We report the spontaneous adsorption of ions on graphene at the interface with electrolytes through an investigation based on the electrolyte-gated field effect transistor configuration. It is found that the gate voltage at which the minimum conductivity occurs in these devices is highly sensitive to the type of ions and their concentrations in the electrolytes; yet the experimental results exhibit non-trivial deviations from the predictions based on the Gouy–Chapman–Stern (GCS) model, which only takes account of the electrostatic interactions among the charges in the system. By incorporating a Langmuir-type adsorption term into the GCS model, we achieve quantitative alignment with the experiments, thus demonstrating that these deviations originate from the spontaneous adsorption of ions onto graphene. Analysis of the transport characteristics in these devices indeed confirms the existence of the adsorbed ions.

中文翻译：

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电解质-石墨烯界面处离子在石墨烯上的自发吸附

我们通过基于电解质门控场效应晶体管配置的研究报告了离子在与电解质界面处石墨烯上的自发吸附。发现在这些器件中出现最小电导率时的栅极电压对离子类型及其在电解质中的浓度高度敏感；然而，实验结果与基于 Gouy-Chapman-Stern (GCS) 模型的预测存在重大偏差，该模型仅考虑了系统中电荷之间的静电相互作用。通过将朗缪尔型吸附项纳入 GCS 模型，我们实现了与实验的定量对齐，从而证明这些偏差源于离子在石墨烯上的自发吸附。