No abstract

Details concernithe relationships between the structural, chemical and catalytic properties o MO nitrides have been elucidated. A series of MO nitride n! catalysts were prepared by the temperature programmed reaction of MoOa with NH3. The structural properties of these nitrides were complex functions

We have employed reflection high energy electron diffraction (RHEED) and high resolution transmission electron microscopy (HREM) to study Cu films grown on hydrogen terminated Si(100) and Si(111) substrates by molecular beam epitaxy. X-ray diffraction and RHEED studies indicate (100) Cu growth on Si(100) and (11 l)Cu growth on Si(111). HREM reveals orientation relationships of [OOl]o,~~ [Ol l]si, (OlO),l] (0ll)si and [i12]c,[j [Ol l]si, (220),,11 (1 li), for Si(100) and Si(1 1 1), respectively. A copper silicide layer forms on Si(100) with deposition and appears to aid in proper lattice matching. No significant interdiffused region was detected in the films deposited on Si(11 l), however, distinct orientational variants were observed in this case.

The crystal structures of Zr2COl~ and HfCo7 intermetallic compounds were examined by transmission electron microscopy using both selected-area and convergent-beam electron diffraction. Results show that both have an orthorhombic crystal structure, space group Pcna. The unit cells of both compounds appear to be comprised of two long-period superlattices in antiphase relation to one another along [001].

We have used high-resolution transmission electron microscopy to resolve the [0001] projected basal plane structure and chirality relationships in boron nitride nanotubes. Evidence for tube growth along both 〈101̄0〉 and 〈112̄0〉 is found. Our results suggest that the 〈112̄0〉 (armchair) tubes form first. Subsequent growth can take the form of a 〈101̄0〉 (zig-zag) tube or additional armchair tubes. In both cases, the additional walls can be accommodated without the need for defect formation for circumferential tube closure. These results suggest that real boron nitride tubes may, in practice, realize their inherently high modulus and display less variation of mechanical properties than tubes comprised of carbon.