Penta-MP5 (M = B, Al, Ga, In) monolayers as high-performance photocatalysts for overall water splitting.

Two-dimensional (2D) phosphorus-rich phosphides generally preserve the excellent electronic properties of phosphorene, making them promising photocatalysts for water splitting. Despite tremendous efforts in the search for potential photocatalysts in 2D phosphides, few known 2D phosphides fully meet the requirements for photocatalytic water splitting. Herein, we systemically investigate a set of penta-MP5 (M = B, Al, Ga, and In) monolayers by first-principles calculations and identify them as potential photocatalysts for water splitting. These penta-MP5 monolayers are found to feature favorable bandgaps of about 2.70 eV with appropriate band edge positions, a high carrier mobility of 1 × 104 cm-2 V-1 s-1, an excellent optical absorption coefficient (OAC) of 1 × 105 cm-1, and a good solar-to-hydrogen (STH) efficiency of 8%. Meanwhile, free energy calculations indicate that these penta-MP5 monolayers present both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) photocatalytic activities under light conditions. All these excellent properties demonstrate that penta-MP5 monolayers are suitable candidates as photocatalysts for promising applications in overall water splitting.

A semiconductor Sc2S3 monolayer with ultrahigh carrier mobility for UV blocking filter application.

For humans, ultraviolet (UV) light from sun is harmful to our eyes and eye-related cells. This detrimental fact requires scientists to search for a material that can efficiently absorb UV light while allowing lossless transmission of visible light. Using an unbiased first-principles swarm intelligence structure search, we explored two-dimensional (2D) Sc-S crystals and identified a novel Sc2S3 monolayer with good thermal and dynamical stability. The optoelectronic property simulations revealed that the Sc2S3 monolayer has a wide indirect bandgap (3.05 eV) and possesses an ultrahigh carrier mobility (2.8 × 103 cm2 V-1 s-1). Remarkably, it has almost transparent visible light absorption, while it exhibits an ultrahigh absorption coefficient up to × 105 cm-1 in the ultraviolet region. Via the application of biaxial strain and thickness modulation, the UV light absorption coefficients of Sc2S3 can be further improved. These findings manifest an attractive UV blocking optoelectronic characteristic of the Sc2S3 configuration as a prototypical nanomaterial for the potential application in UV blocking filters.

Exploring a novel two-dimensional metallic Y4C3 sheet applied as an anode material for sodium-ion batteries.

As novel "post lithium-ion batteries" and promising alternatives to lithium-ion batteries (LIBs) suffering from the limited Li resources, sodium-ion batteries (SIBs) are nowadays emerging and show bright prospects in large-scale energy storage applications due to abundant Na resources. However, a lack of suitable anode materials has become a key obstacle for the development of SIBs. Here we explore the potential of the two-dimensional (2D) Y-C space and identify a novel anode material for SIBs, a new Y4C3 sheet with P3̄m1 crystal symmetry, by means of first-principles swarm structure calculations. This Y4C3P3̄m1 structure has rather good kinetic and thermodynamic stability, possesses intrinsic metallicity, and remains metallic after adsorbing Na atoms, ensuring good electrical conductivity during the SIB cycle. Remarkably, a Y4C3 sheet as an anode for SIBs possesses the essential properties of a high specific capacity (∼752 mA h g-1), a low barrier energy (∼0.1 eV), and suitable open-circuit voltage (0-0.15 V). These characteristics are comparable and even superior to those of another known 2D Y2C anode material, indicating that the Y4C3 sheet can act as an appealing new candidate as an anode material for SIBs and offering new insights into the 2D Y-C space.

A new phosphorene allotrope: the assembly of phosphorene nanoribbons and chains.

Phosphorene allotrope monolayers such as blue and red phosphorus are being designed and synthesized to be used in the optoelectronics field due to their tunable bandgap and high mobility. Using the organic molecule self-assembly method similar to the synthesis of graphene allotropes, a novel phosphorene allotrope, P567 monolayer, with five-, six-, and seven-membered rings is designed through the assembly of black phosphorus chains and blue phosphorene nanoribbons. Ab initio molecular dynamics, phonon dispersion, and elastic constants demonstrate the dynamic, thermal, and mechanical stability of the P567 monolayer. Additionally, the first-principles calculations show that the P567 monolayer is an indirect bandgap semiconductor with moderate bandgap and high anisotropic mobility (4.47 × 103 cm2 V-1 s-1). Compared with black phosphorene, the suitable band edge position and higher optical absorption coefficient (105 cm-1) make the P567 monolayer more likely to be used as a photocatalytic hydrolysis material. The P567 monolayer is a viable candidate for use in innovative optoelectronic devices and the assembly method provides a rational approach to designing phosphorus allotropes with high photocatalytic efficiency.

