Dynamic Behavior of Above-Room-Temperature Robust Skyrmions in 2D Van der Waals Magnet.

Magnetic skyrmions are swirl-like spin configurations that present topological properties, which have great potential as information carriers for future high-density and low-energy-consumption devices. The optimization of skyrmion-hosting materials that can be integrated with semiconductor-based circuits is the primary challenge for their industrialization. Two-dimensional van der Waals ferromagnets are emerging materials that have excellent carrier mobility and compatibility with integrated circuits, making them an ideal candidate for spintronic devices. Here, we report the realization of skyrmions at above room temperature in the 2D ferromagnet Fe3GaTe2. The thickness tunability of their skyrmion size and the formation of the skyrmion lattice are revealed. Furthermore, we demonstrate that the skyrmions can be moved by a low-density current at room temperature, together with an apparent skyrmion Hall effect, which is consistent with our quantitative micromagnetic simulation. Our work offers a promising 2D material platform for harnessing magnetic skyrmions in practical device applications.

Tailoring Heterostructure Growth on Liquid Metal Nanodroplets through Interface Engineering.

Liquid metal (LM) nanodroplets possess intriguing surface properties, thus offering promising potential in chemical synthesis, catalysis, and biomedicine. However, the reaction kinetics and product growth at the surface of LM nanodroplets are significantly influenced by the interface involved, which has not been thoroughly explored and understood. Here, we propose an interface engineering strategy, taking a spontaneous galvanic reaction between Ga0 and AuCl4- ions as a representative example, to successfully modulate the growth of heterostructures on the surface of Ga-based LM nanodroplets by establishing a dielectric interface with a controllable thickness between LM and reactive surroundings. Combining high-resolution electron energy-loss spectroscopy (EELS) analysis and theoretical simulation, it was found that the induced charge distribution at the interface dominates the spatiotemporal distribution of the reaction sites. Employing tungsten oxide (WOx) with varying thicknesses as the demonstrated dielectric interface of LM, Ga@WOx@Au with distinct core-shell-satellite or dimer-like heterostructures has been achieved and exhibited different photoresponsive capabilities for photodetection. Understanding the kinetics of product growth and the regulatory strategy of the dielectric interface provides an experimental approach to controlling the structure and properties of products in LM nanodroplet-involved chemical processes.

Approaching Elaborate Control of the Nano-Products of Carbothermal Reduction Reaction Through In Situ Identification.

Atomic understanding of a chemical reaction can realize the programmable design and synthesis of desired products with specific compositions and structures. Through directly monitoring the phase transition and tracking the dynamic evolution of atoms in a chemical reaction, in situ transmission electron microscopy (TEM) techniques offer the feasibility of revealing the reaction kinetics at the atomic level. Nevertheless, such investigation is quite challenging, especially for reactions involving multi-phase and complex interfaces, such as the widely adopted carbothermal reduction (CTR) reactions. Herein, in-situ TEM is applied to monitor the CTR of Co3 O4 nanocubes on reduced graphene oxide nanosheets. Together with the first-principle calculation, the migration route of Co atoms during the phase transition of the CTR reaction is revealed. Meanwhile, the interfacial edge-dislocations/stress-gradient is identified as a result of the atomistic diffusion, which in turn can affect the morphology variation of the reactants. Accordingly, controllable synthesis of Co-based nanostructure with a desirable phase and structure has been achieved. This work not only provides atomic kinetic insight into CTR reactions but also offers a novel strategy for the design and synthesis of functional nanostructures for emerging energy technologies.

Mitotic Transcription Installs Sgo1 at Centromeres to Coordinate Chromosome Segregation.

Human sister chromatids at metaphase are primarily linked by centromeric cohesion, forming the iconic X shape. Premature loss of centromeric cohesion disrupts orderly mitotic progression. Shugoshin (Sgo1) binds to and protects cohesin at inner centromeres. The kinetochore kinase Bub1 phosphorylates histone H2A at T120 (H2A-pT120) and recruits Sgo1 to kinetochores, 0.5 µm from inner centromeres. Here, we show that Sgo1 is a direct reader of the H2A-pT120 mark. Bub1 also recruits RNA polymerase II (Pol II) to unattached kinetochores and promotes active transcription at mitotic kinetochores. Mitosis-specific inactivation of Pol II traps Sgo1 at kinetochores and weakens centromeric cohesion. Sgo1 interacts with Pol II in human cells and with RNA in vitro. We propose that Pol II-dependent transcription enables kinetochore-bound Sgo1 initially recruited by H2A-pT120 to reach cohesin embedded in centromeric chromatin. Our study implicates mitotic transcription in targeting regulatory factors to highly compacted mitotic chromatin.

