Ma Chuanxu, Wang Jufeng, Ma Huanhuan, Yin Ruoting, Zhao Xin-Jing, Du Hongjian, Meng Xinyong, Ke Yifan, Hu Wei, Li Bin, Tan Shijing, Tan Yuan-Zhi, Yang Jinlong, Wang Bing
Hefei National Research Center for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
Hefei National Laboratory, University of Science and Technology of China, Hefei, Anhui 230088, China.
J Am Chem Soc. 2023 May 10;145(18):10126-10135. doi: 10.1021/jacs.3c00563. Epub 2023 Apr 25.
Cyclodehydrogenation reactions in the on-surface synthesis of graphene nanoribbons (GNRs) usually involve a series of C-C and/or C-C couplings and just happen on uncovered metal or metal oxide surfaces. It is still a big challenge to extend the growth of second-layer GNRs in the absence of necessary catalytic sites. Here, we demonstrate the direct growth of topologically nontrivial GNRs via multistep C-C and C-C couplings in the second layer by annealing designed bowtie-shaped precursor molecules over one monolayer on the Au(111) surface. After annealing at 700 K, most of the polymerized chains that appear in the second layer covalently link to the first-layer GNRs that have partially undergone graphitization. Following annealing at 780 K, the second-layer GNRs are formed and linked to the first-layer GNRs. Benefiting from the minimized local steric hindrance of the precursors, we suggest that the second-layer GNRs undergo domino-like cyclodehydrogenation reactions that are remotely triggered at the link. We confirm the quasi-freestanding behaviors in the second-layer GNRs by measuring the quasiparticle energy gap of topological bands and the tunable Kondo resonance from topological end spins using scanning tunneling microscopy/spectroscopy combined with first-principles calculations. Our findings pave the avenue to diverse multilayer graphene nanostructures with designer quantum spins and topological states for quantum information science.
石墨烯纳米带（GNRs）表面合成中的环脱氢反应通常涉及一系列C-C和/或C-C偶联，且仅在未覆盖的金属或金属氧化物表面发生。在缺乏必要催化位点的情况下，扩展第二层GNRs的生长仍然是一个巨大的挑战。在此，我们通过在Au(111)表面的一个单层上对设计的领结形前驱体分子进行退火，展示了通过第二层中的多步C-C和C-C偶联直接生长拓扑非平凡的GNRs。在700 K退火后，第二层中出现的大多数聚合链与已经部分石墨化的第一层GNRs共价连接。在780 K退火后，第二层GNRs形成并与第一层GNRs相连。受益于前驱体最小化的局部空间位阻，我们认为第二层GNRs经历了在连接处远程触发的多米诺骨牌式环脱氢反应。我们通过使用扫描隧道显微镜/光谱结合第一性原理计算测量拓扑能带的准粒子能隙和拓扑末端自旋的可调近藤共振，证实了第二层GNRs中的准独立行为。我们的发现为具有设计量子自旋和拓扑态的多种多层石墨烯纳米结构通往量子信息科学铺平了道路。
