c-Axis-oriented (Hg0.9Re0.1)Ba2CaCu2Oy thin films were grown on the (100) p
lane of SrTiO3 substrates by a so-called two-step process. Transmission ele
ctron microscopic observation revealed that, in the film annealed under a h
igher temperature, some steplike regions appeared at the top layer of SrTiO
3 substrate. High-resolution transmission electron microscopic images showe
d that the lattice parameters in these regions are about 4.05-4.15 Angstrom
, being longer than the lattice parameter of SrTiO3. It is supposed that a
chemical reaction occurred in these regions, and a phase of (Ba-x,Sr1-x)(Cu
-y,Ti1-y)O3-delta was formed by partially substituted Ba for Sr and Cu for
Ti.