凯发

Borophene, a recently synthesized two-dimensional monolayer of boron atoms, is expected to exhibit anisotropic metallic character with relatively high electronic velocities [1]. At the same time, very low optical conductivities in the infrared-visible light region have been reported. Based on its promising electronic transport properties and a priori high transparency, borophene could become a genuine LEGO piece in the 2D materials assembling game. Such early suggested properties demands for an in depth investigation of borophene electronic structure. Moreover, borophene is naturally degraded in ambient conditions and it is therefore important to assess the mechanisms and the effects of oxidation on borophene layers. Optical and electronic properties of pristine and oxidized borophene have been investigated using first-principles techniques [2]. Optical response of the oxidized layer is found to be strongly modified suggesting that optical measurements can serve as an efficient probe for borophene surface contamination.  

Two-dimensional conjugated polymers exhibit electronic structures analogous to that of graphene with the peculiarity of π–π* bands which are fully symmetric and isolated. Realistic 2D conjugated polymer networks with a structural disorder such as monomer vacancies (unavoidable during bottom-up synthesis) are investigated using both ab initio and tight-binding techniques [3] in order to check their suitability for electronic applications. As expected, long mean free paths and high mobilities are predicted for low defect densities. At low temperatures and for high defect densities, strong localization phenomena originating from quantum interferences of multiple scattering paths are observed in the close vicinity of the Dirac energy region while the absence of localization effects is predicted away from this region suggesting a sharp mobility transition [3].

At last, the resonant Raman spectra of single-layered WS2 and WSe2 have been measured using more than 25 laser lines [4]. Although these two materials present the same crystal arrangement, their Raman excitation profiles exhibit unexpected differences. All Raman features of WS2 monolayers are enhanced by the first-optical excitations (with an asymmetric response for the spin−orbit related XA and XB excitons), whereas Raman bands of WSe2 are not enhanced at XA/B energies. Such an intriguing phenomenon has been addressed by DFT calculations and by solving the Bethe-Salpeter equation. Although the electronic structures of both WS2 and WSe2 are similar, with comparable spin−orbit coupling, our ab initio simulations [4] reveal that the two materials exhibit quite different exciton−phonon interactions that can explain their different Raman responses. These recent results reveal open new avenues for understanding the 2D materials physics, where weak interactions play a key role coupling different degrees of freedom (spin, optic, and electronic).