Lateral Quantum Confinement Effect on High-TC Superconducting FeSe Monolayer.

Despite decades of research in spatially confined superconducting systems to understand the modification of superconductivity from reduced length scales, the investigation of the quantum confinement effect on high-temperature superconductors remains an outstanding challenge. Here, we report scanning tunneling spectroscopy measurements on laterally confined FeSe monolayers on SrTiO3 substrates, which are formed by epitaxially growing FeSe films with a coverage less than one unit cell. Comparing to the uniform regions of FeSe monolayers, the peninsula regions at the monolayer boundary exhibit reduced Fermi energy and undiminished superconductivity, leading to a putative crossover from a Bardeen-Cooper-Schrieffer state to a Bose-Einstein condensate state. In isolated FeSe monolayer islands, superconductivity is shown to exist in samples of smaller volume in contrast to conventional superconductors, while the validity of Anderson's criterion remains fulfilled. Our work reveals lateral quantum confinement effects in unconventional superconductors to enrich the understanding of high-temperature superconductivity in low-dimensional systems.

Electronic States of Single Perovskite Quantum Dots in Weak and Strong Interaction Regimes: Implications in Electrically Pumped Quantum Emitters.

We investigate the effect of Coulomb interactions on the electronic states of a single perovskite quantum dot (PQD), CsPbBr3, through scanning tunneling microscopy/spectroscopy (STM/S). Under a weak interaction regime, where the time-averaged occupation of electrons in a PQD remains zero, the peaks observed in the differential tunneling conductance (dI/dV) spectrum correspond to the single-particle density of states (DOS) without any electron-electron correlation. However, with a shorter tunnel distance between the STM tip and PQD, additional electrons are trapped in the QD, leading to a strong interaction regime with well-defined electronic fine structures due to the lifting of spin degeneracy in the conduction bands. Interestingly, we observe that the strong Coulomb interaction can modify the spin-orbit coupling (SOC) strength in the PQDs. We have concluded that the energy levels under a strong electron-electron interaction regime are of utmost importance since they will be applicable to electrically pumped PQD-based single photon quantum emitters.

Ion Selectivity, Current, and Water Flow Regulation in Ti3C2 MXene Nanopores.

Recent years have seen a growing interest in zero-dimensional (0D) transport phenomena occurring across two-dimensional (2D) materials for their potential applications to nanopore technology such as ion separation and molecular sensing. Herein, we investigate ion transport through 1 nm-wide nanopores in Ti3C2 MXene using molecular dynamics simulations. The high polarity and fish-bone arrangement of the Ti3C2 MXene offer a built-in potential and an atomic-scale distortion to the nanopore, causing an adsorption preference for cations. Our observation of variable cation-specific ion selectivity and Coulomb blockade highlights the complex interplay between adsorption affinity and cation size. The cation-specific ion selectivity can induce both the ion current and electro-osmotic water transmission, which can be regulated by tailoring the ions' preferential pathways through electric field tilting. Our finding underscores the pivotal role of the atomic arrangement of MXenes in 0D ion transport and provides fundamental insight into the application of 2D material in nanopores-based technologies.

Symmetry Breaking and Spin-Orbit Coupling for Individual Vacancy-Induced In-Gap States in MoS2 Monolayers.

Spins confined to point defects in atomically thin semiconductors constitute well-defined atomic-scale quantum systems that are being explored as single-photon emitters and spin qubits. Here, we investigate the in-gap electronic structure of individual sulfur vacancies in molybdenum disulfide (MoS2) monolayers using resonant tunneling scanning probe spectroscopy in the Coulomb blockade regime. Spectroscopic mapping of defect wave functions reveals an interplay of local symmetry breaking by a charge-state-dependent Jahn-Teller lattice distortion that, when combined with strong (≃100 meV) spin-orbit coupling, leads to a locking of an unpaired spin-1/2 magnetic moment to the lattice at low temperature, susceptible to lattice strain. Our results provide new insights into the spin and electronic structure of vacancy-induced in-gap states toward their application as electrically and optically addressable quantum systems.

Achieving Significantly Boosted Dielectric Energy Density of Polymer Film via Introducing a Bumpy Gold/Polymethylsilsesquioxane Granular Blocking Layer.

