Growth of a TiO2 nanotubular layer without presence of nanograss in a short time

Abstract

Many studies, focused in TiO₂ anodized, uses frequently a NH₄F salt concentration from 0.3 – 0.5 wt% and the whole information about how voltage, time and even pH affects to nanotubes morphology, are effective just for these concentration range. It is known, increasing salt concentration, the electrolyte increases their conductivity and anodization speed (oxidation-dissolution) suffer also an increment and for a specifically concentration 1.2wt%, there is no data about morphology repercussions. A TiO₂ nanotubular matrix is synthesized, in order to identify the range of time where it is possible to obtain with no presence of nanograss. The anodization process consists of an organic electrolyte of ethylene glycol, deionized water and 1.2 wt% NH₄F salts, constant potential of 30 V and a time lapse from 10 to 60 minutes (short time). All anodized samples are rinsed and annealed to 400 °C by 4 hours to obtain an anatase crystalline structure; no samples are cleaned in ultrasonic bath to preserve the nanograss structure. Optical characterization was performed by Raman Spectroscopy to identify the increases in signal intensity, associated with thickness. The morphological characterization was carried out by Scanning Electron Microscopy to verify the presence and density of the nanograss and nanotubes.