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The challenge during the characterization of nanostructures is in extracting consistent local and spatially varying information from the structure and correlating it to the new physics that appears at the nanoscale. Recent years have seen exciting advances in imaging and spectroscopy techniques that can achieve this goal. The techniques offer the possibility to directly investigate local properties of materials with sub-nanometre spatial resolution. In this paper we review, from the perspective of our own contributions to the field of carbon nanostructures, recent advances in the application of nanoanalysis. Complementary techniques of spatially resolved electron, and scanning tunneling microscopy and spectroscopy, can be used to characterize and correlate the structure, topology, chemistry and electronic properties of nanostructures. Often the interpretation of the data needs to come from comparison with adequate theoretical models.

Metallic nanocrystals such as cobalt or gold are encapsulated by spherical graphitic shells under high-temperature electron irradiation. The irradiation promotes a heavy contraction of the carbon onions. The contraction forces the metal atoms to migrate outwards through the shells, even without further irradiation. This leads to a gradual but complete displacement of the encapsulated crystals. In-situ observation in an electron microscope allows shrinkage of the encapsulated crystals and migration of the atoms through the shells to be monitored. The experiment shows that spherically curved graphene layers are permeable to metal atoms.

Rate equations for the generation and recombination of vacancies and self-interstitial atoms in a spherical bucky onion under electron irradiation are proposed. They are used to study the temporal development of the point defect concentrations in different shells of onions. The self-interstitial concentration was found to remain low and to be only slightly enriched near the onion centre. The loss of atoms from the outer surface of the bucky onions by sputtering acts as a vacancy source for the whole onion. Irradiation-induced diffusion leads to a net flux of vacancies towards the onion core. The coupling between neighbouring shells necessary for this radial diffusion can be described by the concept of intermediate shells introduced here.

Electron irradiation-induced basal plane disordering in single- and multi-shell carbon nanotubes and onions is found to be inhibited at irradiation temperatures above 300°C. Irradiation-induced defects anneal out due to the thermally activated migration of interstitials at elevated temperatures and leave behind perfectly coherent shells of high tensile stability. Continuous loss of atoms as a result of sputtering induces a surface tension which can be identified as the origin of the formation and self-compression of spherical concentric-shell carbon onions.

Except for atomistic models of individual carbon nanotube growth, there is still no precise understanding of the large scale deposition of carbon during the arc discharge. We study the microstructure of cathode deposits in detail using scanning electron microscopy, focusing on two distinct regimes found in the deposits having different large scale morphology. The shell grown circumferentially consists of extended graphite layers with preferred orientation, and the structure reveals close similarity to pyrolitic graphite. The core region is a porous assembly of nanotubes and nanoparticles. We conclude that closed nanostructures self-assemble from a dense carbon vapor, whereas pyrographitic shell grows by continuous deposition on exposed substrates.

The synthesis of BCN nanotubes and boron doped (1 to 5 at.% B) carbon nanotubes is achieved by an electric arc-discharge between an anode made of homogeneous BC 4 N and a cathode made of graphite. The BC 4 N anode is prepared by pyrolysis of polymer precursors. The effect of boron doping is seen to increase the tube lenghts up to 100 μm and to improve graphitization. Boron and nitrogen are enriched at the surfaces of tubes with overall BCN composition. The observed structure of BCN tubes consists of concentric cylinders of BC 2 N and pure carbon.

SEVERAL techniques have been developed recently for fabricating nanocomposite structures by filling1–3 carbon nanotubes4,5. Here we show that surface-tension effects can induce the growth of uniform, thin metal oxide filmsa€"sometimes only a monolayer thicka€"on the outside of nanotubes, along with oxide fillings in the internal cavities and thin oxide layers between the concentric shells of the tubes. We report the preparation of such nanotube–oxide composites by annealing a mixture of partially oxidized nanotubes and V2O5 powder in air above the melting point of the oxide. The external coatings of the tubes are crystalline sheets of the V2O5 layer-like structure, which grow with the c axis parallel to that of the nanotube layers. Intercalation of the oxide occurs where there are missing shells in the nanotubes. We also show that the nanotubes can be partially removed by oxidation, leaving behind layered oxide fibres. Given the importance of vanadium oxides as catalysts and functional ceramics, this role of nanotubes as removable templates might lead to useful new kinds of nanostructured materials.

The irradiation-induced self-compression of carbon onions and their transformation to diamond crystals are studied in situ by electron energy loss spectroscopy at high specimen temperature in a high-voltage electron microscope. Plasmon peaks in the low-loss region and the carbon K edge with the near-edge fine structure exhibit characteristic changes during irradiation. The spectra show the increasing electron density and the gradual change from sp 2 to sp 3 character of bonding during the selfcompression of carbon onions. The spectra of the diamond cores correspond closely to those of cubic high-pressure diamonds.

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.