Computational Studies of Defects in Nanoscale Carbon Materials

Invited and Contributed Oral Presentations A01. The formation and observation of individual vacancies in carbon nanotubes by a focused electron beam Florian Banhart University of Strasbourg, France Coauthor(s) : J. A. Rodriguez-Manzo Modern scanning transmission electron microscopes (STEM) with aberration correctors enable us to focus an extremely intense electron beam onto an Angstrom-size spot. The highly focused electron beam gives us the possibility of carrying out in-situ electron irradiation on the atomic scale and to displace ballistically pre-selected atoms in the lattice. This technique is applied to singleand multi-wall carbon nanotubes. Irradiation experiments within a wide temperature range show the particular relaxation behavior of different types of nanotubes. Single or multiple vacancies are created in desired positions with the focused beam. This gives us, for the first time, the possibility of observing in real time the response of graphitic materials to the creation of individual point defects. It is shown how the reconstruction of the graphitic lattice after the creation of point defects determines the behavior of carbon nanostructures upon the removal of atoms. A02 Graphene nanostructures: Edges, ribbons, superlattices, and defective tubes Steven G Louie University of California, Berkeley, USA In this talk, I discuss some of our recent work using theory and computation to study the electronic, optical and transport properties of sp2-bonded carbon nanostructures, including those with defects and under external perturbations. Systems investigated include defective carbon nanotubes, graphene, graphene nanoribbons, and graphene subjected to nanoscale external periodic potentials (called graphene superlattices). These nanostructures exhibit a number of unexpected behaviors – novel conductance characteristics, magnetic defect states, extraordinarily large excitonic effects in their optical response, anomalous behaviors in the dynamics of carriers (the 2D massless Dirac fermions) in graphene superlattices, and an electric field-induced half-metallic state for zigzag graphene nanoribbons, among others. Moreover, under specific conditions, graphene superlattices are predicted to be electron supercollimators and new generation of 2D massless Dirac fermions may be created. The physical origins of these interesting properties and phenomena are discussed.