Promising thermoelectric candidate based on a CaAs3 monolayer: A first principles study.

The CaAs3 monolayer is a newly predicted two-dimensional material with attractive properties, such as a moderate direct bandgap, high carrier mobility, prominent visible-light absorption, etc. To evaluate its potential applications in thermoelectric (TE) fields, herein, the thermoelectric properties of CaAs3 monolayers were comprehensively investigated by a first-principles method in combination with Boltzmann transport theory. Our calculated results indicate that the CaAs3 monolayer has an exceptionally low lattice thermal conductivity of 0.44 W m-1 K-1 at 300 K, mainly because of the small group velocity and strong phonon-phonon scattering. The CaAs3 monolayer also exhibits a high power factor due to the large Seebeck coefficient and electrical conductivity. Therefore, large ZT values of 1.72/1.58 were achieved for the n-type/p-type CaAs3 monolayer at 800 K. Compared with conventional 2D TE materials, the CaAs3 monolayer does not contain expensive heavy elements, which is beneficial for its practical applications as a TE material. Our results qualify the CaAs3 monolayer as a promising candidate for building excellent 2D TE devices.

A novel two-dimensional beryllium diphosphide (BeP2) with superconductivity: the first-principles exploration.

In this study, three stable two-dimensional beryllium diphosphide (2D-BeP2) structures with the wrinkle and planar monolayers, namely MoS2-like 6[combining macron]m-BeP2 phase (1H-BeP2), pentagonal 4[combining macron]2m-BeP2 (Penta-BeP2) and planar mm2-BeP2 (Planar-BeP2), have been successfully predicted through the first-principles calculation combined with a global structure search method. The structural stabilities, mechanical properties, electron properties and superconductivities are also systematically investigated. Results indicated that the 2D MoS2-like 1H-BeP2 showed higher stability than the Penta- and Planar-BeP2 structures. The 1H-BeP2 structure possessed an intrinsic metallic characteristics with the bands crossing the Fermi level. Notably, the Penta-BeP2 is a typical semiconductor, and the planar-BeP2 is semi-metal with Dirac corn. Based on the calculation results of the electron properties, phonon properties and electron-phonon coupling (EPC), the layer 1H-BeP2 sheet is a phonon-mediated superconductor with a critical temperature (Tc) of about 1.32 K.

The thermoelectric properties of α-XP (X = Sb and Bi) monolayers from first-principles calculations.

Thermoelectric (TE) materials as one of the effective solutions to the energy crisis are gaining more and more interest owing to their capability to generate electricity from waste heat without generating air pollution. In this work, the TE properties of α-XP monolayers such as the stability, electronic structure, electrical and phonon transport were thoroughly studied in combination with the first-principles calculations and Boltzmann transport equations. We found that α-SbP and α-BiP have indirect bandgaps of 0.85 eV and 0.73 eV, respectively, which are suitable for thermoelectric materials. Furthermore, due to the multiple valleys at the energy band edges and the high carrier mobility, α-XP possesses both large Seebeck coefficients and high electrical conductivities. It is also found that the lattice thermal conductivity of α-BiP is smaller than that of α-SbP due to lower phonon frequencies, smaller phonon group velocities, larger Grüneisen parameters and higher phonon relaxation times. High TE performance was achieved with the ZT values reaching 4.59 (for α-BiP at 500 K) and 1.34 (for α-SbP at 700 K). Our results quantify α-XP monolayers as promising candidates for building outstanding thermoelectric devices.

2D auxetic material with intrinsic ferromagnetism: a copper halide (CuCl2) monolayer.

