Diffraction studies of crystals depend on interferences between planes of electron density, whose spacing must be greater than the wavelength. Since the shortest bonds are about 0.1 nm, such planes are unlikely to be closer than 0.1 nm. Thus this is an appropriate target wavelength to use for crystal structure studies where one wants to determine all the atom positions, and it lies in the x-ray region. If you wished to get the same sort of resolution with an electron beam, you would excite it through a potential gradient (two plates at different voltages with the positive one having an exit hole to form the beam).
i. What would be the momentum of an electron needed to match the ideal 0.1 nm x-ray?
ii. What voltage would be required on the plates to get this beam?