Annealing effects on the characteristics of AuCl₃-doped graphene

Single-layer graphene sheets grown on Cu foils by chemical vapor deposition were transferred on 300 nm SiO₂/n-type Si wafers and subsequently doped with 10 mM AuCl₃ solution. The doped graphene sheets were annealed at various temperatures (T_A) under vacuum below 10 ^-3 Torr for 10 min and characterized by atomic force microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and 4-probe van der Pauw method. The XPS studies show that the compositions of Cl and Au ³⁺ ions in doped graphene sheets increase slightly by annealing at 50°C, but by further increase of T_A above 50°C, they monotonically decrease and become almost negligible at T_A = 500°C. These XPS results are consistent with the corresponding T _A-dependent behaviors of the Raman scattering and the sheet resistance, implying that the doping efficiency is maximized at T_A = 50°C and the Cl and Au³⁺ ions play a major role in the doping/dedoping processes that are very reversible, different from the case of carbon nanotubes. These results suggest that the annealing temperature is a crucial factor to determine the structural and electrical properties of AuCl₃-doped graphene. Possible mechanisms are discussed to explain the doping/dedoping processes of graphene sheets.