NUCLEATION MECHANISM OF YBA2CU3O7-DELTA ON SRTIO3(001)

Using UHV-scanning-tunneling microscopy and spectroscopy we show that submonolayer coverages of YBa2Cu3O7-delta deposited on SrTiO3(001) nuc leate as cubic, semiconducting (Y, Ba)CuO3-x phase as proven by the he ight of the nuclei and their density of states. Nuclei are observed at upper step edges and on the substrate terraces exclusively. Minimizat ion of surface and interface energies forces this nucleation behavior. At about one monolayer, the film transforms into the orthorhombic, me tallic YBa2Cu3O7-delta phase indicating that the formation enthalpy of the bulk phases now dominates the growth process.