In order to engineer a band gap into graphene, covalent bond-forming reactions can be used to change the hybridization of the graphitic atoms from sp 2 to sp 3 , thereby modifying the conjugation length of the delocalized carbon lattice; similar side-wall chemistry has been shown to introduce a band gap into metallic single-walled carbon nanotubes. Here we demonstrate that the application of such covalent bond-forming chemistry modifies the periodicity of the graphene network thereby introducing a band gap (∼0.4 eV), which is observable in the angle-resolved photoelectron spectroscopy of aryl-functionalized graphene. We further show that the chemically-induced changes can be detected by Raman spectroscopy; the in-plane vibrations of the conjugated π-bonds exhibit characteristic Raman spectra and we find that the changes in D, G, and 2D-bands as a result of chemical functionalization of the graphene basal plane are quite distinct from that due to localized, physical defects in sp 2 -conjugated carbon.

Carbon nanotube material can now be produced in macroscopic quantities. However, the raw material has a disordered structure, which restricts investigations of both the properties and applications of the nanotubes. A method has been developed to produce thin films of aligned carbon nanotubes. The tubes can be aligned either parallel or perpendicular to the surface, as verified by scanning electron microscopy. The parallel aligned surfaces are birefringent, reflecting differences in the dielectric function along and normal to the tubes. The electrical resistivities are anisotropic as well, being smaller along the tubes than perpendicular to them, because of corresponding differences in the electronic transport properties.

We describe an improved laser vaporization source for production of intense and stable cluster beams. Intensity and stability are notably improved compared with standard sources by the introduction of a cavity in which the vaporization takes place before expansion. This source has been successfully used for electric deflection studies of highly collimated cluster beams.

International audienceThe authors report the effects of radical functionalization on the electrostatic force microscopy (EFM), the scanning tunneling spectra (STS), and Raman spectroscopy of epitaxial graphene. The EFM studies show the existence of layer dependent trapped charges in the pristine graphene. The uniform enhancement of energy gap is observed through STS. Raman spectra show nonuniformly distributed D-band intensities throughout the functionalized sample as a result of the inhomogeneous distribution of covalent bonds to the graphene sheets. The functionalization chemistry has a marked effect on the homogeneity of the electrostatic charge and leads to an increase of the energy of the band gap