Polymer dielectrics are the key materials for pulsed energy storage systems, but their low energy densities greatly restrict the applications in integrated electronic devices. Herein, a unique bumpy granular interlayer consisting of gold nanoparticles (Au NPs) and polymethyksesquioxane (PMSQ) microspheres is introduced into a poly(vinylidene fluoride) (PVDF) film, forming trilayered PVDF-Au/PMSQ-PVDF films. Interestingly, the Au/PMSQ interlayer arouses a dielectric enhancement of 47% and an ultrahigh breakdown strength of 704 MV m-1, which reaches 153% of pure PVDF. It is revealed that the greatly enhanced breakdown strength originated from the Coulomb-blockade effect of Au NPs and the excellent insulating properties of PMSQ microspheres with a special molecular-scale organic-inorganic hybrid structure. Benefiting from the concurrently enhanced dielectric and breakdown performances, an outstanding energy density of 22.42 J cm-3 with an efficiency of 67.1%, which reaches 249% of that of the pure PVDF, is achieved. It is further confirmed that this design strategy is also applicable to linear dielectric polymer polyethyleneimine. The composites exhibit an energy density of 8.91 J cm-3 with a high efficiency of ≈95%. This work offers a novel and efficient strategy for concurrently enhancing the dielectric and breakdown performances of polymers toward pulsed power applications.

On the Resolution Limit of Electrohydrodynamic Redox 3D Printing.

Additive manufacturing (AM) will empower the next breakthroughs in nanotechnology by combining unmatched geometrical freedom with nanometric resolution. Despite recent advances, no micro-AM technique has been able to synthesize functional nanostructures with excellent metal quality and sub-100 nm resolution. Here, significant breakthroughs in electrohydrodynamic redox 3D printing (EHD-RP) are reported by directly fabricating high-purity Cu (>98 at.%) with adjustable voxel size from >6µm down to 50 nm. This unique tunability of the feature size is achieved by managing in-flight solvent evaporation of the ion-loaded droplet to either trigger or prevent the Coulomb explosion. In the first case, the landing of confined droplets on the substrate allows the fabrication of high-aspect-ratio 50 nm-wide nanopillars, while in the second, droplet disintegration leads to large-area spray deposition. It is discussed that the reported pillar width corresponds to the ultimate resolution achievable by EHD printing. The unrivaled feature size and growth rate (>100 voxel s-1) enable the direct manufacturing of 30 µm-tall atom probe tomography (APT) tips that unveil the pristine microstructure and chemistry of the deposit. This method opens up prospects for the development of novel materials for 3D nano-printing.

Application of Sodium-Rich Multifunctional Hard Carbon Synthesized via Multi-Alloy Grafting Strategy for Presodiation in High-Performance Sodium-Ion Batteries.

In sodium-ion pouch batteries based on hard carbon, an additional source of active sodium significantly enhances the battery's initial coulombic efficiency and compensates for the loss of active sodium ions during cycling. This study investigates the interaction between metallic sodium with carbon materials and develops a composite powder material of sodium-rich lithium-aluminum using a multi-alloy grafting strategy, to replenish the initial loss of active sodium in the hard carbon materials. To enhance the stability and utilization of this highly active sodium source, a novel slurry system based on polyethylene oxide (PEO) as a binder and dimethyl carbonate (DMC) as a solvent is introduced. Furthermore, this study designs a hard carbon composite electrode structure with a stable layer and sacrificial layer (NPH), which not only accommodates current battery processing environments but also demonstrates excellent potential in practical applications. Ultimately, the soft-packed sodium-ion battery consists of NPH electrodes with composite sodium ferric pyrophosphate (NFPP) and demonstrates excellent initial coulombic efficiency (91%) and ultra-high energy density (205 Wh kg-1). These results indicate significant technological and application implications for future energy storage.

Concentration-Dependent Diffusion of Monoclonal Antibodies: Underlying Mechanisms of Anomalous Diffusion.

The development, storage, transport, and subcutaneous delivery of highly concentrated monoclonal antibody formulations pose significant challenges due to the high solution viscosity and low diffusion of the antibody molecules in crowded environments. These issues often stem from the self-associating behavior of the antibody molecules, potentially leading to aggregation. In this work, we used a dissipative particle dynamics-based coarse-grained model to investigate the diffusion behavior of IgG1 antibody molecules in aqueous solutions with 15 and 32 mM NaCl and antibody concentrations ranging from 10 to 400 mg/mL. We determined the coarse-grained interaction parameters by matching the calculated structure factor with the computational and experimental data from the literature. Our results indicate Fickian diffusion for antibody concentrations of 10 and 25 mg/mL and anomalous diffusion for concentrations exceeding 50 mg/mL. The anomalous diffusion was observed for ∼0.33 to 0.4 µs, followed by Fickian diffusion for all antibody concentrations. We observed a strong linear correlation between the diffusion behavior of the antibody molecules (diffusion coefficient D and anomalous diffusion exponent α) and the amount of aggregates present in the solution and between the amount of aggregates and the Coulomb interaction energy. The investigation of underlying mechanisms for anomalous diffusion revealed that in crowded environments at high antibody concentrations, the attractive interaction between electrostatically complementary regions of the antibody molecules could further bring the neighboring molecules closer to one another, ultimately resulting in aggregate formation. Further, the Coulomb attraction can continue to draw more molecules together, forming larger aggregates.

