Increased work function in few-layer graphene sheets via metal chloride Doping

Abstract

A chemical approach to controlling the work function of few-layer graphene is investigated. Graphene films are synthesized on Cu foil by chemical vapor deposition. Six metal chlorides, AuCl 3, IrCl 3, MoCl 3, OsCl 3, PdCl 2, and RhCl 3, are used as dopants. The sheet resistance of the doped graphene decreases from 1100 Ω/sq to ≈500-700 Ω/sq and its transmittance at 550 nm also decreases from 96.7% to 93% for 20 mM AuCl 3 due to the formation of metal particles. The sheet resistance and transmittance are reduced with increasing metal chloride concentration. The G peak in the Raman spectra is shifted to a higher wavenumber after metal chloride doping, which indicates a charge transfer from graphene to metal ions. The intensity ratio of I Cï£C/I C-C increases with doping, indicating an electron transfer from graphene sheets to metal ions. Ultraviolet photoemission spectroscopy data shows that the work function of graphene increases from 4.2 eV to 5.0, 4.9, 4.8, 4.68, 5.0, and 5.14 eV for the graphene with 20 mM AuCl 3, IrCl 3, MoCl 3, OsCl 3, PdCl 2, and RhCl 3, respectively. It is considered that spontaneous charge transfer occurs from the specific energy level of graphene to the metal ions, thus increasing the work function. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.