TLD: Adjust detector settings to capture SE and BSE signal 

This video describes the different "modes" available when using the Through-the-Lens Detector (TLD). Each mode correlates to a different voltage placed on the detector's "suction tube." Positive voltage attracts low energy secondary electrons (SEs) for a topographically contrasted image; negative voltage rejects those low energy SEs and only allows through the high energy backscattered electrons (BSEs) that yield an atomic number (Z) contrasted image; and zero voltage can sometimes help with charging artifacts and/or eliminate beam drift (custom mode allows you to adjust the suction tube voltage slide bar to your liking). Experiment with the detector bias in both field free and immersion mode (most dramatic effects are found in the latter) to vary the type of signal that you collect with the TLD. Note that a similar concept can be applied to the Everhart-Thornley Detector (ETD), although the effects there are less dramatic/useful for e.g. BSE imaging.
Disclaimer: This video intended to serve as supplemental information and cannot replace in-person instrument training. Microscope operators are encouraged to consider which parameter setting is most suitable for their measurements. Caltech and KNI are not responsible for how the presented information is translated for use in other facilities.