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ABSTRACT: 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.
Physical Review Letters 04/2001; 86(11):2385-7. · 7.37 Impact Factor
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ABSTRACT: 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.
Microscopy Research and Technique 09/1999; 46(3):160-77. · 1.79 Impact Factor
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ABSTRACT: 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.
Microscopy Research and Technique 09/1998; 42(4):295-301. · 1.79 Impact Factor
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ABSTRACT: 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. © 1998 American Institute of Physics.
Applied Physics Letters 01/1998; 72(3):314-316. · 3.84 Impact Factor
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ABSTRACT: 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 diffrac-tion 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 ampli-tudes and the Fourier components of |1 À 2(r)| enables direct methods using dynamical intensities to restore structural information present in |1 À 2(r)|. Both the presence of atom-like peaks in |1 À 2(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.
Acta Cryst. 01/1998;
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ABSTRACT: High-energy electrons (300 keV to 1 MeV) 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.
Diamond and Related Materials.
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ABSTRACT: 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.
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ABSTRACT: 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.
Surface Science.
