Surface Dipole Research Articles

Synthesis of N/O Atoms Co-Doped Biochar with 3D Porous Structure for Effective Electromagnetic Wave Absorption.

Developing biochar with large specific surface area (SSA), heteroatom doping, and porous structure is attracting substantial attention to absorb electromagnetic wave (EMW) in recent. Herein, a novel method of ethanol and KOH co-treatment is used to produce the biomass carbon deriving from pitaya peels. The obtained carbon possesses the high SSA of 1580 m2/g, successful N/O atoms co-doping, and massive pores with different size. The results of EMW absorption measurement show that the prepared biochar could achieve over 99 % absorpition to EMW, which the highest reflection loss is of ca. -45.25 dB at 7.54 GHz with an effective absorption bandwidth (EAB) of ca. 4.87 GHz. The execellent microwave absorption property is caused by the surface defects, dipole and interface polarizations of the synthesized biochar owning unique microstructure and N/O atoms co-doping. Hence, this avenue provides a new reference for fabricating low-cost and eco-friendly biochar as a microwave absorber.

Enhancing Extraction and Suppressing Cooling of Hot Electrons in Lead Halide Perovskites by Dipolar Surface Passivation.

Slowing hot carrier (HC) cooling and improving HC extraction are considered two pivotal factors for enhancing power conversion efficiency in emerging HC photovoltaic applications of perovskites and other materials. Employing ab initio quantum dynamics simulations, we demonstrate the simultaneous slow cooling and efficient extraction of hot electrons at the C60/CsPbI3 interface through dipolar surface passivation with phenethylammonium and 4-fluorophenethylammonium ligands. The passivation effectively suppresses I-Pb lattice vibrations, weakens the hot electron-phonon interaction in CsPbI3, and thus slows down the HC cooling. At the same time, the dipolar surface passivation elevates the LUMO + 1 state in C60 and reduces the energy gap for HC extraction. Concurrently, higher-frequency vibrations of the dipolar layer enhance the coupling between C60 and CsPbI3, promoting efficient HC extraction further. These phenomena are intensified with increased polarity of the dipolar layer. Furthermore, we find that dipolar passivation has the opposite influence on cold electron collection at the band edge, underscoring the fact that the observed improvement in photovoltaic performance stems preferentially from the effective utilization of HCs rather than cold electrons. The work provides a new strategy for achieving high-performance HC perovskite solar cells.

Molecularly Modified Electrodes for Efficient Triboelectric Nanogenerators

The integration of organic molecules into monolayers on triboelectric layers and electrodes has significantly improved the performance of triboelectric nanogenerators (TENGs) in recent years. By modifying surfaces at the molecular level, one can enhance durability, power density, and cost‐efficiency, leading to flexible, lightweight, and more efficient devices. A simple chemistry of organic monolayer formation allows a precise control over orientation, coverage, consistency, and functionality. These monolayers boost surface charge density and output voltage while influencing surface polarization and dipole interactions. This review focuses on recent advances in chemical modification of electrodes for controlling surface charge density and altering surface dipoles, emphasizing the significance of organic monolayers. A new concept of Schottky‐based TENGs is also introduced that explores chemically modified sliding surfaces. Furthermore, the importance of flexoelectricity and its contribution to triboelectricity is discussed. By addressing current challenges and outlining future directions, this review underscores the crucial role of surface chemistry in advancing TENGs.

Research on defect image inversion method based on multiple lift-off values magnetic memory signals

Metal magnetic memory (MMM) technique can detect macroscopic defects and stress concentration zones of ferromagnets, and it can identify the approximate positions of these flaws, while a little further information about defects characteristics can be provided. To promote study in this area, defects were modeled as located magnetic dipoles whose strength and locations should be determined, and the technique of truncated generalized inverse and reduced space inversion were used to image the dipole strength. Through the simulation experiment, we found that the inversion image quality was influenced by the lift-off value. When the magnetic field data for inversion was measured with a small lift-off value, the inner dipoles contributions were easily buried and the inversion image can only shown the surface dipole well. In contrast, if the magnetic field data was measured with a greater lift-off value, it was possible to inverse the deep dipoles while the image was somewhat out of focus. To overcome this limitation, we composed the magnetic field data measured under different lift-off values together for inversion. We used the same model to test this approach and applied it on real crack defects magnetic field data. It demonstrates that the new inversion approach shows better accuracy than the single lift-off value and it was possible to infer the location and size of defect by the evaluation of preset dipoles.

