The main objective of our Phase-I Center for Chemical Innovation, the Center for Molecular Interfacing (CMI) was to enable the integration of well-controlled molecular constituents within macroscopic systems by using graphene sheets and CNTs to achieve molecularly well-defined, reproducible and robust connections. Our work involved a combination of synthesis of molecular architectures of deliberate design and function, the development of novel experimental platforms and techniques, and the development of theory and simulation to provide a theoretical framework. While we were not successful in advancing to a Phase II Center, we nonetheless feel that we made very significant advances.

Below we present a summary of the most salient findings of our last year of
support. The report presents findings in the areas of synthesis and characterization of graphene layers, carbon nanotubes and assemblies followed by computational studies.
1. Carbon Nanotubes and Graphene:

A. On-chip Rayleigh imaging of carbon nanotubes Carbon nanotubes are a heterogeneous group of materials. As-grown carbon nanotubes can comprise single-walled carbon nanotubes (SWNTs) with a wide range of structural (n, m) indices, multi-walled carbon nanotubes (MWNTs), nanotube bundles, and SWNTs that change chirality due to structural defects. Furthermore, their interactions with the environment and other neighbouring nanotubes directly affect their electronic and optical properties. Previously demonstrated characterization methods, including transmission electron microscopy, scanning tunnelling microscopy and various optical spectroscopic techniques, usually require long data acquisition times and/or complicated sample preparation, which limits their use as a general characterization method for SWNTs.

Optical imaging of carbon nanotubes placed directly on a solid substrate allows rapid visualization and spectral resolution of individual nanotubes with relative ease. We reported a novel on-chip Rayleigh imaging technique using wide-field laser illumination to measure optical scattering of an array of individual SWNTs on a solid substrate with high spatial and spectral resolution.  This method, in conjunction with calibrated AFM measurements, accurately measures the resonance energies and  diameters for a large number of SWNTs in parallel. We applied this technique for fast mapping of key SWNT parameters, including the electronic-types and chiral indices for individual SWNTs, position and frequency of chirality-changing events, and intertube interactions in both bundled and distant SWNTs. This work was published in Nano Letters as a cover article in Jan 2011. [1]

B. SWNTs as Excitonic Optical Wires
Although metallic nanostructures are useful for nanoscale optics, all of their key optical properties are determined by their geometry. This makes it difficult to adjust these properties independently, and can restrict applications. Recently, we used absolute intensity of Rayleigh scattering to show that SWNTs can form ideal optical wires. [2]  The spatial distribution of the radiation scattered by the nanotubes is determined by their shape, but the intensity and spectrum of the scattered radiation are determined by exciton dynamics, quantum-dot-like optical resonances and other intrinsic properties.  Moreover, the nanotubes display a uniform peak optical conductivity ~ 8 e2/h, which we derived using an exciton model, suggesting universal behaviour similar to that observed in nanotube conductance. Combined, these properties make single-walled carbon nanotubes prototypical one-dimensional optical nanostructures, or excitonic optical wires, whose spectral response is mainly controlled by the intrinsic quantum-mechanical properties of the material, while the scattered field can be independently determined by their shape. We further demonstrated a radiative ...

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