硼-氮有序共掺杂石墨烯的可控生长及强磁场下输运性质研究

The periodic potentials induced by artificial ordered superstructures can be utilized to tailor the electronic structures, thus motivating a considerable fraction of modern research in condensed matter physics. The superlattice formed in an aligned boron nitride/graphene vertical stack leads to the extra periodic potential that modulates the Daric fermion in graphene. A series of novel physics, including the superlattice Dirac points and Hofstadter butterfly states, have been revealed. However, due to the energetically favourable boron-nitrogen chemical bonds when compared with boron-carbon and nitrogen-carbon bonds, the hybridized phases of BN and graphene in the 2D B-C-N ternary compounds hinder the formation of the atomically-ordered structure in the B-C-N system. ..In this proposal, we intend to experimentally investigate the low-temperature controllable growth of B-N co-doped ordered graphene monolayer with the periodical distribution of B-N pairs based on the molecular self-assembly, in which the spatial location of B-N pairs in the starting molecule eventually determines the period of the superlattice potential. By the combination of the Z-contrast atomic-resolution characterization and angle-resolved photoemission spectroscopy, the atom structure, especially the distribution of three atoms, and electronic structure of the B-N co-doped graphene will be investigated thoroughly. Furthermore, the transport properties measurement under the high magnetic field will be performed collaboratively to reveal the effect of the long-range superlattice potential. This proposed study opens the door to the growth of artificial ordered 2D materials and the exploration of the novel superlattice effect.

低维量子体系中超晶格带来的外加周期性势场对能带结构和电子输运行为有着显著的调制作用。在晶格对准的石墨烯和六方氮化硼垂直异质结中，莫尔超晶格诱导第二套狄拉克锥能带结构的出现和强磁场下的能带交叠Hofstadter蝴蝶分形结构。这两种材料的结构相似也决定了六方相硼碳氮三元化合物的存在。但硼-氮原子的优先成键引起石墨相和六方氮化硼相的相分离，从而原子级别的有序结构无法实现。.本项目拟发展基于分子自组装的低温可控生长方法：在不破坏含硼-氮原子对的有机分子构型的前提下，通过有序的脱溴/脱氢反应得到硼-氮有序共掺杂的石墨烯。拟进行元素可分辨的原子尺度结构表征和硼-氮原子对有序占位引起的外加周期势对能带结构的调控研究；进一步开展低温强磁场下的输运性质探索。本项目的开展将深入理解能带结构和电子输运性质受超结构周期性势场的调控机理，为人工有序低维体系提供新的研究思路和方向。

二维碳材料是具有丰富新奇物性和广阔应用前景的低维量子体系。发展新的精准制备方法、进一步对其进行底层结构设计和物性调控，可以丰富其结构体系、拓展科学研究意义。通过本课题的实施，项目负责人（1）建立了以分子为生长前驱物的制备二维非晶碳材料的新方法，并成功利用制备温度调控其无序度；（2）利用透射电镜解析其原子结构，建立二维非晶材料微观结构系统分析的新方法；（3）揭示了二维非晶碳电学性质的奇异温度依赖性，实现了其方块电阻在9个数量级中的连续可调；（4）借助第一性原理和蒙特卡洛计算，成功关联了二维非晶碳的原子结构和电学性质，揭示了导电岛密度这一重要序参量。在项目执行期间，已发表学术论文13篇，其中Nature 1篇，Nat. Mater. 1篇，Phys. Rev. Lett. 2篇，Nano Lett. 1篇，Angew. Chem. Int. Ed. 1篇，Adv. Funct. Mater. 1篇；并毕业1名硕士研究生，6名在读博士得到支持