Compositional analysis of YBaCuO superconducting films with ion beam analysis techniques

High-Tc YBaxCuyO7-δ superconducting films are being developed for applications such as superconducting quantum interference devices. The carrier concentration, critical current density Jc and critical temperature Tc of these films depend sensitively on the oxygen content . Stoichiometry, uniformity with depth, homogeneity across the sample and film thickness are also important quantities for their characterisation. It has been shown, for example, that the stoichiometry of the metallic elements affects the growth characteristics and surface morphology of the films. With the deposit ion techniques used, reproducibility of film properties is difficult. The characterisation of YBaxCuyO7-δ films with ion beam analysis techniques is complex. Whereas the three metallic elements can be detected with helium beams and Rutherford Backscattering (RBS), the oxygen signal is generally obscured by that from substrate elements. It can be better detected using resonant backscattering with 3.04MeV 4He ions or nuclear reaction analysis. Elastic Recoil Detection (ERD) with high-energetic (1MeV/amu), heavy beams (Z > 120), enables all elements to be detected and separated in a single experiment. It is well established that ion bombardment induces vacancies in the oxygen sub-lattice, driving the material to change from crystalline to amorphous, the latter phase having a reduced oxygen content. In previous heavy ion ERD measurements of YBaxCuyOz films with 200MeV 127I beams, the opaque films became transparent in the beam spot area, indicative of the amorphous phase. The accuracy of the oxygen measurement is therefore questionable. Indeed, using Raman spectroscopy, distortions of the crystalline structure above a fluence of 5 x 1011 ion/cm2 and for higher doses some signatures of a reduction in oxygen content have been observed for such beams. It appears therefore that a correct determination of the oxygen content requires either a drastic reduction in fluence or a containment of the oxygen inside the film. In the present study a series of YBaxCuyO films have been analysed with heavy ion ERD using 197Au beams and a gas ionisation detector with large acceptance angle. RBS with 4He and 28Si projectiles was also performed. The results from these three techniques have been compared and the reliability of the oxygen measurement with heavy ion ERD has been evaluated