Optical properties of WO3 thin films modeled by finite-difference time-domain and fabricated by glancing angle...

Optical transmittance spectra between 1.55 eV (800 nm) and 3.10 eV (400 nm) of tungsten oxide (WO3) thin films nanostructured thanks to the Glancing Angle Deposition technique are investigated both experimentally and theoretically, as a function of geometrical parameters. A Finite-Difference Time-Domain code was used to numerically model the films structure and to calculate their optical properties. The corresponding optical index and porosity are considered. It is found that the optical index of columnar structures always follows Cauchy's law as a function of energy and is reduced as the incident angle increases (alpha = 0 to 80 degrees) from n633 = 2.2 to 1.98 for experimental data against 2.1 to 1.75 for those computed with the Finite-Difference Time-Domain code. For zigzag architectures, an increase of the zigzag number from 0.5 to 8, amplifies interference fringes and improves the measured refractive indices. It agrees with modeled optical characteristics since n633 increases from 2.18 to 2.30.