Cu-Nb wire composites with 0.105, 0.148, and 0.182 volume fraction of Nb filaments were produced in situ and their mechanical properties measured as a function of filament size and interfilament spacing. The yield stress and the ultimate tensile strength increased with both niobium volume fraction and overall composite reduction. At room temperature, the ultimate tensile strength of the Cu–18.2 vol% Nb composite reduced by 99.999% in cross-sectional area (100–200 Å filament thickness) reached the value of 2230 MN/m2 (323 ksi) and further increased to 2850 MN/m2 (413 ksi) when measured at 77 °K. These values are higher by a factor of 4 than the values predicted by the rule of mixtures based on the highest reported strength of both niobium and copper. The composite strength is as high as that of the best copper whiskers and is shown to closely approach the theoretical strength of the material. The anomalous increase in strength despite the low volume fraction of reinforcing filaments suggests that the filaments act primarily as barriers to the motion of matrix dislocations and that the strength of the filamentary material is only of secondary importance. This hypothesis is supported by microstructural obsevations (transmission and scanning electron microscopy) which reveal the deformation modes during composite fabrication and mechanical testing. The excellent transport properties (in both the normal and superconducting state) make these composites attractive as conductors for high-stress applications.

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Nanoindentation measurements of electrophoretically deposited films of colloidal CdSe nanocrystals, capped by organic ligands, show the films have an elastic stiffness modulus of approximately 10 GPa and exhibit viscoplasticity. This mechanical response suggests polymeric features that are attributable to the ligands. After particle cross-linking and partial ligand removal, the films exhibit more features of granularity.

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The mechanical stability of nanocrystal films is critical for applications, yet largely unexplored. Raman microprobe analysis used here to probe the nanocrystal cores of thick, fractured electrophoretically deposited films of 3.2 nm diameter CdSe nanocrystals measures approximately 2.5% in-plane tensile strain in cores of unfractured films. The crack dimensions determine the overall in-plane film strain, approximately 11.7%, and the film biaxial modulus, approximately 13.8 GPa, from which the biaxial modulus of the trioctylphosphine oxide ligand matrix is inferred, approximately 5.1 GPa.

Thermally grown Si(001)/SiO2 samples were studied by x-ray reflectivity. Fits of model electron density profiles to the data reveal the existence of an interfacial layer at the Si/SiO2 interface up to 15-Å-thick, with density higher than either the crystalline Si or the main oxide layer. This density of the layer is reduced by a postoxidation anneal.

Single-crystal silicon films grown at 400°C on Si(l 1 l):B(V3x V5) are rotated 180° about the surface normal with respect to the substrate. We discuss a mechanism based on chemical effects due to the boron (VJx VJ) reconstruction that favors the film to grow with a ZMype (twin) orientation. Films grown on the SiCl 1 l)-(7x7) reconstruction under identical conditions have the ^-type (untwinned) orientation. PACS numbers: 68.35.Bs, 61.16.Di, 68.35.DvIn all prior cases of homoepitaxy, the epilayer has been crystallographically aligned with the substrate, irrespective of the surface reconstruction, impurity segregation, or other effects at the substrate surface. The original surface reconstruction has always reordered into an unreconstructed interface between the substrate and film, since epitaxy requires a sufficiently high temperature for surface diffusion to occur. Here, we describe Si homoepitaxial growth on the boron VJxVJ surface of SiC111) with j monolayer of boron. At low temperature, the surface reconstruction is partly preserved, buried under an epilayer, and the homoepitaxial layer grows rotated by 180° with respect to the substrate. Tung et al. x have demonstrated rotated heteroepitaxial films. We will use their notation; if the substrate orientation is denoted as "^-type," the "ZMype" orientation corresponds to a layer rotated by 180° about the normal (111) direction.To our knowledge this is the first example of homoepitaxial growth with the overlayer not crystallographically aligned with the substrate. We show experimentally that this phenomenon is critically sensitive to the presence of boron at the original interface during growth, although after growth boron may be in-diffused with no change in film orientation. Modeling suggests that strain effects cannot account for this phenomena. We suggest that the stabilization of the twin boundary interface is related to chemical (electronic) effects which favor a wurtzite stacking at the VJxVJ interface.Samples were prepared in a molecular-beam-epitaxy (MBE) chamber equipped with a quartz-crystal thickness monitor, an electron-gun evaporator to deposit silicon, and a Knudsen cell to deposit boron from HBO2. Low-energy electron diffraction (LEED) and Auger analysis were performed in situ, and x-ray diffraction, transmission electron microscopy (TEM), Rutherford backscattering spectroscopy, nuclear reaction analysis, and Hall-effect measurements were done after removing samples from the MBE chamber. Surfaces were prepared by chemical growth of a thin protective oxide layer before transferring into the vacuum system. The boron VJxVJ surface reconstruction was prepared either by surface segregation of y monolayer (ML) of boron from boron-implanted samples at 900-1000°C, or by deposition of boron onto /?-type samples from HBO2 while the sample was held at 750°C. The surface structure thus formed is unique to the SiCl 11)/B system since boron occupies a subsurface site in a fivefold-coordinated substitutional site under a silicon adatom. 2 " 4 Silicon films of 350...