Niobium oxide nanocolumns formed via anodic alumina with modulated pore diameters

Porous anodic alumina matrixes (AAM) are characterized by uniform cylindrical pores which can be used for templated synthesis of arrays of various nanostructures. Manipulation of the size, position and regularity of the pores... [ view full abstract ]

Porous anodic alumina matrixes (AAM) are characterized by uniform cylindrical pores which can be used for templated synthesis of arrays of various nanostructures. Manipulation of the size, position and regularity of the pores AAM allow forming conceptually new structures on its base with wide range of applications.

This paper presents the results of forming of metal oxide nanocolumns with variable diameters by high-voltage reanodization via AAM with modulated pore diameters. The main stages of film growth, with the relation between the film layers thick, are depicted in Fig. 1.

Single silicon wafer with magnetron-sputtered layers of 300 nm Nb and 1200 nm Al was used as substrate (Fig. 1, a). Regular AAM with modulated pore diameters was formed by sequential anodization of the Al in 0.2 mol·d^-3 C₄H₆O₆ at 180 V and in 0.4 mol·d^-3 H₂C₂O₄ at 37 V (Fig. 1, b, c). Array of niobium oxide nanocolumns was formed by high-voltage reanodization of the Nb layer via AAM in the mixed solution of 0.5 mol·d^-3 H₃BO₃ and 0.05 mol·d^-3 Na₂B₄O₇ in potentiodynamic mode at 400 V (Fig. 1, d, e). Further AAM was selective dissolved in 50 % H₃PO₄ (Fig. 1, f). As a result, array of Nb₂O₅ nanocolumns high 800 nm was formed on the solid layer NbO₂ thin 450 nm on Si-substrate (Fig. 2).

The nanocolumns consist of upper layer high 630 nm and diameter 100 nm in the base of which are located 4-7 columns high 170 nm and diameter 25 nm. Nanocolumns have an unordered structure because anodization of aluminum was carried out in one step without preliminary structuring of the surface. The additional ordering of the Al layer by the two-step anodization will make possible to form regular AAM and produce high-ordered nanocolumns on their basis.

So, the developed technique based on the combination of the methods of formation of porous anodic alumina with modulated pore diameters and high-voltage reanodization of Nb underlayer via the AAM. The formed structures can be used as photonic crystals, autoemission elements and functional applications of promising devices of nano- and optoelectronics.