Coulomb blockade and Coulomb staircases in CoBi nanoislands on SrTiO3(001).

We successfully fabricated two-dimensional metallic CoBi nanoislands on SrTiO3(001) substrate by molecular beam epitaxy, and systematically investigated their electronic structures by scanning tunneling microscopy and spectroscopyin situat 4.2 K. Coulomb blockade and Coulomb staircases with discrete and well-separated levels are observed for the individual nanoisland, which is attributed to single-electron tunneling via two tunnel junction barriers. They are in excellent agreement with the simulations based on orthodox theory. Furthermore, we demonstrated that the Coulomb blockade becomes weaker with increasing temperature and almost disappears at ∼22 K in our variable temperature experiment, and its full-width at half-maximum of dI/dVpeaks with temperature is ∼6 mV. Our results provide a new platform for designing single-electron transistors that have potential applications in future microelectronics.

Role of Coulomb blockade in nonlinear transport of conducting polymers.

NonlinearI-Vcharacteristics associated with Coulomb blockade (CB) in conducting polymers were systematically investigated. At low temperatures, a crossover from Ohmic to nonlinear behavior was observed, along with drastically enhanced noise in differential conductance right from the crossover. The fluctuation can be well explained by the Coulombic oscillation in the collective percolation system, where the charge transport is related to the Coulombic charging energy between crystalline domains. Furthermore, a distinct quantum conductance, the fingerprint of CB caused by the individual tunneling between crystalline grains, was observed in sub-100 nm devices, confirming a strong association between nonlinearI-Vcharacteristics and CB effect.

Electrochemical Hydrogen Peroxide Generation and Activation Using a Dual-Cathode Flow-Through Treatment System: Enhanced Selectivity for Contaminant Removal by Electrostatic Repulsion.

To oxidize trace concentrations of organic contaminants under conditions relevant to surface- and groundwater, air-diffusion cathodes were coupled to stainless-steel cathodes that convert atmospheric O2 into hydrogen peroxide (H2O2), which then was activated to produce hydroxyl radicals (·OH). By separating H2O2 generation from its activation and employing a flow-through electrode consisting of stainless-steel fibers, the two processes could be operated efficiently in a manner that overcame mass-transfer limitations for O2, H2O2, and trace organic contaminants. The flexibility resulting from separate control of the two processes made it possible to avoid both the accumulation of excess H2O2 and the energy losses that take place after H2O2 has been depleted. The decrease in treatment efficacy occurring in the presence of natural organic matter was substantially lower than that typically observed in homogeneous advanced oxidation processes. Experiments conducted with ionized and neutral compounds indicated that electrostatic repulsion prevented negatively charged ·OH scavengers from interfering with the oxidation of neutral contaminants. Energy consumption by the dual-cathode system was lower than values reported for other technologies intended for small-scale drinking water treatment systems. The coordinated operation of these two cathodes has the potential to provide a practical, inexpensive way for point-of-use drinking water treatment.

Design of Network-on-Chip-Based Restricted Coulomb Energy Neural Network Accelerator on FPGA Device.

Sensor applications in internet of things (IoT) systems, coupled with artificial intelligence (AI) technology, are becoming an increasingly significant part of modern life. For low-latency AI computation in IoT systems, there is a growing preference for edge-based computing over cloud-based alternatives. The restricted coulomb energy neural network (RCE-NN) is a machine learning algorithm well-suited for implementation on edge devices due to its simple learning and recognition scheme. In addition, because the RCE-NN generates neurons as needed, it is easy to adjust the network structure and learn additional data. Therefore, the RCE-NN can provide edge-based real-time processing for various sensor applications. However, previous RCE-NN accelerators have limited scalability when the number of neurons increases. In this paper, we propose a network-on-chip (NoC)-based RCE-NN accelerator and present the results of implementation on a field-programmable gate array (FPGA). NoC is an effective solution for managing massive interconnections. The proposed RCE-NN accelerator utilizes a hierarchical-star (H-star) topology, which efficiently handles a large number of neurons, along with routers specifically designed for the RCE-NN. These approaches result in only a slight decrease in the maximum operating frequency as the number of neurons increases. Consequently, the maximum operating frequency of the proposed RCE-NN accelerator with 512 neurons increased by 126.1% compared to a previous RCE-NN accelerator. This enhancement was verified with two datasets for gas and sign language recognition, achieving accelerations of up to 54.8% in learning time and up to 45.7% in recognition time. The NoC scheme of the proposed RCE-NN accelerator is an appropriate solution to ensure the scalability of the neural network while providing high-performance on-chip learning and recognition.

