Analysis of FeF3 and NiF2 thin films by using RBS, (α, X) reactions, and SIMS measurements

The composition of FeF3 and NiF2 thin films, prepared by sublimation under vacuum, is investigated from several complementary analysis techniques (RBS, α, X reactions, and SIMS measurements). It greatly depends on fabrication parameters and further treatments. For a residual pressure in the preparation enclosure less than 10-7 Torr and a temperature, T/sub s/, of the substrate during the condensation of the vapour greater than 400 K for FeF3 and lower than 550 K for NiF2, the bulk composition of the layers is quasi stoichiometric. A lack of fluorine is observed near the two faces of the films. It is correlated to the presence of oxygen which probably corresponds to water adsorption, after an air exposure of the samples, followed by an hydrolysis of the compounds. This effect is considerably reduced by the presence of gold electrodes which protect the insulating layers, and in the conditions previously mentioned any diffusion can be noted. However in all cases some traces of impurities are pointed out, mainly: sodium, potassium, calcium, and chlorine, which are probably present in the initial powder. On the other hand, it is shown that FeF3 diffuses throughout a gold electrode for T/sub s/ < 400 K, while for NiF2, the content of fluorine decreases when T/sub s/ > 550 K or when the films are annealed. (author)