X-ray diffraction analysis of YBaCuO ultra-thin film growth

The initial growth stages of YBaCuO films deposited by sputtering in the thickness range of 0.6 to 5 nm on (100) SrTiO3 and MgO substrates have been studied by standard X-ray diffraction. A comparison of film thicknesses estimated from line breadth with the nominal values indicates layered growth in a unit cell by unit cell mode on SrTiO3 while island growth occurs on MgO until full coverage is reached at 5 nm. Pseudomorphic growth appears to be present on both substrates but restricted to different film thicknesses, i.e., about 4 nm on SrTiO3 and one unit cell on MgO. In films with thicknesses up to two unit cells the YBaCuO ''123'' phase coexists with oxides of the cations, an appearance which also was observed in the BiSrCaCuO ''2223'' phase. The growth characteristics are in agreement with observations made by high resolution backscattering on similar films.