What kind of microscope is used to see the electronic flow on a microchip?
Conventional electron microscopes, SEMs, can 'see voltage' on conducting surfaces when adjusted just right.  I've seen old still photos from the 1970s where a reversed diode junction is visible, and where metallization has black or silver color depending on surface charge.   I've always wondered if they ever used this technique to observe slow-clocked logic.  (The e-beam may inject negative charge and interfere with analog, or with any floating inputs.)

Just went looking, and immediately found a youtube vid of animated voltage signals, an ad for someone's SEM system.

Here's a much older one: MOS transistor sections viewed with SEM.   Search for keywords "voltage contrast," also VC-SEM