MOTIVATION: The resolution of scanning electron microscope (SEM) images is limited by multiple factors, one of them being relatively low electron-beam current density emitted by cheap tungsten filament sources.
Of course, one can reduce the numerical aperture of the SEM to get somewhat better resolution (20~50 nm), but then the e-beam current drops down to picoampere level, images get noisy and it takes minutes to take them.
Much better scanning speeds and/or image quality can be acquired when extremely bright e-beam is formed by a field-emission gun (FEG) using a cold sharp tungsten tip.
Since I have an access to an older SEM (which needs to replace the filament anyway), to a spot welder and to an inexpensive source of etched tungsten tips with radius well below 50nm, I can quite simply weld the sharp tip to the filament holder and place it in the Wehnelt assembly where normally a hot filament is found.
1) Has anybody tried this before? Is there any fundamental change in the electron source geometry that prevents converting thermal-emission source to FEG source?
2) Field-emission SEM are known to run at ultrahigh vacuum (<10⁻⁸ mbar). Does any FE-SEM user have an experience what happened to the electron gun when this vacuum was compromised to roughly 10⁻⁶ mbar? (This is lower-quality vacuum typically used in a filament SEMs.)
3) Is there some hidden pitfall that could permanently damage the microscope if I do this simple experiment myself? Is there any other risk (except risking the loss of my time)?