  WO3 thin films were grown by atomic layer deposition and spectroscopic
ellipsometry data gathered in the photon energy range of 0.72-8.5 eV and from
multiple samples was utilized to determine the frequency dependent
complex-valued isotropic dielectric function for WO3. We employ a
critical-point model dielectric function analysis and determine a parameterized
set of oscillators and compare the observed critical-point contributions with
the vertical transition energy distribution found within the band structure of
WO3 calculated by density functional theory. We investigate surface roughness
with atomic force microscopy and compare to ellipsometric determined effective
roughness layer thickness.