Alkali Metal‐Doped Fullerenes as Hydrogen Storage—A Quantum Chemical Investigation

AbstractThe quest for alternative energy sources has been spurred by the drawbacks and environmental risks of fossil fuels, with hydrogen emerging as a viable contender. But finding materials that can effectively store hydrogen with the best adsorption energy is a major obstacle to building a hydrogen‐based economy. As a result, a significant amount of research has been conducted worldwide to examine fullerene's (C60) potential for hydrogen adsorption. The results of extensive DFT calculations are presented here, pertaining to the adsorption of hydrogen molecules onto fullerenes doped with alkali metals, namely Rubidium (Rb), Ceasium (Cs), and Fransium (Fr). The study analyzes a number of parameters, such as global properties, electronic, optical, and surface annihilation energy. These analyses are performed using the Gaussian 09 simulation package with the 6–31G/B3LYP level of theory DFT methodology. The findings show that an exothermic process is involved in the adsorption of hydrogen onto fullerene doped alkali elements, as evidenced by the negative adsorption energy. The attractive interactions between the polarized dipole of hydrogen molecules and the surface dipole of doped fullerenes can be the cause of this exothermicity. These results imply that fullerenes decorated with alkali metals are promising as likely hydrogen storage media.

Surface-iodine-grafting-induced local electric field drives charge separation of CdBiO2Br for excellent photocatalytic antibiotic degradation

Photocatalytic technology has demonstrated immense potential in environmental purification, particularly in the degradation of antibiotics that pose serious health risks. However, the rapid recombination of photogenerated charge carriers and the limited light absorption capacity, which are major obstacles, severely hinder the photocatalytic degradation activity. Herein, the surface halogen-grafting strategy is introduced to address these issues in a Sillén-related layer-structured photocatalyst, CdBiO2Br (CBOB). The iodine-grafted CBOB nanosheets deliver a superb tetracycline hydrochloride photodegradation efficiency of 72.36 % within one hour, which is 2.44 times higher than that of the original CBOB. Additionally, they demonstrated a broad-spectrum degradation capability against various antibiotics and phenolic pollutants, such as ciprofloxacin, chloramphenicol hydrochloride, bisphenol A, highlighting their practical and industrial value. Mechanistic studies indicated that the high electronegativity of iodine could induce a surface dipole polarization effect to form localized electric fields that efficiently drive the separation of photogenerated electrons and holes, and, on the other hand, improve light absorption, which profoundly boosts the photocatalytic degradation process, as corroborated by experimental and theoretical results collectively. This work provides a foundation for understanding the highly electronegative halogen grafting-induced surface local electric field and offers new insights for the future design of high-performance environmental purification materials.

Advanced pyro-/piezoelectric catalytic disinfection of water via porous spontaneously polarized ceramic with strong local electric field induced by micro-nano bubbles

In-situ electroporation disinfection technology inactivates microorganisms by local electric field penetrating antioxidant membranes without producing by-products, which reduces the consumption of oxidants. However, this individual technology exhibits weak disinfection performance for high water fluxes. Herein, a disinfection system based on the synergy of porous spontaneously polarized ceramic (PSPC) and micro-nano bubbles (MNB) (PSPC/MNB disinfection system, PMDS) was constructed for efficient disinfection of drinking water. Pyro-/piezoelectric effects of PSPC induced by MNB collapse constructed a 1.92 × 108 V/m of local electric field (simulated by COMSOL Multiphysics) and generated reactive oxygen species (ROS; •OH, 1O2, •O2−, and H2O2), resulting in electroporation damage on microorganisms and subsequent fatal oxidation of the intracellular contents by ROS. PMDS completely inactivated 107 CFU/mL of E. coli within 45 min, about 10 times faster than the MNB process, which is attributed to that the abundant porous and rough surface in PSPC increased the specific surface area and dipoles for pyro-/piezoelectric catalysis. Moreover, MNB collapse enriched •OH and induced pyro-/piezoelectric effects of PSPC through local temperature and pressure gradients. Synergistic interaction of PSPC/MNB collected additional thermal and mechanical energies besides the collapse of MNB, and the pyro-/piezoelectricity-induced in-situ electroporation–ROS deep oxidation avoided oxidant consumption and hazardous by-products. PMDS presented favorable disinfection efficiency in actual drinking water source, expected to be a practical system for eliminating microbial hazards in drinking water.

