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Single-layer graphene (SLG) has received extensive research and attention due to its unique properties such as near-ballistic transport and high mobility, as well as potential applications in nanoelectronics and optoelectronic devices. There is a boundary for each SLG sample, and the physical properties of the SLG associated with the boundary strongly depend on the orientation of its boundaries. The first-order phonon mode-D mode can be observed in the Raman spectrum of the intrinsic SLG boundary, but it is not observed at the position far from the boundary. It was found that there is a critical distance hc for the contribution of the boundary to the D mode, which is about 3.5 nm. However, the D mode modulo-2D mode can be observed at the intrinsic SLG boundary and away from the boundary. Therefore, the D-mode becomes a powerful spectroscopic approach to study the crystal domain boundary, boundary orientation and double resonance Raman scattering of SLG.
SLG has two basic boundary orientations: the "armchair" type and the "zigzag" type. Unlike SLG, each graphene layer in multilayer graphene (MLG) has its own boundary and corresponding boundary orientation. For an actual MLG sample, there is an alignment distance h at the boundary between two adjacent graphene layers. h can grow to several microns or more, or it can be as short as a few nanometers. When the h of all adjacent graphene layers of the MLG is equal to 0, we call it the perfect boundary condition of the MLG. The complicated stacking mode of the MLG boundary and the presence of different h and orientation can significantly affect the transport properties of the boundary, the electronic structure of the nanobelt, and the spin polarization of the boundary local state. Although the Raman spectrum of the SLG boundary has been systematically studied, due to the complicated stacking method of the MLG boundary, the research on the Raman spectrum of the SML is still very few.
Recently, Zhang Jian, Li Qiaoqiao, and researcher Tan Pingheng, PhD students of the Institute of Semiconductors, Chinese Academy of Sciences, systematically studied the Raman scattering of the MLG boundary. They first classified the MLG boundary and found that the basic boundary type of the N-layer graphene (NLG) is NLGjE, ie the jLG with the perfect boundary is placed on (Nj) LG. Therefore, the boundary conditions of the double-layer graphene (BLG) can be divided into two cases: BLG1E+SLG1E and BLG2E. The study found:
(1) The NLG1E boundary is similar to the D mode peak shape of the NLG with a defect structure, and the 2D mode is the superposition of the 2D mode of NLG and (N-1)LG.
(2) Near the multi-graphene boundary in the area covered by the laser spot, the 2D mode intensity of the corresponding layer graphene is proportional to the area, and the corresponding D mode intensity is the alignment distance within the critical distance (if h (3) For a 2D mode near BLG1E, as h gradually decreases from the submicron scale to 0, the intensity from the SLG portion gradually decreases from the maximum value to 0, while the intensity from the BLG portion remains unchanged. For the D mode near BLG1E, as h gradually decreases from the submicron scale to 0, the intensity from the SLG section first increases from 0 to a maximum, once h (4) Through the linearity and intensity of the 2D mode at the BLG boundary, the case where h is 48 nm is successfully identified in the double-layer graphene boundary; even though the line mode and intensity of the D mode at the BLG boundary, it can be identified that h is smaller than 3.5nm situation. These dimensions are well beyond the diffraction limit of the laser spot and are not achievable by general characterization. The series of research work was recently published in Nanoscale 6, 7519-7525 (2014) and Carbon 85, 221-224 (2015). These important findings laid the foundation for further systematic study of multilayer graphene boundaries, and provided references for the study of the boundary of other two-dimensional materials. This work was supported by the National Natural Science Foundation of China. Weld Mesh,Galvanized Welded Wire Mesh,Stainless Steel Wire Mesh Panels,Heavy Gauge Wire Mesh ANPING HONGYU WIREMESH CO.,LTD , https://www.hongyufence.com