NUCLEATION AND GROWTH OF PRBA2CU3O7-DELTA BARRIER LAYERS ON RAMPS IN DYBA2CU3O7-DELTA STUDIED BY ATOMIC-FORCE MICROSCOPY

We studied the microstructure of Ar ion-beam etched ramps in epitaxial DYBa2Cu3O7-delta films by atomic force microscopy. Generally, ramps w ere well aligned (phi approximate to 0 degrees) With one of the crysta l axes of the (001) SrTiO3 substrate. In those cases we observed a sur face reconstruction into a regular pattern of very long (up to 0.5 mu m), about 20 nm wide facets, parallel to the ramp edge. For high misor ientation angles (phi>0 degrees), the reconstruction appeared much mor e complex and less regular. Furthermore, we investigated the nucleatio n and growth of very thin barrier layers of PrBa2Cu3O7-delta on well a ligned ramps. We found that nucleation takes place in the shallow tren ches in the ramp, where facets meet. When more material is deposited, islands coalesce to form closed domains parallel to the trenches. This causes a thickness modulation close to 100% for barrier layer thickne ss up to 6 nm. The conclusions drawn from this research allow for an i mportant improvement of the technology for the fabrication of ramp-typ e junctions. (C) 1996 American Institute of Physics.