Scanning transmission electron microscopy studies of the microstructure and chemistry of the YBa2Cu3O7-delta/BaF2 interface

A scanning transmission electron microscope (STEM) is used to examine the s tructural and chemical quality of the interface between thin films of YBa2C u3O7-delta (YBCO) and BaF2. The STEM images indicate that it is possible to grow a uniform thin film of BaF2 that is relatively free of gross defects via a thermal evaporation method on top of a YBCO thin film. The diffractio n contrast results also suggest that a three-dimensional or "island" growth mechanism is involved in BaF2 films grown by this method. An oxygen map ac ross the YBCO/BaF2 interface produced using core loss energy filtered imagi ng is used to address a concern regarding oxygen diffusion from YBCO into B aF2. It was found that a good quality BaF2 him can play a significant role in reducing outdiffusion of oxygen from YBCO. Quantitative evaluation of th e specimen oxygenation suggests that beam spreading effects may be importan t. The effect of an ultra-high vacuum (UHV) STEM environment on the specime n oxygenation is also considered. (C) 1999 Published by Elsevier Science Lt d. All rights reserved.