Facts and artifacts of TEM specimen preparation for YBa₂Cu₃O_7-x superconductors

In this study, transmission electron microscopy (TEM) specimens of polycrystalline YBa₂Cu₃O_7-x (YBCO) superconductors were prepared by a variety of common techniques: crushing, ion beam thinning, and electrochemical-jet-polishing. Experimental techniques employed in the characterization of these specimens were SQUID measurements, transmission electron energy loss spectroscopy (EELS) analysis, and secondary ion mapping. In addition, a Monte Carlo computer simulation, known as transport of ions in matter (TRIM), was implemented to model the damage introduced during ion milling. Not surprisingly, the results suggest that oxygen stoichiometry of YBCO depends heavily upon the TEM specimen-preparation technique utilized. Crushing is the most optimal technique. The next most favorable technique is ion beam thinning at liquid-nitrogen temperature with low ion energy. Electrochemical-jet-polishing is promising, but care must be taken to remove residual surface contaminants deposited by the electrolyte solution. These results suggest the need for post-TEM specimen-preparation treatments, such as ozone annealing, to facilitate reoxygenation of the as-prepared TEM specimens.