Optical and electrical properties of inner tubes in outer wall-selectively functionalized double-wall carbon nanotubes

Atom-thick materials such as single-wall carbon nanotubes (SWNTs) and graphene are prone to chemical attacks because all constituent atoms are exposed. Here we report the retention of optical and electrical properties of inner tubes in heavily functionalized double-wall carbon nanotubes (DWNTs). Correlated optical absorption spectroscopy, Raman scattering, and thin film electrical conductivity all suggest that an inner tube behaves strikingly similar to a pristine SWNT; however, because of the protection of the outer wall, the inner tube can survive aggressive chemical attacks (e.g., by diazonium chemistry) without compromising physical properties. At the saturation limit of the diazonium functionalization, an SWNT network becomes electrically insulating; in stark contrast, the double-walled structure retains ∼50% of the initial conductivity, owing to the intact inner tube pathway. These results suggest the possibility of high-performance DWNT electronic devices with important capabilities for tailored surface chemistry on the outer walls, whereas the inner tubes are chemically protected.