Inducing Electric Current in Graphene Using Ionic Flow.

Classical nanofluidic frameworks account for the confined fluid and ion transport under an electrostatic field at the solid-liquid interface, but the electronic property of the solid is often overlooked. Harvesting the interaction of the nanofluidic transport with the electron transport in solid requires a route effectively coupling ion and electron dynamics. Here we report a nanofluidic analogy of Coulomb drag for exploring the dynamic ion-electron interactions at the liquid-graphene interface. An induced electric current in graphene by ionic flow with no bias directly applied to the graphene channel is observed experimentally, featuring an opposite electron current direction to the ion current. Our experiments and ab initio calculations show that the current generation stems from the confined ion-electron interactions via a nanofluidic Coulomb drag mechanism. Our findings may open up a new dimension for nanofluidics and transport control by ion-electron coupling.

Spin-Valley Locking for In-Gap Quantum Dots in a MoS2 Transistor.

Spins confined to atomically thin semiconductors are being actively explored as quantum information carriers. In transition metal dichalcogenides (TMDCs), the hexagonal crystal lattice gives rise to an additional valley degree of freedom with spin-valley locking and potentially enhanced spin life and coherence times. However, realizing well-separated single-particle levels and achieving transparent electrical contact to address them has remained challenging. Here, we report well-defined spin states in a few-layer MoS2 transistor, characterized with a spectral resolution of ∼50 µeV at Tel = 150 mK. Ground state magnetospectroscopy confirms a finite Berry-curvature induced coupling of spin and valley, reflected in a pronounced Zeeman anisotropy, with a large out-of-plane g-factor of g⊥ ≃ 8. A finite in-plane g-factor (g∥ ≃ 0.55-0.8) allows us to quantify spin-valley locking and estimate the spin-orbit splitting 2ΔSO ∼ 100 µeV. The demonstration of spin-valley locking is an important milestone toward realizing spin-valley quantum bits.

Study on the Hydrophobic Modification Mechanism of Stearic Acid on the Surface of Coal Gasification Fly Ash.

In this study, the hydrophobic modification of coal gasification fly ash (FA) was investigated given the adverse effects of surface hydrophilic structures on the material field. The surface of FA was modified using stearic acid (SA), which successfully altered its hydrophilic structure. When the contact angle of S-FA increased from 23.4° to 127.2°, the activation index increased from 0 to 0.98, the oil absorption decreased from 0.564 g/g to 0.510 g/g, and the BET-specific surface area decreased from 13.973 m2/g to 3.218 m2/g. The failure temperature of SA on the surface of S-FA was 210 °C. The adsorption mechanism of FA was analyzed using density functional theory (DFT) and molecular dynamics (MD). The adsorption of water molecules by FA involved both chemical and physical adsorption, with active adsorption sites for Al, Fe, and Si. The adsorbed water molecules on the surface of FA formed hydrogen bonds with a bond length of 1.5-2.5 Å, leading to agglomeration. In addition, the long alkyl chain in SA mainly relied on the central carbon atom in the (-CH3) structure to obtain electrons in different directions from the H atoms in space, increasing the Coulomb repulsion with the O atoms in the water molecule and thereby achieving the hydrophobic effect. In the temperature range of 298 K to 358 K, the combination of FA and SA became stronger as the temperature increased.

A formula and numerical study on Ewald 1D summation.

Ewald summation is famous for its successful applications in molecular simulations for systems under 2 dimensional periodic boundary condition (2D PBC, e.g., planar interfaces) and systems under 3D PBC (e.g., bulk). However, the extension to systems under 1D PBC (like porous structures and tubes) is largely hindered by the special functions in the formula. In this work, a simple approximation of Ewald 1D sum is introduced with its error rigorously controlled. To investigate the impacts on the efficiency and accuracy by different parts, a pairwise potential is calculated for a series of screening parameters ( α ) and radial distances ( ρ ) between two point charges. A mapping between the sum of trigonometric functions in Ewald 1D method and the sum of specific vectors further reveals the different converging speeds of different Fourier parts. When choosing α = 0.2 Å-1 , it is appropriate to ignore the insignificant parts in the sum to accelerate the method.

