Interface Coupling in Twisted Multilayer Graphene by Resonant Raman Spectroscopy of Layer Breathing Modes

Abstract

Raman spectroscopy is the prime nondestructive characterization tool for graphene and related layered materials. The shear (C) and layer breathing modes (LBMs) are due to relative motions of the planes, either perpendicular or parallel to their normal. This allows one to directly probe the interlayer interactions in multilayer samples. Graphene and other two-dimensional (2d) crystals can be combined to form various hybrids and heterostructures, creating materials on demand with properties determined by the interlayer interaction. This is the case even for a single material, where multilayer stacks with different relative orientations have different optical and electronic properties. In twisted multilayer graphene there is a significant enhancement of the C modes due to resonance with new optically allowed electronic transitions, determined by the relative orientation of the layers. Here we show that this applies also to the LBMs, which can be now directly measured at room temperature. We find that twisting has a small effect on LBMs, quite different from the case of the C modes. This implies that the periodicity mismatch between two twisted layers mostly affects shear interactions. Our work shows that ultralow-frequency Raman spectroscopy is an ideal tool to uncover the interface coupling of 2d hybrids and heterostructures.

Physical origin of Davydov splitting and resonant Raman spectroscopy of Davydov components in multilayerMoTe2

“…Figure 4 and a recent work [24] indicate that the However, the two modes exhibit different resonant profiles, which may result from the differences in the electron-phonon coupling strength of the two modes. Indeed, similar results have been observed for the different C and LB modes in twisted multilayer graphenes [20,21].…”

“…The typical PL spectra of 1L and 3L MoTe 2 on 300-nm SiO 2 /Si substrate are shown can be treated as a ball to analyze the atomic displacements of the interlayer modes, i.e., the socalled linear chain model (LCM) [13,18,25,29]. When only the interlayer coupling between the nearest-neighbor layers is considered, the eigenfrequencies in NL MoTe 2 for the C and LB modes can be expressed as follows [21]: …”

“…The NL MoTe 2 samples were prepared by mechanical exfoliation from the bulk material (2D [20,21]. We kept the laser power below 0.4 mW to avoid the heating effect to the samples.…”

“…The linear chain model has been used to understand the interlayer vibrations in those layered materials [13,18,20,21] where the interaction between layered materials and substrate is neglected. Also, the second-nearest layer-breathing interlayer coupling has been found to exist in MLGs [21].…”

“…The linear chain model has been used to understand the interlayer vibrations in those layered materials [13,18,20,21] where the interaction between layered materials and substrate is neglected. Also, the second-nearest layer-breathing interlayer coupling has been found to exist in MLGs [21]. Moreover, a recent study revealed that a substrate-induced interface mode has been observed in [24], which is quantitatively described by a force constant model, including interactions up to the second nearest neighbor and surface effects as fitting parameters.…”