Low background estimation of metallic-to-semiconducting carbon nanotube ratio by using infrared spectroscopy

Abstract

The ratio of metallic and semiconducting carbon nanotubes (CNTs) populations is a crucial factor for elucidating their structure-property relationship. Visible-to-near infrared absorption spectroscopy with dispersion is mostly used for the estimation of the metal-to-semiconductor ratio. Due to spectral cofactors including background absorption, however, it is still uneasy to obtain correct population ratios. Herein the detection of pure semiconducting fractions is performed by using the Fourier transform infrared (FTIR) spectroscopy. The working principle is based on the fact that highly pure semiconducting CNTs show no far-infrared (FIR) plasmon resonance while unsorted films containing metallic CNTs have a strong FIR band. This off-on characteristics enables the evaluation of metallic-to-semiconducting CNTs population. Several limitations in this technique are discussed for avoiding significant artifacts. This FTIR-based, solid-state endpoint detection will lead to the straightforward investigation of purity-to-transport properties relationship in solid-state CNT thin films.