Nucleation Mechanism ofYBa2Cu3O7−δonSrTiO3(001)

Abstract

Using UHV-scanning-tunneling microscopy and spectroscopy we show that submonolayer coverages of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ deposited on ${\mathrm{SrTiO}}_{3}(001)$ nucleate as cubic, semiconducting $(\mathrm{Y},\mathrm{Ba}){\mathrm{CuO}}_{3\ensuremath{-}x}$ phase as proven by the height of the nuclei and their density of states. Nuclei are observed at upper step edges and on the substrate terraces exclusively. Minimization of surface and interface energies forces this nucleation behavior. At about one monolayer, the film transforms into the orthorhombic, metallic ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ phase indicating that the formation enthalpy of the bulk phases now dominates the growth process.