蛋盒石墨烯—奔向电子材料的基础性突破

  石墨烯是目前学术界和工业界最有前途的材料之一。尽管石墨烯表现出许多优异的性能,但有两个关键问题限制了它的应用。作为单原子层材料三度- 打造精彩娱乐!,石墨烯很容易折叠或形成褶皱。另外它缺乏带隙,很难成为大规模集成电路的基底材料。那么能否通过改变或调制石墨烯的几何形态来改变它的性能,从而达到同时克服上述两个困难的目的呢? 

  石墨烯之所以容易折叠和形成皱褶是由于它只由一个原子层组成三度- 打造精彩娱乐!三度- 打造精彩娱乐!,正如一张纸容易打皱变形一样∪? 打造精彩娱乐!?墒堑卑岩桓鲋桨逖怪瞥捎凶鸥叩推鸱ㄎ谱唇峁?,形如超市中用来盛装鸡蛋的纸板盒的时候,其力学强度和性能就会瞬间得到大幅度的提升。那么关键的问题是能否在石墨烯的六角蜂窝状原子晶格上构建出鸡蛋盒样的几何形态。

    由美国加州州立大学北岭分校苗茂生教授、北京计算科学研究中心的林海清教授和吉林大学的刘靖尧教授共同组成的研究团队,对这一有趣的重要问题展开了多年的理论计算研究。这一课题的主要承担人是目前任教于浙江农林大学理学院的刘伟副教授。他们首先注意到,石墨烯中的五元环和七元环缺陷能够使石墨烯片层产生不同的拓扑形变三度- 打造精彩娱乐!,包括极大、极小值点和鞍点。如果把这些缺陷有规律地排布,就能让石墨烯形成类似鸡蛋盒的几何形变。通过改变缺陷的密度和排布方式三度- 打造精彩娱乐!,各种不同形态的蛋盒石墨烯都可以被构造出来。利用第一性原理计算方法,刘伟副教授和他的合作者们研究了一系列蛋盒石墨烯的稳定性,以及力学性质和电子结构。他们发现这些新型石墨烯同素异形体独特的几何形态使得该类材料具有更高的力学强度和各异的电子性能。对应于不同的几何形态,蛋盒石墨烯可以是半金属,也可以是具有直接或间接带隙的半导体?;褂幸恍┑昂惺┑哪艽峁怪芯哂械依俗督峁?。值得注意的是,除了提高力学强度外,一些蛋盒石墨烯还显示出负的泊松比,即当蛋盒石墨烯在沿原子层平面内某一方向受压的时候,它在该方向上以及原子层平面内该方向的垂直方向上都会发生收缩。该项研究工作提出了一种有效改善石墨烯力学和电子性能的新方法,可为实现更多具有优良或独特性能的新型石墨烯基材料的设计提供进一步的理论指导。


    The major hindrances of implementing graphene in two-dimensional (2D) electronics are both mechanical (the tendency to crumble and form ripples) and electrical (the lack of a band gap). Moreover, the inevitable structural defects in graphene have a profound influence on its physical and chemical properties. Here, we propose a family of 2D egg-tray graphenes constructed by arranging pentagon and heptagon defects in the graphene lattice based on a careful analysis of the topological distribution of minima, maxima, and saddle points. First-principles calculations show that the egg-tray graphenes are dynamically stable, and their energies, which depend on the concentration of pentagons and heptagons, are the lowest among carbon allotropes. These 2D carbon allotropes exhibit a large variation in their electronic properties, ranging from semimetallic to semiconducting, including some allotropes that have Dirac cones in their band structures. Furthermore, some egg-tray graphenes are predicted to have negative Poisson’s ratios. The adsorption of Li atoms on the egg-tray graphenes is considerably stronger than the adsorption on perfect graphene, therefore they may absorb Li more effectively than graphene, which is important for improving the performance of rechargeable Li batteries.