A method based on a controlled solid-solid reaction was used to fabricate heterostructures between single-walled carbon nanotubes (SWCNTs) and nanorods or particles of silicon carbide and transition metal carbides. Characterization by high-resolution transmission electron microscopy and electron diffraction indicates that the heterostructures have well-defined crystalline interfaces. The SWCNT/carbide interface, with a nanometer-scale area defined by the cross section of a SWCNT bundle or of a single nanotube, represents the smallest heterojunction that can be achieved using carbon nanotubes, and it can be expected to play an important role in the future fabrication of hybrid nanodevices.

We report the first experimental evidence of the cyclic form of ozone, found in three air stable surface reconstructions of MgO (111) annealed above 1450 ± C. The MgO ͑111͒-͑ p 3 3p 3 ͒R30 ± surface consists of equilateral oxygen trimers while the MgO ͑111͒-͑2 3 2͒ and MgO ͑111͒-͑2 p 3 3 2 p 3 ͒R30 ± surfaces are periodic arrangements of trimers and single oxygen atoms. The oxygen trimers appear to be centered over underlying Mg atoms. The structures fit transmission electron diffraction data better than neutral plane faceting based models proposed for the polar MgO (111) surface. [S0031-9007(98)07807-7] PACS numbers: 61.14.Rq, 61.16.Bg, 68.35.BsThe stability of polar oxide surfaces has long been a problematic question in surface science. A bulk terminated polar surface has an infinite surface energy because alternating layers of oppositely charged ions produce a large dipole moment perpendicular to the surface [1]. For the model MgO (111) polar oxide surface theoretical results have pointed to two similar solutions for this problem: microscopic faceting into neutral ͕100͖ planes upon annealing [2-5] and surface reconstructions, which are essentially faceting to neutral planes but on an atomic scale [5][6][7].The microscopic faceting model has long been supported by low energy electron diffraction (LEED) and scanning electron microscopy (SEM) of 1200 ± C annealed MgO (111) surfaces [8,9] which revealed micron-sized triangular facets. These facets were interpreted to be neutral ͕100͖ planes. It has been recently shown, however, that these facets are much shallower vicinal ͕111͖ planes introduced by acid etching in sample preparation [10]

The c(6x2) is a reconstruction of the SrTiO 3 (001) surface that is formed between 1050-1100 o C in oxidizing annealing conditions. This work proposes a model for the atomic structure for the c(6x2) obtained through a combination of results from transmission electron diffraction, surface x-ray diffraction, direct methods analysis, computational combinational screening, and density functional theory. As it is formed at high temperatures, the surface is complex and can be described as a short-range ordered phase featuring microscopic domains composed of four main structural motifs. Additionally, non-periodic TiO 2 units are present on the surface. Simulated scanning tunneling microscopy images based on the electronic structure calculations are consistent with experimental images.

The connection between the crystallographic phase problem and the feasible set approach is explored. It is argued that solving the crystallographic phase problem is formally equivalent to a feasible set problem using a statistical operator interpretable via a log-likelihood functional, projection onto the non-convex set of experimental structure factors coupled with a phase-extension constraint and mapping onto atomic positions. In no way does this disagree with or dispute any of the existing statistical relationships available in the literature; instead it expands understanding of how the algorithms work. Making this connection opens the door to the application of a number of well developed mathematical tools in functional analysis. Furthermore, a number of known results in image recovery can be exploited both to optimize existing algorithms and to develop new and improved algorithms.

The atomic structure of the Au 6×6 on Si(111) phase has been determined using direct methods and surface X-ray diffraction data. This surface structure is very complicated, with 14 independent gold atoms, relaxations in 24 independent silicon sites and three partially occupied gold sites. In one sense the structure can be described as microdomains of the parent ǰ3×ǰ3 Au on Si(111) structure. A better description is in terms of a tiling of incomplete pentagonal and trimer units, essentially a pseudopentagonal glass. In terms of these structural units it is possible to explain all the gold structures in the coverage range 0.8-1.5 monolayers as pseudo-glasses with strong short-range order but varying degrees of long-range order.