Metal-free chemical vapor deposition growth of graphitic tubular structures on engineered perovskite oxide substrates

Metal-free growth of carbon nanotubes/fibers (CNT/Fs) using chemical vapor deposition (CVD) on semiconducting and insulating substrates is of interest in the context of the construction of nanoscale electronic devices. However, controllable synthesis of CNT/Fs without the aid of metal catalysts is an ongoing challenge. Here we report the direct CVD synthesis of CNT/Fs on the perovskite oxides SrTiO3 (STO) and Ba0.6Sr0.4TiO3 (BST). A variety of processing steps were used on STO (001) substrates to create a set of six patterns with varying atomic-scale surface roughnesses. These substrates were all subjected to the same CVD growth conditions, and a correlation was found between the surface roughness of the substrates and the density of CNT/Fs. This indicates that nanometer-scale asperities on the substrates act as the catalytically active sites for CNT/F growth. In a separate set of experiments the surfaces of polished polycrystalline BST samples were investigated. The random orientation of the exposed etched facets of the individual grains revealed significantly different catalytic activity for CNT/F growth. Our study demonstrates the great influence of the nature of the crystal surface condition on the catalytic activity of the substrates and is a critical first step towards perovskite oxide catalyst design.