Restoration of the genuine electronic properties of functionalized single-walled carbon nanotubes

Abstract

Sidewall functionalization of single-walled carbon nanotubes (SWNTs) has previously been used to effectively attach a variety of functional groups onto SWNTs; however, there has been little investigation into the reversibility of these reactions, which is critical for the restoration of the original optical and electrical properties of SWNTs. In this study, we investigated the complete removal of functional groups attached to the sidewalls of SWNTs by a thermal annealing process at high temperature to restore the genuine optical and electrical properties of SWNTs. Hydroxyphenyl groups were covalently attached to SWNTs for this purpose. Functionalized SWNTs typically show a significantly larger sheet resistance and completely lose their typical characteristic optical properties due to the covalent attachment of the functional groups onto the SWNT surfaces. However, we found that all of the functional groups could be effectively removed by an annealing temperature above 400 °C in a nitrogen environment, as confirmed by FT-IR, Raman and UV-vis-nIR absorption analyses. Accordingly, the original optical and electrical properties were also recovered upon annealing at above 400 °C, as confirmed by the recovery of the original sheet resistance value. To demonstrate the effectiveness of annealing, we evaluated transparent films, which were prepared predominantly with metallic SWNTs, using the separation technique, which is based on selective covalent functionalization. A functionalized metallic SWNT film recovers its original high conductivity upon annealing at 400 °C by the removal of the functional groups, which demonstrates the effectiveness of this annealing process.