Charge density fluctuation determined the interlayer friction in bilayer MN4 (M = Be, Mg, and Pt).

MN4 (M = Be, Mg, and Pt) represents a new class of van der Waals materials. These materials are characterized by exceptional electrical and thermal conductivities, remarkable intralayer mechanical strength, and weak interlayer interactions, making them prone to shearing and slipping. Therefore, MN4 has significant potential applications as a solid lubricant. However, until now, there have been only limited comprehensive theoretical investigations focusing on the frictional properties of MN4 systems. Here, the frictional performances of MN4 are systematically analyzed by applying first-principles high-throughput calculations. The results reveal that interlayer friction of MN4 decreases from MgN4 to BeN4 and then to PtN4. The friction is directly determined by charge density variations during the sliding processes. The periodic formation and breaking of quasi-σ bonds in bilayer MgN4 leads to substantial variations in charge density and large interlayer friction. In contrast, the weak charge density alternations in PtN4 lead to rather low frictions in PtN4. Moreover, surface functionalization effectively diminishes friction within bilayer MgN4, but amplifies interlayer friction within bilayer PtN4, and under surface functionalization interlayer friction can be efficiently modulated by out-of-plane polarizations. Interestingly, HBr-MgN4 exhibits two orders of magnitude lower COF compared to intrinsic bilayer MgN4, leading to a phenomenon resembling superlubricity. These results significantly contribute to our understanding of the friction properties, offering valuable guidance for the practical implementation of MN4 in solid lubricants.

Monolithic MOF-Based Metal-Insulator-Metal Resonator for Filtering and Sensing.

Metal-insulator-metal (MIM) configurations based on Fabry-Pérot resonators have advanced the development of color filtering through interactions between light and matter. However, dynamic color changes without breaking the structure of the MIM resonator upon environmental stimuli are still challenging. Here, we report monolithic metal-organic framework (MOF)-based MIM resonators with tunable bandwidth that can boost both dynamic optical filtering and active chemical sensing by laser-processing microwell arrays on the top metal layer. Programmable tuning of the reflection color of the MOF-based MIM resonator is achieved by controlling the MOF layer thicknesses, which is demonstrated by simulation of light-matter interactions on subwavelength scales. Laser-processed microwell arrays are used to boost sensing performance by extending the pathway for diffusion of external chemicals into nanopores of the MOFs. Both experiments and molecular dynamics simulations demonstrate that tailoring the period and height of the microwell array on the MIM resonator can advance the high detection sensitivity of chemicals.

The regulatory mechanism of rapid lignification for timely anther dehiscence.

Anther dehiscence is a crucial event in plant reproduction, tightly regulated and dependent on the lignification of the anther endothecium. In this study, we investigated the rapid lignification process that ensures timely anther dehiscence in Arabidopsis. Our findings reveal that endothecium lignification can be divided into two distinct phases. During Phase I, lignin precursors are synthesized without polymerization, while Phase II involves simultaneous synthesis of lignin precursors and polymerization. The transcription factors MYB26, NST1/2, and ARF17 specifically regulate the pathway responsible for the synthesis and polymerization of lignin monomers in Phase II. MYB26-NST1/2 is the key regulatory pathway responsible for endothecium lignification, while ARF17 facilitates this process by interacting with MYB26. Interestingly, our results demonstrate that the lignification of the endothecium, which occurs within approximately 26 h, is much faster than that of the vascular tissue. These findings provide valuable insights into the regulation mechanism of rapid lignification in the endothecium, which enables timely anther dehiscence and successful pollen release during plant reproduction.

Tunable electrical properties and multiple-phases of ferromagnetic GdS2, GdSe2 and Janus GdSSe monolayers.

