andL+ branches due to the compensation‐limited low mobilities have been observed. The impurity‐induced forbidden mode which had been found in uncompensatedp‐GaAs:Zn has not appeared in the measured spectra. The line‐broadening of plasmon‐coupled LO phonon,L(q), and line and peak shift of TO phonon line are attributed to the impurity‐induced Fro¨hlich interaction and the self‐energy effect, respectively.

ISSN:0021-8979    

DOI:10.1063/1.336338

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The difference in the crystallization transformation of amorphous Fe90Zr10alloy ribbon between the bulk and the surface has been investigated by means of transmission and conversion electron Mo¨ssbauer spectrometries. It is found that the ribbon surface crystallizes at 473 K, which is 340 K lower than the crystallization temperature of the bulk. It is confirmed that the remarkable drop in the onset temperature results from the formation of Zr‐deficient amorphous phases induced by the absorption and diffusion of a large amount of oxygen. The final crystalline products in the bulk are assigned as &agr;‐Fe, Fe3Zr, and Fe2Zr, whereas both surfaces of the ribbon are overlaid with only &agr;‐Fe. Further, the study of the ambient atmosphere during annealing shows that air stimulates the crystallization transformation of the bulk and that the crystallization behavior in air is quite different from that in a vacuum.

ISSN:0021-8979    

DOI:10.1063/1.336339

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The diffusion of10B in the presence of high‐concentration11B and As doping has been studied. Dopants were introduced by ion implantation and profiles after annealing were obtained by secondary ion mass spectrometry. Diffusion coefficients were derived by comparing experimental profiles with those from a computer simulation program and results confirmed that diffusion of boron is enhanced inp+silicon and depressed inn+silicon. These results have been analyzed using the widely accepted vacancy model for boron diffusion and have produced values of the parameter &bgr;, which is related to the ratio of diffusivity for charged and uncharged vacancies, of 0.25 to 3.0 for thep+and 3.0 to 7.7 for then+conditions. This difference cannot be ascribed to experimental error and suggests that further refinement of the vacancy model is required.

ISSN:0021-8979    

DOI:10.1063/1.336340

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The diffusion of Cr in GaAs was investigated under both in‐diffusion and out‐diffusion conditions. In‐diffusion sources were CrAs(s)‐GaAs(s)‐Ga(l), three phase mixtures which, at a given temperature, provide an invariant chemical potential of the components. Unexpectedly deep penetration was observed and complex (two‐branch) concentration profiles were often observed. The profiles were successfully modeled using an interstitial/substitutional/dissociative model. Different regimes of diffusion conditions gave rise to fast and slow effective diffusion coefficients. Subtle effects of doping and preannealing under arsenic overpressures confirmed the proposed model and served as a probe to study these subtle differences. Out‐diffusion experiments led to slow effective diffusion coefficients, consistent with the diffusion model.

ISSN:0021-8979    

DOI:10.1063/1.336341

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Zn accumulation (gettering) in InGaAs/InP interfaces was studied experimentally using secondary ion mass spectrometry (SIMS). The Zn was introduced by diffusion from solid and gaseous sources and was found to often getter in a thin region at the interface when diffused across it. Its peak concentration there increased with diffusion time and temperature and in some cases exceeded the solid solubility value by two orders of magnitude. Possible mechanisms for the Zn gettering are discussed.

ISSN:0021-8979    

DOI:10.1063/1.336342

出版商:AIP    

年代:1986

数据来源: AIP