Two-dimensional (2D) polar materials experience an in-plane charge transfer between different elements due to their electron negativities. When they form vertical heterostructures, the electrostatic force triggered by such charge transfer plays an important role in the interlayer bonding beyond van der Waals (vdW) interaction. Our comprehensive first principle study on the structural stability of the 2D SiC/GeC hybrid bilayer heterostructure has found that the electrostatic interlayer interaction can induce the π-π orbital hybridization between adjacent layers under different stacking and out-of-plane species ordering, with strong hybridization in the cases of Si-C and C-Ge species orderings but weak hybridization in the case of the C-C ordering. In particular, the attractive electrostatic interlayer interaction in the cases of Si-C and C-Ge species orderings mainly controls the equilibrium interlayer distance and the vdW interaction makes the system attain a lower binding energy. On the contrary, the vdW interaction mostly controls the equilibrium interlayer distance in the case of the C-C species ordering and the repulsive electrostatic interlayer force has less effect. Interesting finding is that the band structure of the SiC/GeC hybrid bilayer is sensitive to the layer-layer stacking and the out-of-plane species ordering. An indirect band gap of 2.76 eV (or 2.48 eV) was found under the AA stacking with Si-C ordering (or under the AB stacking with C-C ordering). While a direct band gap of 2.00 eV – 2.88 eV was found under other stacking and species orderings, demonstrating its band gap tunable feature. Furthermore, there is a charge redistribution in the interfacial region leading to a built-in electric field. Such field will separate the photo-generated charge carriers in different layers and is expected to reduce the probability of carrier recombination, and eventually give rise to the electron tunneling between layers.
Two-dimensional (2D) lateral polar heterostructures, constructed by seamlessly stitching 2D polar materials, exhibit unique properties triggered by the in-plane charge transfer between different elements in each domain. Our first-principles study of 2D SiC/GeC lateral polar heterostructures has unraveled their interesting characteristics. The local strain induced by a lattice mismatch leads to an artificial uniaxial strain along the interface. The synergistic effect of such uniaxial strain, the microstructure of interface, and the width of domains modulates the feature of the bandgap with an indirect bandgap nature in armchair lateral heterostructures and a direct bandgap nature in zigzag lateral heterostructures. The bandgap monotonically decreases with increasing the width of domains, showing its tunability. Furthermore, the valence band maximum is found to be mainly contributed from C-2 p orbitals located at both GeC and SiC domains, and the conduction band minimum is mainly contributed from Ge-4 p orbitals located at the GeC domain, implying that most excited electrons prefer to stay at the GeC domain of the SiC/GeC lateral polar heterostructures. Interestingly, a net charge transfer from the SiC domain to the GeC domain was found, resulting in a spontaneous lateral p–n junction, and there is a net charge redistribution at the interfacial region leading to a built-in electric field which is expected to reduce the carrier recombination losses, implying the promising application for visible light photocatalyst, photovoltaics, and water splitting to achieve clean and renewable energy.
A systematic computational calculation based on the state-of-the-art quantum mechanics mothed was carried out to study the response of mechanical properties to various strains exerted on graphene, SiC sheet, and recently predicted twodimensional (2D) sandwiched GaP and InP binary compounds. It was found that these 2D materials undergo an elastic expansion, a structural deformation, and then a structural broken process as the strain increases. Such process strongly depends on the direction of the strain exerted on 2D materials. In particular, a phase transition occurs in 2D sandwiched GaP and InP binary compounds when the strain exerts in zigzag direction. Calculated mechanical properties show that graphene has large linear and nonlinear elastic moduli, followed by 2D SiC monolayer. While the sandwiched GaP and InP structures possess significant anisotropic and nonlinear mechanical properties. Especially, those constants in the zigzag direction are about three to nine times greater than that in the armchair direction. Compared to graphene, they are softer, even along the zigzag direction. Such results provide fundamental information at atomic level for synthesizing, designing, and fabricating nanoelectromechanical and nanoelectronic devices.
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