With the continuous miniaturization and integration of spintronic devices, the two-dimensional (2D) ferromagnet coupling of ferromagnetic and diverse electrical properties has become increasingly important. Herein, we report three ferromagnetic monolayers: GdS2, GdSe2 and Janus GdSSe. They are bipolar magnetic semiconductors and demonstrate ferroelasticity with a large reversible strain of 73.2%. Three monolayers all hold large magnetic moments of about 8µB f.u.-1 and large spin-flip energy gaps in both the conduction and valence bands, which are highly desirable for applications in bipolar field effect spin filters and spin valves. Our calculations have testified to the feasibility of the experimental achievement of the three monolayers and their stability. Additionally, intrinsic valley polarization occurs in the three monolayers owing to the cooperative interplay between spin-orbit coupling and magnetic exchange interaction. Moreover, we identified square lattices for GdS2 and GdSe2 monolayers. The new and stable square lattices of GdS2 and GdSe2 monolayers show robust ferromagnetism with high Curie temperatures of 648 and 312 K, respectively, and the characteristics of spin-gapless semiconductors. Overall, these findings render GdS2, GdSe2 and Janus GdSSe monolayers promising candidate materials for multifunctional spintronic devices at the nanoscale.

Understanding Adsorption Behaviors of Organic Friction Modifiers on Hydroxylated SiO2 (001) Surfaces: Effects of Molecular Polarity and Temperature.

Molecular dynamics simulations are used to investigate the physisorption of organic friction modifiers (OFMs) lubricated by 1-decene trimer (PAO4) representing a base oil and confined between hydroxylated SiO2 (001) surfaces. The results indicate that OFM molecules form dense, tendentiously vertical monolayer films at low temperature but loose adsorption layers at high temperature, particularly for R-NH2 with weaker molecular polarity. The structural information is quantitatively clarified by mass density profiles, radial distribution function, and probability distributions of an end-to-end distance at a perpendicular-to-surface direction. The movement performance of lubricant, reflected by the thickness of the organic part and radius of gyration of PAO4 molecules, strongly depends on temperature. The adsorption amount of OFM molecules decreases dramatically with lowering OFM polarity and increasing temperature above the critical desorption temperatures of about 320, 373, and 453 K for amine (R-NH2), alcohol (R-OH), and acid (R-COOH), respectively. The interaction energies of the OFM-surface decrease continuously for the R-NH2 system with temperature and decrease rapidly as temperature exceeds a critical value for both R-OH and R-COOH systems. The single-molecule geometry optimization validates the significant role of the electrostatic and hydrogen-bond attractions in molecular adsorption. Therefore, the OFMs with stronger polarity (like R-COOH) present stronger adsorption and better temperature resistance. The findings in this work are of particular value and provide a guideline in designing and engineering novel OFM additives for extreme lubrication conditions.

Two-dimensional MN4 materials as effective multifunctional electrocatalysts for the hydrogen-evolution, oxygen-evolution, and oxygen-reduction reactions.

Two-dimensional (2D) materials confining single atoms (SAs) for catalysis, such as graphene confining metal single atoms (M-N-C), integrate both aspects of 2D materials and single-atom catalysts (SACs). Significant advantages have been established in this new category of catalysts, which have seen rapid development in recent years. Recent studies have suggested a new class of novel 2D materials with a chemical formula of MN4 naturally holding a uniformly distributed M-N4 moiety. We investigated MN4 monolayers as multifunctional catalysts for the hydrogen-evolution reaction (HER), oxygen-evolution reaction (OER), and oxygen-reduction reaction (ORR). Among them, the IrN4 monolayer demonstrated high catalytic activity towards these three reactions. The CoN4 monolayer was predicted to be an excellent bifunctional catalyst for the OER and ORR. A uniformly distributed and short-distanced M-N4 moiety on the MN4 monolayer made reactions between the intermediates during the OER and ORR possible, facilitating the release of O2 and H2O, respectively. In addition, the M atom of the MN4 monolayer having electronic states located at the Fermi level was active for catalyzing the HER. More importantly, changes in the Gibbs free energy of the two key intermediates of adsorption (ΔGOH* and ΔGOOH*) correlated closely with the Bader charge on the M atom (BM).

Corrosion-resistant cobalt phosphide electrocatalysts for salinity tolerance hydrogen evolution.

