Investigation of critical currents in YBCO tracks over steps in SrTiO/sub 3/ substrates using low temperature SEM beam induced voltage contrast

Abstract

Electron beam induced voltage contrast has been used to investigate the current flow in thin film YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) tracks, deposited over meanders in SrTiO/sub 3/ substrates. Different film thicknesses and step heights have been studied and related to critical current and atomic force microscopy (AFM) measurements. Tracks with higher critical currents (I/sub c/) exhibited voltage contrast at steps. The contrast along individual step edges and between different step edges was found to be reasonably uniform, AFM measurements indicated that in some tracks step profiles contained two gradients. Such steps were not found to have a major effect on the I/sub c/ of the YBCO track presumably because the extra gradient was very shallow. Tracks with reduced critical currents were limited by one or a few steps and showed non uniform contrast along the steps. AFM measurements indicated a difference in surface roughness between milled and non-milled surfaces. Any such roughness occurring at a step could account for the low I/sub c/'s found in some tracks. One sample exhibited contrast on meander plateaus Rather than at step edges. Critical current measurements prior to and after low temperature scanning electron microscopy (LTSEM) measurements indicated that this sample had become damaged.