Probing Layer Number and Stacking Order of Few-Layer Graphene by Raman Spectroscopy
Probing Layer Number and Stacking Order of Few-Layer Graphene by Raman Spectroscopy
复制标题
DOI：
10.1002/smll.200901173
复制
发表时间：
2010-01-18
期刊：
影响因子：
13.3
通讯作者：
Thong, John T. L.
中科院分区：
文献类型：
--
作者：
Hao, Yufeng;Wang, Yingying;Thong, John T. L.
石墨烯是一种二维材料，被定义为紧密堆积的碳原子的平面蜂窝晶格，其中电子在狄拉克K点附近表现出线性色散，并且表现为无质量的狄拉克费米子。[1，2]然而，AB堆叠的石墨烯双层中的价带和导带在K点附近分裂成两个抛物线分支，起源于π电子的相互作用，因此电子由大量狄拉克费米子描述。[2-4]此外，石墨烯双层在电场偏置下是可调隙半导体。[5]随着层的数量的进一步增加沿着与AB堆叠，电子结构揭示逐步变化，最终接近的三维对应。[6-8]考虑到少层石墨烯（FLG）的电子性质与层数之间的密切关系，准确确定层数并将其与电子结构相关联的能力是理解从二维到三维石墨材料的电子性质演变的先决条件。除了具有AB堆叠的石墨烯层之外，具有任意堆叠的FLG（图1）被认为具有由其不同的晶体结构和π电子相互作用引起的独特性质。[9]实验上，已经观察到折叠石墨烯片的电和磁输运性质与AB堆叠双层的那些不同。[10]此外，在SiC、[11] Ni、[12-14]和Ru [15]上生长的FLG也具有非AB堆叠顺序。因此，阐明这种类型的FLG的详细特性不仅是需要的结构和电子性能的整体理解，但也为FLG为基础的设备的发展。拉曼散射是一种快速、灵敏、无损的碳基材料表征工具。[16]此外，拉曼散射中的声子通过已建立的双共振模型与石墨材料的电子色散直接关联，因此拉曼信号不仅表明晶格振动，而且还表明电子能带结构配置和修改。[17]在过去的两到三年中，已经进行了几项开创性的工作来阐明石墨烯的拉曼特性，例如区分单层和双层与块状石墨，[18-20]检测电荷杂质，[21，22]结构缺陷，[18]边缘状态（扶手椅或锯齿形），[29，30]应变效应，[23]确定晶体取向，[27，28]并研究偏压石墨烯的电子-声子耦合。在本通讯中，对AB堆叠FLG的拉曼光谱研究进行了详细的工作：发现二维带的半高宽（FWHM）是区分FLG层数（单层到五层）的定量指导。根据双共振的理论模型，FLG中电子能带结构的分裂是导致二维能带逐步展宽的原因。随后，以折叠FLG为例，研究了非AB堆叠FLG的电子性质。折叠FLG的2D带的一致的蓝移和形状和FWHM的相似性表明在K点附近略微修改的电子能量色散曲线以及具有任意堆叠的石墨烯层之间的弱耦合。我们强调的拉曼特性之间的联系和层间相互作用的性质，即AB堆叠和非AB堆叠。这一研究为快速确定多层膜的层数和堆积方式提供了一种手段，并有助于深入了解多层膜的电子能带演化。
Graphene is a two-dimensional material defined as a planar honeycomb lattice of close-packed carbon atoms, where the electrons exhibit a linear dispersion near Dirac K points and behave as massless Dirac fermions.[1, 2] However, the valence and conduction bands in an AB stacked graphene bilayer split into two parabolic branches near the K point originating from the interaction of π electrons, and the electrons are hence described by massive Dirac fermions.[2–4] Moreover, a graphene bilayer is a tunable-gap semiconductor under electric-field biasing.[5] With a further increase in the number of layers along with AB stacking, the electronic structure reveals stepwise variations that eventually approach that of the three-dimensional counterpart.[6–8] Considering the close relation between the electronic properties and layer number of few-layer graphene (FLG), the ability to accurately determine the layer number and correlating this with the electronic structure is a prerequisite in understanding the evolution of the electronic properties from two-to threedimensional graphitic materials. In addition to graphene layers with AB stacking, FLG with arbitrary stacking (Figure 1) is considered to possess distinct properties arising from its different crystalline structure and π electron interactions.[9] Experimentally, it has been observed that the electro-and magnetotransport properties for folded graphene sheets are different to those ofABstacked bilayers.[10] Furthermore, FLG grown on SiC,[11] Ni,[12–14] and Ru [15] also have non-AB stacking order. Therefore, elucidating the detailed characteristics of this type of FLG is required not only for the overall understanding of the structural and electronic properties but also for the development of FLG-based devices. Raman scattering is a rapid, sensitive, and non-destructive tool for the characterization of carbon-based materials.[16] Furthermore, the phonons in Raman scattering are directly linked to the electronic dispersion of graphitic materials by the well-established double-resonance model, and thus the Raman signals manifest not only lattice vibrations but also the electronic band structure configuration and modifications.[17] During the past two to three years, several pioneering works have been carried out to elucidate the Raman characteristics of graphene, such as differentiating single-layer and bilayer from bulk graphite,[18–20] detecting charge impurities,[21, 22] structural defects,[18] edge states (armchair or zigzag),[29, 30] strain effects,[23] determining the crystalline orientations,[27, 28] and investigating electron–phonon coupling for biased graphene.[24–26]In this Communication, detailed work is carried out on Raman spectroscopy study of AB-stacked FLG: the full width at half-maximum (FWHM) of the 2D band is found to be a quantitative guide to distinguish the layer number (single-to five-layer) of FLG. The splitting of the electronic band structure in FLG is responsible for the stepwise broadening of 2D bands according to the theoretical model of double resonance. Subsequently, folded FLG is taken as an example to investigate the electronic properties of non-AB stacked FLG. The consistent blueshift and similarity in shape and FWHM of the 2D band of folded FLG suggest slightly modified electronic energy dispersion curves near the K points as well as weak coupling between graphene layers with arbitrary stacking. We emphasize the link between the Raman characteristics and the nature of the interlayer interaction, that is, AB stacking and non-AB stacking. This research provides a means for fast confirmation of layer number and stacking manner, and sheds insight into the evolution of the electronic band …