The formation of nanotubes in sulphuric/hydrofluoric acid electrolyte at controlled voltage is investigated on Ti-6Al-4V alloy used for load-bearing prosthetic applications. The effects of anodizing time and voltage on film morphology, composition and microstructure are studied by scanning and transmission electron microscopy. Rutherford backscattering spectroscopy (RBS), and Raman spectroscopy. Fluorine content in the films was of a particular interest for enhancement of antibacterial properties of the surface. The efficiencies of film formation are determined as about 40% and 80% for anodizing at 20V and 60V respectively for shorter anodizing time and as about 1 and 5% for longer anodizing time. For 5 min of anodizing, higher voltage conditions results in a thicker barrier layer. At extended anodizing time a further disruption of the nanotubular morphology and formation of approximately 1.5 mu m-thick nanoporous film is promoted. The films grown at 20V contain from 4 at.% to 6 at.% of fluorine. RBS detects about 13 at.% of fluorine incorporated in the film formed at 60V for 60 min, possibly associated with a greater film thickness. The oxide film material consists of amorphous titania matrix doped with V2O5 and Al2O3. (C) 2010 Elsevier Ltd. All rights reserved.