The discovery of ferromagnetism in monolayer transition metal halides exemplified by CrI3 has opened a new avenue in the field of two-dimensional (2D) magnetic materials, and more such 2D materials are waiting to be explored. Herein, using an unbiased structure search combined with first-principles calculations, we have identified a novel CuCl2 monolayer, which exhibits not only intrinsic ferromagnetism but also auxetic mechanical properties originating from the interplay of lattice and Cu-Cl tetrahedron symmetries. The predicted Curie temperature of CuCl2 reaches ∼47 K, and its ferromagnetism is associated with the strong hybridization between the Cu 3d and Cl 3p states in the configuration. Moreover, upon biaxial tensile strain or carrier doping, the CuCl2 monolayer can be converted from ferromagnetic to non-magnetic and from half-metal to metal. These properties endow this CuCl2 monolayer with great potential for applications in auxetic/spintronic nanodevices.

Exploring the structures and properties of nickel silicides at the pressures of the Earth's core.

Given the highly possible existence of nickel and silicon in the Earth's core, the study of the reaction between Ni and Si and the resulting structures at the pressure corresponding to that of the Earth's core is highly required. Therefore, we have investigated the crystal structures of Ni-Si compounds at pressures of 0-350 GPa by adopting a crystal structure search algorithm in conjunction with first-principles calculations. We uncover two high Ni-content Ni5Si and Ni6Si compounds with 12-coordination Si bonded with Ni, with both showing strong chemical stability in the Earth's core. Bonding analysis reveals that the Ni atoms in these Ni-Si compounds present oxidant features and act as electron acceptors. This distinctive anomaly is the natural result of the energy shifts of the Ni 3d and Si 3p bands, resulting in charge transfer from Si to Ni. By examining the key properties (e.g., density and sound velocities) of the Ni5Si and Ni6Si compounds, the obtained density lies within the range of the Earth's inner core, and the estimated sound velocities are found to be consistent with seismic data. These results indicate that these two compounds could be considered as possible core constituents. Our findings provide valuable insights into the enigmatic Earth's core as well as geophysical and geochemical processes.

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 ΚL. The subsequent analyses show that the ultralow ΚL 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 Æ© 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.

A novel SiO monolayer with a negative Poisson's ratio and Dirac semimetal properties.

Although a number of interesting physical properties such as a negative Poisson's ratio (NPR) and Dirac semimetal (DS) properties have been recently predicted in two-dimensional (2D) materials, the realization of a 2D material that exhibits both of these DS and NPR features has rarely been reported. Here by adopting particle swarm optimization (PSO) algorithms combined with first-principles methods, we successfully construct a novel SiO monolayer (Pmna), the dynamic and thermal stability of which was characterized using phonon spectrum calculations and molecular dynamics simulations. In particular, Young's modulus and Poisson's ratio calculations showed that the Pmna monolayer exhibits high mechanical anisotropy with an in-plane NPR originating from its puckered atomic arrangement. More notably, the band structure of the Pmna monolayer possesses zero bandgap with four Dirac cones in its first Brillouin zone, exhibiting a DS feature. From the calculations of orbital-resolved band structures, the Dirac cone was revealed to originate from the orbital hybridization of Si and O atoms. The Pmna monolayer is the first 2D structure in the Si-O system that has both an NPR and Dirac semi-metal properties, providing a new model for exploring 2D multifunctional materials.

A Unified Capacitive-Coupled Memristive Model for the Nonpinched Current-Voltage Hysteresis Loop.

The concept of the memristor, a resistor with memory, was proposed by Chua in 1971 as the fourth basic element of electric circuitry. Despite a significant amount of effort devoted to the understanding of memristor theory, our understanding of the nonpinched current-voltage (I-V) hysteresis loop in memristors remains incomplete. Here we propose a physical model of a memristor, with a capacitor connected in parallel, which explains how the nonpinched I-V hysteresis behavior originates from the capacitive-coupled memristive effect. Our model replicates eight types of characteristic nonlinear I-V behavior, which explains all observed nonpinched I-V curves seen in experiments. Furthermore, a reversible transition from a nonpinched I-V hysteresis loop to an ideal pinched I-V hysteresis loop is found, which explains the experimental data obtained in C15H11O6-based devices when subjected to an external stimulus (e.g., voltage, moisture, or temperature). Our results provide the vital physics models and materials insights for elucidating the origins of nonpinched I-V hysteresis loops ascribed to capacitive-coupled memristive behavior.

