High Conformity and Large Domain Monocrystalline Anatase on Multiwall Carbon Nanotube Core–Shell Nanostructure: Synthesis, Structure, and Interface

We report a new facile approach to achieve highly conformal thin layers (similar to 10 nm) of anatase TiO2 on nonfunctionalized carbon nanotubes (CNTs) using atomic layer deposition (ALD). The method adopts an initial deposition of amorphous TiO2 at a low temperature of 60 degrees C to ensure a good conformity followed by postdeposition annealing at 450 degrees C under vacuum to induce a complete phase transformation to crystalline anatase TiO2 while retaining the structural integrity of the CNTs. This approach yields unprecedented sizes of monocrystalline anatase shell domains of up to 500 nm along the CNTs. The high quality of the anatase layer is evidenced directly by high-resolution transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Atomic-scale study of the nanostructure cross-section using electron energy loss spectroscopy provides direct evidence that bonding is formed at the interface after annealing. The low grain boundary anatase shell layer with a well-bonded interface to the CNTs has a high potential of significantly enhanced performance in photocatalysis, solar energy, and nanoelectronics.