Synthesis and characterization of potassium-doped multilayer graphene prepared by wet process using potassium hydroxide

Abstract

Potassium (K) doping of multilayer graphene was demonstrated by means of a wet chemical process using potassium hydroxide (KOH) aqueous solution (KOH treatment). The presence of K atoms along the stacking direction was confirmed from depth profiles of 41K+ ions obtained by time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The intensity images of 41K+ ions obtained by TOF-SIMS suggested that the K atoms existed throughout the whole area. For the KOH-treated multilayer graphene, no peak due to K intercalation between graphene layers was obtained by x-ray diffraction (XRD); in Raman spectra, splitting of the G-band peak and disappearance of the 2D-band peak were not observed. A graphite intercalation compound structure was not determined by either XRD or Raman results. However, the up-shift in the G-band peak position in the Raman spectra suggested that K atoms were doped in the graphene. X-ray photoelectron spectroscopy carbon 1s spectra implied that KOH treatment resulted in K-termination at the edges and/or domains of graphene. In addition, a C1s shoulder peak appeared at 1 eV higher binding energy compared to the C1s peak of pristine graphene. Temperature-dependent conductivity measurement results indicated that the conductivity of multilayer graphene was increased by KOH treatment. In addition, the conductivity increased with increasing temperature, which could be explained by band overlap.