Epitaxial film growths of artificial (Bi-O)/(Sr-Ca-Cu-O) layered structures

Epitaxial film growth of artificial (Bi-O)/(Sr-Ca-Cu-O) layered structures on MgO substrates was carried out using reactive-oxygen-gas dual ion beam sputtering and shuttering technique. A 12 Å Sr-Ca-Cu-O buffer layer seems suitable for perfect epitaxial film growth. Single-phase films having periodicities of 12, 15, and 18 Å (which correspond to bulk 24, 30, and 36 Å phases in Bi oxide superconductors) were selectively grown by adjusting the thickness of a Sr-Ca-Cu-O layer sandwiched by Bi-O bi-planes. A high Tc phase film with a total thickness of about 300 Å showed an onset Tc of 110 K and a zero resistivity temperature of 45 K without post-deposition annealing. The shuttering technique seems to enable the layer-by-layer film growth, and it is very effective for the formation of smooth and perfect epitaxial structures.