Ferroelectricity and Nonlinear Optical Responses in Two-Dimensional Distorted ( = Cu, Ag, Au; = Chalcogens; = Halogen) Monolayers.

Two-dimensional (2D) materials with spontaneous polarization can exhibit large second-order nonlinear optical (NLO) effects. Here, we present a series of stable distorted monolayers by using first-principles calculations and lattice vibration analysis. The structural distortion leads to a lower polar symmetry, giving rise to intrinsic ferroelectricity with a Curie point up to room temperature.

Contact evaluation of the penta-PdPSe/graphene vdW heterojunction: tuning the Schottky barrier and optical properties.

In this work, we design a van der Waals heterojunction composed of semiconducting penta-PdPSe and semi-metallic graphene (G) monolayers based on state-of-the-art theoretical calculations. Our results show that both monolayers well preserve their intrinsic features and possess an n-type near Ohmic Schottky contact with a low Schottky barrier height of 0.085 eV for the electrons at the vertical interface.

Three-dimensional porous borocarbonitride composed of pentagonal motifs as a high-performance pyroelectric material.

Pyroelectric materials have been attracting significant attention due to their intrinsic and permanent polarization, where the induced polarization is not associated with specific conditions, such as ferroelectric phase transition, strain gradient, dopants, and electric field. Thus, these materials have great potential for wide applications in energy conversion. Here, we propose a new 3D porous borocarbonitride termed PH-BCN, which is composed of pentagonal motifs with intrinsic polarization along the [0001] direction.

Immobilized triatomic CuB clusters on 2D carbon nitride: highly selective conversion of CO to ethanol at low potentials.

A promising pathway for carbon usage and energy storage is electrocatalytic reduction of CO to form high-value multi-carbon products. Herein, the d-p coupled triatomic catalyst CuB@g-CN with significant activity and selectivity for ethanol is presented for the first time. Density functional theory calculations elucidate that these spatially confined triatomic centers are capable of immobilizing multiple CO molecules, providing an exclusive reaction channel for direct C-C coupling.

Efficiency and optimization of government service resource allocation in a cloud computing environment.

According to the connotation and structure of government service resources, data of government service resources in L city from 2019 to 2021 are used to calculate the efficiency of government service resource allocation in each county and region in different periods, particularly by adding the government cloud platform and cloud computing resources to the government service resource data and applying the data envelopment analysis (DEA) method, which has practical significance for the development and innovation of government services. On this basis, patterns and evolutionary trends of government service resource allocation efficiency in each region during the study period are analyzed and discussed. Results are as follows.

First-Principles Study of the Structural, Electronic, and Enhanced Optical Properties of SnS/TaS Heterojunction.

Although the electronics and optoelectronics based on two-dimensional (2D) SnS have attracted great interest, their development is hindered by the large contact resistance at the interface of the metal-semiconductor junction. In this work, using first-principles calculations, we evaluate the contact performance in a van der Waals heterostructure composed of 2D SnS and TaS. We demonstrate that holes can freely transfer from the electrode to the channel as a consequence of the Schottky-barrier-free interface as well as an upward band bending.

Downregulation of lncRNA-PVT1 participates in the development of progressive chronic kidney disease among patients with congestive heart failure.

Background: Congestive heart failure (CHF) is a major cause of the development of progressive chronic kidney disease (CKD), while the mechanism is still unknown. LncRNA PVT1 contributes to kidney injury. This study aimed to explore the role of PVT1 in the development of CKD in CHF patients.

Imidazole-graphyne: a new 2D carbon nitride with a direct bandgap and strong IR refraction.

Six-membered rings are common building blocks of many carbon structures. Recent studies have shown that penta-graphene composed of five-membered carbon rings have properties very different from that of graphene. This has motivated the search for new carbon structures.

Penta-BCN: A New Ternary Pentagonal Monolayer with Intrinsic Piezoelectricity.

Going beyond conventional hexagonal sheets, pentagonal 2D structures are of current interest due to their novel properties and broad applications. Herein, for the first time, we study a ternary pentagonal BCN monolayer, penta-BCN, which exhibits intrinsic piezoelectric properties. Based on state-of-the-art theoretical calculations, we find that penta-BCN is stable mechanically, thermally, and dynamically and has a direct band gap of 2.

Symmetry-breaking induced large piezoelectricity in Janus tellurene materials.

Structural symmetry-breaking can lead to novel electronic and piezoelectric properties in two-dimensional (2D) materials. In this paper, we propose a 2D Janus tellurene (Te2Se) monolayer with asymmetric Se/Te surfaces and its derived multilayer structures. The band structure calculations show that the 2D Janus Te2Se monolayer is an indirect gap semiconductor, and the intrinsic mirror asymmetry combined with the spin-orbit coupling induces the Rashba spin splitting and the out-of-plane spin polarization.

