Abstract
Grain boundaries (GBs) commonly exist in crystalline materials and affect various properties of materials. The facile identification of GBs is one of the significant requirements for systematical study of polycrystalline materials including recently emerging two-dimensional materials. Previous observations of GBs have been performed by various tools including high resolution transmission electron microscopy. However, a method to easily identify GBs, especially in the case of low-angle GBs, has not yet been well established. In this paper, we choose graphene bilayers with a GB as a model system and investigate the effects of interlayer rotations to the identification of GBs. We provide a critical condition between adjacent moiré fringe spacings, which determines the possibility of GB recognition. In addition, for monolayer graphene with a grain boundary, we demonstrate that low-angle GBs can be distinguished easily by inducing moiré patterns deliberately with an artificial reference overlay.
Highlights
In the production of large-area two-dimensional (2D) graphene, grain boundaries (GBs) are inevitably produced[1,2,3], which affect various properties of graphene, such as intrinsic tensile strength, fracture, failure, and electrical charge transport[4,5,6,7,8,9,10,11,12]
Yuk et al suggested that the Grain boundaries (GBs) in high θ1−2 is observed readily where two distinct moiré patterns join sharply[37]
The inset fast Fourier transform (FFT) image represents how difficult it is to distinguish two peaks, which is to say the crystallographic orientations of each grain, in the case of low θ1−2
Summary
In the production of large-area two-dimensional (2D) graphene, grain boundaries (GBs) are inevitably produced[1,2,3], which affect various properties of graphene, such as intrinsic tensile strength, fracture, failure, and electrical charge transport[4,5,6,7,8,9,10,11,12]. As a result, developing a method to identify GBs is a crucial requirement for studying polycrystalline graphene as well as other materials. Transmission electron microscopy (TEM) mainly utilizes electron diffraction patterns (DP)[17] and fast Fourier transform (FFT) of atomic resolution images[18,19] to identify GBs. From DP and FFT, GBs can be estimated from compiling and marking the transition peaks of DPs, which is a tedious and time consuming method. We suggest a method to identify GBs directly on real-space images via moiré patterns in the bilayer graphene system. The reason why the moiré pattern is effective at distinguishing the GBs is explained using a concept in visual perception
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