Electrochemical behaviour of low temperature grown iron fluoride thin films

By coupling a homemade substrate holder with a refrigerated ethanol cryogenic system, we succeeded in growing thin films by Pulsed Laser Deposition at substrate temperatures as low as -50 degrees C. The benefit of enlarging substrate temperatures to negative values is illustrated through the example of iron fluoride thin films, for which the substrate temperature is a key factor governing the FeF2 or/and FeF3 phase deposition. Using a FeF3 target, the X-ray diffraction study shows that the FeFx thin films grown at 600 degrees C correspond to a single well-crystallized FeF2 phase (S.G.: P4(2)/mnm) as opposed to a mixture of FeF3 and FeF2 phases for room temperature substrate, and a single FeF3 phase (S.G.: R (3) over barc) having quite an intense (012) Bragg peak at low temperature substrate (-50 degrees C). Such assignments were confirmed by complementary HRTEM and Mossbauer measurements with the exception of the -50 degrees C grown film that was shown to contain amorphous FeF2 together with crystallized FeF3 phases. The electrochemical behaviour of the FeFx thin films, namely their voltage profiles, was found to be dependent on the substrate grown temperature. (c) 2006 Elsevier B.V. All rights reserved.