Carbon nanocylinders with high spectroscopic and electrocatalytic activities: An electrochemical route to superfill the gaps in vertically aligned carbon nanotubes for cutting them into specific lengths

We describe a combination of electrochemical superfilling and oxidative cutting approaches to producing multilayer carbon nanocylinders (ML-CNCs) by cutting off a specific length of vertically-aligned MWNTs (VA-MWNTs) along their circumference. Superfilling the gaps in VA-MWNTs with copper to produce a void-free Cu/VA-MWNT film is mainly based on the competitive diffusion and adsorption of polyethylene glycol and bis-(3-sulfopropyl) disulfide that leads to a peculiar kinetic profile decreasing from the bottom to topside of the gaps. The subsequent etching of copper in Cu/VA-MWNTs forms a fraction of about 30-nm-high VA-MWNTs protruding out of copper, which is cut off to produce ML-CNCs via the thermal oxidation of MWNTs, catalyzed by an ultrathin layer of copper oxide at the topmost side. The mechanisms for both the superfilling and the length-controlled cutting are systematically studied and discussed. ML-CNCs feature the shortest length among the existing MWNTs, minimal damage in the sidewalls, and high spectroscopic and electrocatalytic activities so that they can be used as multi-responsive probes to decipher biomolecules (e.g., β-nicotinamide adenine dinucleotidedinucleotide).