High resolution RES study of the growth and the crystalline quality of ultrathin YBaCuO films

A high energy resolution detection system consisting of a toroidal electrostatic analyzer combined with a novel two-dimensional detector has been installed in a UHV scattering chamber, The angular resolution achieved with this system was 0.33 degrees over a range of 23 degrees, and the energy resolution, Delta E/E, was 1.95 X 10(-3) over a range of 2.1% of the pass energy. We applied medium energy ion scattering (200 keV He+ ions) combined with channeling to study the initial growth phenomena and the crystalline quality of YBaCuO ultrathin films on (100) SrTiO3 and MgO substrates exploiting the high depth resolution of the detection system which was 0.5 nm for YBaCuO, The determination of the coverage as a function of depth revealed that on both substrates the films grow in blocks of one unit cell, But on SrTiO3 the growth of an additional block layer is initiated only after completion of the preceding layer while on MgO island growth is observed with different coverage values on three layer levels appearing simultaneously, On SrTiO3 the growth up to a critical thickness of 4 nm is pseudomorphic (chi(min) = 2%); at larger thicknesses strain release accompanied by defect incorporation leads to chi(min) enhancement (12%).