Molecular-beam epitaxial growth and characterization of Bi–Sr–Co–O thin films

Abstract

The thin-film growth of Co oxides and layered Bi–Sr–Co–O compounds was investigated in detail under an ozone ambient. All samples were prepared using a molecular-beam-epitaxy machine modified for the growth of Bi-based high-temperature superconductors. The temperature versus pressure phase diagram of Co oxidation was determined for growth on Nd:YAlO3 substrates. According to the phase diagram, Bi2Sr2CoO6+α and Bi2Sr3Co2O9+β were grown on Nd:YAlO3 (001). The boundary between the stable regions of them is basically the same as that between CoO and Co3O4. Bi2Sr2CoO6+α was an insulator with an activation energy of approximately 0.20 ± 0.01 eV. Bi2Sr3Co2O9+β shows metallic behavior down to 80 K, and the carriers are revealed to be holes by Hall-effect measurement.