Direct measurements of conductivity and mobility in millimeter-sized single-crystalline graphene via van der Pauw geometry

Ma Rui-Song^{1, 2, 3}, Huan Qing^{1, 2, 3}, Wu Liang-Mei^{1, 2, 3}, Yan Jia-Hao^{1, 2, 3}, Zhang Yu-Yang², Bao Li-Hong^{1, 2, 3, †}, Liu Yun-Qi⁴, Du Shi-Xuan^{1, 2, 3}, Gao Hong-Jun^{1, 2, 3, ‡}

(color online) Optical micrographs of probes during the four-probe measurements. (a)–(c): Optical micrographs showing the probes 1–4 contacting the graphene corners in setup-1. (d)–(g): Optical images of four probes during measurements in setup-2. (h) and (i): Optical images of four-probe measurements in setup-3. Chemical-etched gold probes are used in the measurements. Scale bar: 200 µm.