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石墨烯是单原子层的二维结构材料，其突出的物理、化学性质，以及在微电子学、纳电子学、能源、化学、生物传感器方面的应用前景吸引了众多关注。但完整石墨烯的零带隙特点阻碍了其在半导体器件中的应用。目前有两种方法可以打破零带隙：一种是将石墨烯切割成纳米条带，造成量子限域效应而打开能隙，所获能隙的大小可由纳米条带的宽度调控；另一种是在石墨烯sp2键中添加sp或sp3键，这可通过化学功能化或利用碳本身多样的成键特性而实现。但这两种方法还不足以满足石墨烯的改造，使其能在广泛领域中应用。
中国人民大学物理系的卢仲毅教授和刘凯教授团队、成都大学高等研究院的钟承勇博士与新加坡科技设计大学的杨声远教授合作，结合上述两种方法对能隙的调控提出了第三种策略：用炔键链缝合石墨烯层，构建出一系列碳网络：三维炔键修饰的石墨烯（3D-AMG-n）。3D-AMG-n家族拥有极好的稳定性，在能量上比实验合成的石墨炔以及理论预测的炔属链修饰的碳同素异形体还稳定，热稳定性甚至可达1000 K。更重要的是，石墨烯纳米条带的几何限制以及sp-sp2-sp3杂化键，赋予了3D-AMG-n丰富的电子能带特征。他们进一步研究发现，如果扶手椅型石墨烯纳米条带的宽度n满足n=3p+2 (p是整数)，那么这个系统将是一个拓扑节点环半金属；否则，它便是一个半导体，而且其半导体成员（n=3, 7 , 10）的直接能隙均在1.0-1.5 eV之间。计算研究表明，其光吸收响应能力比大部分光电材料以及其他碳材料都强，在光电应用领域潜力巨大。此外，三维碳网络3D-AMG-n材料在能源存储以及分子筛方面也具有优势。
该研究为碳同素异形体的合成和其晶体特征的探索提供了可参考的实验方案，为石墨烯的能隙调制提出了一种新的策略，有望为构建具有不同功能的碳相提供更多的启发。
该文近期发表于npj Computational Materials 7: 109 (2021)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。
Three-dimensional acetylenic modified graphene for high-performance optoelectronics and topological materials
Yan Gao#, Chengyong Zhong#, Shengyuan A. Yang, Kai Liu*, and Zhong-Yi Lu*
Seeking carbon phases with versatile properties is one of the fundamental goals in physics, chemistry, and materials science. Here, based on the first-principles calculations, a family of three-dimensional (3D) graphene networks with abundant and fabulous electronic properties, including rarely reported dipole-allowed truly direct band gap semiconductors with suitable band gaps (1.07–1.87 eV) as optoelectronic/photovoltaic materials and topological nodal-ring semimetals, are proposed through stitching different graphene layers with acetylenic linkages. Remarkably, the optical absorption coefficients in some of those semiconducting carbon allotropes express possibly the highest performance among all of the semiconducting carbon phases known to date. On the other hand, the topological states in those topological nodal-ring semimetals are protected by the time-reversal and spatial symmetry and present nodal rings and nodal helical loops topological patterns. Those newly revealed carbon phases possess low formation energies and excellent thermodynamic stabilities; thus, they not only host a great potential in the application of optoelectronics, photovoltaics, and quantum topological materials etc., but also can be utilized as catalysis, molecule sieves or Li-ion anode materials and so on. Moreover, the approach used here to design novel carbon allotropes may also give more enlightenments to create various carbon phases with different applications.
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