Local Electric Field Research Articles

The exploitation of local electric field generated by oxygen vacancies on BiOIO3 nano-antibacterial agents for enhanced photocatalytic sterilisation

Methicillin-resistant Staphylococcus aureus (MRSA) is a typical Gram-positive foodborne pathogen, and its infection has been reported since its discovery. Photocatalysis has emerged as a safe and efficient new sterilization method in clinical and food sectors. In this study, we developed an oxygen vacancy-rich BiOIO3 nano-antibacterial agent using a hydrothermal method, which was successfully synthesized and confirmed through various characterization techniques. Notably, the BiOIO3 nano-antibacterial agent exhibits almost complete inactivation of 107 CFU/mL MRSA within 2 h under visible light irradiation. Furthermore, with increasing exposure duration to irradiation, gradual shrinkage and disintegration of the MRSA cell membrane were observed along with inhibition of the intracellular enzyme activity. Haemolysis tests were performed to prove the biological safety of the agent. Mechanistic investigations revealed that surface oxygen vacancies of BiOIO3 facilitated adsorption binding of water and oxygen within a local electric field promoting reactive oxygen species (ROS) generation. This leads to the rapid accumulation of ROS, which attacks the cell membrane causing significant damage, disrupting normal physiological metabolism of the bacteria, and ultimately killing MRSA. The present study is expected to provide a favourable solution for developing novel efficient and green nano-antibacterial agents through surface modifications.

Impact of damaged housing on the performance of field aged composite High Voltage Insulators

Composite High Voltage Insulators (HVIs) are lightweight, inexpensive, and offer superior pollution performance. Consequently, they have replaced ceramic HVIs in highly contaminating coastal and desert regions. However, they are prone to degradation in harsh environments. In this paper, we assess the performance of three identical field-aged 380 kV composite HVIs with a service life of twelve years near the western coastal region of the Kingdom of Saudi Arabia. The housing of all the HVIs showed widespread damage, including cracks on sheds and shanks, partially or fully broken sheds, and rusted end fittings. The changes in morphology and material composition were assessed through SEM and EDX. An electrical breakdown test in the presence of steam fog revealed lowered withstand strength. Electric field distribution, a key design criterion for an HVI, was studied using the Finite Element Model (FEM) of the insulator bearing physical defects. The results reveal localized electric field intensification caused by all types of defects, notably smaller and narrower ones. Our findings indicate that while physical defects in HVIs can cause localized electric field intensification, they are not a significant concern unless accompanied by severe hydrophobicity loss, compromised electrical withstand levels, or extensive erosion exposing the fiberglass rod and jeopardizing mechanical stability.

Development and Optimization of Micro‐Nanotopographical Platforms for Surface Enhanced Raman Scattering Biomolecular Detection

AbstractTopologically designed micro‐ and nanostructured surface‐enhanced Raman scattering (SERS) substrates propel the advancements of innovative applications, including environmental and forensic point‐of‐care miniaturised devices via enhancing the localised electric fields for accurate analyte sensing. Herein, a method for designing, optimising and fabricating fine‐tuneable concentric hexagonal, triangular and rectangular SERS‐active micronano‐substrates is developed, with each unit yielding significant enhancement. Numerical simulations of the 3D near‐field electric field guided the optimal design process. While the coaxial SERS substrates consistently outperformed their solid counterparts, the hexagonal micro‐nano topologies exhibited ×21 higher signal than coaxial square arrays and a 12‐15‐fold increase over the triangle structures. Alternation of the topological designs from square to triangle lattice yielded more uniform plasmonic modes propagating along the 60°‐directions with various resonance modes playing key roles in light reflectance. This enables the engineering of platforms with tailor‐enhanced signals by changing the arrangement of micro‐nano patterned coaxial arrays. The fabricated SERS substrates are validated by detecting traumatic brain injury biomarkers, effectively yielding the characteristic fingerprint spectra of each neuro‐molecule. The straightforward development of sub‐micrometre tuneable SERS‐active architectures enables anelegant route for high‐throughput biochemical sensing, laying a platform for amplified bimolecular detection of disease biomarkers and integration in bioanalytical systems.

Multi-receptor skin with highly sensitive tele-perception somatosensory.