Dynamic Observation of the Coulomb Explosion and Field Evaporation of a Few-Layer Graphene Nanoribbon.

The Coulomb explosion and field evaporation are frequently observed physical phenomena for a metallic tip under an external electric field, which can modify the structures of the tip and have broad applications, such as in the atomic-probe tomography and field ion microscopy. However, the mechanistic comprehending of how they change the structures of the tip and the differences between them are not clear. Here, dynamic observations of Coulomb explosions and field evaporations on the positively biased and charged few-layer graphene (FLG) nanoribbon inside a transmission electron microscope are reported. By combining the atomic-scale molecular dynamic simulations, it is shown that the FLG is split into several sheets under Coulomb explosion. It is also observed to break by emitting the carbon ions/segments under the field evaporation. It is further demonstrated that the split and breaking of FLG can be tuned by the shape of the nanoribbon. FLG ribbons with sharp tips have splitting and breaking occur in sequence. FLG with blunt tips break without a split. These results provide a fundamental understanding of Coulomb explosion and field evaporation in graphene nanomaterials and suggest potential methods to engineer graphene-based nanostructures.

Precursor Induced Assembly of Si Nanoparticles Encapsulated in Graphene/Carbon Matrices and the Influence of Al2 O3 Coating on their Properties as Anode for Lithium-Ion Batteries.

The theoretical capacity of pristine silicon as anodes for lithium-ion batteries (LIBs) can reach up to 4200 mAh g-1 , however, the low electrical conductivity and the huge volume expansion limit their practical application. To address this challenge, a precursor strategy has been explored to induce the curling of graphene oxide (GO) flakes and the enclosing of Si nanoparticles by selecting protonated chitosan as both assembly inducer and carbon precursor. The Si nanoparticles are dispersed first in a slurry of GO by ball milling, then the resulting dispersion is dried by a spray drying process to achieve instantaneous solution evaporation and compact encapsulation of silicon particles with GO. An Al2 O3 layer is constructed on the surface of Si@rGO@C-SD composites by the atomic layer deposition method to modify the solid electrolyte interface. This strategy enhances obviously the electrochemical performance of the Si as anode for LIBs, including excellent long-cycle stability of 930 mAh g-1 after 1000 cycles at 1000 mA g-1 , satisfied initial Coulomb efficiency of 76.7%, and high rate ability of 806 mAh g-1 at 5000 mA g-1 . This work shows a potential solution to the shortcomings of Si-based anodes and provides meaningful insights for constructing high-energy anodes for LIBs.

Laser-Induced Coulomb Explosion Imaging of Aligned Molecules and Molecular Dimers.

We discuss how Coulomb explosion imaging (CEI), triggered by intense femtosecond laser pulses and combined with laser-induced alignment and covariance analysis of the angular distributions of the recoiling fragment ions, provides new opportunities for imaging the structures of molecules and molecular complexes. First, focusing on gas phase molecules, we show how the periodic torsional motion of halogenated biphenyl molecules can be measured in real time by timed CEI, and how CEI of one-dimensionally aligned difluoroiodobenzene molecules can uniquely identify four structural isomers. Next, focusing on molecular complexes formed inside He nano-droplets, we show that the conformations of noncovalently bound dimers or trimers, aligned in one or three dimensions, can be determined by CEI. Results presented for homodimers of CS2, OCS, and bromobenzene pave the way for femtosecond time-resolved structure imaging of molecules undergoing bimolecular interactions and ultimately chemical reactions.

The effect of inter-dot Coulomb interaction on the charge and energy transport properties of a five-terminal system consisting of three Coulomb-coupled quantum dots.

We have studied a 5-terminal system consisting of three single level quantum dots (QDs) that are in contact with their respective reservoirs. In addition to the intra-dot Coulomb interaction, the electron in the dot affected by an inter-dot Coulomb repulsion from its adjacent QD. We describe this system by an Anderson type model Hamiltonian and apply the Greens function method to study the transport properties of the system. Since we are interested in temperatures higher than the Kondo temperature, we use the equations of motion technique to calculate Green's functions. Numerical analysis shows that there is a correlation between the transport characteristics of the lower and upper dot and we can change the conductivity of the lower dot only by varying the parameters of the upper dot and vice versa. We demonstrated that the middle dot play the role of the switch on/off of this correlation. Also, we investigated the effect of thermoelectric properties. We found that the inter-dot Coulomb interaction can improve the thermoelectric performance of the system.