Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
Department of Chemical Engineering and Materials Science, University of Minnesota , 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States.
Nano Lett. 2017 Dec 13;17(12):7586-7592. doi: 10.1021/acs.nanolett.7b03564. Epub 2017 Nov 21.
The ability to improve and to modulate the heterogeneous charge transfer kinetics of two-dimensional (2D) semiconductors, such as MoS, is a major challenge for electrochemical and photoelectrochemical applications of these materials. Here we report a continuous and reversible physical method for modulating the heterogeneous charge transfer kinetics at a monolayer MoS working electrode supported on a SiO/p-Si substrate. The heavily doped p-Si substrate serves as a back gate electrode; application of a gate voltage (V) to p-Si tunes the electron occupation in the MoS conduction band and shifts the conduction band edge position relative to redox species dissolved in electrolyte in contact with the front side of the MoS. The gate modulation of both charge density and energy band alignment impacts charge transfer kinetics as measured by cyclic voltammetry (CV). Specifically, cyclic voltammograms combined with numerical simulations suggest that the standard heterogeneous charge transfer rate constant (k) for MoS in contact with the ferrocene/ferrocenium (Fc) redox couple can be modulated by over 2 orders of magnitude from 4 × 10 to 1 × 10 cm/s, by varying V. In general, the field effect offers the potential to tune the electrochemical properties of 2D semiconductors, opening up new possibilities for fundamental studies of the relationship between charge transfer kinetics and independently controlled electronic band alignment and band occupation.
改善和调节二维（2D）半导体（如 MoS）异质电荷转移动力学的能力，是这些材料在电化学和光电化学应用中的主要挑战。在这里，我们报告了一种连续且可还原的物理方法，用于调节在 SiO2/p-Si 衬底上支撑的单层 MoS 工作电极的异质电荷转移动力学。重掺杂的 p-Si 衬底用作背栅电极；向 p-Si 施加栅极电压 (V) 可调节 MoS 导带中的电子占据情况，并使导带边缘位置相对于与 MoS 前侧接触的电解质中溶解的氧化还原物质发生偏移。电荷密度和能带排列的栅极调制都会影响通过循环伏安法 (CV) 测量的电荷转移动力学。具体来说，循环伏安图结合数值模拟表明，与 ferrocene/ferrocenium (Fc) 氧化还原偶接触的 MoS 的标准异质电荷转移速率常数 (k) 可以通过改变 V 从 4×10 到 1×10 cm/s 调节 2 个数量级。一般来说，场效应提供了调节二维半导体电化学性质的潜力，为电荷转移动力学与独立控制的电子能带排列和能带占据之间的关系的基础研究开辟了新的可能性。
