Effects of oxygen ion assist at 1–10 eV on growth of Bi2(Sr,Ca)2CuOx films at 540 °C by ion–beam sputtering

Abstract

Thin films of Bi2(Sr,Ca)2CuOx were prepared by ion-beam sputtering with low-energy (1–10 eV) oxygen ion assist. The 2201 phase with good crystallinity can be grown dominantly at very low temperature using only oxygen gas at a substrate temperature Ts=540 °C and average oxygen partial pressure Po=0.75 mTorr without assist. Single phase 2201 can be grown with assist under the same Ts and Po conditions. The assist exhibits other effects, such as promotions of 2201 growth and oxidation for lower Ts and Po and suppression of 2201 phase decomposition for higher Ts. The assist enhances Cu atom incorporation, and reduces excess Bi-composition and Bi-related impurity phases in the film. The assist also has effects on surface smoothing and modifies the c parameter. These depend more strongly on the assist ion flux than on energy, indicating that the enhancement of 2201 nucleation is the important mechanism for these effects, as well as the preferential resputtering by the assist ions.