Coordination Desymmetrization of Copper Single-Atom Catalyst for Efficient Nitrate Reduction.

Coordination engineering strategy for optimizing the catalytic performance of single-atom catalysts (SACs) has been rapidly developed over the last decade. However, previous reports on copper SACs for nitrate reduction reactions (NO3RR) have mostly focused on symmetric coordination configurations such as Cu-N4 and Cu-N3. In addition, the mechanism in terms of the regulation of coordination environment and catalytic properties of SACs has not been well demonstrated. Herein, we disrupted the local symmetric structure of copper atoms by introducing unsaturated heteroatomic coordination of Cu-O and Cu-N to achieve the coordination desymmetrization of Cu-N1O2 SACs. The Cu-N1O2 SACs exhibit an efficient nitrate-to-ammonia conversion with a high FE of ~96.5 % and a yield rate of 3120 μg NH3 h-1 cm-2 at -0.60 V vs RHE. As indicated by in situ Raman spectra, the catalysts facilitate the accumulation of NO3 - and the selective adsorption of *NO2, which were further confirmed by the theoretical study of surface dipole moment and orbital hybridization. Our work illustrated the correlation between the coordination desymmetrization and the catalytic performance of copper SACs for NO3RR.

Localized estimation of event-related neural source activity from simultaneous MEG-EEG with a recurrent neural network

Estimating intracranial current sources underlying the electromagnetic signals observed from extracranial sensors is a perennial challenge in non-invasive neuroimaging. Established solutions to this inverse problem treat time samples independently without considering the temporal dynamics of event-related brain processes.This paper describes current source estimation from simultaneously recorded magneto- and electro-encephalography (MEEG) using a recurrent neural network (RNN) that learns sequential relationships from neural data. The RNN was trained in two phases: (1) pre-training and (2) transfer learning with L1 regularization applied to the source estimation layer. Performance of using scaled labels derived from MEEG, magnetoencephalography (MEG), or electroencephalography (EEG) were compared, as were results from volumetric source space with free dipole orientation and surface source space with fixed dipole orientation. Exact low-resolution electromagnetic tomography (eLORETA) and mixed-norm L1/L2 (MxNE) source estimation methods were also applied to these data for comparison with the RNN method.The RNN approach outperformed other methods in terms of output signal-to-noise ratio, correlation and mean-squared error metrics evaluated against reference event-related field (ERF) and event-related potential (ERP) waveforms. Using MEEG labels with fixed-orientation surface sources produced the most consistent estimates.To estimate sources of ERF and ERP waveforms, the RNN generates temporal dynamics within its internal computational units, driven by sequential structure in neural data used as training labels. It thus provides a data-driven model of computational transformations from psychophysiological events into corresponding event-related neural signals, which is unique among MEEG source reconstruction solutions.

Numerical and experimental study on the aerodynamic noise characteristics of 600-km/h high-speed maglev trains

Abstract High-speed maglev trains represent a new mode of transportation; however, their 600-km/h traveling speed causes serious aerodynamic noise problems, with very little research on the aerodynamic noise of such trains. To clarify the aerodynamic noise source and radiation characteristics of high-speed maglev trains, both large eddy simulations and wind tunnel experiments with a 1:8 scale three-train model were conducted to obtain the aerodynamic noise source spectrum and spatial distribution characteristics of the maglev train at different speeds; the contribution of the dipole noise source was also analyzed. The results revealed that the train shape has a significant impact on the frequency distribution of the far-field aerodynamic noise below 1 kHz, with the highest sound power concentrated on the train head, especially in the areas around the track joint and streamlined sections. The surface dipole sound source energy increases linearly with speed and is mainly distributed at the bottom of the train head and tail train body. A short-streamlined train exhibited the highest ratio, especially in the trailing edge area, up to 1.42×1011 dB. The far-field sound pressure level of the short-streamlined maglev train is significantly higher, with a maximum difference of about 10 dB(A). The distribution pattern of far-field sound pressure level is influenced by the train type, reflected in the tail train and wake area. Different frequency intervals have different relationships between the acoustic pressure level and frequency; long-streamlined models may enhance broadband features in the sound field distribution of high-speed maglev trains. These findings could be used to guide the aero-acoustic design of maglev trains with a designed speed of 600 km/h.

