Synthesis of thick and crystalline nanotube arrays by spray pyrolysis

Arrays of aligned nanotubes of large diameter (100–250 nm) are synthesized by pyrolyzing a jet (spray) solution of ${\mathrm{Fe(C}}_{\mathrm{5}}{\mathrm{H}}_5{)}_2$ and ${\mathrm{C}}_{\mathrm{6}}{\mathrm{H}}_6$ in an Ar atmosphere at relatively low temperatures (850 °C). The tubular structures consist of highly crystalline nested graphene cylinders (<200 concentric tubes) with tips that are usually open. Raman studies confirm the high degree of perfection of these “thick” structures. Tube diameter, degree of alignment, and crystallinity can be controlled by varying the Ar flow rate and the Fe:C ratio within the precursor solution. Based on these observations a possible growth mechanism is suggested. This low cost route for the synthesis of carbon nanotubes is advantageous due to the absence of ${\mathrm{H}}_2$ as a carrier gas and the low pyrolytic temperature.