Niobia films: surface morphology, surface analysis, photoelectrochemical properties and crystallization process

The photoelectrochemical properties of sol–gel Nb2O5 coatings have been discussed in terms of their surface morphology. Niobium chloroalkoxide solution was prepared and thin films were deposited by dip-coating on the indium–tin oxide conductor glass. Structural, optical and electro-properties of amorphous and crystalline sol–gel coatings have been determined. Powders were prepared by the hydrolysis of amorphous niobium and were characterized by X-ray diffraction and electron paramagnetic resonance. These measurements indicated which changes were introduced in the photoelectrical behaviour of the semiconductor due to its crystalline structure. The absorption measurements showed an absorption band in the ultraviolet range associated with the electronic transfer O2-→Nb5+ whose energy gap was around 3.3 eV. The photoelectrochemical measurements for the coatings were done in lithium perclorate and were used to determine the flat band potential, Vbp, and the electron diffusion length, L. The influence of particle sizes in the charge-transfer process at the semiconductor–electrolyte interface was discussed according to the models of Gartner and Sodergren. © 1998 Chapman & Hall