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

The photoelectrochemical properties of set-gel Nb2O5 coatings have been dis cussed in terms of their surface morphology. Niobium chloroalkoxide solutio n was prepared and thin films were deposited by dip-coating on the indium-t in oxide conductor glass. Structural, optical and electro-properties of amo rphous 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 in dicated which changes were introduced in the photoelectrical behaviour of t he semiconductor due to its crystalline structure. The absorption measureme nts showed an absorption band in the ultraviolet range associated with the electronic transfer O2- --> Nb5+ whose energy gap was around 3.3 eV. The ph otoelectrochemical measurements for the coatings were done in lithium percl orate and were used to determine the flat band potential, V-bp, and the ele ctron diffusion length, L. The influence of particle sizes in the charge-tr ansfer process at the semiconductor-electrolyte interface was discussed acc ording to the models of Gartner and Sodergren. (C) 1998 Chapman & Hall.