Spectral Manifestations of Nonlinear Resonant Wave Interactions in the Vibrational Spectra of Transition Metal Dichalcogenides

摘要

1 Introduction The unique physicochemical properties of inorganic structural analogues of graphene and graphite-a wide family of two-dimensional (2D) transition metal dichalcnogenides (TMD) MeX_2 (Me= Mo, W, Ti, Nb, Zr, Ta, Hf; X= S, Se, Te) are determined not only by features from the two-dimensional structure, but also by the presence of the forbidden band E_g~ 2 eV, which is associated with their semiconductor properties, and especially their exciton states A_1, B_1, associating with their resonance properties, which are often manifested in Raman spectra (RS). It is significant that TMD excitonic states, unlike traditional semiconductor Raman spectra, are well manifested at room temperatures. Note that this is the subject of scientific discussion to date. The essential role of d-states near the top of the valence band and the bottom of the conduction band, including strong phonon-electron interaction and spin-orbit coupling, in our opinion, is a characteristic feature of TMD. Owing to the combination of layers consisting of different atoms and the difference in charges on them, MeX_2 vibrations are well manifested not only in Raman spectra similar to carbon materials and nanostructures (graphene, fullerenes, nanotubes, onion-like structures, etc.), but also in IR absorption spectra. In addition, semiconductor-metal transitions are characteristic for TMD, as well as superconductivity (especially when they are intercalated by alkali metal atoms). In connection with the noted above properties of TMD, they should be richer than the widely known carbon nanostructures in a purely scientific and technical-applied respects.