Annick Loiseau

Large-scale production of single-walled carbon nanotubes by the electric-arc technique

Single-walled carbon nanotubes (SWNTs) offer the prospect of both new fundamental science and useful (nano)technological applications. High yields (70–90%) of SWNTs close-packed in bundles can be produced by laser ablation of carbon targets. The electric-arc technique used to generate fullerenes and multi-walled nanotubes is cheaper and easier to implement, but previously has led to only low yields of SWNTs,. Here we show that this technique can generate large quantities of SWNTs with similar characteristics to those obtained by laser ablation. This suggests that the (still unknown) growth mechanism for SWNTs must be independent of the details of the technique used to make them. The ready availability of large amounts of SWNTs, meanwhile, should make them much more accessible for further study.

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

Photooxidation and quantum confinement effects in exfoliated black phosphorus

Thin layers of black phosphorus have recently raised interest owing to their two-dimensional (2D) semiconducting properties, such as tunable direct bandgap and high carrier mobilities. This lamellar crystal of phosphorus atoms can be exfoliated down to monolayer 2D-phosphane (also called phosphorene) using procedures similar to those used for graphene. Probing the properties has, however, been challenged by a fast degradation of the thinnest layers on exposure to ambient conditions. Herein, we investigate this chemistry using in situ Raman and transmission electron spectroscopies. The results highlight a thickness-dependent photoassisted oxidation reaction with oxygen dissolved in adsorbed water. The oxidation kinetics is consistent with a phenomenological model involving electron transfer and quantum confinement as key parameters. A procedure carried out in a glove box is used to prepare mono-, bi- and multilayer 2D-phosphane in their pristine states for further studies on the effect of layer thickness on the Raman modes. Controlled experiments in ambient conditions are shown to lower the A(g)(1)/A(g)(2) intensity ratio for ultrathin layers, a signature of oxidation.

Plasma enhanced chemical vapour deposition carbon nanotubes/nanofibres - How uniform do they grow?

The ability to grow carbon nanotubes/nanofibres (CNs) with a high degree of uniformity is desirable in many applications. In this paper, the structural uniformity of CNs produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications. When single isolated CNs were deposited using this technology, the structures exhibited remarkable uniformity in terms of diameter and height (standard deviations were 4.1 and 6.3% respectively of the average diameter and height). The lithographic conditions to achieve a high yield of single CNs are also discussed. Using the height and diameter uniformity statistics, we show that it is indeed possible to accurately predict the average field enhancement factor and the distribution of enhancement factors of the structures, which was confirmed by electrical emission measurements on individual CNs in an array.

Carbon nanotubes: The solar approach

Abstract Using the same experimental set-up as for the solar production of fullerenes, we can also produce carbon nanotubes by direct vaporization of a mixture of powdered carbon and catalyst (Co, Ni, Y). The structure of the nanotubes is strongly dependent on the experimental conditions (pressure and flow rate of Ar gas) and we can obtain either multi-walled nanotubes or ropes of single-walled nanotubes.

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.

Synthesis of long carbon nanotubes filled with Se, S, Sb and Ge by the arc method

Abstract The possibility of forming ‘nanowires’ in carbon nanotubes by the arc-discharge method was investigated for the elements of group B which are of interest in the semiconductor field. Fourteen elements were studied: Zn, Cd (IIB); B, Al, In (IIIB); Si, Ge, Sn, Pb (IVB); Sb, Bi (VB); S, Se, Te (VIB). It was found that long continuous nanowires in carbon nanotubes are produced in large quantities for four elements: Se, S, Sb and Ge.

Boron-nitride and boron-carbonitride nanotubes: synthesis, characterization and theory

We present in this review a joint experimental and theoretical overview of the synthesis techniques and properties of boron-nitride (BN) and boron-carbonitride (BCN) nanotubes. While their tubular structure is similar to that of their carbon analogues, we show that their electronic properties are significantly different. BN tubes are wide band gap insulators while BCN systems can be semiconductors with a band gap in the visible range.

Nano-mechanical cutting and opening of single wall carbon nanotubes

Abstract We pioneered a simple and soft mechanical cutting process for single wall carbon nanotubes involving diamond particles as abrasive material. High resolution transmission electron microscopy observation reveals shortened nanotubes always organised in bundles. Micrograph analysis allows us to determine the breaking mechanism of the bundles. The average nanotube lengths, estimated using AFM images, are ranging from 300 to 700 nm. Adsorption measurements show a topological modification of the material with the presence of new microporosities ranging in the average nanotube diameter.

Raman studies on single walled carbon nanotubes produced by the electric arc technique

Carbon single walled nanotubes (SWNTs) have been produced in high yields using the electric arc technique. TEM studies show that the SWNTs have a narrow diameter distribution around an average value of 1.3 nm. In this paper, we focus on the characterization of these samples by high resolution Raman spectroscopy (HRRS). The presence of large amounts of SWNTs in the samples induces a very rich structure in the Raman spectra, typical for this class of carbonaceous material. Armchair tubes with (8,8) to (12,12) geometry can be detected, in agreement with the narrow diameter distribution observed by TEM measurements. The ability of HRRS as a highly sensitive fingerprint technique in identifying SWNTs with different diameters and geometries is discussed.