The limitations and complexity of traditional noncontact sensors in terms of sensitivity and threshold settings pose great challenges to extend the traditional five human senses. Here, we propose tele-perception to enhance human perception and cognition beyond these conventional noncontact sensors. Our bionic multi-receptor skin employs structured doping of inorganic nanoparticles to enhance the local electric field, coupled with advanced deep learning algorithms, achieving a ΔV/Δd sensitivity of 14.2, surpassing benchmarks. This enables precise remote control of surveillance systems and robotic manipulators. Our long short-term memory-based adaptive pulse identification achieves 99.56% accuracy in material identification with accelerated processing speeds. In addition, we demonstrate the feasibility of using a two-dimensional (2D) sensor matrix to integrate real object scan data into a convolutional neural network to accurately discriminate the shape and material of 3D objects. This promises transformative advances in human-computer interaction and neuromorphic computing.

Dual LSPR and CT synergy: 3D urchin-like Au@W18O49 enables highly sensitive in-situ SERS detection of dissolved furfural in insulating oils

Assessing the levels of furfural in insulating oils is a crucial technical method for evaluating the degree of aging and mechanical deterioration of oil-paper insulation. The surface-enhanced Raman spectroscopy (SERS) technique provides an effective method for enhancing the sensitivity of in-situ detection of furfural. In this study, a homogeneous three-dimensional (3D) urchin-like Au@W18O49 heterostructure was synthesized as a SERS substrate using a straightforward hydrothermal method. The origin of the superior Raman enhancement properties of the 3D urchin-like heterostructures formed by the noble metal Au and the plasmonic semiconductor W18O49, which is rich in oxygen vacancies, is analyzed experimentally in conjunction with density-functional theory (DFT) calculations. The Raman enhancement is further amplified by the remarkable dual localized surface plasmon resonance (LSPR) effect, which generates a strong local electric field and creates numerous "hot spots," in addition to the interfacial charge transport (CT). The synergistic effect of these factors results in the 3D urchin-like Au@W18O49 heterostructure exhibiting exceptionally high SERS activity. Testing the rhodamine 6G (R6G) probe resulted in a Raman enhancement factor of 3.41 × 10−8, and the substrate demonstrated excellent homogeneity and stability. Furthermore, the substrate was effectively utilized to achieve highly sensitive in-situ surface-enhanced Raman scattering (SERS) detection of dissolved furfural in complex plant insulating oils. The development of the 3D urchin-like Au@W18O49 heterostructure and the exploration of its enhancement mechanism provide theoretical insights for the advancement of high-performance SERS substrates.

Flexible Artificial Ag NPs:a-SiC0.11:H Synapse on Al Foil with High Uniformity and On/Off Ratio for Neuromorphic Computing.

A neuromorphic computing network based on SiCx memristor paves the way for a next-generation brain-like chip in the AI era. Up to date, the SiCx-based memristor devices are faced with the challenge of obtaining flexibility and uniformity, which can push forward the application of memristors in flexible electronics. For the first time, we report that a flexible artificial synaptic device based on a Ag NPs:a-SiC0.11:H memristor can be constructed by utilizing aluminum foil as the substrate. The device exhibits stable bipolar resistive switching characteristic even after bending 1000 times, displaying excellent flexibility and uniformity. Furthermore, an on/off ratio of approximately 107 can be obtained. It is found that the incorporation of silver nanoparticles significantly enhances the device's set and reset voltage uniformity by 76.2% and 69.7%, respectively, which is attributed to the contribution of the Ag nanoparticles. The local electric field of Ag nanoparticles can direct the formation and rupture of conductive filaments. The fitting results of I-V curves show that the carrier transport mechanism agrees with Poole-Frenkel (P-F) model in the high-resistance state, while the carrier transport follows Ohm's law in the low-resistance state. Based on the multilevel storage characteristics of the Al/Ag NPs:a-SiC0.11:H/Al foil resistive switching device, we successfully observed the biological synaptic characteristics, including the long-term potentiation (LTP), long-term depression (LTD), and spike-timing-dependent plasticity (STDP). The flexible artificial Ag NPs:a-SiC0.11:H/Al foil synapse possesses excellent conductance modulation capabilities and visual learning function, demonstrating the promise of application in flexible electronics technology for high-efficiency neuromorphic computing in the AI period.

