The anodizing is a high-voltage electrochemical conversion process that forms barrier-type or nanoporous/nanotubular oxides on valve metals and alloys, mainly depending on the composition of electrolyte used. The key to achieve the ordered nanoporous/nanotubular structures is a displacement of the film material above the original surface position due to synergistic effect of pits generation (field assisted oxide dissolution), stress generated at the metal-oxide interface including electrostriction and plastic oxide flow switching the growth of the barrier-film to nanotube/nanopore. Typically, the TiO2
nanotube array formed in organic electrolytes such as glycerol, dimethyl sulfoxide, ethylene-glycol is obtained in the form of close packed structure in which the nanotubes nearly stick together with the tube walls. A fundamentally different nanostructure from that is obtained in diethylene-glycol electrolyte. The nanostructure is characterized by free standing nanotubes separated by an interconnecting space much bigger than the thickness of nanotube wall. [2,3] Such geometry gives possibility for deposition of secondary materials using electrochemical processes in view of improved wetting behavior of the nanostructure.  Herein we report on how to control the electrodeposition process to achieve unique core-shell geometries. We discuss on wetting behavior and nucleation-growth on such porous structures, a key points to achieve controlled electrodeposition. An examples of composites formed between oxide layer and Si, CdSe, Au, Pt will be demonstrated.
 D. Kowalski, D. Kim and P. Schmuki, Nano Today, 8(2013) 235.
 D. Kowalski, J. Mallet, J. Michel, and M. Molinari, J.Mater.Chem.A 3(2015) 6655.
 D. Kowalski, J. Mallet, S. Thomas, J. Rysz, B. Bercu, J. Michel and M. Molinari, Electrochim. Acta, 204(2016) 187.
 D. Kowalski, and P. Schmuki, Chem. Comm., 46(2010) 8585.
Fig. 1 Core-shell structures formed by means of electrodeposition of Si and Au. STEM image (left) shows 60nm thick silicon layer electrodeposited from ionic liquid electrolyte on the outer-shell of TiO2 nanotube. Back scattering electron image (right) shows gold electrodeposited in-between the bottoms of TiO2 nanotubes.