Effect of the anodization voltage on the porewidening rate of nanoporous   anodic alumina
  A detailed study of the pore-widening rate of nanoporous anodic alumina layers as a function of the anodization voltage was carried out. The study focuses on samples produced under the same electrolyte and concentration but different anodization voltages within the self-ordering regime. By means of ellipsometry-based optical characterization, it is shown that in the porewidening process, the porosity increases at a faster rate for lower anodization voltages. This opens the possibility of obtaining three-dimensional nanostructured nanoporous anodic alumina with controlled thickness and refractive index of each layer, and with a refractive index difference of up to 0.24 between layers, for samples produced with oxalic acid electrolytes. 
Mohammad Mahbubur Rahman (DEEEA), Enric Garcia-Caurel (LPICM), Abel   Santos (DEEEA), Lluis F. Marsal (DEEEA), Josep Pallare...
cond-mat.mtrl-sci physics.optics