Achieving metal-like catalysis from semiconductors for on-surface synthesis

Free of posttransfer, on-surface synthesis (OSS) of single-atomic-layer nanostructures directly on semiconductors holds considerable potential for next-generation devices. However, due to the high diffusion barrier and abundant defects on semiconductor surfaces, extended and well-defined OSS on semiconductors has major difficulty. Furthermore, given semiconductors' limited thermal catalytic activity, initiating high-barrier reactions remains a significant challenge. Herein, using TiO2(011) as a prototype, we present an effective strategy for steering the molecule adsorption and reaction processes on semiconductors, delivering lengthy graphene nanoribbons with extendable widths. By introducing interstitial titanium (Tiint) and oxygen vacancies (Ov), we convert TiO2(011) from a passive supporting template into a metal-like catalytic platform. This regulation shifts electron density and surface dipoles, resulting in tunable catalytic activity together with varied molecule adsorption and diffusion. Cyclodehydrogenation, which is inefficient on pristine TiO2(011), is markedly improved on Tiint/Ov-doped TiO2. Even interribbon cyclodehydrogenation is achieved. The final product's dimensions, quality, and coverage are all controllable. Tiint doping outperforms Ov in producing regular and prolonged products, whereas excessive Tiint compromises molecule landing and coupling. This work demonstrates the crucial role of semiconductor substrates in OSS and advances OSS on semiconductors from an empirical trial-and-error methodology to a systematic and controllable paradigm.

Bilayer interface engineering through 2D/3D perovskite and surface dipole for inverted perovskite solar modules

The persistency of passivation and scalable uniformity are vital issues that limit the improvement of performance and stability of large-area perovskite solar modules (PSMs). Here, we design a bilayer interface engineering strategy that takes advantage of the stability and passivation ability of low-dimensional perovskite and the dipole layer. Introducing phenethylammonium iodide (PEAI) can form 2D/3D heterojunctions on the perovskite surface and effectively passivate defects of perovskite film. Interestingly, the upper piperazinium iodide (PI) layer can still form surface dipoles on the 2D/3D perovskite surface to optimize energy-level alignment. Moreover, the bilayer interface engineering enables large-area perovskite films with uniform surface morphology, lower trap-state density and stability against environmental stress factors. The final devices achieved a small-area PCE of 25.20% and a large-area (1 cm2) PCE of 23.96%. A perovskite mini-module (5 × 5 cm2 with an active area of 14.28 cm2) could also be fabricated to achieve a PCE of 23.19%, ranking it among the highest for inverted PSMs. Additionally, the device could retain over 93% of its initial efficiency after MPP tracking at 45 °C for 1280 hours. This study successfully demonstrates a bilayer interface engineering with respective functions, offering valuable insights for producing efficient and stable large-area PSCs.

Quantifying Hydrogen-Bonding Interactions in the Self-Assembly of Photoresponsive Azobenzene Amphiphiles at the Air-Water Interface.

Amphiphilic azobenzene molecules offer ample scope to design functional supramolecular systems in an aqueous medium that can be controlled by light. Despite their widespread applications in photopharmacology and optoelectronics, the self-assembly pathways and energy landscapes of these systems are not well understood. Here, we report combined molecular dynamics (MD) simulation and surface manometry studies on a specially designed alkylated, meta-substituted azobenzene derivative to quantify the hydrogen-bonding interactions in the self-assembled monolayers of its photoisomers. The z-density profile, radial distribution function, order parameters, and hydrogen bond analyzed using MD simulations corroborated the experimental observations of changes in surface pressure, dipole moment, and thickness of the monolayers. Even a small change in the number of hydrogen bonds in the molecule-molecule and molecule-water interactions causes significant changes in the monolayer properties. These results are fundamentally important for engineering photoresponsive molecules with tailored properties for applications in targeted drug delivery and other industrial applications.