3D self-supporting core-shell silicon-carbon nanofibers-based host enables confined Li+ deposition for lithium metal battery

Three-dimensional (3D) porous hosts play pivotal roles in realizing dendrite-free lithium metal anodes (LMAs) owing to their high specific area. However, uneven local electric field and lack of lithiophilic sites on the reactive interface cause nonuniform lithium ion (Li+) deposition, leading to Li dendrite growth and parasitic reactions. These issues will inevitably incur short cycling life and severe safety hazards of lithium metal batteries. Herein, a 3D self-supporting host composed of hollow carbon nanofibers incorporated with silicon (Si) nanoparticles inside (Si-HCF) is constructed as Li metal host by a scalable coaxial electrospinning technique. During the first cycle, the Si nanoparticles is alloyed with Li+ to form lithiophilic Li-Si alloy, contributing to deliver a low nucleation overpotential and homogeneous surface potential confirmed by Kelvin probe force microscopy, finally guiding Li+ flux homogeneously throughout the fibrous mat. As expected, the Li metal can percolate through Si-HCF host reversibly without uncontrollable Li dendrites and the Si-HCF exhibits a stable cycle life of Li plating/stripping over 1400 h. Additionally, the full cell combined with LiFePO4 cathodes presents steady cycling over 400 cycles with a high average coulombic efficiency of 99.4 %. This work provides new insights for the synthesis of 3D hosts with controllable nucleation sites to homogenize Li+ deposition in LMAs.

Photo-Thermal Conversion and Raman Sensing Properties of Three-Dimensional Gold Nanostructure.

Three-dimensional plasma nanostructures with high light-thermal conversion efficiency show the prospect of industrialization in various fields and have become a research hotspot in areas of light-heat utilization, solar energy capture, and so on. In this paper, a simple chemical synthesis method is proposed to prepare gold nanoparticles, and the electrophoretic deposition method is used to assemble large-area three-dimensional gold nanostructures (3D-GNSs). The light-thermal water evaporation monitoring and surface-enhanced Raman scattering (SERS) measurements of 3D-GNSs were performed via theoretical simulation and experiments. We reveal the physical processes of local electric field optical enhancement and the light-thermal conversion of 3D-GNSs. The results show that with the help of the efficient optical trapping and super-hydrophilic surface properties of 3D-GNSs, they have a significant effect in accelerating water evaporation, which was increased by nearly eight times. At the same time, the three-dimensional SERS substrates based on gold nanosphere particles (GNSPs) and gold nanostar particles (GNSTs) had limited sensitivities of 10-10 M and 10-12 M to R6G molecules, respectively. Therefore, 3D-GNSs show strong competitiveness in the fields of solar-energy-induced water purification and the Raman trace detection of organic molecules.

Boosting pH-universal electrosynthesis of hydrogen peroxide by regulating three-phase interface of carbon gas penetration electrode

Electrochemical oxygen reduction is a sustainable method for onsite H2O2 production. However, pH-universal H2O2 electrosynthesis still suffered from low kinetics and efficiency. Here carbon nanotube hollow fiber (CNT-HF) with porous fiber wall is designed to enhance H2O2 electrosynthesis via tailoring the three-phase interface. The CNT-HF gas penetration electrode with enhanced local electric field is favorable for boosting oxygen mass transfer and regulating catalyst-electrolyte interfacial protons, resulting in significantly enhanced H2O2 production performance in comparison with CNT planar gas diffusion electrode under pH-universal media. Its H2O2 production efficiency is 98.1% at pH 13. Meanwhile, H2O2 production efficiency of 96.1% and high H2O2 concentration of 46.4 g L-1 are achieved at pH 1 with 20 mM K+. Experimental and simulation results reveal the boosted H2O2 electrosynthesis on CNT-HF is mainly contributed from its significantly reduced diffusion layer thickness, enhanced local electric field and interfacial proton regulation by K+ enriched at electrode surface.

