Effects of Substrate and Molecular Adsorption on Raman Scattering From Individual Single -Walled Carbon Nanotubes

Abstract

We have explored effects of molecular adsorption, either un-intentional (from ambient environment) or intentional and substrate on resonance Raman scattering measurements on isolated SWCNTs. By correlating Raman scattering measurements with electronic properties of nanotubes, we show that adsorption of O2 from ambient environment leads to charge transfer (and the Fermi level shift below the Dirac point) in metallic nanotubes while no significant effects of O2 adsorption are observed for semiconducting nanotubes from Raman scattering measurements. In metallic nanotubes, adsorption of O 2 is enhanced by the presence of substrate and also leads to significant physical disorder. Variation and complexity in the G-band of metallic nanotube Raman spectrum is explained in terms of Kohn anomalies (KAs) leading to broad and softened ALO1 phonon modes, as well as O2 induced enhancement of double resonance processes. Effects of adsorption of NH3 on Raman scattering measurements are also explored and correlated to charge transfer (Fermi level shift) in carbon nanotubes.