Dynamics of the charging-induced imaging instability in transmission electron microscope

Revolutionary microscopy technologies for aberration correction in spatial and energy aspects have exhibited continuous progress, pushing forward the information limit of materials research down to a scale of sub-angstrom and milli-electron voltage. Nevertheless, imaging quality could still suffer due to sample instability, e.g. the charging effect, which always comes along with electron microscopy characterizations. Herein, using a defocus estimation algorithm and an in situ image feature tracking method, we quantitatively studied the image drifting dynamics induced by the charging on transmission electron microscopy (TEM) carrier grids with tunable electrical conductivity. Experimental evidence clarifies the debate about the charge types, proving that the irradiation of the electron beam induces a positive charge on the grid sample of poor electrical conductivity. Such charge accumulation accounts for subsequent imaging instability, including the increase of defocus and the drift of lateral images. Particularly, the competition between charging and discharging was found to dynamically modulate the propagation of electron beam, resulting in a periodically reciprocating movement on TEM images. These findings enrich understanding on the dynamic principle of charging effects as well as the details of image drifting behaviors. It also suggests specific attention on the importance of conductivity control on a TEM specimen, beyond all the efforts for instrumental improvements.