A first-principles prediction of the structural, electronic, transport and photocatalytic properties of GaGeX3 (X = S, Se, Te) monolayers.

The discovery of new 2D materials with superior properties motivates scientists to make breakthroughs in various applications. In this study, using calculations based on density functional theory (DFT), we have comprehensively investigated the geometrical characteristics and stability of GaGeX3 monolayers (X = S, Se, or Te), determining their electronic and transport properties, and some essential optical and photocatalytic properties. AIMD simulations show that these materials are highly structurally and thermodynamically stable. Notably, the GaGeSe3 monolayer is a semiconductor with a band gap of 1.9 eV and has a high photon absorption coefficient of up to 1.1 × 105 cm-1 in the visible region. The calculated solar-to-hydrogen conversion efficiency of the GaGeSe3 monolayer is 11.33%, which is relatively high compared to some published 2D materials. Furthermore, the electronic conductivity of the GaGeSe3 monolayer is 790.65 cm2 V-1 s-1. Our findings suggest that the GaGeSe3 monolayer is a new promising catalyst for the solar water-splitting reaction to give hydrogen and a potential new 2D material for electrical devices with high electron mobility.

First principles study of strain effects on prospective 2D photocatalysts Sn2Se2X4 (X = P, As) with ultra-high charge carrier mobility.

Ab initio calculations were employed to investigate the properties of Sn2Se2P4 and Sn2Se2As4, which are new semiconductors formed based on the 2D SnP3 structure. A comprehensive analysis was conducted to examine the structural characteristics and stability of both compounds. It was observed that both Sn2Se2P4 and Sn2Se2As4 exhibit notable toughness and ductility, characterized by a Poisson's ratio ranging from 0.16 to 0.20 and a Young's modulus ranging from 42.12 to 49.84 N m-1. The investigation focused on the examination of the electronic characteristics of the two compounds, as well as their correlation with optical properties, charge transport, and potential as photocatalysts. Being ductile semiconductors, the effects of strains on the properties of Sn2Se2P4 and Sn2Se2As4 were also investigated. The charge carrier mobility in the y-direction ranges from 103 to 104 cm2 V-1 s-1. Moreover, the electron-hole separation is expected to be very high as the difference in the mobilities of holes and electrons is really large. Moreover, it is worth noting that both Sn2Se2P4 and Sn2Se2As4 exhibit a significantly high absorption rate of 106 cm-1 in the visible region. The observed features of Sn2Se2P4 and Sn2Se2As4 indicate their potential as effective photocatalysts for the process of water splitting through the utilization of solar energy.

First-principles study on the structural properties of 2D MXene SnSiGeN4 and its electronic properties under the effects of strain and an external electric field.

The MXene SnSiGeN4 monolayer as a new member of the MoSi2N4 family was proposed for the first time, and its structural and electronic properties were explored by applying first-principles calculations with both PBE and hybrid HSE06 approaches. The layered hexagonal honeycomb structure of SnSiGeN4 was determined to be stable under dynamical effects or at room temperature of 300 K, with a rather high cohesive energy of 7.0 eV. The layered SnSiGeN4 has a Young's modulus of 365.699 N m-1 and a Poisson's ratio of 0.295. The HSE06 approach predicted an indirect band gap of around 2.4 eV for the layered SnSiGeN4. While the major donation from the N-p orbitals to the band structure makes SnSiGeN4's band gap close to those of similar 2D MXenes, the smaller distributions from the other orbitals of Sn, Si, and Ge slightly vary this band gap. The work functions of the GeN and SiN surfaces are 6.367 eV and 5.903 eV, respectively. The band gap of the layered SnSiGeN4 can be easily tuned by strain and an external electric field. A semiconductor-metal transition can occur at certain values of strain, and with an electric field higher than 5 V nm-1. The electron mobility of the layered SnSiGeN4 can reach up to 677.4 cm2 V-1 s-1, which is much higher than the hole mobility of about 52 cm2 V-1 s-1. The mentioned characteristics make the layered SnSiGeN4 a very promising material for use in electronic and photoelectronic devices, and for solar energy conversion.

Electronic structure and interface contact of two-dimensional van der Waals boron phosphide/Ga2SSe heterostructures.

In this work, we systematically examine the electronic features and contact types of van der Waals heterostructures (vdWHs) combining single-layer boron phosphide (BP) and Janus Ga2SSe using first-principles calculations. Owing to the out-of-plane symmetry being broken, the BP/Ga2SSe vdWHs are divided into two different stacking patterns, which are BP/SGa2Se and BP/SeGa2S. Our results demonstrate that these stacking patterns are structurally and mechanically stable. The combination of single-layer BP and Janus Ga2SSe gives rise to an enhancement in the Young's modulus compared to the constituent monolayers. Furthermore, at the ground state, the BP/Ga2SSe vdWHs possess a type-I (straddling) band alignment, which is desired for next-generation optoelectronic applications. The interlayer separation and electric field are effectively used to tune the electronic features of the BP/Ga2SSe vdWH from the type-I to type-II band alignment, and from semiconductor to metal. Our findings show that the BP/Ga2SSe vdWH would be appropriate for next-generation multifunctional optoelectronic and photovoltaic devices.

