Raman Signature of Graphene Superlattices

Abstract

When two identical two-dimensional periodic structures are superposed, a mismatch rotation angle between the structures generates a superlattice. This effect is commonly observed in graphite, where the rotation between graphene layers generates Moiré patterns in scanning tunneling microscopy images. Here, a study of intravalley and intervalley double-resonance Raman processes mediated by static potentials in rotationally stacked bilayer graphene is presented. The peak properties depend on the mismatch rotation angle and can be used as an optical signature for superlattices in bilayer graphene. An atomic force microscopy system is used to produce and identify specific rotationally stacked bilayer graphenes that demonstrate the validity of our model.

Specific heat of twisted bilayer graphene: Engineering phonons by atomic plane rotations

“…The energies of these phonons depend on the twist angle. The rotation angle -dependent Raman peaks, associated with hybrid folded phonons have been observed experimentally [28][29][30][32][33][34][35][36][37], confirming the theoretical predictions.…”

“…Recently the attention has been shifted to twisted few-layer graphene (T-FLG), which demonstrates intriguing electron [24][25][26][27] and phonon properties [28][29][30][31][32][33][34][35][36]. Several independent experimental Raman studies of twisted graphene found series of phonon peaks in different energy regions, which are absent in FLG without the twist [28][29][30][32][33][34][35][36][37].…”

Resonant Raman spectroscopy of twisted multilayer graphene

“…y t can also be expressed in terms of the twist vector 7,37 (p,q). The so-called R and R 0 Raman bands have been suggested as probes of y t in t (1 þ 1)LG 38,39 . As shown in Fig.…”

Raman modes in transferred bilayer CVD graphene

“…Among other characterization techniques such as scanning tunneling microscopy (STM), Landau level (LL) spectroscopy [6], high-resolution transmission electron microscopy (HRTEM) [10], optical microscopy and infrared spectroscopy, Raman spectroscopy has also been widely used in the studies of tBLG [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. This is because Raman spectroscopy is a very sensitive and versatile tool to probe the electron-phonon and phononphonon coupling in graphene samples [11].…”

“…In addition to the resonant G and 2D bands, the spectra also contain weak Raman peaks due to in-plane combination modes and overtones (LOTA, TOLA, LOLA, TOTA, and 2LO) [15][16][17][18]. The tBLG contains, besides the aforementioned spectral bands, out-of-plane modes such as breathing (ZO ′ and ZO [19][20][21]), rotation (R and R ′ [22][23][24][25][26]), and shear (C [27]) modes. Although these modes generally produce only weak Raman peaks compared with the G and 2D bands, they carry important information for characterizing the perfection, stacking order, and carrier transport in graphene samples.…”