ELECTRICAL AND OPTICAL CHARACTERISTICS OF SNO2 THIN-FILMS PREPARED BYDIP COATING FROM AQUEOUS COLLOIDAL SUSPENSIONS

Starting from aqueous colloidal suspensions, undoped and Nb5+ doped Sn O2 thin films have been prepared by using the dip-coating sol-gel proc ess. X-ray diffraction results show that films are polycrystalline wit h crystallites of average size 1-4 nm. Decreasing the thickness of the films and increasing the Nb5+ concentration limits the crystallite si ze growth during firing. Complex impedance measurements reveal capacit ive and resistive effects between adjacent crystallites or grains, cha racteristic of electrical potential barriers. The transfer of charge t hroughout these barriers determines the macroscopic electrical resista nce of the layer. The analysis of the optical absorption spectra shows that the samples present more than 80% of their transmittance in the visible region and the value of the band gap energy increases with dec reasing crystallite size.