Strong Sliding Ferroelectricity and Interlayer Sliding Controllable Spintronic Effect in Two-Dimensional HgI2 Layers.

Exploration of two-dimensional (2D) sliding ferroelectric (FE) materials with experimentally detectable ferroelectricity and value-added novel functionalities is highly sought for the development of 2D "slidetronics". Herein, based on first-principles calculations, we identify the synthesizable van der Waals (vdW) layered crystals HgX2 (X = Br and I) as a new class of 2D sliding ferroelectrics. Both HgBr2 and HgI2 in 2D multilayered forms adopt the preferential stacking sequence, leading to room temperature stable out-of-plane (vertical) ferroelectricity that can be reversed via the sliding of adjacent monolayers. Owing to strong interlayer coupling and interfacial charge rearrangement, 2D HgI2 layers possess strong sliding ferroelectricity up to 0.16 µC/cm2, readily detectable in experiment. Moreover, robust sliding ferroelectricity and interlayer sliding controllable Rashba spin texture of FE-HgI2 layers enable potential applications as 2D spintronic devices such that the electric control of electron spin detection can be realized at the 2D regime.

Two-Dimensional Ferroelasticity and Domain-Wall Flexoelectricity in HgX2 (X = Br or I) Monolayers.

Electromechanical phenomena in two-dimensional (2D) materials can be related to sizable electric polarizations and switchable spontaneous ferroelasticity, allowing them to be used as miniaturized electronic and memory devices. Even in a parent centrosymmetric (nonpolar) ferroelastic (FE) material, non-zero polarization can be produced around the FE domain wall, owing to the strain-gradient-induced flexoelectricity. Compared with the negligibly weak flexoelectric effect in bulk compounds, significant electric polarizations can be expected in 2D FE materials that sustain a large elastic strain and a strain gradient. Using first-principles calculations, we predict that spontaneous 2D ferroelasticity and domain-wall flexoelectricity can be simultaneously realized in synthetic HgX2 (X = Br or I) monolayers. The FE phase renders three oriented variants, which form FE domain walls with a large strain gradient and the associated domain-wall flexoelectric polarizations. Our thermodynamic stability analysis and kinetic barrier simulations allow us to manipulate the domain-wall flexoelectricity via applied mechanical stress, thereby enabling future electromechanical applications in nanoelectronics.

Two-dimensional semiconducting Cu(I)/Sb(III) bimetallic hybrid iodides with a double perovskite structure and photocurrent response.

Stable lead-free hybrid halide double perovskites have sparked widespread interest as a new kind of photoelectric material. Herein, for the first time, we successfully incorporated copper(I) and antimony(III) into two two-dimensional (2D) hybrid bimetallic double perovskite iodides, namely (NH3C6H11)4CuSbI8·H2O (CuSbI-1) and (NH3C6H10NH3)2CuSbI8·0.5H2O (CuSbI-2), using cyclohexylamine and 1,4-cyclohexanediamine as organic components. The band gaps for CuSbI-1 and CuSbI-2 were determined to be 2.22(2) eV and 2.21(2) eV, respectively. Furthermore, these two layered perovskites were readily dissolved in an organic solvent (1 mL DMF can dissolve 1 g sample for each compound) and could form smooth, pinhole-free, and uniform thin films through a facile spin-coating method. Photocurrent experiments with xenon lamp irradiation revealed the obvious photoelectric responses for both 2D double perovskites. The ratio of the photocurrent to the dark current (Ilight/Idark) for CuSbI-1 and CuSbI-2 is about 23 and 10, respectively, further suggesting their potential to be applied as light harvesters or light detectors. More importantly, these 2D double perovskite iodides show high moisture and thermal stabilities, indicating their potential for optoelectronic applications.

Flow force research and structure improvement of cartridge valve core based on CFD method.

