Jean-Christophe Charlier

Identification of electron donor states in N-doped carbon nanotubes

Nitrogen-doped carbon nanotubes have been synthesized using pyrolysis and characterized by scanning tunneling spectroscopy and transmission electron microscopy. The doped nanotubes are all metallic and exhibit strong electron donor states near the Fermi level. Using tight-binding and ab initio calculations, we observe that pyridine-like N structures are responsible for the metallic behavior and the prominent features near the Fermi level. These electron rich structures are the first example of n-type nanotubes, which could pave the way to real molecular heterojunction devices.

Electronic and optical properties of pristine and oxidized borophene

Borophene, a two-dimensional monolayer of boron atoms, was recently synthesized experimentally and was shown to exhibit polymorphism. In its closed-packed triangular form, borophene is expected to exhibit anisotropic metallic character with relatively high electron velocities. At the same time, very low optical conductivities in the infrared-visible light region were predicted. Based on its promising electronic transport properties and its high transparency, borophene could become a genuine lego piece in the 2D materials assembling game known as the van der Waals heterocrystal approach. However, borophene is naturally degraded in ambient conditions and it is therefore important to assess the mechanisms and the effects of oxidation on borophene monolayers. Optical and electronic properties of pristine and oxidized borophene are here investigated by first-principles approaches. The transparent and conductive properties of borophene are elucidated by analyzing the electronic structure and its interplay with light. Optical response of borophene is found to be strongly affected by oxidation, suggesting that optical measurements can serve as an efficient probe for borophene surface contamination.

Advances on the growth and properties of N- and B-doped carbon nanotubes

The synthesis of crystalline C3N4 and CN nanotubes, predicted to be super-hard and metallic respectively, remains a challenge for the future. However, small quantities of nitrogen (<15%) have been incorporated into carbon nanotubes and/or filaments. Particular attention will be focused on efficient self-assembly pyrolytic routes to large arrays (2.5 cm2) of aligned CNx nanotubes/nanofibers (15–80 nm od and <100 microns length). These routes include hydrocarbon decomposition over preformed metal-cluster substrates and the pyrolysis organometallic compounds. State-of-the-art EELS that two N bonding types within the hexagonal C network occur. We note that it is difficult to generate highly ordered structures in which large concentrations of N are incorporated into the network [e.g. C9Nx (x⩽1)]. However, these ‘hollow’ fibers do not easily break upon bending and may behave as shock absorbing fillers in the fabrication of robust composites. The N-doped nanostructures have also been studied using tunneling spec...