Template-free synthesis of vertically aligned crystalline indium oxide nanotube arrays by pulsed argon flow in a tube-in-tube chemical vapor deposition system

Vertically aligned crystalline indium oxide (IO) nanotube arrays without using any special templates or expensive epitaxial substrates were synthesized on Si (100) substrates by using a tube-in-tube horizontal chemical vapor deposition (CVD) system. The pulsed flow of argon (Ar) gas in rectangular pulse mode appears to be a key factor in deciding the steady state of local vapor flux which further decides the growth alignment and yield of 10 nanotubes. The dimensional distribution of IO nanotubes was simply controlled by varying the pulse width of the Ar gas flow rate. This strategy of controlling dimensions and vertical alignment for making 1-D nanostructures may find potential applications in back electrode photoelectrochemical cells, field emitters and solar cells.