In classical Physics wave theory (GCSE level) we talk about waves diffracting through a gap if the gap is similar size to (or smaller than) the wavelength of the waves. When firing fast electrons at a carbon target (teltron tube A level type apparatus) is it sufficient to say that if the de Broglie wavelength of the electrons (h/momentum) is similar to the interatomic spacing ( so the 'gaps') then we get good diffraction? If this interpretation is acceptable (ish) then my question is that if you slow down the electrons then their deBroglie wavelength increases (smaller momentum) but then they should still then show good diffraction because good diffraction occurs if wavelength is similar to (or larger than) the gap the 'wave' is passing through. If indeed slow electrons do show good diffraction then why the need for high voltages to accelerate the electrons to such a high speed using large voltages? Would love to have the kit myself to play with, unfortunately not!! Appreciate any thoughts. Glenn.