The role of interference and polarization effects in the optical visualization of carbon nanotubes

Abstract

This manuscript presents an experimental study on the optical visualization of single- and multi-walled carbon nanotubes. Optical micrographs of single-nanotubes and multi-walled carbon nanotubes sitting on SiO2/Si substrates are presented. Atomic force microscopy and Raman spectroscopy analysis provide morphological and structural characterization of the carbon nanotubes. Measurements taking into account different substrates, and also different values of wavelength of the incoming light, show that the optical contrast between the nanotubes and the SiO2 surface strongly depends on these two factors. A model based on interference effects explains the experimental results and establishes a route for substrate engineering that allows direct and fast observation of carbon nanotubes, as well as the measurement of their refractive indexes. Analysis on the polarization properties of the reflected light confirms the strong anisotropy on the optical absorption of carbon nanotubes.