THE FORMATION, TRANSPORT-PROPERTIES AND MICROSTRUCTURE OF 45-DEGREES [001]GRAIN-BOUNDARIES INDUCED BY EPITAXY MODIFICATION IN YBA2CU3O7-X THIN-FILMS

Tilt grain-boundary junctions with a 45 degrees [001] misorientation w ere formed in YBa2Cu3O7-x (YBCO) thin films grown by pulsed organometa llic beam epitaxy on (100) MgO substrates. The junctions were introduc ed at predetermined locations due to a modification of the orientation relation between the thin film and substrate following a low-energy a rgon ion irradiation of specific areas of the substrate surface prior to film deposition. Rutherford backscatter spectrometry and certain su rface Features observed by atomic force microscopy indicate that impla ntation of ions is necessary to cause the modified epitaxy. The low-te mperature transport characteristics of individual isolated grain bound aries were determined by electromagnetic characterizations of the junc tion behavior. The same grain boundaries were examined by transmission electron microscopy and high-resolution electron microscopy and it wa s found that the boundaries are for the most part free of precipitates and well structured at the atomic scale. Regardless of the average gr ain boundary inclination, asymmetric (110)(100) facets dominate the mi crostructure of the junctions. Possible mechanisms for epitaxy modific ation and the transport properties in relation to the observed microst ructure are discussed.