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    Electronic and optical characteristics of graphene on the molybdenum ditelluride substrate under the uniform mechanical stress
    (Elsevier Science Sa, 2023) Kulyamin, Pavel A.; Kochaev, Aleksey I.; Maslov, Mikhail M.; Flores -Moreno, Roberto; Kaya, Savas; Katin, Konstantin P.
    The study presents the effect of opening a semiconductor gap in graphene on the molybdenum ditelluride substrate under mechanical stresses using the density functional theory. It has been shown that uniform compression cannot only open the gap due to graphene sheet deformation but also adjust the gap size depending on the compression strength. The maximum gap found was 0.8 eV when the structure was compressed by 8 %, which is confirmed by further analysis of the UV-vis spectrum. Uniform stretching in contrast does not lead to a significant gap opening. The binding energy of the graphene sheet with the molybdenum ditelluride substrate does not change significantly when mechanical stresses are applied. An additional analysis of the Raman and IR spectra will make it possible to determine the degree of compression of graphene on a molybdenum ditelluride substrate in the experiment. In this case, the corresponding modes mainly correspond to vibrations of carbon atoms in the graphene plane or perpendicular to the substrate. The substrate itself does not make a significant contribution to these vibrational modes.
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    On point perforating defects in bilayer structures
    (Royal Soc Chemistry, 2023) Kochaev, Aleksey I.; Efimov, Vladimir V.; Kaya, Savas; Flores-Moreno, Roberto; Katin, Konstantin P.; Maslov, Mikhail M.
    This article deals with the issue of perforating point defects (pores) in a bilayer heterostructure composed of striped borophene and graphene. Three types of non-equivalent vacancies of the minimum size are considered. These include a single vacancy and two double vacancies. The study of the properties and stability of the perforating defects in borophene-graphene heterostructures is important given the increasing role of such structures in membranes for water purification, renewable energy generation, and other osmotic applications. Using the DFT method, the atomic configurations and main energy characteristics of the proposed defects are obtained. The results show that the formation of a single boron vacancy on the borophene side of borophene-graphene requires less energy than the formation of a carbon vacancy in graphene. Comparisons between double vacancies in nanoscale materials are unreliable because different reference systems produce the different chemical potentials. The problem of choosing the reference system for reliable calculation of the vacancy formation energies is posed and discussed. Using borophene-graphene as an example, it is shown that the reference system strongly affects the magnitude and sign of the vacancy formation energy. Hydrogenation is tested to stabilize the proposed defects. This article deals with the issue of perforating point defects (pores) in a bilayer heterostructure composed of striped borophene and graphene.