Darren LeClere

Influence of Water Content on the Growth of Anodic TiO2 Nanotubes in Fluoride-Containing Ethylene Glycol Electrolytes

The effect of water additions, from 0 to 50 vol %, to an ammonium fluoride/ethylene glycol electrolyte on the composition and morphology of titania-based nanotubes was investigated by scanning and transmission electron microscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis. Further to the presence of units of TiO 2 , the films contained fluorine, carbon, nitrogen, and probably hydrogen species derived from the electrolyte. The compositions of the films appeared to be relatively independent of the water content of the electrolyte. Following a small increase in efficiency of film growth for additions between 0 and 1 vol % water, the efficiency decreased from about 25 to about 10% between water contents of 1 and 25 vol %, respectively, possibly due to a combination of loss of titanium species to the electrolyte and evolution of oxygen. The densities of the nanotube layers were estimated to be in the range of 1.25―1.75 g cm ―3 , with an average value of 1.47 g cm ―3 .

Tracer Investigation of Pore Formation in Anodic Titania

Using a sputtering-deposited titanium substrate, incorporating six equally spaced nanolayers of Ti-W alloy, the volume and composition changes accompanying the formation of porous anodic films on titanium in 0.5 wt % NH 4 F in glycerol are investigated. The findings reveal amorphous films with nanotubes of TiO 2 , containing fluoride ions and possibly glycerol derivatives. Tungsten and titanium species are lost to the electrolyte at differing rates during anodizing, leading to an enrichment of tungsten in the film relative to the composition of the substrate. The spacing of tungsten-containing bands in the film is ∼2.3 that of the original alloy layers during growth of the major pores. The generation of the nanotubes can be explained either by field-assisted flow of film material within the barrier layer to the pore walls, with cation and anion transport numbers of anodic titania in the barrier layer region similar to those of barrier films and with field-assisted ejection of Ti 4+ ions to the electrolyte, or by field-assisted dissolution, but with a reduction in cation transport number.

Influence of Applied Potential on Titanium Oxide Nanotube Growth

The effect of applied potential on the morphology, growth efficiency, and composition of self-organized titanium oxide nanotubes, generated in 0.2 M N H4 F /glycerol electrolyte, has been examined by electron microscopy, Rutherford backscattering spectroscopy, and nuclear reaction analysis. A linear increase in nanotube diameter, length, and wall thickness, with increasing applied potential is evident up to 40 V, whereas the growth efficiency decreases with increase of the applied potential. Due to the semiconductive properties of the titanium oxide, at potentials above 40 V some of the oxygen anions migrating across the barrier layer lose electrons and generate oxygen gas within the oxide. This results in a morphological transition above 40 V, characterized by the degeneration of nanotube geometry and uniformity, and the appearance of oxygen-filled voids within the barrier layer and nanotubes walls.

Conical tungsten stamps for the replication of pore arrays in anodic aluminium oxide films

A tungsten master stamp has been generated by applying a novel procedure that includes two-step anodizing, followed by sequential anodizing and pore widening to develop nominally funnelled pores. These conical-shaped pores were filled with tungsten by sputter coating to manufacture a master stamp. Under a pressure of 65 MPa, the master stamp successfully embossed the surface of annealed and electropolished aluminium. The embossed surface was then used to control the position of pores created by anodizing under the conditions used to produce the original pore array.