Permittivity enhancement of Al2O3/ZrO2 dielectrics with the incorporation of Pt nanoparticles

Al2O3/ZrO2 (A/Z) layers with embedded Pt nanoparticles (Pt-nps) at the interface of A/Z have been used to create a dielectric film with an enhanced permittivity. The Pt-nps and dielectrics are both grown by the atomic layer deposition process, which is complementary metal–oxide–semiconductor compatible. In order to control the thickness ratio of Pt-nps in the overall dielectrics more easily, the thickness of the ZrO2 layer is changed from 12 to 30 nm with a fixed thickness of 12 nm for Al2O3 and constant growth cycles of 70 for Pt-nps. The results show that the introduction of Pt-nps is beneficial to the enhancement of the dielectric permittivity. As the thickness of ZrO2 is 30 nm, the capacitance density increases from 2.5 to 5.1 fF/μm2 with the addition of Pt-nps, i.e., a doubling of the capacitance density achieved. Additionally, the leakage current at 2 V increases from 1.1 × 10−8 to 1.5 × 10−7 A/cm2. Furthermore, the dielectric breakdown field decreases from 5.4 to 2.7 MV/cm. The electric field distribution simulation and charging–discharging test imply that interfacial polarization is built at the interface of Pt-nps and the dielectric films, which contributes to the dielectric permittivity enhancement, and local electric field increasing in the affinity of Pt-nps gives rise to the deterioration of the leakage current and breakdown electric field.

Comparative study on the impact of different E-J relations on the performance of resistive superconducting fault current limiters under high and low impedance faults in cryo-electric aircraft

To achieve the goal of zero emission in aviation, it is critical to advance electric aircraft technologies, especially in short to medium range flights. Superconducting fault current limiters (SFCLs) have shown promising potential in electric aircraft system as a protection solution to limit the peak of fault current. Many research works focused on the SFCL performance under low impedance faults, where the fault current is much higher than the nominal current and the SFCL will transit to normal (metal) state quickly. However, there are limited reports on investigating the SFCL reacting to high impedance faults for electric aircraft system, where the SFCL does not abruptly transit to normal state. In this paper, we built an electric-thermal coupled model in MATLAB which simulates the behaviour of a resistive type SFCL both under low and high impedance faults. We investigated three mathematical relations of local electric field E and local current density J representing the transition from superconducting state to normal state, both under high and low impedance fault. The three mathematical relations are classic E-J power-law, modified E-J power-law and two- stage E-J power law. The electric-thermal model of the SFCL incorporating all these three types of mathematical relations, respectively, have been used to calculate the SFCL responses under high and low impedance faults, and compared with each other, as well as testing results. The limited fault current, voltage drop, resistance and temperature variations in the SFCL are observed and analysed. The results have shown that the proposed SFCL model is able to accurately characterise a resistive type SFCL under both high impedance and low impedance fault.

Supported Au single atoms and nanoparticles on MoS2 for highly selective CO2-to-CH3COOH photoreduction

Effectively controlling the selective conversion of CO2 photoreduction to C2 products presents a significant challenge. Here, we develop a heterojunction photocatalyst by controllably implanting Au nanoparticles and single atoms into unsaturated Mo atoms of edge-rich MoS2, denoted as Aun/Au1-CMS. Photoreduction of CO2 results in the production of CH3COOH with a selectivity of 86.4%, which represents a 6.4-fold increase compared to samples lacking single atoms, and the overall selectivity for C2 products is 95.1%. Furthermore, the yield of CH3COOH is 22.4 times higher compared to samples containing single atoms and without nanoparticles. Optical experiments demonstrate that the single atoms domains can effectively capture photoexcited electrons by the Au nanoparticles, or the local electric field generated by the nanoparticles promotes the transfer of photogenerated electrons in MoS2 to Au single atoms, prolonging the relaxation time of photogenerated electrons. Mechanistic investigations reveal that the orbital coupling of Au5d and Mo4d strengthens the oxygen affinity of Mo and carbon affinity of Au. The hybridized orbitals reduce energy splitting levels of CO molecular orbitals, aiding C–C coupling. Moreover, the Mo−Au dual-site stabilize the crucial oxygen-associated intermediate *CH2CO, thereby enhancing the selectivity towards CH3COOH. The cross-scale heterojunctions provide an effective strategy to simultaneously address the kinetical and thermodynamical limitations of CO2-to-CH3COOH conversion.