Spherical coupling probe for measuring inner dimensions of microstructures.

Probes with spherical couplings are widely used to measure microstructures with a high aspect ratio. The measurement accuracy of spherical coupling fibre probes is limited by the low stability and signal-to-noise ratio of the output spot. This paper presents a specially designed probe with a polished spherical coupler and micro-axicon lensed output fibre. The effectiveness of the probe was verified experimentally. Compared to a common spherical coupling fibre probe, the proposed probe improves the signal-to-noise ratio of the output spot by 42.95%, the stability of the spot by 36%, and the resolution from 30 nm to 10 nm (by 66%).

Ceramide production mediates cinobufotalin-induced growth inhibition and apoptosis in cultured hepatocellular carcinoma cells.

Hepatocellular carcinoma (HCC) is a highly aggressive and lethal neoplasm with poor prognosis. The aim of this study is to investigate the anticancer activity of cinobufotalin, a bufadienolide isolated from toad venom, in cultured HCC cells, and to study the underlying mechanisms. We found that cinobufotalin (at nmol/L) significantly inhibited HCC cell growth and survival while inducing considerable cell apoptosis. Further, cinobufotalin inhibited sphingosine kinase 1 (SphK1) activity and induced pro-apoptotic ceramide production. Ceramide synthase-1 small hairpin RNA (shRNA)-depletion inhibited cinobufotalin-induced ceramide production and HCC cell apoptosis. On the other hand, the glucosylceramide synthase (GCS) inhibitor 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) facilitated cinobufotalin-induced ceramide production and cell apoptosis. SphK1 inhibitor II (SKI-II), similar to cinobufotalin, increased cellular ceramide level and promoted HCC cell apoptosis. Finally, we observed that cinobufotalin inactivated Akt-S6K1 signaling in HepG2 cells, which was again inhibited by ceramide synthase-1 shRNA-depletion. In conclusion, the results of this study suggest that cinobufotalin induces growth inhibition and apoptosis in cultured HCC cells through ceramide production. Cinobufotalin may be investigated as a novel anti-HCC agent.

Extension of light transmission distance of single-mode fiber using a microaxicon-lensed fiber end.

The light signal through single-mode fiber is unstable, rapidly decays as it propagates, and has limited effective transmission distance. In this study, to extend its transmission distance, a microaxicon was designed at the single-mode fiber end and the emitted light analyzed via simulations and experiments. Results indicate that an 80 µm maximum transmission distance is achievable with the microaxicon at a 45° base angle. Further, the divergence angle of the light is reduced from 4.1° to 0.47°, its stability is improved by 97%, and the light spot is sharp at 70-80 µm away from the fiber end.

Anharmonic coupling between fundamental modes in tetramethylurea.

In situ high pressure Raman spectra of tetramethylurea have been measured up to 25 GPa, liquid-solid and solid-solid phase transitions were detected at 0.2 GPa and 7.4 GPa, respectively. An unprecedented spectral phenomenon is the observation of a Fermi resonance between the fundamental modes. An exponential relationship between the intensity and the frequency difference was concluded. Pressure provides us a new way to study the correlation between Fermi resonance parameters.

From Porphyrin-Like Rings to High-Density Single-Atom Catalytic Sites: Unveiling the Superiority of p-C2N for Bifunctional Oxygen Electrocatalysis.

With effective utilization of the catalytic site, single-atom catalysts (SACs) supported by nitrogen atoms surrounding built-in pores of two-dimensional (2D) materials, such as porphyrin/phthalocyanine-based covalent organic frameworks, have been highly promising electrocatalysts in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) processes for the air electrode of the metal-air battery. However, the number of stable single-atom anchoring sites, i.e., accessible single-atom metal sites, has been concerning as a result of the appearance of heterogeneous or large and even supersized pores in substrate materials. 2D porous graphitic carbon nitride (PGCN) with a stronger stability and smaller component is regarded as a more potential alternative owing to similar controllability and designability. In this work, inspired by the robust coordinated TM-N4 environment of porphyrin/phthalocyanine molecules, novel p-C2N with a high density of porphyrin-like organic units is rationally designed. In well-designed p-C2N, a higher homogeneity and uniformity of coordination sites can enhance the electrocatalytic activity in the whole catalytic material and better prevent SACs from sintering and agglomerating into thermodynamically stable nanoclusters. Utilizing density functional theory (DFT), the stability of the p-C2N monolayer, TM@p-C2N, and OER/ORR catalytic activities of TM@p-C2N (TM including Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) are systematically evaluated. Among them, Ir@p-C2N (0.31 V of the OER and 0.36 V of the ORR), Co@p-C2N (0.47 and 0.22 V), and Rh@p-C2N (0.55 and 0.27 V) are screened as promising SACs for the bifunctional ORR and OER. The proposal of p-C2N guides a new direction for the development of TM-N-C-based SAC bifunctional electrocatalysts.

