Interfacial Potential Research Articles

Analytical theoretical framework for closed bipolar electrochemical cells under homogeneous molecular catalysis: Implications for electrochemiluminescence applications

A novel analytical framework has been formulated to describe the current-potential-time response in systems with two polarized interfaces where one charge transfer process follows a catalytic mechanism, as found in co-reactant electrochemiluminescence (ECL) systems. The developed theory provides mathematical expressions for electrochemical and ECL signals, concentrations, and interfacial potentials upon the application of a constant potential pulse. Theoretical analysis reveals that the chemical regeneration of the redox reactant within the catalytic cycle has a remarkable impact on the chronoamperometric, voltammetric, and ECL responses, thereby providing means to estimate the catalytic rate constant and to optimize light emission. The system's behaviors are rationalized through the influence of catalysis on the interfacial concentrations and potentials. Also, the primary theoretical predictions have been experimentally validated using the [Ru(bpy)₃]²⁺/oxalate ECL system.

Potential Control for Bipolar Electrochemical Systems By Closed Circuits Including Ion-Selective Electrodes

Introduction Bipolar electrode (BPE) is an independent conductor immersed in the electrolyte and without directly connected to the external electronic circuit. Compared with the traditional three-electrode system, a BPE has unique advantages including a simple electrode structure, flexible sensing design, as well as the wireless driving (1). Therefore, in promoting multiplexed electrochemical detection, bipolar electrochemistery provides an effective solution for integrated design. However, given the absence external electronic circuit connection, precise control of the interfacial potential for a single BPE has been an issue in realizing reliable quantitative sensing (2). To solve this problem, we reported a new strategy for highly sensitive potential control of bipolar systems. An ion-selective electrode (ISE) which maintain a stable potential in ISE/solution interface with different ionic strengths coupled with BPE. An electrochemical closed circuit forms by Ag/AgCl electrode bridged BPE and ISE cells. The potential at the BPE/solution interface was controlled based on the potential of ISE and the position of the closed circuit. This technique enables single BPE on a highly array device to achieve sensitive potential control, which promotes the identification of informative biomarkers in large scale and real-time clinical studies. Experiment method Fig. 1 (A) shows the schematic of the closed bipolar system used for illustrating the potential control. The BPEs, ISE, and driving electrodes (Pt) are consolidated on a glass substrate. BPE (Ⅱ) branched out an arm electrode in the middle and modified with Na+ ion-selective membrane (ISM) at the terminal. BPE (Ⅰ) was employed as a control group without potential control unit. Electrochemiluminescence (ECL) was introduced as a powerful biosensing technique for BPE. Adopting the concept of closed BPE, signaling reaction (chemiluminescence) at anode as a reporter for sample reduction at cathode of BPE that can be triggered by electrical potential. These two reactions took place in separate chambers that were only connected through a BPE. In the anodic chamber (red in Fig. 1A), 5 mM tripropylamine (TPA) and 1 mM [Ru(bpy)3]2+ in 100 mM phosphate buffer (PBS) (pH 6.9) was used for ECL reaction. The cathodic chamber was filled with 100 mM PBS (pH 6.9) containing 1 mM KCl (green in Fig. 1A). The ISE chamber (blue in Fig. 1A) was filled with NaCl solution of predetermined concentrations. Given the isolated chambers of BPE, two cases are explored, the ISE chamber and anodic chamber or cathodic chamber are bridged with a silver electrode with AgCl growing at both ends. When a constant voltage is applied into BPE chambers, [Ru(bpy)3]2+/TPA are oxidized on the anodes accompanied by photon emitting. These ECL signals are observed by CCD camera correspond to the reduction of O2 at the cathode due to the current flow through BPE. The different of ECL intensity reveals the situation of potential different at the BPE/solution interface. Results and discussion The closed bipolar system was first characterized with O2 reduction in the cathodic chamber, the curve for ECL intensity with driving voltage moved significantly depending on the location of the Ag/AgCl (Fig. 1 (B)). The peak of ECL was observed under larger driving voltage when the Ag/AgCl coupled the cathodic and control chamber. The effect of using the ISE was also examined by changing the concentration of NaCl in the control chamber. ECL intensity of BPE (Ⅱ) was decreased with the concentration of NaCl when Ag/AgCl connected anodic chamber (Fig. 1 (C)), in converse, ECL increased with NaCl when Ag/AgCl connected cathodic chamber. (Fig. 1 (D)). The results can be explained considering that the interfacial potential differences at both the anodic and cathodic poles shift in a more positive direction under the rate-limiting condition for the anodic pole.Fosdick, S. E., Knust, K. N., Scida, K., & Crooks, R. M., Angewandte Chemie, 52, 40(2013).A. A. Mutalib, Y. Deng, A. Hsueh, K. Kariya,T. Kurihara,H. Suzuki, Electroanalysis, 13, 10(2021). Figure 1

