srep01595.pdf 710 KB
Uesugi, Eri Okayama Univ, Surface Sci Res Lab
Goto, Hidenori Okayama Univ, Surface Sci Res Lab
Eguchi, Ritsuko Okayama Univ, Surface Sci Res Lab
Fujiwara, Akihiko SPring 8, Japan Synchrotron Radiat Res Inst
Kubozono, Yoshihiro Okayama Univ, Surface Sci Res Lab
Ionic-liquid gates have a high carrier density due to their atomically thin electric double layer (EDL) and extremely large geometrical capacitance C-g. However, a high carrier density in graphene has not been achieved even with ionic-liquid gates because the EDL capacitance C-EDL between the ionic liquid and graphene involves the series connection of C-g and the quantum capacitance C-q, which is proportional to the density of states. We investigated the variables that determine C-EDL at the molecular level by varying the number of graphene layers n and thereby optimising C-q. The C-EDL value is governed by C-q at n, 4, and by C-g at n > 4. This transition with n indicates a composite nature for C-EDL. Our finding clarifies a universal principle that determines capacitance on a microscopic scale, and provides nanotechnological perspectives on charge accumulation and energy storage using an ultimately thin capacitor.
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