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Role of Metal Cations in Alkali Metal Chloride Doped Graphene

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journal contribution
posted on 17.04.2014, 00:00 by Ki Chang Kwon, Kyoung Soon Choi, Cheolmin Kim, Soo Young Kim
The doping mechanism of graphene with chlorides of low work-function metals was investigated using NaCl, KCl, MgCl2, and CaCl2. After graphene was doped with 1.0 M dopants, the sheet resistance of the graphene increased from 780 Ω sq–1 to 1350–1620 Ω sq–1 after doping. Its transmittance at 550 nm also decreased from 97% to 90–94% owing to the presence of metal particles. The shift of G and 2D peaks in the Raman spectra coincided with n-type doping phenomena. The shift of the peak for the CC bond to high binding energy and the decrease of the ICC/ICC intensity ratio in spectra acquired using synchrotron radiation photoemission spectroscopy (SRPES) provided further evidence of n-type doping. Furthermore, secondary cutoff spectra in SRPES showed that the work function of the doped graphene progressively decreased from 4.32 eV to 3.7, 3.66, 3.81, and 3.9 eV. The formation of interfacial dipole complexes between the oxidized functional group on graphene and metal cations with low work functions is considered to induce n-type doping, resulting in a decrease of both the conductivity and work function of the graphene sheet. Therefore, metal cations may play an important role in an alkali or alkaline metal chloride doping system.