Pergamon 1 . INTRODUCTION
Many fields of application, including solid-state systems (window coatings, solar cells, electrochromics, display panels) and electrochemical interfaces (spectro and photoelectrocheniistry) require transparent conductors[)-4] Instead of the very thin metal layers, wide band-gap oxides, especially indium and tin oxides, offer a satisfying compromise between a good optical transparency in the visible light spectrum and a high electrical conductivity For all these purposes, thin polycrystalline films are generally deposited onto glass or semiconducting substrates Various deposition techniques can be used to ensure a good crystallinity for the transparency and a control of electrical conduction by creating welldefined structural defects (oxygen vacancies, substitutional or interstitial doping by foreign atoms) Note that these materials can also be used just for their electrical properties, for instance as gas sensors[5] (surface conduction) or as bulk electrodes to oxidize organics in waste water [6] In this paper, we are dealing with tin dioxide films (SnO 2) prepared by spray pyrolysis Among the variety of the existing deposition methods, spray pyrolysis is attractive because of its relative simplicity, its reproducibility and the possibility to vary the conditions of film preparation over a wide scale depending on the application considered [3, 4] Tin oxide is formed by thermal decomposition of methanolic solutions of Keynote lecture presented at the 44th ISE Meeting m Berlin 0013-4686(94)E0044-Z