Nanoporous oxides of refractory metals : fabrication and properties

A new approach to fabrication of nanoporous oxides of refractory metals is presented. It is based on the magnetron co-sputtering of aluminum and refractory metal (titanium, niobium or tungsten) followed by porous electrochemical anodization of the composite film and selective etching of alumina. The nanoporous oxide films with a thickness up to 5 µm were fabricated and studied. The porosity of the oxide films characterized by the surface area of 230 – 460 m2/cm3 can betuned by the aluminum content in the as-deposited composite films. The pore diameters are found to be varied in nanometer and subnanometer ranges. The parameters of porous titania within porous alumina matrix for different titanium concentrations are presented. The fabricated porous composite oxide films are characterized by the refractive index in the range from 1.45 to 1.77. The dielectric permeability for these films is found to be varied from 6.7 to 24. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)