Oxygen molecule is more effective than plasma on ultralow temperature growth of Bi2Sr2CuOx thin films by ion beam sputtering

Excellent Bi 2 Sr 2 CuO x (2201) thin films were fabricated by ion beam sputtering at extremely low substrate temperatures ( T s =400–550°C) by supplying oxygen molecules or plasma. The 2201 crystalline films could be grown at 450°C by the plasma, whereas unexpectedly be grown at 400°C by the molecules. Their crystallinity and surface morphology were improved by the supply of molecules instead of plasma. A half width of (008) peak in X-ray diffraction was 0.06° for T s =550°C and a surface roughness was 4.5 nm for 400°C. However, the crystal growth of Ca-doped Bi2201 was improved by the plasma. Collisions between the oxygen molecules and sputtered particles in gas phase play important roles on these effects. This result implies a possibility of very low temperature growth of other perovskite oxide films.