Thermal exfoliation of stoichiometric single-layer silica from the stishovite phase: insight from first-principles calculations

Computational insights into structural, electronic, and optical properties of Janus GeSO monolayer

Although O is an element of chalcogen group, the study of two-dimensional (2D) O-based Janus dichalcogenides/monochalcogenides, especially their 1T-phase, has not been given sufficient attention. In this work, we systematically investigate the structural, electronic, and optical properties of 1T Janus GeSO monolayer by using the density functional theory. Via the analysis of phonon spectrum and evaluation of elastic constants, the GeSO monolayer is confirmed to be dynamically and mechanically stable. Calculated results for the elastic constants demonstrate that the Janus GeSO monolayer is much mechanically flexible than other 2D materials due to its small Young's modulus. At the ground state, while both GeS₂ and GeO₂ monolayers are indirect semiconductors, the Janus GeSO monolayer is found to be a direct band gap semiconductor. Further, effective masses of both electrons and holes are predicted to be directionally isotropic. The Janus GeSO monolayer has a broad absorption spectrum, which is activated from the visible light region and its absorption intensity is very high in the near-ultraviolet region. The calculated results not only systematically provide the fundamental physical properties of GeSO monolayer, but also stimulate scientists to further studying its importance both theoretically and experimentally.

First-principles study of graphenylene/MoX2 (X = S, Te, and Se) van der Waals heterostructures

New van der Waals (vdW) heterostructures obtained by stacking monolayers of recently synthesized graphenylene (Gr) and two-dimensional 1H-MoX2 (X = S, Te, and Se) are proposed and analyzed using ab initio calculations. These heterostructures are stable under normal conditions and have unique crystalline lattices. The study of electronic properties shows that the proposed materials are direct-gap semiconductors with a narrow band gap, which can be controlled by in-plane tensile strain or a transverse electric field. The considered vdW heterostructures demonstrate the transition of band alignments between types I, II and III, when in-plane stress or a transverse electric field is applied, and hold great potential for creating multifunctional devices for stretched electronics. Computations based on the non-equilibrium Green's function method indicate a high rectification factor of the order of 103-104 for a diode based on the Gr/MoS2 vdW junction. The studied structures exhibit broad optical absorption across the entire visible range and represent a promising material for optoelectronic applications.

Square transition-metal carbides MC6 (M = Mo, W) as stable two-dimensional Dirac cone materials

We identify the existence of Dirac cones in 2D square transition-metal carbides MC₆ (M = Mo, W) with an ultrahigh Fermi velocity comparable to that of graphene.

Structural and electronic properties of two-dimensional stanene and graphene heterostructure

Structural and electronic properties of two-dimensional stanene and graphene heterostructure (Sn/G) are studied by using first-principles calculations. Various supercell models are constructed in order to reduce the strain induced by the lattice mismatch. The results show that stanene interacts overall weakly with graphene via van der Waals (vdW) interactions. Multiple phases of different crystalline orientation of stanene and graphene could coexist at room temperature. Moreover, interlayer interactions in stanene and graphene heterostructure can induce tunable band gaps at stanene's Dirac point, and weak p-type and n-type doping of stanene and graphene, respectively, generating a small amount of electron transfer from stanene to graphene. Interestingly, for model [Formula: see text] , there emerges a band gap about 34 meV overall the band structure, indicating it shows semiconductor feature.