Sandia National Laboratories , Albuquerque, New Mexico, United States.
ACS Nano. 2014 Feb 25;8(2):1655-63. doi: 10.1021/nn405999z. Epub 2014 Jan 29.
Conventional means of stacking two-dimensional (2D) crystals inevitably leads to imperfections. To examine the ramifications of these imperfections, rotational disorder and strain are quantified in twisted bilayer graphene (TBG) using a combination of Raman spectroscopic and low-energy electron diffraction imaging. The twist angle between TBG layers varies on the order of 2° within large (50-100 μm) single-crystalline grains, resulting in changes of the emergent Raman response by over an order of magnitude. Rotational disorder does not evolve continuously across the large grains but rather comes about by variations in the local twist angles between differing contiguous subgrains, ∼ 1 μm in size, that themselves exhibit virtually no twist angle variation (ΔΘ ∼ 0.1°). Owing to weak out-of-plane van der Waals bonding between azimuthally rotated graphene layers, these subgrains evolve in conjunction with the 0.3% strain variation observed both within and between the atomic layers. Importantly, the emergent Raman response is altered, but not removed, by these extrinsic perturbations. Interlayer interactions are therefore resilient to strain and rotational disorder, a fact that gives promise to the prospect of designer 2D solid heterostructures created via transfer processes.
传统的二维（2D）晶体堆叠方法不可避免地会导致不完美。为了研究这些不完美的影响，使用拉曼光谱和低能电子衍射成像相结合的方法，对扭曲双层石墨烯（TBG）中的旋转无序和应变进行了量化。在大（50-100 μm）单晶颗粒中，TBG 层之间的扭转角在 2°量级变化，导致出现的拉曼响应变化超过一个数量级。旋转无序不是在大晶粒中连续演变，而是由于不同连续子晶粒之间的局部扭转角变化引起的，这些子晶粒的大小约为 1 μm，本身几乎没有扭转角变化（ΔΘ ∼ 0.1°）。由于在径向上旋转的石墨烯层之间存在较弱的范德华键合，这些子晶粒与在原子层内和层间观察到的 0.3%应变变化一起演变。重要的是，这些外在的干扰会改变但不会消除出现的拉曼响应。因此，层间相互作用对应变和旋转无序具有弹性，这一事实为通过转移过程创建设计的 2D 固体异质结构的前景带来了希望。