Piezoelectric Effects in Surface-Engineered Two-Dimensional Group III Nitrides.

Piezoelectric effects of two-dimensional (2D) group III-V compounds have received considered attention in recent years because of their wide applications in semiconductor devices. However, they face a problem that only metastable or unstable structures are noncentrosymmetric with piezoelectricity, thus leading to the difficulty in experimental observation. Motivated by the recent advances in the synthesis of 2D group III nitrides, in this paper, for the first time, we study the piezoelectric properties of the 2D group III nitrides (XN, X = Al, Ga, and In) with buckled hexagonal configurations by surface passivation, which are thermodynamically stable.

Physical Properties and Photovoltaic Application of Semiconducting Pd₂Se₃ Monolayer.

Palladium selenides have attracted considerable attention because of their intriguing properties and wide applications. Motivated by the successful synthesis of Pd₂Se₃ monolayer (Lin et al., Phys.

2D SnSe-based vdW heterojunctions: tuning the Schottky barrier by reducing Fermi level pinning.

Two-dimensional (2D) SnSe is a very promising material for semiconducting devices due to its novel properties. However, the contact behavior between a 2D SnSe sheet and a three-dimensional (3D) metal surface shows an un-tunable Schottky barrier because of the metallization of the SnSe sheet induced by strong Fermi level pinning at the contact interface. In this work, we use graphene rather than 3D metals as the metal electrode which comes into contact with a single-layer SnSe sheet to form a van der Waals (vdW) heterojunction.

A C fullerene-based sheet with ultrahigh thermal conductivity.

A new two-dimensional (2D) carbon allotrope, Hexa-C20, composed of C20 fullerene is proposed. State-of-the-art first principles calculations combined with solving the linearized phonon Boltzmann transport equation confirm that the new carbon structure is not only dynamically and thermally stable, but also can withstand temperatures as high as 1500 K. Hexa-C20 possesses a quasi-direct band gap of 3.

TiS sheet based van der Waals heterostructures with a tunable Schottky barrier.

Monolayer titanium trisulfide (TiS), synthesized recently through exfoliation [Adv. Mater., 2015, 27, 2595], has emerged as a new 2D material with outstanding electronic and optical properties.

Phosphorus K Crystal: A New Stable Allotrope.

The intriguing properties of phosphorene motivate scientists to further explore the structures and properties of phosphorus materials. Here, we report a new allotrope named K phosphorus composed of three-coordinated phosphorus atoms in non-layered structure which is not only dynamically and mechanically stable, but also possesses thermal stability comparable to that of the orthorhombic black phosphorus (A17). Due to its unique configuration, K phosphorus exhibits exceptional properties: it possesses a band gap of 1.

Tuning the electronic and mechanical properties of penta-graphene via hydrogenation and fluorination.

Penta-graphene has recently been proposed as a new allotrope of carbon composed of pure pentagons, and displays many novel properties going beyond graphene [Zhang et al., Proc. Natl.

Thermal exfoliation of stoichiometric single-layer silica from the stishovite phase: insight from first-principles calculations.

Mechanical cleavage, chemical intercalation and chemical vapor deposition are the main methods that are currently used to synthesize nanosheets or monolayers. Here, we propose a new strategy, thermal exfoliation for the fabrication of silica monolayers. Using a variety of state-of-the-art theoretical calculations we show that a stoichiometric single-layer silica with a tetragonal lattice, T-silica, can be thermally exfoliated from the stishovite phase in a clean environment at room temperature.

TiC2: a new two-dimensional sheet beyond MXenes.

MXenes are attracting attention due to their rich chemistry and intriguing properties. Here a new type of metal-carbon-based sheet composed of transition metal centers and C2 dimers rather than individual C atom is designed. Taking the Ti system as a test case, density functional theory calculations combined with a thermodynamic analysis uncover the thermal and dynamic stability of the sheet, as well as a metallic band structure, anisotropic Young's modulus and Poisson's ratio, a high heat capacity, and a large Debye stiffness.

A New Silicon Phase with Direct Band Gap and Novel Optoelectronic Properties.

Due to the compatibility with the well-developed Si-based semiconductor industry, there is considerable interest in developing silicon structures with direct energy band gaps for effective sunlight harvesting. In this paper, using silicon triangles as the building block, we propose a new silicon allotrope with a direct band gap of 0.61 eV, which is dynamically, thermally and mechanically stable.

Electronic and optical properties of silicon based porous sheets.

Si based sheets have attracted tremendous attention due to their compatibility with the well-developed Si-based semiconductor industry. On the basis of state-of-the-art theoretical calculations, we systematically study the stability, electronic and optical properties of Si based porous sheets including g-Si4N3, g-Si3N4, g-Si3N3 and g-Si3P3. We find that the g-Si3N3 and g-Si3P3 sheets are thermally stable, while the g-Si4N3 and g-Si3N4 are unstable.