Atomic scale engineering of SrTiO_3 single crystal surfaces and bicrystal boundaries for epitaxial growth of oxide thin films

摘要

We introduce a new annealing procedure to prepare well defined surfaces of SrtiO_3 single crystal and bicrystal substrates. Annealing SrTiO_3 (001) substrates in oxygen and then in ultra high vacuum produces a uniformly TiO_2-terminated, atomically flat and ordered SrTiO_3 (001) surfaces, as revealed by Auger electron spectroscopy, low energy electron diffraction, and high resolution scanning tunneling microscopy. Applying this annealing procedure to slightly off-cut (approx 1.2 deg) SrTiO_3(001) surfaces has a strong influence on the resulting step structure. Patticular annealing procedures can be used to tailor the structure and morphology of the surface and of bicrystal boundaries down to the atomic level. For example, steps of SrTiO_3 (001) surfaces can be adjusted to a height of one, two, or multiple times the unit-cell size of STO (a_STO= 0.3905 nm). Atomically flat SrTiO_3(001) substrates were used for deposition of SmBa_2Cu_3O_7- delta (SBCO) thin films. The thickness (in range from 10 nm to 200 nm) dependency of the surface morphology of SmBa_2Cu_3O_7- delta films was investigated with UHV-STM.No spiral growth was observed. Surfaces of all films exhibit stacks of flat terraces which are frequently separated by steps, smaller than the c-axis length c_SBCO of SBCO (c_SBCO=1.17 nm).