Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan.
Department of Physics, National Central University, Jungli 32054, Taiwan, ROC.
ACS Appl Mater Interfaces. 2023 Apr 5;15(13):17019-17028. doi: 10.1021/acsami.3c00037. Epub 2023 Mar 22.
Interfacial water molecules affect carrier transportation within graphene and related applications. Without proper tools, however, most of the previous works focus on simulation modeling rather than experimental validation. To overcome this obstacle, a series of graphene field-effect transistors (GFETs) with suspended (substrate-free, SF) and supported (oxide-supported, OS) configurations are developed to investigate the graphene-water interface under different hydrophilic conditions. With deionized water environments, in our experiments, the electrical transportation behaviors of the graphene mainly originate from the evolution of the interfacial water-molecule arrangement. Also, these current-voltage behaviors can be used to elucidate the first-water layer at the graphene-water interface. For SF-GFET, our experimental results show positive hysteresis in electrical transportation. These imply highly ordered interfacial water molecules with a separated-ionic distributed structure. For OS-GFET, on the contrary, the negative hysteresis shows the formation of the hydrogen-bond interaction between the interfacial water layer and the SiO substrate under the graphene. This interaction further promotes current conduction through the graphene/water interface. In addition, the net current-voltage relationship also indicates the energy required to change the orientation of the first-layer water molecules during electro-potential change. Therefore, our work gives an insight into graphene-water interfacial evolution with field-effect modulation. Furthermore, this experimental architecture also paves the way for investigating 2D solid-liquid interfacial features.
界面水分子会影响石墨烯内的载流子输运和相关应用。然而，由于缺乏适当的工具，之前的大多数工作都侧重于模拟建模，而不是实验验证。为了克服这一障碍，我们开发了一系列具有悬浮（无基底，SF）和支撑（氧化物支撑，OS）结构的石墨烯场效应晶体管（GFET），以在不同亲水条件下研究石墨烯-水界面。在我们的实验中，使用去离子水环境时，石墨烯的输运行为主要源于界面水分子排列的演变。此外，这些电流-电压行为可用于阐明石墨烯-水界面的第一层水。对于 SF-GFET，我们的实验结果显示出输运过程中的正滞后现象。这表明界面水分子具有分离离子分布结构的高度有序排列。对于 OS-GFET，相反，负滞后现象表明在石墨烯下，界面水层与 SiO 基底之间形成了氢键相互作用。这种相互作用进一步促进了通过石墨烯/水界面的电流传导。此外，净电流-电压关系还表明，在电势变化期间改变第一层水分子取向所需的能量。因此，我们的工作深入了解了场效应调制下的石墨烯-水界面演化。此外，这种实验架构还为研究二维固液界面特征铺平了道路。