Memristor-Based Artificial Chips.

Memristors, promising nanoelectronic devices with in-memory resistive switching behavior that is assembled with a physically integrated core processing unit (CPU) and memory unit and even possesses highly possible multistate electrical behavior, could avoid the von Neumann bottleneck of traditional computing devices and show a highly efficient ability of parallel computation and high information storage. These advantages position them as potential candidates for future data-centric computing requirements and add remarkable vigor to the research of next-generation artificial intelligence (AI) systems, particularly those that involve brain-like intelligence applications. This work provides an overview of the evolution of memristor-based devices, from their initial use in creating artificial synapses and neural networks to their application in developing advanced AI systems and brain-like chips. It offers a broad perspective of the key device primitives enabling their special applications from the view of materials, nanostructure, and mechanism models. We highlight these demonstrations of memristor-based nanoelectronic devices that have potential for use in the field of brain-like AI, point out the existing challenges of memristor-based nanodevices toward brain-like chips, and propose the guiding principle and promising outlook for future device promotion and system optimization in the biomedical AI field.

Condensable and filterable particulate matter emitted from typical diesel vehicles in steady and transient driving conditions.

Condensable particulate matter (CPM) and filterable particulate matter (FPM) emitted from industrial sources have been well studied, but their emissions from vehicles have not yet been covered. This study explores the emission characteristics of CPM and FPM from typical diesel vehicles under various driving conditions. The emission factors (EFs) of CPMs under driving conditions were 5.4-10.4 times higher than those of FPMs, while CPMs EFs under transient driving conditions were about 2.5 times higher than those under steady driving conditions. CPM and FPM are mainly composed of organic matter accounting for 53.3 %-92.9 %, while the intermediate and semi-volatile organic compounds dominate the organic matter accounting for 86.3 %-98.6 %. Similar to industrial sources, alkanes are the predominant organic species emitted by diesel vehicles, comprising 42.0 %-64.0 % of the detected organic components. Inorganic CPM is primarily composed of NH4+ , representing 84.9 %-87.6 % of the total, in contrast to industrial sources where SO42- and Cl- dominate. Interestingly, the air pollution control devices installed on diesel vehicles under steady driving conditions perform better in removing organic CPM and producing higher inorganic CPM emissions than those under transient driving conditions. These findings will enhance the comprehensive understanding of particulate matter emitted from diesel vehicles and provide a scientific foundation for the development of related control technologies.

Co-delivery of drugs by adhesive transdermal patches equipped with dissolving microneedles for the treatment of rheumatoid arthritis.

In this study, a dosage form consisting of dissolving (D) microneedles (M) and an adhesive (A) transdermal patch (P; DMAP) was designed and pre-clinically evaluated for the treatment of rheumatoid arthritis (RA). The tip of the dissolving microneedles (DMNs) was loaded with the macromolecular drug melittin (Mel@DMNs), this to treat joint inflammation and bone damage, while the adhesive transdermal patches contained the low molecular weight drug diclofenac sodium (DS; DS@AP) for pain relief. Mel@DMNs and DS@AP were ingeniously connected through an isolation layer for compounding Mel-DS@DMAP for the simultaneous delivery of the drugs. In vitro and in vivo experiments showed that DS@AP did not affect the mechanical properties and dissolution process of Mel@DMNs while the pores formed by the microneedles promoted the skin penetration of DS. Treatment of rats suffering from RA with Mel-DS@DMAP reduced paw swelling and damage of the synovium, joint and cartilage, suggesting that the 'patch-microneedle' dosage form might be promising for the treatment and management of RA.