The hydraulic force has a great negative effect on the cartridge poppet valve system. Based on the law of momentum, the calculation formula of flow force of outflow poppet valve is modified, and a new valve core structure is designed. The compensation effect of the improved main valve core structure on the hydraulic force is discussed; secondly, CFD simulation is carried out to obtain the influence rules of these parameters on hydrodynamic forces. According to the analysis, the influence of main valve core arc structure on hydrodynamic force compensation under different opening degrees is also studied; then the optimal parameters of the arc structure are obtained through analysis. AMEsim system simulation model and test-bed are built to verify the hydrodynamic formula and simulation results. The experimental results verify that the new valve core structure has a good hydrodynamic compensation effect.

InBi: A Ferroelastic Monolayer with Strain Tunable Spin-Orbit Dirac Points and Carrier Self-Doping Effect.

Semimetallic two-dimensional (2D) Dirac materials beyond graphene, especially 2D materials with robust Dirac points against the spin-orbit coupling (SOC), are still highly sought. Herein, we theoretically demonstrate the InBi monolayer as a long-sought 2D Dirac material whose exotic Dirac Fermionic states cannot be gapped out by SOC. The InBi monolayer with the litharge crystal structure possesses not only 4-fold band degeneracy, linear energy dispersion, and ultrahigh Fermi velocity in the order of 105 m/s, but also spontaneous ferroelasticity that can lead to the orthorhombic lattice deformation and semimetallic electronic structure. Specifically, the symmetry protected spin-orbit Dirac points in 2D InBi are located at the Brillouin Zone (BZ) boundary and near the Fermi level in energy. More importantly, with coexisting spin-orbit Dirac points and spontaneous ferroelasticity, the InBi monolayer exhibits an additional advantage for engineering Dirac Fermionic states by ferroelastic (FE) strain. Energy levels of Dirac points are strongly coupled to FE strain, and the semimetallic electronic structure of the InBi monolayer is also susceptible to the FE strain induced carrier self-doping effect. Depending on the strain orientation within the InBi monolayer, electron and hole Fermi pockets will develop along the two planar directions, leading to the characteristic transport coefficients (as evidenced by our transport simulations based on Boltzmann formalism) for future experimental detection. FE strain tunable Dirac Fermionic states together with the carrier self-doping effect will benefit future development of ultrathin electronic devices with both high carrier mobility and controllable charge conductivities.

Two-dimensional ferroelasticity and ferroelastic strain controllable anisotropic transport properties in CuTe monolayer.

Two-dimensional ferroelastic (2D-FE) materials where FE strain originates from the lattice deformation associated with spontaneous FE phase transition, hold great promise as miniaturized shape-memory devices. Moreover, the structural anisotropy within the low-symmetry 2D-FE materials can usually lead to intrinsic anisotropy in their electronic or transport properties as well. As a result, the strong coupling of FE strain with the anisotropic electronic structure or electric-/thermoelectric-transport will largely extend the functionality and device applications for 2D-FE materials. In the current work, after performing comprehensive first-principles calculations in combination with transport simulations based on the Boltzmann formalism, we identify the experimentally synthesizable CuTe monolayer as a new 2D-FE material whose anisotropic electric- and thermoelectric-transport properties can be effectively manipulated by FE strain. Typically, CuTe monolayers that can be potentially exfoliated from the synthesized van der Waals (vdW) layered CuTe bulk are predicted to exhibit the room temperature stable ferroelasticity and large axial FE strain (up to 18.4%) created by the in-plane orthorhombic lattice deformation. Owing to the planar orientation dependent metallic vs. nearly semiconducting electronic structure, highly anisotropic electric conductivity and thermopower coefficient can be obtained along the two planar principal axes of the CuTe monolayer. To simulate the more realistic experimental scenarios, coherent formation of FE domain walls and domain-wall motion assisted FE switching have also been evaluated in CuTe multi-domain configurations. Based on the transverse thermoelectric effect inherent in anisotropic CuTe monolayers, the schematic model for obtaining the FE strain controllable electric current within CuTe multi-domain configurations has been proposed, which can be verified experimentally.