Carbon nanotube diameter control via catalytic Co nanoparticles electrodeposited in porous alumina membranes

Use of porous anodic alumina (PAA) membranes prevents sintering of metal catalyst particles during growth of carbon nanotubes (CNTs) by chemical vapour deposition (CVD). When a metal catalyst fills the base of the pores, the diameters of the resulting CNTs match those of the pores. This approach is generally limited to PAA membranes with pores >= 50 nm in diameter presumably due to difficulties associated with metal deposition in very narrow pores and with mass transport of gases during CVD. However, PAA membranes offer the opportunity to grow CNTs using catalyst particles with diameters that are significantly smaller than the pores. Here we investigate the electrodeposition of small amounts of Co into the pores of shallow PAA membranes. Using alternating voltage deposition with membranes that have intact, but thinned, barrier layers we demonstrate that CNTs with a diameter of 25 +/- 3 nm can be grown from pores with diameters of 60 +/- 4 nm.