Nanoscale visualization of metallic electrodeposition in a well-controlled chemical environment.

Liquid phase transmission electron microscopy (TEM) provides a useful means to study a wide range of dynamics in solution with near-atomic spatial resolution and sub-microsecond temporal resolution. However, it is still a challenge to control the chemical environment (such as the flow of liquid, flow rate, and the liquid composition) in a liquid cell, and evaluate its effect on the various dynamic phenomena. In this work, we have systematically demonstrated the flow performance of anin situliquid TEM system, which is based on 'on-chip flow' driven by external pressure pumps. We studied the effects of different chemical environments in the liquid cell as well as the electrochemical potential on the deposition and dissolution behavior of Cu crystals. The results show that uniform Cu deposition can be obtained at a higher liquid flow rate (1.38µl min-1), while at a lower liquid flow rate (0.1µl min-1), the growth of Cu dendrites was observed. Dendrite formation could be further promoted byin situaddition of foreign ions, such as phosphates. The generality of this technique was confirmed by studying Zn electrodeposition. Our direct observations not only provide new insights into understanding the nucleation and growth but also give guidelines for the design and synthesis of desired nanostructures for specific applications. Finally, the capability of controlling the chemical environment adds another dimension to the existing liquid phase TEM technique, extending the possibilities to study a wide range of dynamic phenomena in liquid media.

Kondo Holes in the Two-Dimensional Itinerant Ising Ferromagnet Fe3GeTe2.

Heavy Fermion (HF) states emerge in correlated quantum materials due to the intriguing interplay between localized magnetic moments and itinerant electrons but rarely appear in 3d-electron systems due to high itinerancy of d-electrons. Here, an anomalous enhancement of Kondo screening is observed at the Kondo hole of local Fe vacancies in Fe3GeTe2 which is a recently discovered 3d-HF system featuring Kondo lattice and two-dimensional itinerant ferromagnetism. An itinerant Kondo-Ising model is established to reproduce the experimental results and provides insight into the competition between Ising ferromagnetism and Kondo screening. Our work explains the microscopic origin of the d-electron HF states in Fe3GeTe2 and inspires future studies of the enriched quantum many-body effects with Kondo holes.

Atomic Structural Evolution of Single-Layer Pt Clusters as Efficient Electrocatalysts.

The rational synthesis of single-layer noble metal directly anchored on support materials is an elusive target to accomplish for a long time. This paper reports well-defined single-layer Pt (Pt-SL) clusters anchored on ultrathin TiO2 nanosheets-as a new frontier in electrocatalysis. The structural evolution of Pt-SL/TiO2 via self-assembly of single Pt atoms (Pt-SA) is systematically recorded. Significantly, the Pt atoms of Pt-SL/TiO2 possess a unique electronic configuration with PtPt covalent bonds surrounded by abundant unpaired electrons. This Pt-SL/TiO2 catalyst presents enhanced electrochemical performance toward diverse electrocatalytic reactions (such as the hydrogen evolution reaction and the oxygen reduction reaction) compared with Pt-SA, multilayer Pt nanoclusters, and Pt nanoparticles, suggesting an efficient new type of catalyst that can be achieved by constructing single-layer atomic clusters on supports.

Hydrogen Terminated Germanene for a Robust Self-Powered Flexible Photoelectrochemical Photodetector.

As a rising star in the family of graphene analogues, germanene shows great potential for electronic and optical device applications due to its unique structure and electronic properties. It is revealed that the hydrogen terminated germanene not only maintains a high carrier mobility similar to that of germanene, but also exhibits strong light-matter interaction with a direct band gap, exhibiting great potential for photoelectronics. In this work, few-layer germanane (GeH) nanosheets with controllable thickness are successfully synthesized by a solution-based exfoliation-centrifugation route. Instead of complicated microfabrication techniques, a robust photoelectrochemical (PEC)-type photodetector, which can be extended to flexible device, is developed by simply using the GeH nanosheet film as an active electrode. The device exhibits an outstanding photocurrent density of 2.9 µA cm-2 with zero bias potential, excellent responsivity at around 22 µA W-1 under illumination with intensity ranging from 60 to 140 mW cm-2 , as well as short response time (with rise and decay times, tr = 0.24 s and td = 0.74 s). This efficient strategy for a constructing GeH-based PEC-type photodetector suggests a path to promising high-performance, self-powered, flexible photodetectors, and it also paves the way to a practical application of germanene.

