INVESTIGATION OF CRITICAL CURRENTS IN YBCO TRACKS OVER STEPS IN SRTIO3 SUBSTRATES USING LOW-TEMPERATURE SEM BEAM-INDUCED VOLTAGE CONTRAST

Electron beam induced voltage contrast has been used to investigate th e current flow in thin film YB2Cu3O7-x (YBCO) tracks, deposited over m eanders in SrTiO3 substrates. Different film thicknesses and step heig hts have been studies and related to critical current and atomic force microscopy (AFM) measurements. Tracks with higher critical currents ( I-c) exhibited voltage contrast at steps. The contrast along individua l step edges and between different step edges was found to be reasonab ly uniform. AFM measurements indicated that in some tracks step profil es contained two gradients. Such steps were not found to have a major effect on the I-c of the YBCO track presumably because the extra gradi ent was very shallow. Tracks with reduced critical currents were limit ed by one or a few steps and showed non uniform contrast along the ste ps. AFM measurements indicated a difference in surface roughness betwe en milled and non-milled surfaces. Any such roughness occurring at a s tep could account for the low I-c's found in some tracks. One sample e xhibited contrast on meander plateaus rather than at step edges. Criti cal current measurements prior to and after low temperature scanning e lectron microscopy (LTSEM) measurements indicated that this sample had become damaged.