Atomic layer-by-layer epitaxy of oxide superconductors by MOCVD

We have prepared thin films of c-axis oriented YBa2Cu3OX (YBCO) with a very smooth surface and roughness of less than a monomolecular layer of YBCO by atomic layer-by-layer metalorganic chemical vapor deposition on SrTiO3(100) and NdGaO3(110) substrates. A YBCO film with a large terrace width of 660 nm has been obtained on a NdGaO3(110) substrate. We have clarified the correlation between boulder formation and dislocations in the substrates by atomic force microscope observation. We have attempted to avoid producing boulder nuclei on dislocations exposed on the substrate surface by changing the usual sequence of source supply, Ba/Cu/Ba/Cu/Y/Cu, for 1 cycle into a new sequence, Ba/Ba/Y/Cu/Cu/Cu, and have successfully prevented the boulders. We also discuss issues of third generation precursors which are used in the liquid phase. We have also investigated hetero epitaxy of Sm2O3 ultrathin insulating films on YBCO thin films.