The formation of oxynitride films less than 2.0 nm by using oxygen and nitrogen radicals produced by an electron cyclotron resonance plasma in an ultrahigh-vacuum system has been studied. We found that the N concentration can be controlled at values up to 15% and that, although the interface roughness tends to increase with increasing N concentration, supplying oxygen and nitrogen radicals simultaneously decreases the roughness of the film and increases its nitrogen concentration (N: 12.1%, root mean square: 0.12 nm). We also could easily control the nitrogen profile in the oxynitride less than 2.0-nm-thick by using different processing sequences.
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.
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