Return of the Vacuum Tube (2012)
news.sciencemag.org
news.sciencemag.org
There are better articles.[1]
It's a low-power device, so it's not going to power terahertz radars. Fast logic, maybe, but that's a ways off.
[1] http://spectrum.ieee.org/semiconductors/devices/introducing-...
My understanding is that electrons wouldn't move at all in a vacuum because they require a conductor.
Electrons can propagae in the absense of a medium, in addition to within a conductor. You might thinking of their motion through conductors relative to insulators; but in that comparison, electrons don't (readily) move through insulators because they are impeded.
In the particular case of a vacuum tube, the electrons are freed from the surface of the filament, where they travel through the vacuum in a tube and are attracted via electrostatic forces, to the positively charged plate at the top of the tube.
Language is ambiguous, so it's important when asking questions like this to be really clear about what you mean by terms.
In particular: "insulator" is a term of convenience that groups together materials of sufficiently low conductivity under fairly normal conditions. What constitutes "sufficiently low" and "fairly normal" are both highly context dependent. Heat anything up enough and it'll become a conductor (it'll also become a plasma). If you use a term like "insulator" without keeping all this in mind it'll produce some pretty weird results.
So you can answer this question all kinds of ways. In normal high-voltage parlance, vacuums are considered insulators. But unlike insulating materials, which are full of electrons that can't move, vacuums are insulators purely because they don't contain any electrons.
If you inject electrons, the vacuum becomes a conductor... or at least the electrons do. After all, a vacuum is an absence of matter, and where there is an electron there is matter, so where there is an electron there is not a vacuum...