GROWTH, MICROSTRUCTURE, AND ELECTROCHEMICAL OXIDATION OF MBE-GROWN C-AXIS LA2CUO4 THIN-FILMS

The growth, microstructure, and electrochemical oxygen intercalation o f c-axis La(2)CuO4(+delta) thin films on substrates with different lat tice mismatch [SrTiO3 (001) and SrLaAlO4 (001) substrates] are compare d. Except for the absence of planar defects in the latter case, the mi crostructural properties of both film types are very similar. For film s on SrTiO3, oxygen can be intercalated electrochemically into the gro wn c-axis thin film with a high diffusion coefficient (D-ox=10(-13)-10 (-14) cm(2)/s), and subsequently additional (001) reflections, l=2n+1, are observed by x-ray diffraction measurements. A double transition w ith a resistivity drop at similar or equal to 55 - 58 K, suggesting a more strongly oxidized phase, and a zero-resistance state at similar o r equal to 42 K are found. For films on SrLaAlO4, the value of T-c cou ld not be raised further, as the films decompose during the anodic pol arization. This comparison reveals the role of planar defects, and we propose an electrochemical oxidation mechanism that occurs in two step s: First oxygen is transported into the film by intercalation into the planar defects, and then a slower oxygen diffusion into the interstit ial sites occurs along the ab planes.