Aptamer Immobilization on Transistor-Based Biosensor Via Crosslinker for Amine-to-Thiol Conjugation Toward Cortisol Detection

A Field-effect transistor (FET) biosensor is a sensing device that detect changes in the interfacial potential associated with the adsorption of target molecules. FET biosensor is expected to be a simple measurement method by detecting target biomarkers without any labeling process. Recently, aptamers, single-stranded DNA molecules with specificity and stability, have attracted attention as receptors of FET biosensor [1,2]. Immobilization of aptamer onto metal oxide insulator surface of FET biosensors is often achieved by combining self-assembled monolayer (SAM) with cross-linking agents. Generally, an immobilization method using cross-linking agent, glutaraldehyde, between amino-modified aptamer and aminopropylsilane (APS) monolayer is often employed [3]. However, there is concern that aptamers may be immobilized by non-terminal amino group, because amino groups are also present within the bases constituting DNA structure. Consequently, decrease in affinity of the aptamer to the target molecule by involving collapse of the higher-order structure and inhibition of conformational change. In this study, we attempted immobilization method on the FET gate surface utilizing cross-linking thiol groups of aptamers to self-assembled monolayer instead of that between amino groups. By immobilizing thiol-modified aptamers onto APS monolayer via N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP), we demonstrated specific immobilization at the aptamer termini for increasing the number of effective aptamers for binding of cortisol, which is stress-related hormone, was selected as a target.The SiO2 gate insulator of the FET was treated by piranha solution (H2O2 : H2SO4 = 1:4) for introduction of hydroxyl groups. Then, the FET chip was immersed in toluene solvent including 1%(v/w) 3-aminopropyltriethoxysilane in an argon atmosphere (60ºC for 7 min.). The SPDP was reacted with amino group of APS monolayer. After that, dithiothreitol (DTT) was added to the FET gate surface to form thiol group by cleavage of the disulfide bond within the SPDP. 100 nM 3’-thiol modified cortisol aptamer was immobilized to the FET gate surface by forming disulfide bond. Finally, 1 μM 2-mercaptoethanol was reacted with residual thiol sites to prevent non-specific adsorption of contaminating proteins. The FET characteristics were measured before and after the addition of cortisol for obtaining the threshold voltage shift (ΔV g).First, we compared the ability of reducing regent for cleavage of disulfide bond within SPDP to form the thiol group on the FET gate surface. A 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), which reacts with thiol group, was added to SPDP-modified surface treated by DTT, ascorbic acid or l-cysteine ethyl ester (LCEE). Following that, the absorbance derived from 5-mercapto-2-nitrobenzoic acid, which was generated from DTNB depending on the amount of thiol groups, was measured. As a result, thiol groups derived from SPDP were formed on the FET gate surface upon treatment with DTT. On the other hand, no absorbance of 5-mercapto-2-nitrobenzoic acid was observed when ascorbic acid or LCEE was used as reducing regents. Additionally, thiol groups were increased with SPDP concentrations in the range from 0.5 to 25 mM by DTNB absorbance measurements. Subsequently, electrical responses to cortisol using aptamer-immobilized FET were measured upon varying SPDP concentrations, with maximum response obtained at 1 mM. It should be noted that the FET response was acquired by increase in charge within the Debye length due to the conformational changes of the aptamer upon cortisol binding [4]. Finally, the sensitivity of aptamer-immobilized FET biosensor, which was fabricated using SPDP, were compared with that obtained using glutaraldehyde as the cross-linking agent. As a result, the gate voltage shift by addition of 1 μM cortisol when SPDP was utilized to fabricate the aptamer-immobilized FET biosensor was greater than the case of glutaraldehyde (Figure 1). These results indicated that cortisol was efficiently captured by the increase in the amount of aptamer, which was immobilized by 3’-terminus via disulfide bond. Therefore, the utilization of cross-linker for amine-to-thiol conjugation to nucleic acid immobilization could be useful for improving the sensitivity of FET biosensors.[1] H. Chen et al., Analyst, 141, 2335-2346 (2016).[2] N. Nakatsuka et al., Science, 362, 319-324 (2018).[3] S. K. Vashist et al., Chem. Rev., 114, 11083−11130 (2014).[4] H. Hayashi et al., Electrochemistry, 89, (2), 134-137 (2021). Figure 1

