Field-effect transistors made of graphene grown on recycled copper foils

Abstract

In this paper, recycled low purity copper foils (98%) are tested after a multiple-use process for obtaining single-layer graphene (SLG). The graphene transfer technique based on water electrolysis (bubbling) is used for the preservation of the Cu foils in multiple graphene deposition cycles. Preliminary cleaning by O2 plasma remove carbon residues from the copper surface. The Cu foils are then cleaned with hydrochloric (HCl) or acetic acid (CH3COOH) solutions, used as chemical baths, and the results compared. Atomic force microscopy used to check the Cu foil roughness, a critical parameter for the growth of SLG, shows root-mean-square roughness of 4.61, 28.00, 3.50 nm, for new Cu foil, after acetic acid, and after hydrochloric acid treatments, respectively. Full coverage of SLG was obtained only during the third usage of Cu foils, i.e., after two recycling cycles. Carrier mobility measured on graphene field-effect transistors fabricated after each recycling cycle, show values of 814 (1728) and 1847 cm2/V (1147 cm2/V), for electrons (holes) after one and two recycling cycles, respectively, thus demonstrating the improvement of the quality of the graphene with the number of Cu recycling cycles. Devices fabricated with graphene grown on the initial, low-purity, Cu foil did not show transistor behavior.