Ionic Transport in Anodically Oxidised Al/Ta Layers during the Growth of Metal-Oxide Nanostructures

Recent study has shown that anodic processing of a specimen consisting of a layer of aluminium deposited upon a layer of tantalum (Al/Ta) results in the formation of self-organized arrays of metal-oxide 'nanocolumns' in the alumina pores. In the present study, we have justified experimentally and described conceptually the model of ionic transport and film growth during the anodic process. Experimental samples were Al/Ta (250/100 nm) metal bilayers sputtering-deposited onto Si wafers. The processing resulted in initial growth of porous anodic alumina film, followed by uniform penetration of the alumina pores by columns of tantalum oxide at the commencement of high voltage reanodising (Fig. 1b). The growth and field-assisted dissolution of the nanostructured anodic oxides were studied by SEM, XPS and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES)