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Structural, mechanical and electronic properties of two-dimensional single-layer hexagonal structures in the (1 1 1) crystal plane of IIIAs-ZnS systems (III = B, Ga and In) are studied by first-principles calculations based on density functional theory (DFT). Elastic and phonon dispersion relation display that 2D h-IIIAs systems (III = B, Ga and In) are both mechanical and dynamically stable. Electronic structures analysis show that the semiconducting nature of the 3D-IIIAs compounds is retained by their 2D single layer counterpart. Furthermore, density of states reveals the influence of σ and π bonding in the most stable geometry (planar or buckled) for 2D h-IIIAs systems. Calculations of elastic constants show that the Young's modulus, bulk modulus and shear modulus decrease for 2D h-IIIAs binary compounds as we move down on the group of elements of the periodic table. In addition, as the bond length between the neighboring cation-anion atoms increases, the 2D h-IIIAs binary compounds display less stiffness and more plasticity. Our findings can be used to understand the contribution of the σ and π bonding in the most stable geometry (planar o buckled) for 2D h-IIIAs systems. Structural and electronic properties of h-IIIAs systems as a function of the number of layers have been also studied. It is shown that h-BAs keeps its planar geometry while both h-GAs and h-InAs retained their buckled ones obtained by their single layers. Bilayer h-IIIAs present the same bandgap nature of their counterpart in 3D. As the number of layers increase from 2 to 4, the bandgap width for layered h-IIIAs decreases until they become semimetal or metal. Interestingly, these results are different to those found for layered h-GaN. The results presented in this study for single and few-layer h-IIIAs structures could give some physical insights for further theoretical and experimental studies of 2D h-IIIV-like systems.

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2D-GaAs bandgap nature and graphene opening bandgap have been investigated in unexplored Graphene/GaAs bilayer van der Waals heterostructure under both uniaxial stress along c axis and different planar strain distributions using a 551/331 supercell geometry by DFT-VdW-Tkatchenko-Scheffler method and spinorbit coupling. The 2D-GaAs bandgap nature changes from Γ-K indirect in isolated monolayer to Γ-Γ direct in Graphene/GaAs bilayer heterostructure. In the same latter physical conditions, the graphene displays a bandgap of 5.0 meV. The uniaxial stress strongly influences the graphene electronic bandgap. Symmetrical in-plane strain does not open the graphene bandgap. Nevertheless, it induces remarkable changes on the GaAs width around the Fermi level. However, when applying asymmetrical in-plane strain to graphene/GaAs, the graphene sublattice symmetry is broken, and the graphene bandgap is open at the Fermi level to a maximum width of 814 meV. This value is much higher than that reported for graphene under asymmetrical strain. The Γ-Γ direct nature of GaAs remains unchanged in Graphene/GaAs under different types of applied strain. Phonon dispersion and elastic constants analysis display the dynamical and mechanical stability of Graphene/GaAs system, respectively. The calculated mechanical properties for bilayer heterostructure are better than those of their constituent monolayers. This latter finding, together with the tunable graphene bandgap not only by the strength but also by the direction of the strain, feature the likelihood of enhancing the physical characteristics of potential graphene-based group-IIIV electronic devices by strain engineering.

The electronic and vibrational properties of germanane and fluorinated germanene are studied within density functional theory (DFT) and density functional perturbation theory frameworks. Different structural configurations of germanane and fluorinated germanene are investigated. The energy difference between the different configurations are consistently smaller than the energy of thermal fluctuations for all the analyzed DFT functionals LDA, GGA, and hybrid functionals, which implies that, in principle, it is possible to find these different configurations in different regions of the sample as minority phases or local defects. We calculate the Raman and infrared spectra for these configurations by using ab initio calculations and compare it with available experimental spectra for germanane. Our results show the presence of minority phases compatible with the configurations analyzed in this work. As these low energy configurations are metastable the present work shows that the synthesis of these energy competing phases is feasible by selectively changing the synthesis conditions, which is an opportunity to expand in this way the availability of new two-dimensional compounds.