Synthesis of aligned carbon nanotubes

Vertically aligned carbon nanotubes (ACNTs) are bundles of carbon nanotubes oriented perpendicular to a substrate, and horizontally aligned CNTs are parallel to the substrate. Their dense and orderly arrangement, along with outstanding physical and chemical properties, enables ACNTs to be used in various fields. The methods of synthesising ACNTs can be classified into single-step and double-step techniques. Thermal pyrolysis and flame synthesis are the common single-step methods, and both are relatively simple. The double-step methods, including catalyst coating and chemical vapour deposition, provide more control over the catalyst morphology. This review explores different methods used for ACNT growth, the process parameters that determine the morphology of ACNTs and the applications of structured ACNTs.