Monosteps on extremely flat YBa2Cu3O7−x surfaces grown by liquid-phase epitaxy

Abstract
We report the growth of extremely flat YBa2Cu3O7−x (YBCO) films onto NdGaO3 substrates by liquid‐phase epitaxy (LPE). Macroscopic growth spirals with large interstep distances (several μm) and with hollow cores are observed by optical (Nomarski) microscopy and by atomic force microscopy, in contrast to the microscopic spiral islands formed in epitaxy from the vapor phase. Typical step heights of LPE‐grown YBCO vary between monosteps (1.2 nm) and 7.2 nm. Extremely flat epitaxial YBCO surfaces with continuous step flow have been achieved. They are of interest for fundamental physical studies (gap, photoemission) and for a reliable high‐temperature superconductivity tunnel‐device technology.