Jl. Lee et al., Scanning transmission electron microscopy studies of the microstructure and chemistry of the YBa2Cu3O7-delta/BaF2 interface, MICRON, 30(5), 1999, pp. 437-447
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.