Two-dimensional (2D) materials with negative Poisson’s ratio (NPR) attract considerable attention because of their exotic mechanical properties. We propose a new 2D material, monolayer GaPS4, which shows NPR for both in-plane (−0.033) and out-of-plane (−0.62) directions. Such coexistence of NPR in two distinct directions could be explained by its corner- and edge-shared tetrahedra pucker structure. GaPS4 has an ultralow cleavage energy of 0.23 J m–2 according to our calculation, such that exfoliation of the bulk material is feasible for the preparation of mono- and few-layer GaPS4. Direct wide band gap of 3.55 eV and moderate electron mobility have been revealed in monolayer GaPS4, while the direct gap feature is robust within a strain range of −6% to 6%. These findings render 2D GaPS4 a promising candidate for applications in nanoelectronics and low-dimensional electromechanical devices.

Two-dimensional (2D) layered Ti2C MXene has been synthesized experimentally, and the magnetism of monolayer Ti2C MXene has been predicted theoretically.

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Two-dimensional (2D) materials with high carrier mobility and tunable magnetism are in high demand for nanoelectronics and spintronic applications. Herein, we predict a novel two-dimensional monolayer KTlO that possesses an indirect band gap of 2.25 eV (based on HSE06) and high carrier mobility (1.86×10 3 cm 2 V -1 s -1 for electron and 2.54 ×10 3 cm 2 V -1 s -1 for hole) by means of ab initio calculations. KTlO monolayer has a calculated cleavage energy of 0.56 J m -2 , which suggests exfoliation of bulk material as viable means for the preparation of mono-and few-layer materials. Remarkably, the KTlO monolayer suggests tunable magnetism and half-metallicity with hole doping, which are attributed to the novel Mexican-hat-like bands and van Hove singularities in its electron structure. Furthermore, monolayer KTlO exhibits moderate optical 2 absorption over visible light and ultraviolet region. The band gap value and band characteristics of monolayer KTlO can be strongly manipulated by biaxial and uniaxial strains to meet the requirements of various applications. All these novel properties render monolayer KTlO a promising functional material for future nanoelectronics and spintronic applications.

Ti vacancies in 18-electron half-Heusler compound Ti0.75NiSb cause lower lattice thermal conductivity.