C. Colliex

Aligned Carbon Nanotube Arrays Formed by Cutting a Polymer Resin—Nanotube Composite

A simple technique is described here that produces aligned arrays of carbon nanotubes. The alignment method is based on cutting thin slices (50 to 200 nanometers) of a nanotube-polymer composite. With this parallel and well-separated configuration of nanotubes it should be possible to measure individual tube properties and to demonstrate applications. The results demonstrate the nature of rheology, on nanometer scales, in composite media and flow-induced anisotropy produced by the cutting process. The fact that nanotubes do not break and are straightened after the cutting process also suggests that they have excellent mechanical properties.

Doping Graphitic and Carbon Nanotube Structures with Boron and Nitrogen

Composite sheets and nanotubes of different morphologies containing carbon, boron, and nitrogen were grown in the electric arc discharge between graphite cathodes and amorphous boron-filled graphite anodes in a nitrogen atmosphere. Concentration profiles derived from electron energy-loss line spectra show that boron and nitrogen are correlated in a one-to-one ratio; core energy-loss fine structures reveal small differences compared to pure hexagonal boron nitride. Boron and carbon are anticorrelated, suggesting the substitution of boron and nitrogen into the carbon network. Results indicate that singlephaase CyBxNx as well as separated domains (nanosize) of boron nitride in carbon networks may exist.

Growth morphologies during cobalt-catalyzed single-shell carbon nanotube synthesis

Abstract We report interesting growth morphologies produced during the electric arc-discharge between a graphite cathode and a composite cobalt—graphite anode, which includes the abundant formation of single-shell carbon nanotubes of 1–2 nm diameter. As the pressure inside the chamber and the cobalt content of the electrode are varied these “carbon monotubes” are formed in bundles and in high density under certain conditions in the soot, webs and string-like structures that decorate the chamber and also on a collaret that forms around the conventional deposit containing multi-shell nanotubes. We present high-resolution transmission electron microscopy images of these structures and propose conditions that promote single-tube growth. We also notice, in some cases, novel formation of regularly spaced cobalt particles enclosed in graphitic capsules and surrounded by sheaths of soot.

Boron nitride nanotubes

Abstract Pure boron nitride (BN) nanotubes have been synthesised by arc discharge between HfB2 electrodes in a nitrogen atmosphere. The high resolution electron microscopy (HREM) observations reveal that this route leads to the formation of highly crystalline tubes with reduced numbers of layers, including tubes with only one or two layers. These nanotubes are found to be chiral or non-chiral, however, a preference towards the armchair and zig-zag configurations is suggested. Electron energy loss spectroscopy yields a B:N ratio of approximately one and a perfect chemical homogeneity. Tubes are empty and closed at their ends by flat layers perpendicular to the tube axis. A tip model consisting of a triangular facet based on three 120 ° disclinations and preserving BN bonds in the honeycomb network accounts for the observations. Finally, preliminary electron irradiation experiments on these tubes reveal a specific behaviour. BN tubes transform into aggregates of small cages with diameter between 0.5 and 0.8 nm. These diameters suggest that these shells might be B12N12, B16N16 and B28N28 fullerenes which were predicted to be magic clusters.Boron nitride nanotubes are prepared by a process which includes: (a) creating a source of boron vapor; (b) mixing the boron vapor with nitrogen gas so that a mixture of boron vapor and nitrogen gas is present at a nucleation site, which is a surface, the nitrogen gas being provided at a pressure elevated above atmospheric, e.g., from greater than about 2 atmospheres up to about 250 atmospheres; and (c) harvesting boron nitride nanotubes, which are formed at the nucleation site.

Improving energy resolution of EELS spectra: an alternative to the monochromator solution

In this paper, we propose a numerical method which can routinely improve the energy resolution down to 0.2-0.3eV of electron energy-loss spectra acquired in a transmission electron microscope. The method involves measurement of the point-spread function (PSF) corresponding to the spectrometer aberration and to the incident energy spread, and then an inversion of this PSF so as to restore the spectrum. The chosen algorithm is based on an iterative calculation of the maximum likelihood solution known to be very robust against small errors in the PSF used. Restorations have been performed on diamond and graphite C-K edges acquired with an initial energy resolution of around 1eV. After reconstruction, the sharp core exciton lines become clearly visible for both compounds and the final energy resolution is estimated to be about 200-300meV. In the case of graphite, restorations involving both energy resolution and angular resolution have been successfully conducted. Finally, restorations of Fe L(2,3) and O-K edges measured for various iron oxides will be shown.

