We propose a conceptually new structure, in which mono- or few BN layers seamlessly wrap around a single-walled carbon nanotube (SWNT), and result in an atomically smooth coaxial tube consisting two different materials, as shown in Figure 1. The structure is synthesized by chemical vapor deposition (CVD). As the reaction occurs on outer surface of the existing SWNTs, we name this process conformal CVD. Various SWNTs, e.g. vertically aligned array, horizontally aligned arrays, suspended SWNTs, random network and films, are employed as the starting material, and successful coating are achieved on all of them. Our characterizations confirm that the outside BN coating started locally on the wall of a SWNT and then merge into a BN nanotube on the curved surface of the SWNT which served as a template. The number of walls can be tuned from 1 to few by controlling the CVD condition. The structure of inside SWNTs are almost not effected by the conformal CVD, as evidenced by Raman and many other characterizations. The crystallization and cleanness of the starting SWNT template are believed to be critical for the successful fabrication of outside walls. This structure is expected to have a broad interest and impact in many fields, which include but not limited in investigating the intrinsic optical properties of environment-isolated SWNTs, fabricating BN-protected or gated SWNT devices, and building more sophisticated 1D material systems.
Part of this work was supported by JSPS KAKENHI Grant Numbers JP25107002 and JP15H05760.
Professor Shigeo Maruyama received his Ph.D. in 1988 from the School of Engineering at the University of Tokyo. He joined the University of Tokyo as a research associate in 1991 and has remained as a distinguished professor since 2014. He holds a cross-appointment at the National Institute of Advanced Industrial Science and Technology (AIST) and has also served as a guest professor at Peking University since 2016. Professor Maruyama joined Professor Richard Smalley's group at Rice University as a visiting fellow from 1989-1991, where he began to study the chemical physics of clusters, fullerenes, and carbon nanotubes. He invented the Alcohol Catalytic CVD (ACCVD) technique of fabricating SWNTs from low pressure alcohol in 2002. His current research topics are the growth, optical characterization, thermal characterization and solar cell application of carbon nanotubes and graphene. He has been the president of "The Fullerenes, Nanotubes and Graphene Research Society" since 2011, and is the co-chair of the steering committee for Carbon Nanotube conferences. He has also served as Director of The Japan Society of Applied Physics since 2014 and was Executive Director in 2015. Currently, he is also the Deputy Research Supervisor of the CREST project 'Creation of Innovative Core Technologies for Nano-enabled Thermal Management' by the Japan Science and Technology Agency (JST). Professor Maruyama has published more than 210 ISI-listed papers which have been cited more than 9,200 times.