Sorting out semiconducting single-walled carbon nanotube arrays by preferential destruction of metallic tubes using water

Abstract

The coexistence of metallic (m-) and semiconducting (s-) single-walled carbon nanotubes (SWNTs) in grown samples remains an obstacle in the application of SWNTs in nano-electronics. We report herein a rational approach to prepare well-aligned s-SWNTs using water vapor as a weak oxidant to etch the m-SWNTs during or after SWNTs growth. Water vapor with controlled concentration is carried into the furnace by argon gas during or after the SWNTs growth. It is found that the oxidation temperature and the concentration of water have a clear effect on the destruction of m-SWNTs. During SWNT growth (temperature above 800 °C), the introduction of water at a certain concentration only etches the SWNTs with small diameters and shows no selectivity between m-SWNTs and s-SWNTs. After SWNT growth, the water can etch m-SWNTs effectively with optimized oxidation temperatures and water concentrations. Micro-Raman spectra and electrical transport characterization confirm the selective etching effects. The mechanism of the selective etching of SWNTs with water is discussed based on the electronic structures of SWNTs. Using this method, densely packed and well aligned semiconductor SWNT arrays can be obtained. We believe this selective etching approach would largely broaden the application of SWNTs, especially for future nano-electronic and molecular detection devices.