Role of self-assembled molecules’ anchoring groups for surface defect passivation and dipole modulation in inverted perovskite solar cells

Abstract Inverted perovskite solar cells have gained prominence in industrial advancement due to their easy fabrication, low hysteresis effects, and high stability. Despite these advantages, their efficiency is currently limited by excessive defects and poor carrier transport at the perovskite–electrode interface, particularly at the buried interface between the perovskite and transparent conductive oxide (TCO). Recent efforts in the perovskite community have focused on designing novel self-assembled molecules (SAMs) to improve the quality of the buried interface. However, a notable gap remains in understanding the regulation of atomic-scale interfacial properties of SAMs between the perovskite and TCO interfaces. This understanding is crucial, particularly in terms of identifying chemically active anchoring groups. In this study, we used the star SAM ([2-(9H-carbazol-9-yl)ethyl] phosphonic acid) as the base structure to investigate the defect passivation effects of eight common anchoring groups at the perovskite–TCO interface. Our findings indicate that the phosphonic and boric acid groups exhibit notable advantages. These groups fulfill three key criteria: they provide the greatest potential for defect passivation, exhibit stable adsorption with defects, and exert significant regulatory effects on interface dipoles. Ionized anchoring groups exhibit enhanced passivation capabilities for defect energy levels due to their superior Lewis base properties, which effectively neutralize local charges near defects. Among various defect types, iodine vacancies are the easiest to passivate, whereas iodine-substituted lead defects are the most challenging to passivate. Our study provides comprehensive theoretical insights and inspiration for the design of anchoring groups in SAMs, contributing to the ongoing development of more efficient inverted perovskite solar cells.

Exploring Macroscopic Dipoles of Designed Cyclic Peptide Ordered Assemblies to Harvest Piezoelectric Properties

AbstractCrystalline materials exhibiting non‐centrosymmetry and possessing substantial surface dipole moments play a critical role in piezoelectricity. Designing biocompatible self‐assembled materials with these attributes is particularly challenging when compared to inorganic materials and ceramics. In this study, we elucidate the crystal conformations of novel cyclic peptides that exhibit self‐assembly into tubular structures characterized by unidirectional hydrogen bonding and piezoelectric properties. Unlike cyclic peptides derived from alternating L‐ and D‐amino acids, those derived from new δ‐amino acids demonstrate the formation of self‐assembled tubes with unidirectional hydrogen bonds. Further, the tightly packed tubular assemblies and higher macrodipole moments result in superior piezoelectric coefficients compared to peptides with lower macrodipole moments. Our findings underscore the potential for designing cyclic peptides with unidirectional hydrogen bonds, thereby paving the way for their application in design of biocompatible piezo‐ and ferroelectric materials.

Exploring Macroscopic Dipoles of Designed Cyclic Peptide Ordered Assemblies to Harvest Piezoelectric Properties.

Crystalline materials exhibiting non-centrosymmetry and possessing substantial surface dipole moments play a critical role in piezoelectricity. Designing biocompatible self-assembled materials with these attributes is particularly challenging when compared to inorganic materials and ceramics. In this study, we elucidate the crystal conformations of novel cyclic peptides that exhibit self-assembly into tubular structures characterized by unidirectional hydrogen bonding and piezoelectric properties. Unlike cyclic peptides derived from alternating L- and D-amino acids, those derived from new δ-amino acids demonstrate the formation of self-assembled tubes with unidirectional hydrogen bonds. Further, the tightly packed tubular assemblies and higher macrodipole moments result in superior piezoelectric coefficients compared to peptides with lower macrodipole moments. Our findings underscore the potential for designing cyclic peptides with unidirectional hydrogen bonds, thereby paving the way for their application in design of biocompatible piezo- and ferroelectric materials.

