Electronic structure of carbon nanotube systems measured with scanning tunneling microscopy

Carbon fullerenes are unusually structured molecules with robust mechanical and electronic properties. Their versatility is astounding; envisioned applications range from field emission displays to impregnated metal composites, battery storage media, and nanoelectronic devices. The combination of simple constituency, diverse behavior, and ease of fabrication makes these materials a cornerstone topic in current research.; This thesis details scanning tunneling microscopy (STM) experiments investigating how carbon nanotube fullerenes interact with and couple to their local environment. Scanning tunneling microscopy continues to be a key method for characterizing fullerenes, particularly in regards to their electronic properties. The atomic scale nature of this technique makes it uniquely suited for observing individual molecules and determining correlations between locally measured electronic properties and the particular environment of the molecule.; The primary subject of this study is single-wall carbon nanotubes (SWNTs), which were observed under various perturbative influences resulting in measurable changes in the electronic structure. Additionally, fullerene heterostructures formed by the encapsulation of C₆₀ molecules within the hollow interiors of SWNTs were characterized for the first time with STM. These novel macromolecules (dubbed “peapods”) demonstrate the potential for custom engineering the properties of fullerene materials.; Measurements indicate that the properties of individual nanotubes depend sensitively on local interactions. In particular, pronounced changes in electronic behavior are observed in nanotubes exhibiting mechanical distortion, interacting with extrinsic materials (including other nanotubes), and possessing intrinsic defects in the atomic lattice. In fullerene peapods, while no discernable change in the atomic ordering of the encapsulating nanotubes was evident, the presence of interior C₆₀ molecules has a dramatic effect on the electronic structure of the composite molecule. This manifests as a pronounced spatial modulation in electron density at energies near 1 eV. Coincident with this modulation is the appearance of characteristic features in the electronic band structure indicative of coupling between the unoccupied electronic states of the component fullerenes. These results illustrate the important role local environment plays in the behavior of nanotubes, and suggest the possibility of harnessing these effects to tailor nanotube properties for specific functionality.