Work Functions of Pristine and Heteroatom-Doped Graphenes under Different External Electric Fields: An <i>ab Initio</i> DFT Study

Low contact barrier electrodes and various field-emitting devices require a tunable work function, and graphene is a dream material for these applications. In this work, the theoretical investigations on the variation of the work function for monolayer graphene doped with different kinds of atoms from groups IIA–VIA of the Periodic Table are reported. The geometry, density of states, dipole moment, and work function of each heteroatom-doped graphene are calculated using <i>ab initio</i> density functional theory with a dispersion correction. The obtained formation energy of the heteroatom-doped graphenes is in the order: N < B < P < O < S < Si < As < Se < Ge < Al < Ga. The work functions without an electric field abide by a periodic law in terms of doping atoms except for O-doped graphene. The calculated results demonstrate that the work functions of all heteroatom-doped graphenes are a linear function of the applied external electric field intensity, and the slopes of the lines deviate from the ideal value to a different extent, which is mainly dependent on the polarization of the heteroatom–carbon bonds and the production of the induced dipole moments of the doped graphenes. The present calculated results make it known that the graphene work function can be tinkered up from 0.5 to 8.5 eV by using different kinds of doping atoms of group IIIA–VIA elements and applying an electric field with various intensities. Such a wide range of adjustable work function makes graphene a very promising material for contact electrodes and field-emitting devices