Researchers at University of Tsukuba have demonstrated that graphitizing the apex of a mechanical pencil lead (PL) produces vertically aligned graphene edges that function as efficient electron emission sources. Due to their pointed morphology, these graphene edges enabled stable field emission at relatively small macroscopic electric fields of several V/µm, without the need for an ultra-high vacuum environment.
Field emission microscopy revealed the distinctive “dragonfly pattern” characteristic of graphene edge emission, confirming the nearly vertical alignment of graphene flakes at the apex of PL. Analysis of the energy spectrum of emitted electrons showed a distribution slightly broader than that of metals, reflecting the density of states of graphene’s π-bands. This observation was further supported by recursion-transfer-matrix simulations.
The chemical stability and abundance of emission sites at the graphitized apex resulted in stable electron emission, even under elevated pressures up to 10⁻⁴ Pa of N₂.
These findings demonstrate that graphitized pencil leads can serve as low-cost, high-performance electron sources and, at the same time, provide a robust platform for fundamental investigations of graphene edge properties, with potential applicability in next-generation electron microscopy and related technologies.