Reducing the field emission energy spread of metal tip by tailoring the barrier shape

Finding alternative ways to reduce the field emission energy spread is highly significant for advancing high monochromatic electron sources. This work is proposed to utilize the fractional barrier shape of the metal tip structure, induced by the field concentration effect, to suppress the energy spread. Simulations indicated that the tip radius plays the most important role in the barrier shape among the geometrical parameters of the metal tip field emitter. As the tip radius decreased from 50 nm (where the barrier can be approximated as triangular) to 0.5 nm, the theoretical minimum of full width at half maximum (FWHM) of the energy spread at room temperature was reduced from ∼0.165 to ∼0.153 eV due to the fractional barrier shape. With further consideration of quantum confinement effect, this value could be reduced to ∼0.131 eV. The optimal tip radius for obtaining the minimum FWHM under an applicable emission current ranging from 1 to 100 nA was ∼1 nm. All results present the concept of modulating field emission electron energy spread by tailoring the barrier shape, which is useful for developing high monochromatic electron sources.