A Yolk-Shell Structured Silicon Anode with Superior Conductivity and High Tap Density for Full Lithium-Ion Batteries.

The poor cycling stability resulting from the large volume expansion caused by lithiation is a critical issue for Si-based anodes. Herein, we report for the first time of a new yolk-shell structured high tap density composite made of a carbon-coated rigid SiO2 outer shell to confine multiple Si NPs (yolks) and carbon nanotubes (CNTs) with embedded Fe2 O3 nanoparticles (NPs). The high tap density achieved and superior conductivity can be attributed to the efficiently utilised inner void containing multiple Si yolks, Fe2 O3 NPs, and CNTs Li+ storage materials, and the bridged spaces between the inner Si yolks and outer shell through a conductive CNTs "highway". Half cells can achieve a high area capacity of 3.6 mAh cm-2 and 95 % reversible capacity retention after 450 cycles. The full cell constructed using a Li-rich Li2 V2 O5 cathode can achieve a high reversible capacity of 260 mAh g-1 after 300 cycles.

Construction of a series of pCS2+ backbone-based Gateway vectors for overexpressing various tagged proteins in vertebrates.

Gateway vectors have been extensively developed to facilitate gene cloning in numerous species; however, a universal system that is compatible for multiple organisms was lacking. As a multipurpose expression vector, pCS2+ backbone-based expression plasmids are widely used for high-level expression of messenger RNAs (mRNAs) or proteins in mammalian/avian culture cells or Xenopus/zebrafish embryos. To date, a suite of vectors with pCS2+ backbone applicable for Gateway cloning system were unavailable yet. Here, we generated a set of Gateway destination vectors, named as pGCS (plasmids of Gateway in pCS2+) vectors, which can be fused to a choice of frequently used amino- or carboxyl-terminal tags, including MYC, HA, FLAG, His, GST, as well as eGFP fluorescent epitope. The systematic generation of this set of pCS2+ backbone-based Gateway destination vectors allows for in vitro recombination of DNA with high speed, accuracy, and reliability compared with the traditional 'digestion-ligation' cloning approach. Thus, our system accelerates the production of functional proteins, which could be widely expressed in a large variety of vertebrate organisms without tediously transferring genes into different expression vectors. Moreover, we make this series of Gateway vectors available to the research community via the non-profit Addgene Plasmid Repository.

Cobalt phosphide nanowires: efficient nanostructures for fluorescence sensing of biomolecules and photocatalytic evolution of dihydrogen from water under visible light.

The detection of specific DNA sequences plays an important role in the identification of disease-causing pathogens and genetic diseases, and photochemical water splitting offers a promising avenue to sustainable, environmentally friendly hydrogen production. Cobalt-phosphorus nanowires (CoP NWs) show a high fluorescence quenching ability and different affinity toward single- versus double-stranded DNA. Based on this result, the utilization of CoP NWs as fluorescent DNA nanosensors with a detection limit of 100 pM and a selectivity down to single-base mismatch was demonstrated. The use of a thrombin-specific DNA aptamer also enabled the selective detection of thrombin. The photoinduced electron transfer from the excited dye that labels the oligonucleotide probe to the CoP semiconductor led to efficient fluorescence quenching, and largely enhanced the photocatalytic evolution of hydrogen from water under visible light.

NiSe Nanowire Film Supported on Nickel Foam: An Efficient and Stable 3D Bifunctional Electrode for Full Water Splitting.

Active and stable electrocatalysts made from earth-abundant elements are key to water splitting for hydrogen production through electrolysis. The growth of NiSe nanowire film on nickel foam (NiSe/NF) in situ by hydrothermal treatment of NF using NaHSe as Se source is presented. When used as a 3D oxygen evolution electrode, the NiSe/NF exhibits high activity with an overpotential of 270 mV required to achieve 20 mA cm(-2) and strong durability in 1.0 M KOH, and the NiOOH species formed at the NiSe surface serves as the actual catalytic site. The system is also highly efficient for catalyzing the hydrogen evolution reaction in basic media. This bifunctional electrode enables a high-performance alkaline water electrolyzer with 10 mA cm(-2) at a cell voltage of 1.63 V.

