多波长电子衍射作为识别二维材料中堆积序列的工具
Multiwavelength electron diffraction as a tool for identifying stacking sequences in 2D materials
摘要：
二维（2D）材料是当今研究最多的材料之一，因为它们具有独特的性质。这些材料由通过范德华力组装的单个或几个原子厚的层制成，因此允许各种堆叠序列，只要序列是周期性的，就可能导致各种晶体结构。以几层石墨烯（FLG）为例，确定层数和堆叠顺序至关重要，因为这些参数对性能具有驱动作用。为此目的，分析电子衍射图案（DP）的斑点强度是常用的，以及尝试改变层数和样品倾斜角。然而，由于DP之间的相似性，能够以这种方式区分的序列的数量仍然很少。此外，在FLG中除了A和/或B层之外还存在C层的可能性很少被考虑。为了克服这一限制，我们在这里提出了一种新的方法，基于多波长电子衍射，它能够区分堆叠序列多达6层（可能更多），涉及A，B和C层。我们还提出了一种创新的方法来计算光斑强度在一个更容易和更快的方式比标准的。此外，我们表明，该方法是有效的过渡金属dichalcogenides，以二硫化钼的例子。
英文摘要：
Two-dimensional (2D) materials are among the most studied ones nowadays, because of their unique properties. These materials are made of, single- or few atom-thick layers assembled by van der Waals forces, hence allowing a variety of stacking sequences possibly resulting in a variety of crystallographic structures as soon as the sequences are periodic. Taking the example of few layer graphene (FLG), it is of an utmost importance to identify both the number of layers and the stacking sequence, because of the driving role these parameters have on the properties. For this purpose, analysing the spot intensities of electron diffraction patterns (DPs) is commonly used, along with attempts to vary the number of layers, and the specimen tilt angle. However, the number of sequences able to be discriminated this way remains few, because of the similarities between the DPs. Also, the possibility of the occurrence of C layers in addition to A and/or B layers in FLG has been rarely considered. To overcome this limitation, we propose here a new methodology based on multi-wavelength electron diffraction which is able to discriminate between stacking sequences up to 6 layers (potentially more) involving A, B, and C layers. We also propose an innovative method to calculate the spot intensities in an easier and faster way than the standard ones. Additionally, we show that the method is valid for transition metal dichalcogenides, taking the example of MoS2.
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