Field-Effect Transistor Biosensor By Capture of Nucleic Acid Strands with Isothermal Amplification for RNA Detection

Nucleic acid amplification methods are widely used for sensitive detection of biomolecules utilizing signals derived from amplified DNA strands[1]. Signal amplification by ternary initiation complexes (SATIC) has been attracted attention as high specific RNA detection method, because rolling circle amplification (RCA) by φ29 DNA polymerase requires the formation of ternary initiation complexes with DNA primers, circular DNA templates, and target RNAs[2]. In SATIC system, target RNA was detected via fluorescence derived from the complex of guanine quadruplex (G4) structure, which generated within the amplified DNA strands, and thioflavin T (ThT)[3]. To further simplify RNA detection using the SATIC system, it was expected to be effective to combine it with a field-effect transistor (FET) biosensor. A FET biosensor detects target molecules by altering the interfacial potential through the adsorption of charged molecules, thereby enabling simple label-free detection. Previously, we demonstrated the RNA detection via the negative charges of amplified DNA strands using the SATIC system, which originated from the DNA primer-immobilized FET sensor surface[4]. This approach will be required the immobilization of different DNA primers for the detection of various targets. As the immobilization conditions of the DNA primers needed to be optimized for detection of each target RNA, there was concern that the versatility of the FET biosensor would be reduced. Here, the versatility of the FET biosensor could be reinforced by the capture of nucleic acid strands amplified in the bulk by the sensing interface formed under the same conditions. For the realizing the above approach, the interaction between the G4 structure and ThT was considered to be effective in capturing amplified DNA strands. In this study, we attempted to detect target RNA by capture of the amplified DNA strands containing the G4 structures using ThT-immobilized FET biosensor.ThT derivatives (ThT-OE11[5]) were immobilized to aminopropylsilane-modified FET gate surface via cross-linking by glutaraldehyde (1 h). After that, residual aldehyde group were capped by the ethanolamine (1 h). Subsequently, amplified DNA strands were generated by mixing target RNAs, DNA primers, circular DNA templates, the four deoxynucleotide triphosphates (dNTPs), and φ29 DNA polymerase at 37°C. Following that, the SATIC reaction solution was added to the ThT-immobilized FET (30 min.). Finally, the gate voltage (V g)-drain current (I d) characteristics were measured before and after the addition of the SATIC reaction solution for calculating gate voltage shift (ΔV g).The FET response to 100 nM target RNA was measured when the SATIC reaction solution was added ThT-immobilized FET biosensor. As shown in Figure 1(a), ΔV g in the positive direction was obtained, indicating that the electron concentration in the channel was decreased by electrostatic interaction from negative charges of the amplified DNA strands. To optimize ThT immobilization condition, we evaluated the relationship between concentrations of ThT-OE11 solution and the sensor responses to target RNA. As a result, maximum response obtained at 500 mM ThT-OE11 solution. Subsequently, the sensor signal to 1 base-mismatched RNA as a negative control was almost no response (Figure. 1(b)). This result suggested that the nucleic acid strands were not generated by SATIC system, because the ternary initiation complexes did not form with 1 base-mismatched RNA. Thus, the ThT-immobilized FET with SATIC system specifically detected target RNAs. Finally, the measurement of ΔV g at different concentrations of target RNAs were conducted using ThT-immobilized FET to examine the quantitative detectability. As a result, ThT-immobilized FET with SATIC system showed a concentration dependence in the range of 1 pM to 100 nM. In addition, we plan to obtain additional data on sensitivity by controlling the reaction time of FET biosensor with SATIC system. From these results, the capture of nucleic acid strands containing G4 structure by ThT-immobilized FET could be effective for RNA detection.[1] M. Falco et al., TrAC Trends in Anal. Chem., 2022, 148, 3, 116538[2] H. Fujita et al., Anal. Chem., 2016, 88, 7137−7144[3] J. Mohanty et al., J. Am. Chem. Soc., 2013, 135, 1, 367–376[4] H. Hayashi et al., Talanta, 2023, 273, 125846[5] M. Kuwahara et al., Molecules, 2020, 25, 4936 Figure 1

