Scandium: An efficient dopant to modulate the optical spectrum of vanadium dioxide (VO2)

Abstract

Transparency of VO2 thin films in the visible region is an important aspect of study for its use in smart window applications. In this regard, we experimentally validate the theoretical prediction regarding the influence of scandium (Sc) doping on modulating the optical spectrum of VO2. Sc-doped nano-crystalline VO2, bulk and thin films were synthesised using a two-step process involving a rapid non-equilibrium solution combustion process and ultrasonic nebulised spray pyrolysis of aqueous combustion mixture respectively; followed by a reduction step. The presence of Sc was determined by X-ray photoelectron spectroscopy where a peak observed at 530.06 eV is attributed to Sc–O interaction. Raman spectra showed a shift in 611 cm−1 peak position to a lower wavenumber due to tensile strain arising from Sc doping. Sc-doped VO2 thin films showed semiconductor to metal transition of four orders of magnitude change in resistance. Sc-doping increased the band gap from 1.76 eV for undoped to 2.02 eV with 2.0 at. % of doping thereby making the films more transparent in the visible region of the optical spectrum. This shift in the band gap of VO2 was consistent with the theoretical reports. Thus, Sc is a potential dopant for modulating the optical spectrum of VO2 for its application in smart windows.