Graphitic carbon nitride nanosheets: one-step, high-yield synthesis and application for Cu2+ detection.

In this article we report on the one-step, rapid, high-yield synthesis of graphitic carbon nitride (g-C3N4) nanosheets for the first time. The nanosheets were obtained by pyrolyzing a melamine-KBH4 mixture under Ar. As a fluorosensor for Cu(2+), the g-C3N4 nanosheets exhibit a detection limit as low as 0.5 nM and high selectivity in buffer solutions, and this sensor was applied to the analysis of lake water samples. The electrogenerated chemiluminescence (ECL) behavior of the g-C3N4 nanosheets using Na2S2O8 as the coreactant was also studied. Results suggest that the ECL intensity of the g-C3N4 nanosheets was linear over concentrations of 0-45 nM, with a detection limit of 1.2 nM for Cu(2+).

Self-supported Cu3P nanowire arrays as an integrated high-performance three-dimensional cathode for generating hydrogen from water.

Searching for inexpensive hydrogen evolution reaction (HER) electrocatalysts with high activity has attracted considerable research interest in the past years. Reported herein is the topotactic fabrication of self-supported Cu3 P nanowire arrays on commercial porous copper foam (Cu3 P NW/CF) from its Cu(OH)2 NW/CF precursor by a low-temperature phosphidation reaction. Remarkably, as an integrated three-dimensional hydrogen-evolving cathode operating in acidic electrolytes, Cu3 P NW/CF maintains its activity for at least 25 hours and exhibits an onset overpotential of 62 mV, a Tafel slope of 67 mV dec(-1) , and a Faradaic efficiency close to 100 %. Catalytic current density can approach 10 mA cm(-2) at an overpotential of 143 mV.

Carbon nanotubes decorated with CoP nanocrystals: a highly active non-noble-metal nanohybrid electrocatalyst for hydrogen evolution.

The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. The strongly acidic conditions in proton exchange membranes create a need for acid-stable HER catalysts. A nanohybrid that consists of carbon nanotubes decorated with CoP nanocrystals (CoP/CNT) was prepared by the low-temperature phosphidation of a Co3O4/CNT precursor. As a novel non-noble-metal HER catalyst operating in acidic electrolytes, the nanohybrid exhibits an onset overpotential of as low as 40 mV, a Tafel slope of 54 mV dec(-1), an exchange current density of 0.13 mA cm(-2), and a Faradaic efficiency of nearly 100 %. This catalyst maintains its catalytic activity for at least 18 hours and only requires overpotentials of 70 and 122 mV to attain current densities of 2 and 10 mA cm(-2), respectively.

Tuning Carbon Dioxide Reduction Reaction Selectivity of Bi Single-Atom Electrocatalysts with Controlled Coordination Environments.

Control over product selectivity of the electrocatalytic CO2 reduction reaction (CO2RR) is a crucial challenge for the sustainable production of carbon-based chemical feedstocks. In this regard, single-atom catalysts (SACs) are promising materials due to their tunable coordination environments, which could enable tailored catalytic activities and selectivities, as well as new insights into structure-activity relationships. However, direct evidence for selectivity control via systematic tuning of the SAC coordination environment is scarce. In this work, we have synthesized two differently coordinated Bi SACs anchored to the same host material (carbon black) and characterized their CO2RR activities and selectivities. We find that oxophilic, oxygen-coordinated Bi atoms produce HCOOH, while nitrogen-coordinated Bi atoms generate CO. Importantly, use of the same support material assured that alternation of the coordination environment is the dominant factor for controlling the CO2RR product selectivity. Overall, this work demonstrates the structure-activity relationship of Bi SACs, which can be utilized to establish control over CO2RR product distributions, and highlights the promise for engineering atomic coordination environments of SACs to tune reaction pathways.

FeN4 Active Sites Electronically Coupled with PtFe Alloys for Ultralow Pt Loading Hybrid Electrocatalysts in Proton Exchange Membrane Fuel Cells.