The formation of an radial edge electric field due to finite ion orbit width effects is the possible root cause of the H-mode edge

Abstract Full orbit-following simulations of thermal ions show that finite ion-orbit width effects create charge separation near the last closed flux surface (LCFS) which generates a localized radial electric field. Experimentally, edge electric fields are observed in H-mode plasmas and they are necessary for the edge turbulence suppression via the E × B flow shear mechanism. Confined trapped (and to a lesser extent co-passing) ions near the plasma edge form a positive charge distribution outside the LCFS, while thermal electrons are tied more tightly to field lines owing to their small mass and are poorly confined outside the LCFS, hence charge neutrality is violated outside the LCFS. A large number of reported observations from spherical and conventional tokamaks support the results from the simulations although the simulations were not performed fully self consistently. The results suggest ways to lower the H-mode power threshold and optimize the H-mode plasma edge.

Enantioselective Molecular Detection by Surface Enhanced Raman Scattering at Chiral Gold Helicoids on Grating Surfaces.

Distinct advantages of surface enhanced Raman scattering (SERS) in molecular detection can benefit the enantioselective discrimination of specific molecular configurations. However, many of the recent methods still lack versatility and require customized anchors to chemically interact with the studied analyte. In this work, we propose the utilization of helicoid-shaped chiral gold nanoparticles arranged in an ordered array on a gold grating surface for enantioselective SERS recognition. This arrangement ensured a homogeneous distribution of chiral plasmonic hot spots and facilitated the enhancement of the SERS response of targeted analytes through plasmon coupling between gold helicoid multimers (formed in the grating valleys) and adjacent regions of the gold grating. Naproxen enantiomers (R(+) and S(-)) were employed as model compounds, revealing a clear dependence of their SERS response on the chirality of the gold helicoids. Additionally, propranolol and penicillamine enantiomers were used to validate the universality of the proposed approach. Finally, numerical simulations were conducted to elucidate the roles of intensified local electric field and optical helicity density on the SERS signal intensity and on the chirality of the nanoparticles and enantiomers. Unlike previously reported methods, our approach relies on the excitation of a chiral plasmonic near-field and its interaction with the chiral environment of analyte molecules, obviating the need for the enantioselective entrapment of targeted molecules. Moreover, our method is not limited to specific analyte classes and can be applied to a broad range of chiral molecules.

Miniaturized quasi-BICs based on a two-dimensional heterostructure to realize a low-threshold nanolaser.

Bound states in the continuum (BICs) have been demonstrated as an effective mechanism to achieve high quality (Q)-factor cavities for nanolasers. However, the development of a compact BIC laser with a low threshold has remained elusive. Here, we numerically report lasing action from symmetry-protected BICs in a two-dimensional heterostructure, which consists of compound gratings with finite cells surrounded by orthogonal distributed Bragg reflectors (DBRs). The compound grating is used to excite quasi-BIC resonance with a high Q-factor, and DBRs enable light confinement and localized electric fields to enhance light-matter interaction. The nanolaser with a threshold of 16.8 µJ/cm2 is achieved within a footprint as small as 3.35 × 3.35 µm2. By changing the phase adjusting gap or asymmetry degree, it is possible to control the lasing emission. This work reveals a new, to our knowledge, path toward compact BIC lasers with a simple scheme for applications that require a small footprint and low threshold.

Observation of Fast Low-Temperature Oxygen Ion Conduction in CeO2/β"-Al2O3 Heterostructure.

Semiconductor ion fuel cells (SIFCs) have demonstrated impressive ionic conductivity and efficient power generation at temperatures below 600°C. However, the lack of understanding of the ionic conduction mechanisms associated with composite electrolytes has impeded the advancement of SIFCs toward lower operating temperatures. In this study, a CeO2/β″-Al2O3 heterostructure electrolyte is introduced, incorporating β″-Al2O3 and leveraging the local electric field (LEF) as well as the manipulation of the melting point temperature of carbonate/hydroxide (C/H) by Na+ and Mg2+ from β″-Al2O3. This design successfully maintains swift interfacial conduction of oxygen ions at 350°C. Consequently, the fuel cell device achieved an exceptional ionic conductivity of 0.019S/cm and a power output of 85.9mW/cm2 at 350°C. The system attained a peak power density of 1W/cm2 with an ultra-high ionic conductivity of 0.197S/cm at 550°C. The results indicate that through engineering the LEF and incorporating the lower melting point C/H, there approach effectively observed oxygen ion transport at low temperatures (350°C), effectively overcoming the issue of cell failure at temperatures below 419°C. This study presents a promising methodology for further developing high-performance semiconductor ion fuel cells in the low temperature range of 300-600°C.

