MONOSTEPS ON EXTREMELY FLAT YBA2CU3O7-X SURFACES GROWN BY LIQUID-PHASE EPITAXY

We report the growth of extremely flat YBa2Cu3O7-x (YBCO) films onto N dGaO3 substrates by liquid-phase epitaxy (LPE). Macroscopic growth spi rals with large interstep distances (several mum) and with hollow core s are observed by optical (Nomarski) microscopy and by atomic force mi croscopy, in contrast to the microscopic spiral islands formed in epit axy 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 s urfaces with continuous step flow have been achieved. They are of inte rest for fundamental physical studies (gap, photoemission) and for a r eliable high-temperature superconductivity tunnel-device technology.