物理化学学报

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基于吡嗪连接的石墨烯电极单分子场效应晶体管

孙汉涛1,2, 廖建辉1, 侯士敏1,2   

  1. 1 北京大学电子学系, 纳米器件物理与化学教育部重点实验室, 北京 100871;
    2 北京大学纳米科学与技术研究中心, 北京 100871
  • 收稿日期:2019-06-05 修回日期:2019-06-18 录用日期:2019-06-20 发布日期:2019-07-01
  • 通讯作者: 侯士敏, 廖建辉 E-mail:smhou@pku.edu.cn;jianhui.liao@pku.edu.cn
  • 基金资助:
    国家自然科学基金(21573014,61671021,61621061)和国家重点基础研究发展规划(2017YFA0204903,2016YFA0201901)资助项目

Single-Molecule Field-Effect Transistors with Graphene Electrodes and Covalent Pyrazine Linkers

Hantao Sun1,2, Jianhui Liao1, Shimin Hou1,2   

  1. 1 Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871, P. R. China;
    2 Centre for Nanoscale Science and Technology, Peking University, Beijing 100871, P. R. China
  • Received:2019-06-05 Revised:2019-06-18 Accepted:2019-06-20 Published:2019-07-01
  • Contact: Shimin Hou, Jianhui Liao E-mail:smhou@pku.edu.cn;jianhui.liao@pku.edu.cn
  • Supported by:
    The project was supported by the National Natural Science Foundation of China (21573014, 61671021, 61621061) and the National Key R&D Program of China (2017YFA0204903, 2016YFA0201901).

摘要: 在单分子结中,核心分子与电极之间的连接基团对器件的力学、电学特性有着重要影响。连接基团的力学强度影响着器件的稳定性而其电子耦合强度则影响着分子结的电导值和导电极性。两端带邻苯二胺基团的分子可以和石墨烯电极边缘的邻醌基团发生缩合反应,生成基于吡嗪连接的分子结。我们实验制备了基于吡嗪连接的石墨烯电极单分子场效应晶体管(FET)并研究了其电学性质。我们发现分子组装后器件的产率可以达到26%,证明了吡嗪连接基团用于构建石墨烯电极单分子器件的可行性。通过测量器件的电学性质,我们发现吡嗪连接与石墨烯电极之间的耦合强度对单分子场效应晶体管的导电极性有着决定性的影响。具体而言,弱耦合时器件为核心分子的最高占据轨道起主导作用的p-型FET而强耦合时器件为核心分子的最低空轨道起主导作用的n-型FET。

关键词: 分子电子学, 石墨烯电极, 吡嗪连接基团, 单分子场效应晶体管, 耦合强度

Abstract: In single-molecule junctions, anchoring groups that connect the central molecule to the electrodes have profound effects on the mechanical and electrical properties of devices. The mechanical strength of the anchoring groups affects the device stability, while their electronic coupling strength influences the junction conductance and the conduction polarity. To design and fabricate high-performance single-molecule devices with graphene electrodes, it is highly desirable to explore robust anchoring groups that bond the central molecule to the graphene electrodes. Condensation of ortho-phenylenediamine terminated molecules with ortho-quinone moieties at the edges of graphene generates graphene-conjugated pyrazine units that can be employed as anchoring groups for the construction of molecular junctions with graphene electrodes. In this study, we investigated the fabrication and electrical characterization of single-molecule field-effect transistors (FETs) with graphene as the electrodes, pyrazine as the anchoring groups, and a heavily doped silicon substrate as the back-gate electrode. Graphene nano-gaps were fabricated by a high-speed feedback-controlled electro-burning method, and their edges were fully oxidized; thus, there were many ortho-quinone moieties at the edges. After the deposition of phenazine molecules with ortho-phenylenediamine terminals at both ends, a large current increase was observed, indicating that molecular junctions were formed with covalent pyrazine anchoring groups. The yield of the single-molecule devices was as high as 26%, demonstrating the feasibility of pyrazine as an effective anchoring group for graphene electrodes. Our electrical measurements show that the ten fabricated devices exhibited a distinct gating effect when a back-gate voltage was applied. However, the gate dependence of the conductance varied considerably from device to device, and three types of different gate modulation behaviors, including p-type, ambipolar, and n-type conduction, were observed. Our observations can be understood using a modified single-level model that takes into account the linear dispersion of graphene near the Dirac point; the unique band structure of graphene and the coupling strength of pyrazine with the graphene electrode both crucially affect the conduction polarity of single-molecule FETs. When the coupling strength of pyrazine with the graphene electrode is weak, the highest occupied molecular orbital (HOMO) of the central molecule dominates charge transport. Depending on the gating efficiencies of the HOMO level and the graphene states, devices can exhibit p-type or ambipolar conduction. In contrast, when the coupling is strong, the redistribution of electrons around the central molecule and the graphene electrodes leads to a realignment of the molecular levels, resulting in the lowest unoccupied molecular orbital (LUMO)-dominated n-type conduction. The high yield and versatility of the pyrazine anchoring groups are beneficial for the construction of single-molecule devices with graphene electrodes.

Key words: Molecular electronics, Graphene electrode, Pyrazine anchoring group, Single-molecule field-effect transistor, Coupling strength

MSC2000: 

  • O641