  Thresholds for beam damage have been assessed for La$_{0.7}$Sr$_{0.3}$MnO$_3$
and SrTiO$_3$ as a function of electron probe current and exposure time at 80
and 200 kV acceleration voltage. The materials were exposed to an intense
electron probe by aberration corrected scanning transmission electron
microscopy (STEM) with simultaneous acquisition of electron energy loss
spectroscopy (EELS) data. Electron beam damage was identified by changes of the
core loss fine structure after quantification by a refined and improved model
based approach. At 200 kV acceleration voltage, damage in SrTiO$_3$ was
identified by changes both in the EEL fine structure and by contrast changes in
the STEM images. However, the changes in the STEM image contrast as introduced
by minor damage can be difficult to detect under several common experimental
conditions. No damage was observed in SrTiO$_3$ at 80 kV acceleration voltage,
independent of probe current and exposure time. In La$_{0.7}$Sr$_{0.3}$MnO$_3$,
beam damage was observed at both 80 and 200 kV acceleration voltages. This
damage was observed by large changes in the EEL fine structure, but not by any
detectable changes in the STEM images. The typical method to validate if damage
has been introduced during acquisitions is to compare STEM images prior to and
after spectroscopy. Quantifications in this work show that this method possibly
can result in misinterpretation of beam damage as changes of material
properties.
