最小蛋盘形状的2D笼形石墨烯：\textit{ab initio}研究
2D clathrate graphene in minimum egg-tray-shape: An \textit{ab initio} study
摘要：
在碳同素异形体合成领域的蓬勃发展见证了许多新的二维石墨烯结构的理论建议和实验合成，这些结构通常是通过在石墨烯中仔细排列非六边形$\mathrm{sp^2}$缺陷来实现的。在这里，我们将金字塔$\mathrm{sp^3}$杂化引入到$\mathrm{sp^2}$网络中，并提出了一种新的具有笼形图案和最小蛋盘形状的碳多晶型物（称为笼形石墨烯）。其四方原始晶胞中的八个对称等效的$\mathrm{sp^2}$碳原子和两个对称等效的$\mathrm{sp^2}$碳原子形成两个垂直取向的矩形和四个桥接六边形。虽然键长和键角发生了变形，但四元环和六边形的平面几何结构仍得以保留。六边形的高百分比和小变形使得该亚稳态$\mathrm{sp^2}$ - $\mathrm{sp^3}$同素异形体在能量学上与纯$\mathrm{sp^2}$ $T$ -石墨烯和五-石墨烯相当。详尽的\textit{ab initio}计算证实了它的动力学和弹性稳定性，揭示了其半导体性质的间接带隙为0.90 eV的无应力样品，并提出了一个巨大的应变调谐效应，赋予多才多艺的电子性能，从金属到半导体。此外，我们观察到费米能附近的多重冯霍夫奇异性，这些显著的性质可能暗示潜在的纳米电子应用。这些发现有助于理解二维碳同素异形体的结构-性质关系，并有助于寻找新的碳同素异形体。
英文摘要：
The thriving area of synthetic carbon allotropes witnesses theoretic proposals and experimental syntheses of many new two-dimensional ultrathin structures, which are often achieved by careful arrangement of non-hexagon $\mathrm{sp^2}$ defects in graphene. Here, we introduce pyramid $\mathrm{sp^3}$ hybridization into $\mathrm{sp^2}$ network and propose a new carbon polymorph with clathrate pattern and with minimum egg-tray shape (termed as clathrate graphene). Eight symmetrically equivalent $\mathrm{sp^2}$ carbon atoms and two symmetrically equivalent $\mathrm{sp^2}$ carbon atoms in its tetragonal primitive unit cell form two perpendicularly oriented rectangles and four bridging hexagons. Though deformed bond lengths and bond angles, the planar geometry of both tetrarings and hexagons are retained. High percentage and small deformation of hexagons make this metastable $\mathrm{sp^2}$-$\mathrm{sp^3}$ allotrope comparable with pure $\mathrm{sp^2}$ $T$-graphene and penta-graphene in energetics. Exhaustive \textit{ab initio} calculations confirm its dynamical and elastic stabilities, reveal its semiconducting nature with an indirect band gap of 0.90 eV for unstressed sample, and suggest a giant strain tuning effect which endows versatile electronic properties ranging from metallic to semiconducting. Furthermore, we observe multiple von Hove singularities near the Fermi energy.These salient properties may imply potential nanoelectronic applications. These findings help understand structure-property relationship for two-dimensional carbon allotropes, and help search new carbon polymorphs.
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