Dual-wavelength superscattering in plasmonic core-shell nanostructures for transparent structural color

Structural coloration generates some of the most vibrant colors in nature and has numerous applications. Inspired by the recently reported transparent displays relying on wavelength-selective scattering, we address the novel problem of transparent structural color, which requires nanoparticles to have a narrow-band and broad-angle scattering response. Although superscattering beyond the single-channel limit has important prospects for enhancing transparent displays, it has not yet been reported. Here, we propose a simple dielectric-gold core–shell nanoparticle capable of superscattering at blue (λ = 450 nm) and green (λ = 532 nm) wavelengths, along with a dipolar surface plasmon resonance (SPR) at the red wavelength (λ = 640 nm), making it suitable for full-color transparent displays. We demonstrate that the superscattering at λ = 450 nm arises from the overlap of the epsilon-near-zero (ENZ) dipolar and quadrupolar modes. Furthermore, the coupling of conventional quadrupolar and dipolar modes can also enhance the scattering efficiency at λ = 532 nm, breaking the single-channel limit. Lastly, we show that the optimized nanoparticles can confine the scattering light within the forward hemisphere at λ = 450 nm and 532 nm, due to the interaction of quadrupolar and dipolar modes. Additionally, they exhibit dipole far-field radiation characteristics at λ = 640 nm with a wide angular beamwidth > 60°. The simple structural nature and unique scattering properties of proposed dielectric-gold core–shell nanoparticles hold promise applications in full-color transparent displays, spectroscopy, and biomedical imaging.

Coordination Desymmetrization of Copper Single‐Atom Catalyst for Efficient Nitrate Reduction

AbstractCoordination engineering strategy for optimizing the catalytic performance of single‐atom catalysts (SACs) has been rapidly developed over the last decade. However, previous reports on copper SACs for nitrate reduction reactions (NO3RR) have mostly focused on symmetric coordination configurations such as Cu‐N4 and Cu‐N3. In addition, the mechanism in terms of the regulation of coordination environment and catalytic properties of SACs has not been well demonstrated. Herein, we disrupted the local symmetric structure of copper atoms by introducing unsaturated heteroatomic coordination of Cu−O and Cu−N to achieve the coordination desymmetrization of Cu‐N1O2 SACs. The Cu‐N1O2 SACs exhibit an efficient nitrate‐to‐ammonia conversion with a high FE of ~96.5 % and a yield rate of 3120 μg NH3 h−1 cm−2 at −0.60 V vs RHE. As indicated by in situ Raman spectra, the catalysts facilitate the accumulation of NO3− and the selective adsorption of *NO2, which were further confirmed by the theoretical study of surface dipole moment and orbital hybridization. Our work illustrated the correlation between the coordination desymmetrization and the catalytic performance of copper SACs for NO3RR.

Revealing the Properties of Electrically Driven Optical Antennas via Conductive Atomic Force Microscope.

Light emission from ultracompact electrically driven optical antennas (EDOAs) has garnered significant attention due to its terahertz modulation bandwidth. Typically, the EDOAs are fixed and nonadjustable once fabricated, thus hindering the attempts to investigate the influence of structural geometry on light emission properties. Here, we propose and demonstrate that the EDOAs can be constructed by carefully manipulating the gold-coated tips of atomic force microscopy operated in conductive mode into contact with the optical antennas covered by insulating film, where the position of the tunnel junction on the antenna surface can be controlled with high accuracy and flexibility. Taking gold nanorod antennas covered by HfO2 film as an example, we found that the highest light generation efficiency is obtained when the tunnel junction is located at the shoulder edge of the nanorod antenna, where the bonding dipolar surface plasmon mode in the junction is spectrally and spatially coupled with the longitudinal radiation mode of the EDOAs. Besides, position variation of the tunnel junction on the nanorod surface also strongly influences the far-field radiation angular distribution and emission spectrum. Numerical simulations are in good agreement with the experimental results. Our findings offer fundamental insights into the influence of structural parameters on the light emission performance of EDOAs, thus leading to better design of EDOAs with high light generation efficiency and powerful functionality.

Low-frequency Noise Reduction Mechanism and Acoustic Characteristics of the Dipole Surface Source Structure

Low-frequency Noise Reduction Mechanism and Acoustic Characteristics of the Dipole Surface Source Structure