STUDIES OF METALLIC SPECIES INCORPORATION DURING GROWTH OF SrBi_2Ta_2O_9 FILMS ON YBa_2Cu_3O_(7-x) SUBSTRATES USING MASS SPECTROSCOPY OF RECOILED IONS

摘要

The incorporation of metallic species (Bi, Sr and Ta) during the growth of layered perovskite SrBi_2Ta_2O_9 (SBT) on a-axis oriented YBa_2Cu_3O_(7-x) (YBCO) conducting oxide substrates has been investigated using in situ low energy mass spectroscopy of recoiled ions (MSRI). This technique is capable of providing monolayer-specific surface information relevant to the growth of single and multi-component thin films and layered heterostructures. The data show a temperature dependence of metallic species incorporation during co-deposition of Sr, Bi and Ta on YBCO surfaces. At high temperatures (400 < T ≤ 700°C), negligible incorporation of Bi is observed as compared to Ta and Sr. At low temperatures (≤ 400°C), there is a substantial incorporation of Bi, Sr and Ta on the surface of YBCO, and the MSRI signal intensities for Sr, Bi and Ta are nearly independent of substrate temperature. According to thermodynamic calculations, the presence of Ba and Y on the YBCO surface inhibit the incorporation of Bi due to competition for oxygen required to establish bonding of metallic species to the surface. This may be the explanation for the observed Bi deficiency in films grown on YBCO surfaces at temperatures > 400 °C. SBT films grown at temperatures ≤ 400 °C and annealed in oxygen or air at 800 °C exhibit a polycrystalline structure with partial a-axis orientation.