SURFACE AND INTERFACE CHARACTERIZATION OF HIGH-T(C) RELATED EPITAXIAL-FILMS BY STM STS AND XPS/

We have fabricated high quality and chemically stable epitaxial films of YBa2Cu3O7-delta (YBCO) and SrTiO3 by pulsed laser deposition (PLD) technique and investigated their surface morphology, electronic state, and growth mode. The cryoganic STM/STS measurements on small area (4x 4nm) c-oriented YBCO films resulted in the simultaneous observations o f lattice images and tunneling spectra with 20meV energy gap. A gap sp ectrum exhibited almost zero conductance, favoring s-wave superconduct ivity. Wider scans of the film surfaces by AFM and SEM, however, revea led granular structure of the surfaces with a root mean square (rms) r oughness of 5nm, which is far larger than the coherence length of YBCO . Much smoother surfaces were obtained for a- and (110) oriented films . Atomic images and conductive layers could be identified by STM for t hese films. The surface morphology of epitaxial SrTiO3 films prepared under high vacuum (<10(-5)Torr:MBE) conditions was found to be improve d to such an extent as to show atomically flat images in AFM and STM a nalyses. By in situ XPS analyses, valence states and film growth mode of SrTiO3 epitaxial films were elucidated on an atomic layer level. Di scussions are extended to the processes for controlling the growth mod e and carrieres of high Tc related oxide films as well s for fabricati ng SIS tunnel junctions.