Regulating thermal management by a CsPbClBr2/Ag hybrid microcavity for stable room temperature blue lasing with low threshold

Realization of long-term stable lasing from all-inorganic perovskite supercrystals is highly desirable for practical applications in optoelectronic devices. However, lasing from perovskite supercrystals excited by continuous wave laser light remains a challenge due to the photoluminescence degradation induced by thermal accumulation. Here, we report highly stable lasing with low threshold fom a CsPbClBr2 supercrystal placed on a thin Ag film, which form a CsPbClBr2/Ag microcavity, by managing the thermal distribution inside the CsPbClBr2 supercrystal. Combined numerical simulations and lifetime measurements, the localized electric field in such a hybrid microcavity leads to a spatially localized temperature distribution, which plays a crucial role in suppressing the thermal accumulation on the surface and in eliminating non-radiative recombination defects. The effective thermal management in the hybrid microcavity renders highly stable lasing with low threshold under the irradiation of continuouw wave laser light. Our findings provide a feasible and universal approach to the development of long-term stable perovskite laser.

Controlling action potentials with magnetoelectric nanoparticles

Non-invasive or minutely invasive and wireless brain stimulation that can target any region of the brain is an open problem in engineering and neuroscience with serious implications for the treatment of numerous neurological diseases. Despite significant recent progress in advancing new methods of neuromodulation, none has successfully replicated the efficacy of traditional wired stimulation and improved on its downsides without introducing new complications. Due to the capability to convert magnetic fields into local electric fields, MagnetoElectric NanoParticle (MENP) neuromodulation is a recently proposed framework based on new materials that can locally sensitize neurons to specific, low-strength alternating current (AC) magnetic fields (50Hz 1.7 kOe field). However, the current research into this neuromodulation concept is at a very early stage, and the theoretically feasible game-changing advantages remain to be proven experimentally. To break this stalemate phase, this study leveraged understanding of the non-linear properties of MENPs and the nanoparticles' field interaction with the cellular microenvironment. Particularly, the applied magnetic field's strength and frequency were tailored to the M − H hysteresis loop of the nanoparticles. Furthermore, rectangular prisms instead of the more traditional “spherical” nanoparticle shapes were used to: (i) maximize the magnetoelectric effect and (ii) improve the nanoparticle-cell-membrane surface interface. Neuromodulation performance was evaluated in a series of exploratory in vitro experiments on 2446 rat hippocampus neurons. Linear mixed effect models were used to ensure the independence of samples by accounting for fixed adjacency effects in synchronized firing. Neural activity was measured over repeated 4-min segments, containing 90 s of baseline measurements, 90 s of stimulation measurements, and 60 s of post stimulation measurements. 87.5 % of stimulation attempts produced statistically significant (P < 0.05) changes in neural activity, with 58.3 % producing large changes (P < 0.01). In negative controls using either zero or 1.7 kOe-strength field without nanoparticles, no experiments produced significant changes in neural activity (P > 0.05 and P > 0.15 respectively). Furthermore, an exploratory analysis of a direct current (DC) magnetic field indicated that the DC field could be used with MENPs to inhibit neuron activity (P < 0.01). These experiments demonstrated the potential for magnetoelectric neuromodulation to offer a near one-to-one functionality match with conventional electrode stimulation without requiring surgical intervention or genetic modification to achieve success, instead relying on physical properties of these nanoparticles as “On/Off” control mechanisms. One-sentence summaryThis in vitro neural cell culture study explores how to exploit the non-linear and anisotropic properties of magnetoelectric nanoparticles for wireless neuromodulation, the importance of magnetic field strength and frequency matching for optimization, and demonstrates, for the first time, that magnetoelectric neuromodulation can inhibit neural responses.

