Researchers at Rice University and Oak Ridge National Laboratory determined that two-dimensional materials grown onto a cone allow control over where defects called grain boundaries appear. These defects can be used to enhance the materials’ electronic, mechanical, catalytic and optical properties. image credit: Yakobson Research Group/Rice University
赖斯大学的研究人员已经学会了操纵二维材料，以设计缺陷以增强材料的性质。
理论物理学家鲍里斯Yakobs的大米实验室on and colleagues at Oak Ridge National Laboratory are combining theory and experimentation to prove it’s possible to give 2-D materials specific defects, especially atomic-scale seams called grain boundaries. These boundaries may be used to enhance the materials’ electronic, magnetic, mechanical, catalytic and optical properties.
The key is introducing curvature to the landscape that constrains the way defects propagate. The researchers call this “tilt grain boundary topology,” and they achieve it by growing their materials onto a topographically curved substrate — in this case, a cone. The angle of the cone dictates if, what kind and where the boundaries appear.
The research is the subject of a paper in the American Chemical Society journalACS Nano。
Grain boundaries are the borders that appear in a material where edges meet in a mismatch. These boundaries are a series of defects; for example, when two sheets of hexagonal graphene meet at an angle, the carbon atoms compensate for it by forming nonhexagonal (five- or seven-member) rings.
Yakobson and his team have already demonstrated that these boundaries can be electronically significant. They can, for instance, turn perfectly conducting graphene into a semiconductor. In some cases, the boundary itself may be a conductive subnanoscale wire or take on magnetic properties.
但是到目前为止，研究人员几乎无法控制这些边界在种植石墨烯，二硫化钼或其他二维材料时通过化学蒸气沉积而出现的位置。
大米开发的理论表明，在锥体上生长的2D材料将迫使边界出现在某些地方。Yakobson说，锥体的宽度控制了位置，更重要的是，倾斜角度是调整材料的电子和磁性特性的关键参数。
Experimental collaborators from Oak Ridge led by co-author David Geohegan provided evidence backing key aspects of the theory. They achieved this by growing tungsten disulfide onto small cones similar to those in Rice’s computer models. The boundaries that appeared in the real materials matched those predicted by theory.
“The nonplanar shape of the substrate forces the 2-D crystal to grow in a curved ‘non-Euclidian’ space,” Yakobson said. “This strains the crystal, which occasionally yields by giving a way to the seams, or grain boundaries. It’s no different from the way a tailor would add a seam to a suit or a dress to fit a curvy customer.”
不同宽度的建模锥还揭示了38.9度的“魔法锥”，生长的2-D材料根本不会留下晶粒边界。
赖斯团队扩展了理论，看看如果锥坐在飞机上会发生什么。他们预测了晶界如何在整个表面形成，橡树岭实验再次证实了它们的结果。
Yakobson说，稻米和橡树岭团队都在独立研究研究方面。他说：“直到几年前我们在佛罗里达举行的一次会议上见面并意识到我们应该继续在一起。”“当然，看到实验如何证实模型，同时有时会带来重要的惊喜。现在，我们还需要做其他工作来理解它们。”
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