We describe in situ synthesis and characterization of single-walled BN nanotubes terminated by fullerenelike structures using electron-cyclotron resonance nitrogen and electron beam boron sources onto polycrystalline tungsten substrates. Detailed comparisons of experimental high-resolution electron microscopy images and simulations based upon molecular models show a dominance of kinks and bends involving fourfold and eightfold ring structures as against fivefold or sevenfold which have been found with carbon. Analysis of the structures as a function of film thickness indicates that they are growing by addition of atoms to the exposed ends of single sheets, not at the substrate-nanostructure interface.

A technique is described for the model-independent analysis of x-ray or neutron reflectivity data. Rather than trying to find just one optimum solution, the idea is to find the set of solutions that are feasible. The approach is based on inversion of the missing phase information using a feasible set approach coupled with a genetic algorithm search for the set of solutions. It does not require previous knowledge of the chemical constituents or any type of initial model, thus adding a higher degree of objectivity to the analysis. The algorithm is tested on both simulated data and observed data. Issues regarding inversion problems and multisolution algorithms, such as the uniqueness of the solutions, are also briefly discussed.

Based on results from recent structural studies and an overview of the literature, we propose surface phase diagrams for the Au–Si(111) system in the supermonolayer regime and for the Ag–Ge(111) system in the submonolayer region. In addition, time–temperature–transformation (T–T–T) curves are proposed to represent the metastable structures present in surface phase systems.

High-energy electrons (300keV to 1MeV) in a transmission electron microscope have been used to cause ballistic atomic displacements in hexagonal boron nitride. The high-resolution imaging capabilities of the TEM have allowed us to study the effect of the atomic displacements on the crystal structure of the BN. We report the formation of nanoarches — fullerene structures consisting of half of a BN nanotube capping the ends of the planar BN graphitic sheets. To form a basis of comparison between the high-energy electron bombardment and the ion bombardment typically used for cubic BN film growth, TRIM calculations were also performed to simulate Ar+ ion bombardment of hexagonal BN. A model is presented, indicating a process through which the nanoarches can serve as nucleation sites for the cubic phase of BN. The nucleation model is consistent with current experimental reports on the formation of cubic BN thin films.

Surface structure analysis is an important area of research, and in recent years notable advances have been made in this field, both in improved techniques for studying surfaces and in methods of analyzing them. This review aims to summarize the techniques available, particularly those relating to electron microscopy, and also to outline one of the newest areas of development, the application of direct methods to surface structure analysis.

For the first time, during the investigation of the Ag submonolayer on the Ge(111) system, large, independent domains of the Ge(111)-(3×1)Ag phase were imaged and investigated. Previous studies have reported it only as small insets between Ge(111)-(4×4)Ag and Ge(111)-c(2×8) domains. The transmission electron diffraction data were analyzed using a Direct Methods approach and "heavy-atom holography," with the result of an atomic model of the structure similar to that of Ge(111)-(3×1)Ag.

The crystal structures of two previously unknown bulk phases in the Ga-In-Sn-O system have recently been solved using direct methods applied to electron diffraction intensities. In both cases, phasing of dynamical diffraction intensities clearly indicated the positions of O atoms in the crystal structures. It is shown here that a correlation between the dynamical diffraction amplitudes and the Fourier components of |1 - ψ(r)| enables direct methods using dynamical intensities to restore structural information present in |1 - ψ(r)|. Both the presence of atom-like peaks in |1 - ψ(r)| as well as the emphasis of light atoms are explained using electron channeling theory. Similar results can be expected for any structure consisting of well resolved atomic columns parallel to the zone-axis direction for which data are recorded. With (Ga, In) 2 SnO 5 as a model structure, it is shown that the combination of strongly dynamical electron diffraction with direct methods is a powerful technique for detecting light-atom positions in bulk inorganic crystal structures without the need to grow single crystals.

The formation of epitaxial nanotubes (nanoarches) on the surface of hexagonal BN (h-BN) during electron irradiation is reported. In addition to implications in terms of understanding fullerene based structures, we suggest that these act as the nucleation sites for cubic BN (c-BN) growth and may lead to improved film growth. We also report a strong dependence upon the microscope vacuum, which may be critical in understanding irreproducibility in film growth.

This paper reviews recent progress in the application of Direct Methods to solve surface structures using surface X-ray or transmission electron diffraction data. The basic ideas of (crystallographic) Direct Methods are presented, as well as the additional problems posed by trying to apply them to surfaces and how they connect to the mathematical theory of projections. Surface crystallography notation is presented, which differs from the widely used LEED notation in that it emphasizes the surface symmetry. This is followed by a description of methods for structure completion and refinement, followed by applications to some experimental systems, both those where the structure was previously known (calibration tests) and a few where it was not, concluding with problems and limitations.

Results concerning the operation of a new ultrahigh vacuum (UHV) ion-beam assisted deposition system for in situ investigation of ultrahard thin films are reported. A molecular beam epitaxy (MBE) chamber attached to a surface science system (SPEAR) has been redesigned for deposition of cubic-boron nitride thin films. In situ thin film processing capability of the overall system is demonstrated in preliminary studies on deposition of boron nitride films on clean Si (001) substrates, combining thin film growth with electron microscopy and surface characterization, all in situ.

The crystal structures of two previously unknown bulk phases in the Ga-In-Sn-O system have recently been solved using direct methods applied to electron diffraction intensities. In both cases, phasing of dynamical diffraction intensities clearly indicated the positions of O atoms in the crystal structures. It is shown here that a correlation between the dynamical diffraction amplitudes and the Fourier components of \1 -psi(r)\ enables direct methods using dynamical intensities to restore structural information present in \1 - psi(r)\. Both the presence of atom-like peaks in \1 - psi(r)\ as well as the emphasis of light atoms are explained using electron channeling theory. Similar results can be expected for any structure consisting of well resolved atomic columns parallel to the zone-axis direction for which data are recorded. With (Ga, In)(2)SnO5 as a model structure, it is shown that the combination of strongly dynamical electron diffraction with direct methods is a powerful technique for detecting light-atom positions in bulk inorganic crystal structures without the need to grow single crystals.

Recent developments have shown that it is possible to obtain information at the atomic level from surfaces, in some cases to one Angstrom or better resolution. This paper reviews these developments, discusses their current limitations, and points out that they can be used as readily for buried interfaces.

Recent work has demonstrated that high resolution electron microscopy in plan-view imaging mode is capable of directly imaging surfaces at a resolution of better than 2 Å. For the particular case of the Si (111) 7x7 surface, we have been able to image not only the adatoms visible in STM images, but all the atoms in the top three atomic layers including the dimers. The potential applications of this approach and its limitations will be discussed.