Seawater electrolysis is a viable method for producing hydrogen on a large scale and low-cost. However, the catalyst activity during the seawater splitting process will dramatically degrade as salt concentrations increasing. Herein, CoP is discovered that could reject chloride ions far from catalyst in electrolyte based on molecular dynamic simulation. Thus, a binder-free electrode is designed and constructed by in-situ growth of homogeneous CoP on rGO nanosheets wrapped around the surface of Ti fiber felt for seawater splitting. As expected, the as-obtained CoP/rGO@Ti electrode exhibits good catalytic activity and stability in alkaline electrolyte. Especially, benefitting from the highly effective repulsive Cl- intrinsic characteristic of CoP, the catalyst maintains good catalytic performance with saturated salt concentration, and the overpotential increasing is less than 28 mV at 10 mA cm-2 from 0 M to saturated NaCl in electrolyte. Furthermore, the catalyst for seawater splitting performs superior corrosion-resistance with a low solubility of 0.04%. This work sheds fresh light into the development of efficient HER catalysts for salinity tolerance hydrogen evolution.

Controlled Growing of Graphdiyne Film for Friction Reduction and Antiwear.

Like the multilayered graphene which is the most widely used solid lubricant, graphdiyne (GDY) as a 2D material holds potential similar prospects but has been rarely researched so far. One reason is that growing a GDY film in a controllable manner on diverse material surfaces remains a great challenge. To address the issue, a catalytic pregrowth and solution polymerization method is developed to synthesize a GDY film on various substrates. It allows fine control over film structure and thickness. A macroscopic ultralow friction coefficient of 0.08 is obtained, and a relatively long life of more than 5 h under a high load of 1378 MPa is achieved. Molecular dynamics simulations together with the surface analysis demonstrate that the increased deformation degree and weakened relative motion between GDY layers contribute to the low friction. Especially, different from graphene, the friction of GDY exhibits a double increase and decrease in one period of λ ≈ 8-9 Å, and it is roughly equal to the distance between two adjacent alkyne bonds in the x direction, indicating GDY's structure and lattice play an important role in reducing friction.

Weak Interaction-Tailored Catalytic Interface of Ultrasmall Gold Nanoclusters as Enzyme Mimics for Enhanced Colorimetric Biosensing.

Gold nanoclusters (AuNCs) represent an emerging type of engineered nanomaterials with intrinsic enzymatic activity for both chemical and biological applications, but the catalytic activity of most reported AuNCs remains rather limited. Herein, we report a new, efficient strategy of promoting the peroxidase-mimic activity of AuNCs by tailoring their catalytic interfaces via small molecule-mediated weak interactions. Inspired by the presence of imidazole structures in many biocatalytic centers, we screened a series of imidazole-containing small molecules to evaluate their impact on the enzymatic activity of AuNCs. Through monitoring the absorbance change of 3,3',5,5'-tetramethylbenzidine, 1-methyl-2-imidazolecarboxaldehyde (MCA) was identified to possess the most significant effect on enhancing the peroxidase-mimic activity of glutathione-stabilized AuNCs (GSH-AuNCs) among all the examined molecules. Interestingly, the enhancement effect of MCA on the catalytic activity of these AuNCs was found to be highly reversible and can be switched on/off by simply adding MCA/dialysis treatment. Molecular dynamics simulations and further experimental analysis confirmed that these MCA molecules were adsorbed on the surface of GSH-AuNCs through weak non-covalent interactions. The underlying mechanism analysis suggested that the presence of MCA can efficiently promote the production of •OH in the GSH-AuNC system. As a proof of example, we then demonstrated that the presence of MCA can greatly increase the bioanalytical performance of AuNC-based peroxidase mimics, as evidenced by a 65-fold lower LOD for glucose detection of AuNCs@MCA than that using AuNCs only. Finally, the present system has been successfully applied for sensing the blood glucose level of both healthy people and diabetics with promising results.

Robust Superlubricity and Moiré Lattice's Size Dependence on Friction between Graphdiyne Layers.

