Effects of alkali metal adsorption on the structural and field emission properties of graphene

We systematically investigate the structural and field emission properties of alkali metal atoms adsorbed on graphene using first-principles density-functional theoretical calculations. The calculated results indicate that the center of the hexagonal ring of graphene is the most stable adsorption site, and the alkali metal atom can stay stably on graphene by donating their charges to graphene, which results in the redistribution of the Mulliken charges on graphene. Also, we explore the effects of alkali metal atom adsorption on the field emission properties of graphene, in which the magnitude of the ionization potential of graphene becomes smaller and the Fermi level increases after adsorption. Moreover, the Cs adsorption on graphene is believed to be the best choice for enhancing the field emission properties. The mechanism of the enhanced field emission has been analyzed in terms of the modification of the density of states and the band structures caused by the adsorption. Our findings suggest that graphene can be applied as field emission electron source material, and the adsorption of alkali metal atoms can improve its emission performance, which will be helpful in the design of functionalized graphene electronic devices. (C) 2010 Elsevier B.V. All rights reserved.