J. H. Li

RELAXED SI0.7GE0.3 LAYERS GROWN ON LOW-TEMPERATURE SI BUFFERS WITH LOW THREADING DISLOCATION DENSITY

Si0.7Ge0.3 epilayers with low threading dislocation density have been grown on Si (001) substrates by introducing a low temperature Si buffer. Such a structure can be used as the buffer for the growth of device structures. In comparison with the conventional compositionally graded buffer system, it has the advantages of having lower threading dislocation density, smaller thickness for required degree of relaxation, and smoother surface. Experimental evidence suggests that an anomalous relaxation mechanism has been involved.

Property-microstructure correlation in in situ formed Al2O3, TiB2 and Al3Ti mixture-reinforced aluminium composites

The in situ formed Al2O3, TiB2 and Al3Ti mixture-reinforced aluminium composites were successfully fabricated by the reaction sintering of the TiO2-B-Al system in a vacuum. With increasing boron content in the TiO2-B-Al system, the amount of generated TiB2 in the composites increased and Al3Ti content decreased. At the same time the distribution uniformity of the in situ formed Al2O3 and TiB2 particulates was obviously improved, and the size of the Al3Ti particles was reduced. The in situ Al2O3 and TiB2 particulates had sizes from 0.096–1.88 μm. The interface between the in situ formed particulates and the aluminium matrix was clean, and no consistent crystallographic orientation relationship was found. The strength and elastic modulus of the composites was significantly improved by lowering the Al3Ti content. When the boron content in the TiO2-B-Al system rose, the morphology of the tensile fracture surface of the composites was changed from large fractured Al3Ti blocks and fine dimples, to fine dimples and pulled-out particulates. The strengthening and fracture of the composites have been modelled.

X-RAY ANALYSIS OF STRAIN RELAXATION IN STRAINED-LAYER SUPERLATTICES

Theoretical simulations of x‐ray double‐crystal‐diffraction rocking curves for strain‐relaxed superlattices have been successfully carried out based on x‐ray dynamical diffraction theory. The strain relaxation, the misorientation between the superlattice layers and the substrate, and the effect of peak broadening due to the formation of misfit dislocations have been taken into account. The influence of possible strain relaxation mechanisms and relaxation ratios on the rocking curves have been investigated. It was found that both the mechanism and degree of the strain relaxation of the superlattice can be determined by fitting the angular positions and the relative intensities of the experimental superlattice satellites. By using this method, an InxGa1−xAs/GaAs superlattice sample and a GexSi1−x/Si superlattice sample were analyzed. The different strain‐relaxation mechanisms were found in these two samples.

Planar Hall effect and magnetoresistance in spin valve multilayers

Magnetoresistance (MR) and planar Hall effect (PHE) in spin valves were simultaneously measured in fields applied at different angles (α) in the film plane with respect to the easy axis of the free layer. MR curve measurements showed that the MR response to the field was linear in the α angle range from ±60° to ±120°. However, it was found that when the applied field was near perpendicular to the easy axis of the free layer, PHE curves were nonsymmetrical on both sides of the axis along the sample height. The Boltzmann transport equation was used to simulate the MR and PHE curves and determine magnetization orientation of the free layer. Results showed that the nonsymmetrical PHE curves originated from the interaction of the interlayer exchange coupling field between the pinned and free layers. Consequently, the magnetization reversal was a coherent rotation when the applied field angle α>90° and incoherent when α<90°.

Aluminium borate whisker reinforced Al-8.5 Fe-1.3 V-1.7 Si composite

changsha inst technol,changsha 410073,peoples r china.;ma, zy (reprint author), chinese acad sci,inst met res,atom imaging solids lab,shenyang 110015,peoples r china

HRTEM investigations of the relationship between the surfaces of whiskers and interfacial structures in whisker-reinforced aluminium metal matrix composites

Abstract The relationship between surfaces of isolated SiC, Si 3 N 4 , Al 18 B 4 O 33 , K 2 Ti 6 O 13 and K 2 Ti 8 O 17 ceramic whiskers and the whisker/matrix interfaces in whisker-reinforced aluminium metal matrix composites have been studied by high resolution transmission electron microscopy (HRTEM). We find that the interfacial region at the interfaces depends upon the whisker surface structure of the whiskers, while the interfacial reaction depends upon te structural stability of the whisker surfaces and the matrix chemistry. The Mg segregation at interfaces was the main reason resulting in interfacial reactions in Mg-doped aluminium alloy matrix composites.

Determination of surface roughness of InP (001) wafers by x‐ray scattering

The surface roughness of polished InP (001) wafers were examined by x‐ray reflectivity and crystal truncation rod (CTR) measurements. The root‐mean‐square roughness and the lateral correlation scale were obtained by both methods. The scattering intensities in the scans transverse to the specular reflection rod were found to contain two components. A simple surface model of surface faceting is proposed to explain the experimental data. The sensitivities of the two methods to the surface structure and the role of the resolution functions in the CTR measurements are discussed.

X-RAY-DIFFRACTION ANALYSIS OF SI1-XGEX/SI SUPERLATTICES

Si1−xGex/Si strained‐layer superlattices grown by molecular‐beam epitaxy on Si substrates were investigated by x‐ray double‐crystal diffraction and x‐ray grazing incidence diffraction. Both coherent and incoherent interfaces between the two components of the superlattices were observed. By fitting computer‐simulated double‐crystal x‐ray‐diffraction rocking curves to the experimental data, it is determined that there exist graded variations in both the component thickness ratio t1/t2 (t1 and t2 are the thickness of the Si1−xGex and the Si layers, respectively) and the fraction x in one sample. The x‐ray grazing incidence diffraction experiments reveal a lattice strain relaxation of about 27% in another sample. The lattice relaxation and the influence of variations of x and t1/t2 on the rocking curves are discussed.

Observation of the in-plane spin-dephasing anisotropy in [111]-grown GaAs/AlGaAs quantum well

The electron density and temperature dependent in-plane spin-dephasing anisotropy in [111]-grown GaAs quantum well (QW) has been investigated by time-resolved magneto-Kerr rotation technique. Due to the specific symmetry of [111]-grown quantum well, the in-plane Rashba and linear Dresselhaus effective spin-orbit magnetic field is parallel to each other for electron wave vectors in all directions. However, an obvious in-plane spin-dephasing anisotropy comparing [2¯11] with [01¯1] crystalline orientations has been observed and discussed in this work. Our results demonstrate the innegligible spin dephasing channel through inhomogeneous broadening induced by the out-of-plane non-linear Dresselhaus field, which arises naturally from the C3 symmetry of [111]-grown GaAs QW.

Effect of graded layer on the X-ray double-crystal diffraction rocking curve

The composition gradient in an InAlAs epitaxial layer on InP (0 0 1) substrate has been investigated using an X-ray double-crystal diffraction technique and a computer simulation method. Good agreement has been obtained between theoretical and experimental rocking curves when the correct graded layers are assumed in the samples. The results show that the graded layer introduces very sensitive asymmetric changes in layer peak and interference fringes. The intensities of the interference increase more strongly on the higher or lower angle side, while they are reduced on the other side, and the layer peak shifts to the higher or lower angle direction according to the positive or negative gradient. In all cases, however, the angle separations of the interference fringes do not change if the total thickness of the epilayer is unchanged.