Structural superlubricity is a fascinating physical phenomenon that plays a significant role in many scientific and technological fields. Here, we report the robust superlubricating state achieved on the interface of relatively rotated graphdiyne (GDY) bilayers; such an interface with ultralow friction is formed at nearly arbitrary rotation angles and sustained at temperatures up to 300 K. We also identified the reverse correlation between the friction coefficient and size of the Moiré lattice formed on the surface of the incommensurate stacked GDY bilayers, particularly in a small size range. Our investigations show that the ultralow friction and the reduction of the friction coefficient with the increase in size of the Moiré lattice are closely related to the interfacial energetics and charge density as well as the atomic arrangement. Our findings enable the development of a new solid lubricant with novel superlubricating properties, which facilitate precise modulation of the friction at the interface between two incommensurate contacting crystalline surfaces.

Clinical Characteristics of Pneumocystis Pneumonia After Parental Renal Transplantation.

PURPOSE: To analyze the clinical characteristics of Pneumocystis pneumonia (PCP) in renal transplant recipients, identify early sensitivity indicators, and optimize clinical strategies. PATIENTS AND METHODS: We retrospectively analyzed clinical data for 24 patients with confirmed PCP who underwent renal transplantation (RT) between 2010 and 2019, encompassing a mean follow-up of 29 (range, 11-49) d. RESULTS: A 71% incidence was observed for PCP during the first 6 months after RT. Progressive dyspnea (79%) was the most common symptom, followed by fever (75%) and dry cough (67%). In the initial phase of PCP, the most frequent computerized tomography (CT) finding was the presence of symmetric, apically distributed ground-glass opacities. Nine of 11 patients (82%) were diagnosed by induced sputum testing, 14 of 17 (82%) by bronchoalveolar lavage, and 1 of 24 (4%) by sputum smear. The 1,3-ß-D-glucan level was elevated (mean, 259.16 ± 392.34 pg/mL) in 80% of patients, while 75% had elevated C-reactive protein levels (median, 37.85 mg/L). Two of 18 patients (11%) were positive for cytomegalovirus. All patients were treated with trimethoprim-sulfamethoxazole (3 doses of 1-6 g/kg) and third-generation cephalosporin or moxifloxacin monotherapy to prevent bacterial infection. The methylprednisolone dose (40-400 mg/d) varied according to illness. Most patients were treated using a nasal cannula or oxygen mask, and 2 by mechanical ventilation. CT showed improved lesions after treatment, and completely absorbed lesions or residual fibrosis at follow-up. The mean hospitalization cost was 14,644.73 ± 11,101.59 RMB. CONCLUSION: Peak PCP incidence occurred during the first 6 months after surgery. Progressive dyspnea, fever, and dry cough are important indicators for PCP. Bilateral and diffuse ground-glass opacities involving both lung apexes are often the first indication for PCP diagnosis. Induced sputum testing may be the method-of-choice for pathogen detection. The cure rate can be improved through early antipathogen, glucocorticoid, and preventive anti-infection therapies, as well as respiratory support.

Nanoindentation and deformation behaviors of silicon covered with amorphous SiO2: a molecular dynamic study.

A fundamental understanding of the mechanical properties and deformation behaviors of surface modified silicon during chemical mechanical polishing (CMP) processes is difficult to obtain at the nanometer scale. In this research, MD simulations of monocrystalline silicon covered with an amorphous SiO2 film with different thickness are implemented by nanoindentation, and it is found that both the indentation modulus and hardness increase with the growing indentation depth owning to the strongly silicon substrate effect. At the same indentation depth, the indentation modulus decreases shapely with the increase of film thickness because of less substrate influence, while the hardness agrees well with the trend of modulus at shallow depth but mismatches at larger indentation depth. The observed SiO2 film deformation consists of densification and thinning along indentation direction and extension in the deformed area due to the rotation and deformation of massive SiO4 tetrahedra. The SiO2 film plays an important role in the onset and development of silicon phase transformation. The thinner the SiO2 film is, the earlier the silicon phase transformation takes place. So the numbers of phase transformation atoms increase with the decrease of SiO2 film thickness at the same indentation depth. It is suggested that the thicker film should be better during CMP process for higher material removal rate and less defects within silicon substrate.