Ion beam analysis of laser-deposited high T c YBa 2 Cu 3 O 7 superconducting thin films
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We have performed Rutherford backscattering spectrometry, non-Rutherford proton elastic scattering, and axial ion channeling analysis to determine the composition, the crystallinity, and the epitaxial quality of YBa2Cu3O7 superconducting thin films on (100) SrTiO3 and (100) yttria stabilized zirconia (YSZ) substrates. YBa2Cu3O7 superconducting thin films were fabricated both by high and low temperature laser ablation techniques. The former method requires high temperature annealing in oxygen to recover the superconducting properties, whereas in the latter method as-deposited in situ superconducting thin films are formed at low processing temperatures (500 °C-650 °C). Helium ions in the energy range of 2.0-2.5 MeV were used to determine the relative stoichiometries of the heavier atomic number elements (Y, Ba, Cu) in the film, but are not sensitive enough to determine the relative amount of oxygen in the superconducting phase. The detection sensitivities to oxygen can be greatly enhanced by using the proton elastic scattering [16O(p,p) 16O] reaction, which was found to increase the scattering cross section by a factor of 3 to 5 relative to the Rutherford scattering cross section. The ion-channeling of YBa2Cu3O7 superconducting thin films on (100) SrTiO3 substrates showed excellent minimum channeling yields corresponding to epitaxial growth, but the presence of defects increased the channeling yields for films deposited on (100) YSZ substrates. The ion channeling yields are compared with the microstructure of the films determined by transmission electron microscopy.
I. INTRODUCTION
High energy ion beams have been extensively used in compositional as well as structural analysis of new high Tc YBa2Cu3O7 superconductors.1 4 As the Rutherford scattering cross section of different elements is known, Rutherford backscattering spectrometry (RBS) involving He + ions provides an absolute quantitative compositional analysis of materials, and is particularly well suited in the analysis of YBa 2Cu3O7 materials which contain heavy atomic number elements (e.g., Cu, Y, and Ba).5 The Rutherford scattering cross section depends on the ratio of the square of the atomic number of the target element with the incident energy of the ions. Thus, the main drawback of RBS is the poor sensitivity of 4He+ to detect light elements on heavier substrates, which considerably decreases the statistical accuracy. As a consequence, oxygen concentrations below 50 at.% are not detectable in YBa 2 Cu 3 O 7 thin films.2 Nuclear reactions including nuclear resonant scattering and nuclear potential scattering can be used effectively in increasing the scattering cross section a)Current
address: Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611.
J. Mater. Res., Vol. 5, No. 9, Sep 1990
http://journals.cambridge.org
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of oxygen.6"10 The nuclear resonance reaction, 16O(a,a) 16O, at 3.045 MeV has been employed to profile the oxygen concentration in superconducting thin films.1'4 However
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