Electronic and optical properties of a Janus SnSSe monolayer: effects of strain and electric field.

In this paper, detailed investigations of the electronic and optical properties of a Janus SnSSe monolayer under a biaxial strain and electric field using ab initio methods are presented. Our calculations indicate that the Janus SnSSe monolayer is a semiconductor with an indirect band gap larger/lower than that of the SnSe2/SnS2 monolayer. To obtain accurate estimates of the band gap, both Perdew-Burke-Ernzerhof (PBE) and Heyd-Scuseria-Ernzerhof (HSE06) hybrid functionals have been used and the effect of spin-orbit coupling has also been included. While the influence of the electric field on the electronic and optical properties of the Janus SnSSe monolayer is quite weak, biaxial strain plays a key role in controlling these properties. The Janus SnSSe monolayer has a wide absorption spectrum, from visible light to the ultraviolet region. At equilibrium, the maximum absorption coefficient of the monolayer is up to 11.152 × 104 cm-1 in the ultraviolet region and it can be increased by strain engineering. With high absorption intensity in the visible light area and being able to tune the absorbance by strain, the Janus SnSSe monolayer becomes a promising material for applications in optoelectronic devices.

Theoretical and experimental study on the electronic and optical properties of K0.5Rb0.5Pb2Br5: a promising laser host material.

The data on the electronic structure and optical properties of bromide K0.5Rb0.5Pb2Br5 achieved by first-principle calculations and verified by X-ray spectroscopy measurements are reported. The kinetic energy, the Coulomb potential induced by the exchange hole, spin-orbital effects, and Coulomb repulsion were taken into account by applying the Tran and Blaha modified Becke-Johnson function (TB-mBJ), Hubbard U parameter, and spin-orbital coupling effect (SOC) in the TB-mBJ + U + SOC technique. The band gap was for the first time defined to be 3.23 eV. The partial density of state (PDOS) curves of K0.5Rb0.5Pb2Br5 agree well with XES K Ll and Br Kß2, and XPS spectra. The valence band (VB) is characterized by the Pb-5d3/2 and Pb-5d5/2 sub-states locating in the vicinities of -20 eV and -18 eV, respectively. The VB middle part is mainly formed by K-3p, Rb-4p and Br-4s states, in which the separation of Rb-4p3/2 and Rb-4p1/2 was also observed. The strong hybridization of Br-p and Pb-s/p states near -6.5 eV reveals a major covalent part in the Br-Pb bonding. With a large band gap of 3.23 eV, and the remarkably high possibility of inter-band transition in energy ranges of 4-7 eV, and 10-12 eV, the bromide K0.5Rb0.5Pb2Br5 is expected to be a very promising active host material for core valence luminescence and mid-infrared rare-earth doped laser materials. The anisotropy of optical properties in K0.5Rb0.5Pb2Br5 is not significant, and it occurs at the extrema in the optical spectra. The absorption coefficient α(ω) is in the order of magnitude of 106 cm-1 for an energy range of 5-25 eV.

Electronic and optical properties of Janus ZrSSe by density functional theory.

In the present work, we investigate systematically the electronic and optical properties of Janus ZrSSe using first-principles calculations. Our calculations demonstrate that the Janus ZrSSe monolayer is an indirect semiconductor at equilibrium. The band gap of the Janus ZrSSe is 1.341 eV using the Heyd-Scuseria-Ernzerhof hybrid functional, larger than the band gap of ZrSe2 monolayer and smaller than that of ZrS2 monolayer. Based on the analysis of the band edge alignment, we confirm that the Janus ZrSSe monolayer possesses photocatalytic activities that can be used in water splitting applications. While strain engineering plays an important role in modulating the electronic properties and optical characteristics of the Janus ZrSSe monolayer, the influence of the external electric field on these properties is negligible. The biaxial strain, ε b, has significantly changed the band of the Janus ZrSSe monolayer, and particularly, the semiconductor-metal phase transition which occurred at ε b = 7%. The Janus ZrSSe monolayer can absorb light in both visible and ultraviolet regions. Also, the biaxial strain has shifted the first optical gap of the Janus ZrSSe monolayer. Our findings provide additional information for the prospect of applying the Janus ZrSSe monolayer in nanoelectronic devices, especially in water splitting technology.