The opposite of thermionic emission "Thermionic emission is the liberation of electrons from an electrode by virtue of its temperature (releasing of energy supplied by heat). This occurs because the thermal energy given to the charge carrier overcomes the work function of the material. The charge carriers can be electrons or ions, and in older literature are sometimes referred to as thermions. After emission, a charge that is equal in magnitude and opposite in sign to the total charge emitted is initially left behind in the emitting region." Source Wiki.
With this definition in mind, what is the opposite of this process? Upon subsequent cooling, would the object/electrode that has recently had its electrons thermionically emitted end up receiving electrons from the surrounding environment? If so, how does this process occur, and what is the term for this process? I've tried searching, but I'm lacking the write search term. How fascinating this is!
 A: What happens next depends on the circumstances.
If the heated object is is in a low air pressure environment and electrically isolated then as electrons are emitted from its surface the electrical potential of the object (relative to the Earth) will increase as the object will have a net positive charge.
Over time, as the potential of the object rises, it will be harder and harder for the electrons to escape from the object due to the electrostatic attraction between the electrons and the object and some emitted electrons will return back to the object.
Eventually when the potential of the object is high enough almost all the electrons will return back to the object.
On cooling the object will (slowly) loses its net positive charge depending on the number of electrons (eg produced by natural radiation) in the air and the resistivity of insulator that the object is resting on.
The more common scenario is that the heated object is electrically connected to earth and so that offers a "return" path for electrons back to the objects although in general the "returning" electrons will not be the same ones as those that ere emitted.
Thus the heated object stays electrically neutral and remains so when it is cooled.
I do not think that there is term which is the oppose of thermionic emission.
