No abstract

Using first principles calculations we showed that the electronic and optical properties of single-layer black phosphorus (BP) depend strongly on the applied strain. Due to the strong anisotropic atomic structure of BP, its electronic conductivity and optical response are sensitive to the magnitude and the orientation of the applied strain. We found that the inclusion of many body effects is essential for the correct description of the electronic properties of monolayer BP; for example, while the electronic gap of strainless BP is found to be 0.90 eV by using semilocal functionals, it becomes 2.31 eV when many-body effects are taken into account within the G 0 W 0 scheme. Applied tensile strain was shown to significantly enhance electron transport along zigzag direction of BP. Furthermore, biaxial strain is able to tune the optical band gap of monolayer BP from 0.38 eV (at −8% strain) to 2.07 eV (at 5.5%). The exciton binding energy is also sensitive to the magnitude of the applied strain. It is found to be 0.40 eV for compressive biaxial strain of −8%, and it becomes 0.83 eV for tensile strain of 4%. Our calculations demonstrate that the optical response of BP can be significantly tuned using strain engineering which appears as a promising way to design novel photovoltaic devices that capture a broad range of solar spectrum.

Heterostructure made of MXenes and graphene enhances the Li storage and increases the stability of the system for its application in a promising Li-ion battery.

Recently, rhenium disulfide (ReS 2) monolayers were experimentally extracted by conventional mechanical exfoliation technique from as-grown ReS 2 crystals. Unlike the well-known members of transition metal dichalcogenides (TMDs), ReS 2 crystallizes in a stable distorted-1T structure and lacks an indirect to direct gap crossover. Here we present an experimental and theoretical study of the formation, energetics, and stability of the most prominent lattice defects in monolayer ReS 2. Experimentally, irradiation with 3-MeV He +2 ions was used to break the strong covalent bonds in ReS 2 flakes. Photoluminescence measurements showed that the luminescence from monolayers is mostly unchanged after highly energetic α particle irradiation. In order to understand the energetics of possible vacancies in ReS 2 we performed systematic first-principles calculations. Our calculations revealed that the formation of a single sulfur vacancy has the lowest formation energy in both Re and S rich conditions and a random distribution of such defects are energetically more preferable. Sulfur point defects do not result in any spin polarization whereas the creation of Re-containing point defects induce magnetization with a net magnetic moment of 1-3µ B. Experimentally observed easy formation of sulfur vacancies is in good agreement with first-principles calculations.