In this work, we present the results of measurements of the Raman spectrum of the √3x√3R30° reconstruction of graphene grown on 4H-SiC(0001), the so-called buffer layer. The extracted Raman spectrum of the buffer layer shows bands, different from those of graphene, which can be attributed to the interaction of the buffer layer with the SiC substrate. In particular, in the high-wavenumber region, at least three bands are observed in the wavenumber regions 1,350–1,420, 1,470–1,490 and 1,520–1,570 cm⁻¹. The assignment of the buffer layer bands is supported here by tight-binding simulations of the one-phonon density of states for structures with a sufficiently large number of Si-C bilayers for reaching convergence. The converged phonon density of states is found to be in semi-quantitative agreement with the latter two bands, and therefore, the tight-binding predictions of the lattice dynamics of the structure can be used for their assignment to buffer layer vibrations. Namely, the Raman band at about 1,550 cm⁻¹ can be assigned to modified in-plane optical phonon branches of graphene, while the Raman band at about 1,490 cm⁻¹ can be assigned to modified folded parts of these branches inside the Brillouin zone of the buffer layer and can be considered as a Raman fingerprint of the buffer layer.

中文翻译：

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4H-SiC(0001) Si 端面上生长的石墨烯缓冲层的拉曼指纹：实验与理论

在这项工作中，我们展示了在 4H-SiC(0001)（所谓的缓冲层）上生长的石墨烯的 √3x√3R30° 重建拉曼光谱的测量结果。提取的缓冲层拉曼光谱显示出与石墨烯不同的谱带，这可归因于缓冲层与 SiC 衬底的相互作用。^{特别地，在高波数区域中，在波数区域1,350-1,420、1,470-1,490和1,520-1,570 cm -1}中观察到至少三个带。此处，缓冲层能带的分配通过对具有足够多的 Si-C 双层的结构的单声子态密度的紧束缚模拟来支持，以达到收敛。发现收敛的声子态密度与后两个能带半定量一致，因此，结构晶格动力学的紧束缚预测可用于将其分配给缓冲层振动。即，约1,550 cm ^-1处的拉曼带可归属于石墨烯的修改的面内光学声子分支，而约1,490 cm ^-1处的拉曼带可归属于这些分支在石墨烯布里渊区内的修改折叠部分。缓冲层，可以被认为是缓冲层的拉曼指纹。