Evaluation of doped potassium concentrations in stacked Two-Layer graphene using Real-time XPS

The immersion of graphene in potassium hydroxide solutions improves its electron mobility on SiO2/Si substrates. This has been attributed to doping with K atoms, but the K concentration xK has not been determined. Here, xK was determined with X-ray photoelectron spectroscopy using intense synchrotron radiation. The K 2p peak intensity decreased with increasing irradiation time. Curve fitting analysis was performed to quantitatively evaluate the change in xK with irradiation time. However, because the K 2p peak was affected by the asymmetric tail of the C 1 s peak, background removal and peak separation analysis were performed simultaneously using the "active Shirley" method. The change in xK was determined by real-time observations, and xK before irradiation was estimated to be 1.00 +/- 0.09 mol %. Furthermore, the C 1 s spectrum shifted to lower binding energy with radiation exposure. This indicated that electron carriers in the graphene decreased because of K desorption.