SCANNING-TUNNELING-MICROSCOPY OF EPITAXIAL YBA2CU3O7-X FILMS PREPAREDBY THERMAL PLASMA FLASH EVAPORATION METHOD

The surface morphology of epitaxial YBa2Cu3O7-x films prepared by ther mal plasma flash evaporation was extensively investigated by scanning tunneling microscopy. Under epitaxial film growth conditions with the deposition rate up to 0.42 mu m/min, two-dimensional nucleus growth an d spiral growth were observed. The main deposition species in this pro cess was found to be the cluster ranging from 0.3 to 9 nm and the size of the cluster influenced the growth mode strongly. Theoretical analy sis based on the two-dimensional critical radius revealed that smaller clusters became weakly bended nuclei resulting in spiral growth and l arger clusters became stable nuclei resulting in two-dimensional nucle us growth, which we named two-dimensional cluster nucleus growth. The clusters generated in the plasma boundary layer undoubtedly involve su fficient energy necessary for crystallization and show quite different characteristics from those of the clusters generated in vacuum by adi abatic expansion process. Hence, this process must be named ''hot clus ter epitaxy.'' (C) 1997 American Institute of Physics.