Fine tuning of optoelectronic properties of single-walled carbon nanotubes from conductors to semiconductors

Abstract

Controlling both conductivity and bandgap chemistry of carbonaceous fillers could broaden up their application potential. However, it has been a difficult synthetic goal for more than a decade. We describe a methodology to do so in a very controlled manner on single-walled carbon nanotubes (SWNT). The approach relies on the extreme extension of a functionalization by 4-nitrobenzenediazoether. We show that the water-soluble Z-diazoether already known to react selectively with metallic m-SWNTs, can also extract electrons from sc-SWNTs. The gradual formation of a covalent aryl bond alters the SWNT electrical conductivity in two steps depending on the functionalization degree. The two consecutive regimes correspond to the grafting of conductor and semiconductor nanotubes. The extent of functionalization was assessed in situ using UV–Vis spectroscopy. The covalent coupling was first evidenced by spectroscopic characterizations of the chemical structure. The consequences on the physical properties of the SWNTs were also measured. The functionalization method reported here brings unprecedented hope for preparing, at large scale, semiconducting SWNTs as excellent-conductivity building blocks for an array of applied semiconductors. This is the first example of the visualization and measurement of optical and electrical properties in function of the progress of nitrophenyl coupling to nanocarbon scaffolds.