Vertical Single-Walled Carbon Nanotube Arrays via Block Copolymer Lithography

Abstract

The growth of vertical single-walled carbon nanotube (SWNT) arrays of uniform aerial distribution is achieved by oxygen assisted plasma enhanced chemical vapor deposition (PECVD) growth from nanopatterned catalyst arrays prepared by block copolymer lithography. Block copolymer lithography is an attractive nanopatterning method for generating a uniform catalyst particle array for carbon nanotube growth. Nevertheless, the scale of the catalyst particles patterned by block copolymer lithography is usually not small enough for SWNT growth. In this work, various methods to reduce the catalyst size have been investigated for SWNT growth. Nanopatterned iron catalyst arrays having a mean diameter of 9 nm were prepared via tilted evaporation of thin iron catalyst films over a block copolymer template with the nanopore size of 20 nm, followed by heat treatment at 600 °C. The catalyst particle size was further reduced to the size required for SWNT growth (∼3 nm) by the following two methods. In method i, the catalyst particles were sequentially annealed at 800 °C first in air and then in an H2 atmosphere. The evaporation of iron atoms and subsequent reduction during heat treatment produced catalyst particles sufficiently small for SWNT growth. In method ii, an Al layer was deposited over the catalyst array, which decreased the exposed area of the catalyst particles. The effective catalyst particle size was thus reduced, which enabled the growth of SWNTs.