The exorbitant cost of Pt-based electrocatalysts and the poor durability of non-noble metal electrocatalysts for proton exchange membrane fuel cells limited their practical application. Here, FeN4 active sites electronically coupled with PtFe alloys (PtFe-FeNC) were successfully prepared by a vapor deposition strategy as an ultralow Pt loading (0.64 wt %) hybrid electrocatalyst. The FeN4 sites on the FeNC matrix are able to effectively anchor the PtFe alloys, thus inhibiting their aggregation during long-life cycling. These PtFe alloys, in turn, can efficiently restrain the leaching of the FeN4 sites from the FeNC matrix. Thus, the PtFe-FeNC demonstrated an improved Pt mass activity of 2.33 A mgPt-1 at 0.9 V toward oxygen reduction reaction, which is 12.9 times higher than that of commercial Pt/C (0.18 A mgPt-1). It demonstrated great stability, with the Pt mass activity decreasing by only 9.4% after 70,000 cycles. Importantly, the fuel cell with an ultralow Pt loading in the cathode (0.012 mgPt cm-2) displays a high Pt mass activity of 1.75 A mgPt-1 at 0.9 ViR-free, which is significantly better than commercial MEA (0.25 A mgPt-1). Interestingly, PtFe-FeNC catalysts possess enhanced durability, exhibiting a 12.5% decrease in peak power density compared to the 51.7% decrease of FeNC.

Tailoring coordination environments of single-atom electrocatalysts for hydrogen evolution by topological heteroatom transfer.

The rational design of carbon-supported transition-metal single-atom catalysts requires the precise arrangement of heteroatoms within the single-atom catalysts. However, achieving this design is challenging due to the collapse of the structure during the pyrolysis. Here, we introduce a topological heteroatom-transfer strategy to prevent the collapse and accurately control the P coordination in carbon-supported single-atom catalysts. As an illustration, we have prepared self-assembled helical fibers with encapsulated cavities. Within these cavities, adjustable functional groups can chelate metal ions (Nx···Mn+···Oy), facilitating the preservation of the structure during the pyrolysis based phosphidation. This process allows for the transfer of heteroatoms from the assembly into single-atom catalysts, resulting in the precise coordination tailoring. Notably, the Co-P2N2-C catalyst exhibits electrocatalytic performance as a non-noble metal single-atom catalyst for alkaline hydrogen evolution, attaining a current density of 100 mA cm-2 with an overpotential of only 131 mV.

Modulation of Kondo Behavior in a Two-Dimensional Epitaxial Bilayer Bi(111)/Fe3GeTe2 Moiré Heterostructure.

Artificial two-dimensional (2D) moiré superlattices provide a platform for generating exotic quantum matter or phenomena. Here, an epitaxial heterostructure composed of bilayer Bi(111) and an Fe3GeTe2 substrate with a zero-twist angle is acquired by molecular beam epitaxy. Scanning tunneling microscopy and spectroscopy studies reveal the spatially tailored Kondo resonance and interfacial magnetism within this moiré superlattice. Combined with first-principles calculations, it is found that the modulation effect of the moiré superlattice originates from the interfacial orbital hybridization between Bi and Fe atoms. Our work provides a tunable platform for strong electron correlation studies to explore 2D artificial heavy Fermion systems and interface magnetism.

Mo-doping heterojunction: interfacial engineering in an efficient electrocatalyst for superior simulated seawater hydrogen evolution.

Exploring economical, efficient, and stable electrocatalysts for the seawater hydrogen evolution reaction (HER) is highly desirable but is challenging. In this study, a Mo cation doped Ni0.85Se/MoSe2 heterostructural electrocatalyst, Mox-Ni0.85Se/MoSe2, was successfully prepared by simultaneously doping Mo cations into the Ni0.85Se lattice (Mox-Ni0.85Se) and growing atomic MoSe2 nanosheets epitaxially at the edge of the Mox-Ni0.85Se. Such an Mox-Ni0.85Se/MoSe2 catalyst requires only 110 mV to drive current densities of 10 mA cm-2 in alkaline simulated seawater, and shows almost no obvious degradation after 80 h at 20 mA cm-2. The experimental results, combined with the density functional theory calculations, reveal that the Mox-Ni0.85Se/MoSe2 heterostructure will generate an interfacial electric field to facilitate the electron transfer, thus reducing the water dissociation barrier. Significantly, the heteroatomic Mo-doping in the Ni0.85Se can regulate the local electronic configuration of the Mox-Ni0.85Se/MoSe2 heterostructure catalyst by altering the coordination environment and orbital hybridization, thereby weakening the bonding interaction between the Cl and Se/Mo. This synergistic effect for the Mox-Ni0.85Se/MoSe2 heterostructure will simultaneously enhance the catalytic activity and durability, without poisoning or corrosion of the chloride ions.