Zhang Yong, Lu Jianchen, Li Baijin, Chen Weiben, Xiong Wei, Ruan Zilin, Zhang Hui, Sun Shijie, Chen Long, Gao Lei, Cai Jinming
Faculty of Materials Science and Engineering, Kunming University of Science and Technology, No. 68 Wenchang Road, Kunming 650093, China.
College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
J Chem Phys. 2022 Jul 21;157(3):031103. doi: 10.1063/5.0099995.
Atomically precise fabrication of covalent-organic frameworks with well-defined heteroatom-dopant sites and further understanding of their electronic properties at the atomic level remain a challenge. Herein, we demonstrate the bottom-up synthesis of well-organized covalent-organic frameworks doped by nitrogen atoms on an Ag(111) substrate. Using high-resolution scanning tunneling microscopy and non-contact atomic force microscopy, the atomic structures of the intermediate metal-organic frameworks and the final covalent-organic frameworks are clearly identified. Scanning tunneling spectroscopy characterization reveals that the electronic bandgap of the as-formed N-doped covalent-organic framework is 2.45 eV, in qualitative agreement with the theoretical calculations. The calculated band structure together with the projected density of states analysis clearly unveils that the incorporation of nitrogen atoms into the covalent-organic framework backbone will remarkably tune the bandgap owing to the fact that the foreign nitrogen atom has one more electron than the carbon atom. Such covalent-organic frameworks may offer an atomic-scale understanding of the local electronic structure of heteroatom-doped covalent-organic frameworks and hold great promise for all relevant wide bandgap semiconductor technologies, for example, electronics, photonics, high-power and high-frequency devices, and solar energy conversion.
原子精确制备具有明确杂原子掺杂位点的共价有机框架，并在原子水平上进一步了解其电子性质仍然是一个挑战。在此，我们展示了在Ag(111)衬底上通过自下而上的方法合成由氮原子掺杂的有序共价有机框架。利用高分辨率扫描隧道显微镜和非接触原子力显微镜，清晰地识别了中间金属有机框架和最终共价有机框架的原子结构。扫描隧道谱表征表明，所形成的氮掺杂共价有机框架的电子带隙为2.45 eV，与理论计算定性一致。计算得到的能带结构以及态密度投影分析清楚地表明，由于外来氮原子比碳原子多一个电子，将氮原子掺入共价有机框架主链会显著调节带隙。这种共价有机框架可能为杂原子掺杂共价有机框架的局部电子结构提供原子尺度的理解，并在所有相关的宽带隙半导体技术中，例如电子学、光子学、高功率和高频器件以及太阳能转换方面，具有巨大的应用前景。
