X-RAY-DIFFRACTION ANALYSIS OF YBACUO ULTRA-THIN FILM GROWTH

The initial growth stages of YBaCuO films deposited by sputtering in t he thickness range of 0.6 to 5 nm on (100) SrTiO3 and MgO substrates h ave been studied by standard X-ray diffraction. A comparison of film t hicknesses estimated from line breadth with the nominal values indicat es layered growth in a unit cell by unit cell mode on SrTiO3 while isl and growth occurs on MgO until full coverage is reached at 5 nm. Pseud omorphic growth appears to be present on both substrates but restricte d to different film thicknesses, i.e., about 4 nm on SrTiO3 and one un it cell on MgO. In films with thicknesses up to two unit cells the YBa CuO ''123'' phase coexists with oxides of the cations, an appearance w hich also was observed in the BiSrCaCuO ''2223'' phase. The growth cha racteristics are in agreement with observations made by high resolutio n backscattering on similar films.