Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material

Abstract

Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets exhibit remarkable electronic and optical properties. The 2D features, sizable bandgaps, and recent advances in the synthesis, characterization, and device fabrication of the representative MoS2, WS2, WSe2, and MoSe2 TMDs make TMDs very attractive in nanoelectronics and optoelectronics. Similar to graphite and graphene, the atoms within each layer in 2D TMDs are joined together by covalent bonds, while van der Waals interactions keep the layers together. This makes the physical and chemical properties of 2D TMDs layer dependent. In this review, we discuss the basic lattice vibrations of monolayer, multilayer, and bulk TMDs, including high-frequency optical phonons, interlayer shear and layer breathing phonons, the Raman selection rule, layer-number evolution of phonons, multiple phonon replica, and phonons at the edge of the Brillouin zone. The extensive capabilities of Raman spectroscopy in investigating the properties of TMDs are discussed, such as interlayer coupling, spin-orbit splitting, and external perturbations. The interlayer vibrational modes are used in rapid and substrate-free characterization of the layer number of multilayer TMDs and in probing interface coupling in TMD heterostructures. The success of Raman spectroscopy in investigating TMD nanosheets paves the way for experiments on other 2D crystals and related van der Waals heterostructures.

Gate‐Tunable Resonant Raman Spectroscopy of Bilayer MoS2

“…[7] Raman spectroscopy is a versatile probe in studying the crystalline and vibrational properties of TMDs. [8][9][10][11][12] Gatetunable phonon properties in graphene, [13,14] MoS 2 , [15] and black phosphorus [16] have also been reported. With a gateinduced electron doping, the out-of-plane A 1g mode in mono layer MoS 2 is down-shifted while the in-plane vibrational mode E 2g 1 does not show observable change.…”

Ising-Type Magnetic Ordering in Atomically Thin FePS3

“…Raman spectroscopy is widely used for nondestructive characterization of 2D crystals such as graphene and transition metal 5 dichalcogenides. 14,15 In magnetic crystals, low energy excitations such as two magnon scattering appears in the Raman spectrum, 16 or some of the Raman peak positions or intensities change when spins are ordered. 17,18 Since direct measurement of the magnetic properties of atomically thin magnetic materials is difficult, especially in the case of antiferromagnetism, the changes in the Raman spectrum concomitant with a magnetic transition are good alternatives for monitoring magnetic ordering in such materials.…”

Vibrational and optical properties of MoS2: From monolayer to bulk

“…Earlier studies of bulk MoS 2 using Raman and infrared spectroscopy [53,54] as well as Neutron scattering [55] and electron-energy-loss spectroscopy [56] had already well characterized the phonons at Γ and the phonon dispersion. In the recent years, a large number of Raman studies on mono-and few-layer systems has emerged [57,58,59,60,61,62,63,64,65]. The Raman frequencies are correlated with the number of layers which allows their unequivocal identification.…”