Carbon nitride nanotubulite – densely-packed and well-aligned tubular nanostructures

Tubular carbon nitride (CNx, x=0.01–0.32) nanoparticles were successfully synthesized by d.c. magnetron sputtering. These tubes were grown in a highly packed form perpendicularly on a sodium chloride substrate. Their number density is estimated to be ∼1×104 per μm2 and is constant over macroscopic regions. Sub-nanometer scale chemical mapping shows that the nitrogen to carbon atomic ratio is rather constant across these tubes. This successful synthesis of a nanotubulite – made of a rather compact aggregation of tubular nanoparticles – could facilitate experimental approaches to measure mechanical or electrical transport properties of such nanotubes and to open the way to variable nanotube applications.

About the use of electron energy-loss spectroscopy for chemical mapping of thin foils with high spatial resolution

Core-loss energy-filtered images have been suggested as a substantial contribution to the development of an analytical electron microscope with high spatial resolution. However, for many problems in complex materials, the characteristic signals can only be detected as slope variations of the continuously decreasing background. Therefore further data processing techniques are needed to extract satisfactorily the true chemical information. A discussion of the present limits and of the existing solutions clearly shows that the method can only be developed at the expense of more elaborate systems such as simultaneous detection channels (quite well suited to the STEM instruments). Typical numbers for realistic situations illustrate the field of application of the technique.

Radially modulated nitrogen distribution in CNx nanotubular structures prepared by CVD using Ni phthalocyanine

Abstract Chemical mapping with sub-nanometer-scale resolution across the CN x tubular nanostructures synthesized by chemical vapor deposition (CVD) has revealed nitrogen enrichment at the periphery and at the inner hollow while these tubules do not contain much nitrogen in the graphitic layers. This result indicates that the solubility of nitrogen in the graphitic layers is slight, at least under the catalytic CVD condition. It is supposed that the nitrogen atoms are bonded to the edges of layers, otherwise they form amorphous carbon nitride in the nanotube hollow.

Two-Dimensional Quasistatic Stationary Short Range Surface Plasmons in Flat Nanoprisms

We report on the nanometer scale spectral imaging of surface plasmons within individual silver triangular nanoprisms by electron energy loss spectroscopy and on related discrete dipole approximation simulations. A dependence of the energy and intensity of the three detected modes as function of the edge length is clearly identified both experimentally and with simulations. We show that for experimentally available prisms (edge lengths ca. 70 to 300 nm) the energies and intensities of the different modes show a monotonic dependence as function of the aspect ratio of the prisms. For shorter or longer prisms, deviations to this behavior are identified thanks to simulations. These modes have symmetric charge distribution and result from the strong coupling of the upper and lower triangular surfaces. They also form a standing wave in the in-plane direction and are identified as quasistatic short range surface plasmons of different orders as emphasized within a continuum dielectric model. This model explains in simple terms the measured and simulated energy and intensity changes as function of geometric parameters. By providing a unified vision of surface plasmons in platelets, such a model should be useful for engineering of the optical properties of metallic nanoplatelets.

Morphology control of the supported islands grown from soft-landed clusters

Abstract The morphology of islands grown on surfaces from soft-landed clusters has been investigated by electron microscopy. Compact islands have been observed on amorphous carbon surfaces, whereas an evolution from compact to ramified shapes occurs on graphite surfaces as the mean size of deposited clusters increases. Moreover, by increasing the surface defect density on graphite, a continuous variation of the island morphology is observed, from extended ramified shapes to small compact shapes. In order to account for the island morphologies observed, we propose a crude model involving a competition between the time for aggregated clusters to coalesce and the time interval between successive arrivals of clusters to grow the islands. It shows that there exists a critical island size R 0 dividing island shapes into compact shapes for R R 0 and into ramified shapes for R > R 0 . This critical size R 0 varies as a function of the incident cluster size. Relying on our experimental results, we show how the morphology of the islands can be controlled by the size of the incident clusters and the presence of surface defects.