Investigation of a single crystal YBCO superconductor by micro-RBS technique

The stoichiometry of a single crystal (1.5 × 1.3 × 0.075 mm³) of YBCO superconductor was investigated using Rutherford Backscattering Spectrometry (RBS). Initially a 2 MeV α-macrobeam of ≈ 2 mm diameter was used encompassing the entire crystal. The macrobeam-RBS spectrum had an unusual shape, indicating lateral and/or depth nonuniformity in the crystal, and could not be analyzed to obtain stoichiometric information. SEM micrographs revealed a small crystal overgrowth (0.34 × 0.34 × 0.1 mm³) protruding out of the main crystal, with an uneven interface between the two parts. An α-microbeam of 80 μm resolution was then used to investigate each of the three regions separately. The microbeam-RBS spectra from the main crystal and the smaller crystal over-growth could be fitted reasonably well with RUMP simulation assuming lateral and depth uniformity, both yielding a stoichiometry of Y₁Ba_1.8Cu₃O_6.7/Au_0.08 (Au being a contaminant). This is close to the ideal stoichiometry of Y₁Ba₂Cu₃O_6.9.