(Invited) Resonance Raman Spectroscopy Studies in 2D and 1D Nanocarbons

Abstract

Raman spectroscopy is a nondestructive tool widely used to characterize a variety of nanomaterials including the novel 2D and 1D systems such as graphene and MoS2, linear carbon chains, among others. Since electrons and phonons are specially coupled to each other due to the reduced dimensionality, this technique provides detailed information about the structure and electronic properties of theses layered systems thus allowing one to probe in the phonon spectra the numbers of layers and their interactions with the environment. Most of these 2D materials are on substrate and the understanding on how the substrate affects the physical properties of these atomic thickness layers is a key point for fully characterize the materials. In this regard, strain is an important variable to take into account because the adhesion of the layered materials depends on the nature of the substrate and a key question is how the strain is transferred from a given substrate to the 2D material, for instance. The use of hydrostatic pressure has been an effective method modulate the interactions between the 2D materials with substrates and environment and Raman spectroscopy has been important for investigating these strained 2D nanomaterials because the Raman cross section of these low dimensional materials is very large. In this talk, we discuss recent results obtained for high-pressure Raman studies of graphene (mono- and bilayer) and MoS2 (mono-, bi-, tri- and many layers) sitting on substrate. Depending on the pressure transmitting medium, the pressure-induced changes in the Raman modes frequency at different rates, which has been attributed to different strain transferred from the substrate to the 2D materials. In the case of MoS2, the behavior of Raman modes suggested that a biaxial stress is transmitted from substrate to the MoS2 layers by means of the substrate deformation due to pressure and the magnitude of such stress transfer is found to be dependent of the number of layers. We also discuss the effects of strain on the vibrational properties of linear carbon chains encapsulated in carbon nanotubes.