Influence of the crystallization process on the photoelectrochemical behaviour of anodic TiO₂ films

Abstract

On the basis of kinetic and photoelectrochemical studies we show that the formation of amorphous or strongly disordered TiO, f i i s on electropolished titanium rods can occur upon anodization in 0.5 M H,SO, solution in a range of thickness which depends on the anodization rate. This finding is confirmed both by the changes in the shape of the photocurrent vs. potential curves with the energy of the incident photons, and by the impedance behaviour of the junction.Our data indicate that TiO, films having different degree of disorder are formed depending on the anodization rate and oxide thickness. Crystalline films are formed at very low growth rates since very low thicknesses. Amorphous or strongly disordered films can be grown at high oxidation rates ( 2 100 mV/s) before the onset of a crystallization process. At higher thicknesses a gradual crystallization process takes place, as revealed both by the decrease of the anodizing current during the tensiodynamic growth and by the changes in the shape of the photocurrent vs. potential curves. The onset of the crystallization process of the film occurs at higher thicknesses with increasing the growth rate.

Photo-electrochemical investigation of anodic oxide films on cast Ti–Mo alloys. I. Anodic behaviour and effect of alloy composition

“…The behaviour depicted above resembles that of pure Ti metal [17][18][19][20][21], which forms in the exploited solutions barrier-type oxide films, growing according to the high-field law:…”

Effect of Composition on the Photoelectrochemical Behavior of Anodic Oxides on Binary Aluminum Alloys

“…36 The larger value measured for the Al-Ta alloy is unsurprising, as amorphous alumina and tantala films form under the current growth conditions, while partially crystalline oxides occur for titanium. 38 With increased formation voltage, E g opt for the Al-Ta mixed oxide decreases which, according to Eq. 5 and 6, can only be related to a reduced ⌬E am , as the Pauling electronegativities of aluminum and tantalum are equal.…”

“…This value is lower than the previous one and is in agreement with the tendency of TiO 2 film to crystallize during the anodizing process since low voltages and more easily as lower the growth rate is. 38 For the Al-53 atom % Ti alloy, E g opt decreases with increase of forming voltage ͑Table VIII͒. In this case a decrease in ⌬E am cannot explain the photocurrent spectra behavior of the films, since ⌬E am Յ 0 is required to fit results using Eq.…”

Photoelectrochemical properties of MoO2 thin films

“…5) was built (Table 3) were used for diagrams drawing. The conduction band mobility edge (E CB ) by analogy with (E CB −E F ) values reported for amorphous metal oxide films [43,45,46] was assumed to be approximately 0.4 eV above the E F .…”