Fabrication and optical characterization of nanoporous alumina films annealed at different temperatures

We report on the structural and optical properties of self-ordered nanoporous anodic alumina (NAA) films annealed at different temperatures. The morphology of NAA films is examined by scanning electron microscopy (SEM). The results show that the porous structure have hexagonally ordered arrays of nanopores with interpore distance in the range of 90–100 nm and pore size between 30 and 40 nm. The structural properties studied by X-ray diffraction (XRD) show out that the nanoporous alumina experiences a transition from the amorphous phase to gamma and alpha phase when annealed from 800 to 1200 °C. The optical transmission spectra of the annealed NAA films with different thicknesses (9, 24 and 45 μm) are measured in the wavelength range of 300–1000 nm. Numerical simulations based on an optical model of the films show a good agreement with the measurements. The refractive index (n) and the extinction coefficient (k) are determined for each annealed temperature.