GROWTH AND ETCHING PHENOMENA OBSERVED BY STM AFM ON PULSED-LASER DEPOSITED YBA2CU3O7-DELTA FILMS/

The surface morphology of pulsed-laser deposited YBa2Cu3O7-delta films is investigated by STM AFM. Instead of spiral growth, a 2D nucleation and growth behaviour is observed. As we find these 2D nuclei also on high-oxygen pressure DC sputtered films grown at a much lower growth r ate, we conclude that the supersaturation is not a decisive parameter for the predominance of either growth mode. Instead, we attribute the absence of growth spirals to the non-steady state growth conditions in herent to the pulsed nature of the laser-ablation process. Growth spir als only develop, if a non-vanishing diffusional flow of adatoms towar ds the step edge is maintained. The number of growth spirals observed on a film is therefore not necessarily a measure for the number of scr ew dislocations. After wet-etching the films in Br-ethanol, we observe that etch pits are formed consisting of concentric steps. We conclude that these pits are due to repetitive nucleation around linear defect s. The etchpit density identified in this way is of the order of 1 per mu m(2).