Lattice Thermal Transport in Monolayer Group 13 Monochalcogenides MX (M = Ga, In; X = S, Se, Te): Interplay of Atomic Mass, Harmonicity, and Lone-Pair-Induced Anharmonicity

Angle-Dependent Raman Spectra of Crystal Polymorphs of GaO: A Computational Study

Two crystal polymorphs of GaO consisting of GaO-H and GaO-T monolayers are proposed in this study. Based on the density functional theory calculations, the phonon dispersion demonstrates that both GaO-H and GaO-T monolayers could be stable. The band gaps of GaO-H and GaO-T monolayers are 1.51 and 1.43 eV, respectively. When an external electric field is applied, the band gaps of GaO monolayers are reduced dramatically, down to 0.13 eV with the field of 0.7 V/Å. Because of the decreased symmetry of C3v under an external electric field, more peaks of Raman spectra can be obtained. The angle-dependent Raman spectra ofA ' 1 1 ${{\rm{A}}{{^\prime}}_1^1 }$ andA ' 1 2 ${{\rm{A}}{{^\prime}}_1^2 }$ of GaO-H monolayer, andA 1 g 1 ${{\rm{A}}_{1{\rm{g}}}^1 }$ andA 1 g 2 ${{\rm{A}}_{1{\rm{g}}}^2 }$ of GaO-T monolayer are discussed seperately, with the incident lasers of 488 and 532 nm. Additionally, the Raman intensity distribution shows that the incident light should be parallel to the plane of the GaO monolayer to obtain more comparable Raman spectra. These investigations of the crystal polymorphs of GaO monolayers may guide the experimental investigations of GaO monolayers and potential optoelectronic applications.

Z-scheme Al2SeTe/GaSe and Al2SeTe/InS van der Waals heterostructures for photocatalytic water splitting

Designing Z-scheme van der Waals (vdW) heterostructured photocatalysts is a promising strategy for developing highly efficient overall water splitting. Herein, by employing density functional theory calculations, we systematically investigated the stability, electronic structures, photocatalytic and optical properties of Al2SeTe, GaSe, and InS monolayers and their corresponding vdW heterostructures. Interestingly, electronic structures show that all vdW heterostructures have direct band gaps, which is conducive to the transition of electrons from the valence band to the conduction band. Notably, Al2TeSe/GaSe and Al2TeSe/InS vdW heterostructures possess large overpotentials for Z-scheme photocatalytic water splitting, as proved by the results of band edge positions and band structure bending. Moreover, these vdW heterostructures exhibit good optical absorption in ultraviolet and visible light regions. We believe that our findings will open a new avenue for the modulation and development of Al2TeSe/GaSe and Al2TeSe/InS vdW heterostructures for photocatalytic water splitting.

Lattice Thermal Conductivity of Monolayer InSe Calculated by Machine Learning Potential

The two-dimensional post-transition-metal chalcogenides, particularly indium selenide (InSe), exhibit salient carrier transport properties and evince extensive interest for broad applications. A comprehensive understanding of thermal transport is indispensable for thermal management. However, theoretical predictions on thermal transport in the InSe system are found in disagreement with experimental measurements. In this work, we utilize both the Green-Kubo approach with deep potential (GK-DP), together with the phonon Boltzmann transport equation with density functional theory (BTE-DFT) to investigate the thermal conductivity (κ) of InSe monolayer. The κ calculated by GK-DP is 9.52 W/mK at 300 K, which is in good agreement with the experimental value, while the κ predicted by BTE-DFT is 13.08 W/mK. After analyzing the scattering phase space and cumulative κ by mode-decomposed method, we found that, due to the large energy gap between lower and upper optical branches, the exclusion of four-phonon scattering in BTE-DFT underestimates the scattering phase space of lower optical branches due to large group velocities, and thus would overestimate their contribution to κ. The temperature dependence of κ calculated by GK-DP also demonstrates the effect of higher-order phonon scattering, especially at high temperatures. Our results emphasize the significant role of four-phonon scattering in InSe monolayer, suggesting that combining molecular dynamics with machine learning potential is an accurate and efficient approach to predict thermal transport.

Carrier and phonon transport in 2D InSe and its Janus structures

Recently, two-dimensional (2D) Indium Selenide (InSe) has been receiving much attention in the scientific community due to its reduced size, extraordinary physical properties, and potential applications in various fields. In this review, we discussed the recent research advancement in the carrier and phonon transport properties of 2D InSe and its related Janus structures. We first introduced the progress in the synthesis of 2D InSe. We summarized the recent experimental and theoretical works on the carrier mobility, thermal conductivity, and thermoelectric characteristics of 2D InSe. Based on the Boltzmann transport equation (BTE), the mechanisms underlying carrier or phonon scattering of 2D InSe were discussed in detail. Moreover, the structural and transport properties of Janus structures based on InSe were also presented, with an emphasis on the theoretical simulations. At last, we discussed the prospects for continued research of 2D InSe.

Novel two-dimensional beta-XTe (X = Ge, Sn, Pb) as promising room-temperature thermoelectrics

In this paper, we designed novel low-symmetry two-dimensional (2D) structures based on conventional XTe (X = Ge, Sn, Pb) thermoelectrics with large average atomic mass. The first-principles calculations combined with Boltzmann transport theory show that the beta-XTe exhibit good stability, high electron carrier mobility, and ultralow Κ_L. The subsequent analyses show that the ultralow Κ_L stems from the coexistence of resonant bonding, weak bonding, and lone-pair electrons in beta-XTe, which leads to large anharmonicities. On the other hand, the lowest energy conduction band of beta-GeTe and beta-SnTe show the convergence of the low-lying Ʃ band, which is the source of the high-power factor in the two systems. The calculated maximum ZT of beta-XTe (X = Ge, Sn, Pb) are 3.08, 1.60, and 0.57 at 300 K, respectively, which is significantly greater than that of the previously reported high-symmetry 2D alpha-XTe and the commercial thermoelectrics. We hope that this work can provide important guidance for the development of thermoelectric materials.