We show that covalent sidewall functionalization of single-wall nanotubes leads to drastic changes of nanotube electronic states near the Fermi level. The sp3 hybridization between the functional group and nanotube induces an impurity state near the Fermi level. The impurity state is found to be extended over a large distance (>1 nm) even though the structural deformation is confined to the vicinity of the functionalizing site. Thus, dramatic changes in the conductive properties of the nanotube can be expected even if the concentration of functionalization molecules is small. This effect provides an effective pathway for band structure engineering, nanoelectronic device, and sensor applications through covalent sidewall functionalization.

We investigated the conducting properties of functionalized single wall nanotubes (SWNTs) with a finite addend concentration. Robust differences are found between monovalent and divalent additions. For the former a small number of addends can significantly disrupt the ballistic conductance of nanotubes near the Fermi level. As the concentration increases the conductance decreases rapidly and approaches zero at addend to C ratio around 25%. In contrast, divalent functionalizations have weak effects, and the nanotube quantum conductance remains above 50% of that of a perfect tube even for an addend concentration as large as 25%. These differences can be attributed to the formation of impurity states near the Fermi level for monovalent additions, while divalent addends create impurity states far away from the Fermi level.