Preparation of Oxide Nanofibers for Analysis by Transmission Electron Microscopy

The low electronic conductivity and rigid structure make sample preparation for in situ transmission electron microscopy (TEM) of oxide nanofibers challenging. This work evaluates three sample preparation approaches for mounting single oxide nanofibers on MEMS chips: (i) drop casting combined with focused ion beam (FIB) cutting and metal deposition, (ii) single-probe micromanipulation, and (iii) double-probe micromanipulation inside a FIB-SEM. Advantages and limitations of each method are discussed, including issues of fiber agglomeration, positioning/orientation, and charging in the electron or ion beam. Drop casting offers simplicity but poor positional control. The probe-based methods enable precise positioning; charging however remains a major challenge which is best compensated for by using more than one microprobe. Strategies for improving electrical contact and minimizing contamination during metal deposition are also addressed. The findings provide practical guidelines for preparing oxide nanofibers for operando TEM experiments involving electrical and thermal stimuli.