Morphology--composition correlations in carbon nanotubes synthesised with nitrogen and phosphorus containing precursors.

We have correlated the elemental composition with the structure of multi-wall carbon nanotubes synthesised with nitrogen and phosphorus containing precursors and identified two chemically distinct dominant morphologies. The first type are cone-structured tubes and the second are nanotubes with fewer walls which can accommodate N2 gas along their inner channel and contain up to ten times more nitrogen than the cone-structured nanotubes. Phosphorus was present in the catalyst particles but was not detected within the walls of either type of nanotube.

Subangstrom edge relaxations probed by electron microscopy in hexagonal boron nitride.

Theoretical research on the two-dimensional crystal structure of hexagonal boron nitride (h-BN) has suggested that the physical properties of h-BN can be tailored for a wealth of applications by controlling the atomic structure of the membrane edges. Unexplored for h-BN, however, is the possibility that small additional edge-atom distortions could have electronic structure implications critically important to nanoengineering efforts. Here we demonstrate, using a combination of analytical scanning transmission electron microscopy and density functional theory, that covalent interlayer bonds form spontaneously at the edges of a h-BN bilayer, resulting in subangstrom distortions of the edge atomic structure.

Boron-mediated nanotube morphologies.

The "doping" of carbon nanotubes with heteroatoms is an established method of controlling their properties. However, variations in heteroatom concentration in multiwalled carbon nanotubes (MWCNTs) tend to produce nanotubes with different morphologies, and hence varying properties, within the same sample. Electron energy loss spectroscopy in conjunction with imaging using a scanning transmission electron microscope (STEM) is a powerful tool to precisely map the spatial variation and bonding state of heteroatoms, e.

Point defect characterization in HAADF-STEM images using multivariate statistical analysis.

Quantitative analysis of point defects is demonstrated through the use of multivariate statistical analysis. This analysis consists of principal component analysis for dimensional estimation and reduction, followed by independent component analysis to obtain physically meaningful, statistically independent factor images. Results from these analyses are presented in the form of factor images and scores.

Synthesis and molecular structures of mononitrosyl (N2S2)M(NO) complexes (M = Fe, Co).

A series of tetragonally distorted square pyramids of formula N2S2M(NO) (M = Fe, Co) is prepared and characterized by nu(NO) IR and EPR spectroscopies, magnetism and electrochemical properties, as well as solid-state crystal structure determinations. While the nu(NO) IR frequencies and the angleM-N-O angles indicate differences in the electronic environment of NO consistent with the Enemark-Feltham notation of [Fe(NO)]7 and [Co(NO)]8, the reduction potentials, assigned to [Fe(NO)]7 + e- <==> [Fe(NO)]8 and [Co(NO)]8 + e- <==> [Co(NO)]9 respectively, are very similar, and in cases identical, for most members of the series. Coupled with the potential for the M(NO) units to breathe out of and into the N2S2 core plane are unique S-M-N-O torsional arrangements and concomitant pi-bonding interactions which may account for the unusual coherence of reduction potentials within the series.