Ordered YBCO sub-micron array structures induced by pulsed femtosecond laser irradiation

We report on the formation of organized sub-micron YBa₂Cu ₃O₇ (YBCO) dots induced by irradiating femtosecond laser pulses on YBCO films prepared by pulse laser deposition with fluence in the range of 0.21∼0.53 J/cm². The morphology of the YBCO film surface depends strongly on the laser fluences irradiated. At lower laser fluence (∼0.21 J/cm²) the morphology was pattern of periodic ripples with sub-micrometer spacing. Slightly increasing the laser fluence to 0.26 J/cm ² changes the pattern into organized sub-micron dots with diameters ranging from 100 nm to 800 nm and height of 150 nm. Further increase of the laser fluence to over 0.32 J/cm², however, appeared to result in massive melting and led to irregular morphology. The mechanism and the implications of the current findings will be discussed. Arrays of YBCO sub-micron dots with T_c = 89.7 K were obtained.