Based on the constructed atomistic models of graphene/nanotube films with different numbers of nanotubes in supercells, we carried out in silico studies of the regularities of the nonuniform density distribution, which determine the presence of an island structure in such films. As a result of quantum molecular dynamics modeling, it is found that thin tubes of subnanometer diameter are enveloped in graphene sheets, which makes them energetically stable and stable. We also studied tunneling contacts between individual film fragments that are not covalently bound, in particular, between graphene sheets with different topologies of contacting zigzag and armchair edges, depending on the distance between them, and between tubes of different chiralities, including (6,3), (4,4), (6,5), (12,6) and (16,0). It is found that the tunnel contacts of tubes with a semiconductor type of conductivity are characterized by the presence of voltage intervals with a negative differential resistance in the I – V characteristic. Such voltage intervals are not observed at all for tubes with a metallic character of conductivity. The new knowledge obtained is important for assessing the electrical conductivity of such films, two-thirds of which are semiconductor tubes.
In this paper, we consider two new atomic models of van der Waals vertical heterostructures of metal-semiconductor type based on a 2D buckled triangular borophene with metallic conductivity and graphene-like 2D monolayers of gallium nitride GaN and zinc oxide ZnO, which are semiconductors. Using the density functional theory, the equilibrium configurations of supercells of the borophene/GaN and borophene/ZnO heterostructures are found and their thermodynamic stability at room temperature is shown. Within the framework of the nonstationary first-order perturbation theory, the optical characteristics (complex permittivity and absorption coefficient) are calculated in the electromagnetic radiation wavelength range of 0.2–2 μm. The presence of anisotropy in the optical properties of the borophene/GaN and borophene/ZnO heterostructures is established when the direction of light polarization is chosen. This is due to different manifestations of the optical properties of the constituent monolayers of the heterostructure. When light is polarized in the direction of the zigzag edge of the GaN/ZnO (along the X axis), the optical properties of GaN and ZnO semiconductor monolayers are predominantly manifested. When light is polarized in the direction of the zigzag edge of the borophene monolayer (along the Y axis), the optical properties of borophene manifest themselves. A synergistic effect has been found from the combination of borophene and ZnO monolayers in the composition of the borophene/ZnO vertical heterostructure, which manifests itself in the form of a section of the increasing plot of the real and imaginary parts of the complex permittivity in the infrared region for both directions of light polarization. It is shown that the difference in the values of the absorption coefficient of the borophene/GaN heterostructure between the UV and visible ranges can reach ~ 7 times, between the UV and near IR ranges - ~ 14 times, and for the borophene/ZnO heterostructure this difference can be up to ~ 6 times and up to ~18 times, respectively. It is predicted that borophene/GaN and borophene/ZnO heterostructures can be used to create UV radiation detectors.
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