单层二维有机共价薄膜的超高真空表面在位合成及其器件应用

Monolayer two-dimensional (2D) covalent organic frameworks (COFs) featuring atom-thick periodic covalent molecular sheets have attracted great attention in recent years. They provide a new way to control carrier transport through quantum effects and tune device properties by rational chemical design. However, the synthesis of monolayer 2D COFs with well-defined structures remains a great challenge. On-surface synthesis offers a promising “bottom-up” way that can restrict the reactions to the surfaces of the substrates and confine synthesized materials strictly to monolayer. Most 2D COFs synthesized via on-surface method still suffer from small domain sizes and non-uniform frameworks. To solve this problem, we propose two possible methods to control the structures of on-surface synthesized 2D COFs by hierarchical growth and self-assembly assisted low-temperature photoinduced polymerization. With the help of scanning tunneling microscope, the chemical and electronic structures of monolayer 2D COFs can be examined at the atomic scale. By constructing devices such as thin film transistors, the carrier mobilities of monolayer 2D COFs can be measured. Combined with special dielectric materials and microfluidic technique, its further applications in low operation bias devices and high sensitivity photo-detectors and chem-/bio- sensors can be explored.

单层二维有机共价薄膜是原子厚度的周期性共价键分子薄膜，能够通过量子效应调节载流子传输，调节场效应晶体管等器件的性能，具有重要的研究意义。然而，目前单层二维有机共价薄膜的精准合成仍面临很大挑战。表面在位合成将化学反应严格限制在衬底表面，可以有效地控制产物层数，为其“自下而上”的合成提供了一种可控的有效手段。目前超高真空表面在位合成方法制备单层二维有机共价薄膜的主要问题是结构缺陷较多。为了解决这一问题，本项目提出了分步偶联和组装诱导-低温活化-就近偶联的方法，增强结构的自修复能力，制备高度有序的单层二维有机共价薄膜材料。利用扫描隧道显微镜原位表征其化学结构和电学性质；结合转移技术，制备场效应晶体管研究其器件性能，测量载流子迁移率等；通过特定介电材料的选择，结合微流控技术等，探索低压工作器件和具有高灵敏度光响应及化学/生物传感性能的多功能器件的开发。

本项目围绕超高真空低维有序结构的可控表面构筑展开，研究了前体分子的活性官能团差异、热活化温度、金属配位、衬底化学成分及晶体学结构差异等因素对最终表面合成纳米结构的调控作用，原位制备了基于氢键、卤键等弱相互作用的单一分子自组装、多种分子共组装和分子-金属非键共组装等多种结构，原位合成了基于有机金属键和共价键的零维有机金属分子大环、一维聚合物链和二维长程有序结构。对反应路径的调控、反应过程中的协同效应等反应机理进行了深入分析讨论。我们的结果对于理解表面反应过程从而实现低维纳米结构可控精准原位制备有重要意义。

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