Probing the doping in metallic and semiconducting carbon nanotubes by Raman and transport measurements

TL;DR

This study combines Raman spectroscopy and transport measurements to investigate doping effects in metallic and semiconducting carbon nanotubes, revealing how doping influences vibrational modes and demonstrating Raman's effectiveness in quantifying doping levels.

Contribution

It provides a detailed analysis of doping effects on carbon nanotubes using combined experimental and ab-initio theoretical approaches, highlighting Raman spectroscopy as a precise doping probe.

Findings

Doping causes a significant increase in the G- band frequency in metallic tubes.

Doping results in an increased G+ band frequency in semiconducting tubes.

Raman spectroscopy can accurately measure doping levels in both metallic and semiconducting nanotubes.

Abstract

In-situ Raman experiments together with transport measurements have been carried out on carbon nanotubes as a function of gate voltage. In metallic tubes, a large increase in the Raman frequency of the $G^-$ band, accompanied by a substantial decrease of its line-width, is observed with electron or hole doping. In addition, we see an increase in Raman frequency of the $G^+$ band in semiconducting tubes. These results are quantitatively explained using ab-initio calculations that take into account effects beyond the adiabatic approximation. Our results imply that Raman spectroscopy can be used as an accurate measure of the doping of both metallic and semiconducting nanotubes.