Vanadium oxide–carbon nanotube composite films characterized by spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) is utilized to characterize the vanadium oxide (VO_x)–single walled carbon nanotube (SWCNT) composite films prepared by sol–gel. Five Tauc–Lorentz oscillators model is employed to describe the dispersions in the optical responses of VO_x and VO_x –SWCNT thin films. Results reveal that if the SWCNT concentration in the composite film is increased, the refractive index is decreased, while the extinction coefficient is increased. Moreover, higher SWCNT content leads to lower optical band gap (E_g) but larger localized state (E_e). Interestingly, both E_g and E_e values reach saturated at a SWCNT content of ∼8 wt%. Particularly, the peak transition energies of the 5 Tauc–Lorentz oscillators have been assigned to the specific transitions according to the band structures of VO_x. This work reveals the feasibility of investigating the optical properties and microstructures of VO_x –SWCNT composite films by SE. These experimental results will be helpful for better understanding the VO_x –SWCNT composite films, and promoting future characterizations of other SWCNT-based composites by SE. (paper)