Evaluation of doped potassium concentrations in stacked Two-Layer graphene using Real-time XPS
Shuichi Ogawa, Yasutaka Tsuda, Tetsuya Sakamoto, Yuki Okigawa, Tomoaki Masuzawa, Akitaka Yoshigoe, T. Abukawa, Takatoshi Yamada
Abstract
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.