Fabrication of monodomain porous alumina using nanoimprint lithography and its applications

Abstract

The self-ordering regimes associated with specific anodization conditions obeying the 10 % porosity rule are described which allow to obtain self-ordered porous alumina structures by electrochemical anodization. Monodomain porous alumina templates with very high aspect ratios are synthesized by nanoimprint lithography using a novel master stamp with periodic pyramids of 500 nm lattice constant, which have been fabricated on a 4 in. wafer by silicon processing technology. The combination of self-assembly and nanoimprint lithography allows the preparation of porous alumina templates with various configurations of pore arrangement that are not accessible by other state-of-the-art methods. Smart nanoimprint lithography, nanobranches, Moire patterns, porous films on a Si substrate and porous alumina channels with a modulated di- ´ ameter are discussed in detail. The same concepts are applied to prepare nanostructured porous oxides on another valve metals. Anodic oxides grown on a Ti substrate above and below the breakdown potential, respectively, are discussed in detail and compared with the mechanisms governing the formation of porous alumina. Two promising applications of porous alumina are investigated: First, it is successfully used as template for the synthesis of silver nanowires by electrochemical deposition. Secondly, optical properties of the porous alumina structures are measured. These show in principle the feasibility of their application as photonic crystals.