The pioneering experiments with graphene in 2004 opened the new area of two-dimensional (2D) systems in science. Several new 2D systems have been studied, such as the semiconducting transition metal dichalcogenides MX₂ (M = Mo, W and X = S, Se, Te), and a phosphorus crystalline halotropic called black phosphorus. The behavior of the electrons in these materials depends not only on the atoms in the crystalline structure but also on the number of layers and the form of stacking. We have in recent years studied some of these 2D materials by Raman spectroscopy, which provides us with information about phonons and their interactions with electrons and excitons. In this work, I will initially present Raman spectroscopy results in MoS₂, [1,2], WS₂ and WSe₂ [3] compounds, which show that Raman modes are intensified by resonances with excitons, allowing us to obtain dependence of their energies with the number of atomic layers. We observed that the electron-phonon coupling is dependent on the symmetry of the excitons and phonons [1] and we could evidence electron scattering processes between different valleys by acoustic phonons [2]. Finally, I will present results on black phosphorus, which has peculiar anisotropic electronic bands. Different edges of black phosphorus were studied using Raman spectroscopy and the results show the appearance of new modes at the edges of the sample, which depend on the atomic structure of the edges (zig-zag or armchair). Theoretical simulations confirm that the existence of new modes is due to edge phonons, which are originated by the atomic rearrangements at the crystalline terminations [4]..

[1] B. R. Carvalho, Phys. Rev. Letters 114, 136403 (2015)

[2] B. R. Carvalho et al. Nature Comm. (2017)

[3] E. del Corro et al, Nano Letters 16 (4), pp 2363–2368 (2016)

[4] H. B. Ribeiro et al, Nature Comm. vol 7, 12191 (2016)