Interrelation between nanostructure and optical properties of oxide thin films by spectroscopic ellipsometry

Nanostructured thin oxide films of SnO2, V2O5 and indium tin oxide (ITO)
were deposited by conventional and plasma-assisted chemical vapor
deposition (CVD, PECVD) on different substrates and at different
temperatures. Optical properties of the films were determined by
spectroscopic ellipsometry in the energy range 1.5–5.5 eV. A parameterized
analysis, based on Lorentzian oscillators combined with the Drude model,
along with Bruggeman effective-medium approximation (BEMA) modeling, was
used to determine the optical constants of thin films independently from
the reference dielectric functions of the bulk materials. In this way,
correlation between the optical properties and nanostructure of thin films
could be established. In particular, in order to discuss the dependence of
optical constants on grain size, SnO2 nanostructured films have been
considered, using a parameterization based on a double Lorentzian
oscillator. Nanocrystalline V2O5 thin films have demonstrated the
correlation between optical constants (described by four Lorentzian
oscillators) and crystallineyamorphous volume fractions. Finally, ITO thin
film optical properties are described by a combination of a double
Lorentzian oscillator with the Drude model;
by this analysis, gradients in the structural and optical properties of
ITO are demonstrated.