Study of the fluorine content in precursor and Tl-based thin films by resonant nuclear reaction method

We prepared thin Tl-based films from Ba-Ca-Cu(O,F) precursors containing va rious amount of fluorine. The precursor films, 150 200 nm thick, were depos ited on MgO substrates by sequential thermal evaporation of BaF2, Cu and Ca F2 components. Before thallination, some of these precursors underwent a va rious degree of an ex-situ vacuum annealing with the aim to remove fluorine from the films. The fluorine content of three types of precursor films (as -deposited, partially annealed, fully annealed) was investigated by the res onant nuclear reaction method. Precursors were then thallinated and the amount of fluorine in superconduct ing films was measured again. Besides, films were characterized by resistan ce vs. temperature measurements and by X-ray diffraction (Bragg-Brentano an d grazing incidence geometry) as well as by Rutherford back-scattering spec trometry (chemical composition). Results of these investigations are report ed. (C) 2001 Elsevier Science B.V. All rights reserved.