Anisotropic excitonic magnetism from discrete C4 symmetry in CeRhIn5

Anisotropy in strongly correlated materials is a central parameter in determining the electronic ground state and is tuned through the local crystalline electric field. This is notably the case in the CeCoxRh1−xIn5 system where the ground-state wave function can provide the basis for antiferromagnetism and/or unconventional superconductivity. We develop a methodology to understand the local magnetic anisotropy and experimentally investigate with neutron spectroscopy applied to antiferromagnetic (TN=3.8K) CeRhIn5, which is isostructural to d-wave superconducting (Tc=2.3K) CeCoIn5. Through diagonalizing the local crystal field Hamiltonian with discrete tetragonal C4 point group symmetry and coupling these states with the random phase approximation, we find two distinct modes polarized along the crystallographic c and a−b planes, agreeing with experiment. The anisotropy and bandwidth, underlying the energy scale of these modes, are tuneable with a magnetic field which we use experimentally to separate in energy single and multiparticle excitations thereby demonstrating the instability of excitations polarized within the crystallographic a−b plane in CeRhIn5. We compare this approach to a Seff=12 parametrizations and argue for the need to extend conventional SU(2) theories of magnetic excitations to utilize the multilevel nature of the underlying crystal-field basis states constrained by the local point-group C4 symmetry. Published by the American Physical Society 2024

2D Carbonaceous Materials for Molecular Transport and Functional Interfaces: Simulations and Insights.

ConspectusCarbon-based two-dimensional (2D) functional materials exhibit potential across a wide spectrum of applications from chemical separations to catalysis and energy storage and conversion. In this Account, we focus on recent advances in the manipulation of 2D carbonaceous materials and their composites through computational design and simulations to address how the precise control over material structure at the atomic level correlates with enhanced functional properties such as gas permeation, selectivity, membrane transport, and charge storage. We highlight several key concepts in the computational design and tuning of 2D structures, such as controlled stacking, ion gating, interlayer pillaring, and heterostructure charge transfer.The process of creating and adjusting pores within graphene sheets is vital for effective molecular separation. Simulations show the power of controlling the offset distance between layers of porous graphene in precisely regulating the pore size to enhance gas separation and entropic selectivity. This strategy of controlled stacking extends beyond graphene to include covalent organic frameworks (COFs) such as covalent triazine frameworks (CTFs). Experimental assembly of the layers has been achieved through electrostatic interactions, thermal transformation, and control of side chain interactions.Graphene can interface with ionic liquids in various forms to enhance its functionality. A computational proof-of-concept showcases an ion-gating concept in which the interaction of anions with the pores in graphene allows the anions to dynamically gate the pores for selective gas transport. Realization of the concept has been achieved in both porous graphene and carbon molecular sieve membranes. Ionic liquids can also intercalate between graphene layers to form interlayer pillaring structures, opening the slit space. Grand canonical Monte Carlo simulations show that these structures can be used for efficient gas capture and separation. Experiments have demonstrated that the interlayer space can be tuned by the density of the pillars and that, when fully filled with ionic liquids and forming a confined interface structure, the graphene oxide membrane achieves much higher selectivity for gas separations. Moreover, graphene can interface with other 2D materials to form heterostructures where interfacial charge transfers take place and impact the function. Both ion transport and charge storage are influenced by both the local electric field and chemical interactions.Fullerene can be used as a building block and covalently linked together to construct a new type of 2D carbon material beyond a one-atom-thin layer that also has long-range-ordered subnanometer pores. The interstitial sites among fullerenes form funnel-shaped pores of 2.0-3.3 Å depending on the crystalline phase. The quasi-tetragonal phases are shown by molecular dynamics simulations to be efficient for H2 separation. In addition, defects such as fullerene vacancies can be introduced to create larger pores for the separation of organic solvents.In conclusion, the key to imputing functions to 2D carbonaceous materials is to create new interactions and interfaces and to go beyond a single-atom layer. First-principles and molecular simulations can further guide the discovery of new 2D carbonaceous materials and interfaces and provide atomistic insights into their functions.