Mexican-hat dispersions and high carrier mobility of γ-SnX (X = O, S, Se, Te) single-layers: a first-principles investigation

Strain-induced excellent photocatalytic performance in Z-scheme BlueP/γ-SnS heterostructures for water splitting

Constructing Z-scheme heterojunction photocatalysts with high solar-to-hydrogen (STH) efficiency is a practical alternative to produce clean and recyclable hydrogen energy on a large scale. This paper presents the design of stable Z-scheme blue phosphorene (BlueP)/γ-SnS heterostructures with excellent photocatalytic activities by applying strains. The first-principles calculations show that the BlueP/γ-SnS heterobilayer is a type-I heterojunction with an indirect bandgap of 1.41 eV and strong visible-light absorption up to 105 cm-1. Interestingly, biaxial strains (ε) can effectively regulate its bandgap width (semiconductor-metal) and induce the band alignment transition (type-I-type-II). Compressive and tensile strains can significantly enhance the interfacial interaction and visible-light absorption, respectively. More intriguingly, compressive strains can not only modulate the heterojunction types but also make the band edges meet the requirements for overall water splitting. In particular, the Z-scheme (type-I) BlueP/γ-SnS bilayer at -8% (-2%) strain exhibits a relatively high STH efficiency of 18% (17%), and the strained Z-scheme system (-8% ≤ ε ≤ -6%) also exhibits high and anisotropic carrier mobilities (158-2327 cm2 V-1 s-1). These strain-induced outstanding properties make BlueP/γ-SnS heterostructures promising candidates for constructing economically feasible photocatalysts and flexible nanodevices.

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.

Monolayer Ge2Te2P4 as a promising photocatalyst for solar driven water-splitting: a DFT study

The buckling hexagonal structure of Ge2Te2P4 was studied by first-principles calculations. The newly proposed structure was proven to be stable by analyzing its cohesive energy, phonon dispersion, elastic constants and AIMD results. Poisson's ratio of the Ge2Te2P4 monolayer is in the range 0.16-0.18, and Young's modulus is in the range 40.16-43.74 N m-1. The substituted Te atoms enhance the sp2 orbitals which strengthen the σ-bonds and therefore the thickness of the Ge2Te2P4 monolayer is smaller than that of monolayer GeP3. The Ge2Te2P4 monolayer has an indirect band gap of 1.85 eV, which can be narrowed by strains. The compressive band gaps from -2% to -4% change the electronic structure from the indirect band gap into the direct band gap. Strains can also increase the light absorption rate α(ω) in the visible region, which is 2-3 × 105 cm-1 at equilibrium. The Ge2Te2P4 monolayer has a suitable band gap and an appropriate VBM and CBM position for hydrogen generation. Under strain rate of 4% and higher, the VBM and CBM remain at suitable positions for hydrogen production. Another advantage of the Ge2Te2P4 monolayer is that its charge carrier mobilities are really high. The highest electron mobility is 1301.47 cm2 V-1 s-1, and the highest hole mobility is 28627.24 cm2 V-1 s-1, which are much higher than the mobility in monolayer GeP3. The Ge2Te2P4 monolayer has advantages for photocatalytic applications and it is necessary to perform further study on the material.

Novel two-dimensional Janus β-Ge2XY (X/Y = S, Se, Te) structures: first-principles examinations

Two-dimensional (2D) structures can stably exist in different allotropes. In this manuscript, we propose a new series of Janus structures based on the β-phase of germanium monochalcogenides, namely, β-Ge2XY (X/Y = S, Se, and Te) monolayers. Our calculations indicate that Janus β-Ge2XY monolayers have a stable crystal structure and possess anisotropic mechanical properties. At the ground state, β-Ge2XY monolayers are semiconductors with a large bandgap and their electronic properties depend strongly on a biaxial strain. Strains not only change the bandgap but can also lead to a change in the bandgap characteristic, namely transitions from indirect to direct bandgap. Our findings not only introduce a new structure of germanium chalcogenide compounds but also show that they have superior physical properties suitable for applications in nanoelectronics.