(Invited) Effect of Electrode Polarization on Oxide Ion-Conducting and Proton-Conducting Electrolytes

Polarization at the electrode/electrolyte interface has been a central issue in electrochemistry, which is also true for high-temperature ion conducting devices. Charge transfer limitation does not simply apply to such interfaces where electrons make direct exchange. Thus, overpotentials have been discussed in terms of a shift of local oxygen activity from equilibrium with the gas phase [1]. This approach has been successful in explaining phenomena at high temperature electrodes, such as large chemical capacitance of mixed-conducting film electrodes and appearance of Gerischer-type impedance with porous electrodes [2,3]. As well as the effect on the electrode properties, the interface potential shift can also affect the electrolyte. The Hebb-Wagner polarization technique utilizes the polarization at ion-blocking electrode to control the chemical potential within the electrolyte. The enhanced n-type or p-type conduction of ceria-based or proton conducting oxide electrolyte under water electrolysis operations is recognized as a practical problem of reduced energy conversion efficiency. However, the effect of overpotential at practical semi-blocking electrodes (or incompletely reversible electrodes) on the electrolyte is not well understood. The aims of this study is to elucidate whether the overpotential directly defines the chemical potential shift in the electrolyte near the interface.Two kinds of approaches were taken: i.e. direct measurement of the chemical potential in the electrolyte and non-linear equivalent circuit analysis of electrochemical responses. The direct measurements were made by using embedded probes in an oxide ion conductor. Yttria stabilized zirconia powder was pressed and sintered with five platinum wires of 0.1~0.2 mm thick. Porous platinum electrodes were pasted on the both ends of the sample and direct or alternating current was applied. Electric fields between the probes/electrodes were estimated by high frequency response of ac impedance, and subtracted from the electrical potential of the probes under dc. The distribution of chemical potential of electron, and thus, of oxygen was obtained assuming constant chemical potential of oxide ion. When oxygen exchange on the cathode was blocked using a glass paste, the oxygen potential at each probe shifted to the negative direction, and the change propagated slowly from the cathode side to the anode side. The result was in close agreement with the estimation from the mobility and carrier concentration of electrons in YSZ, suggesting that the probes successfully detected the local oxygen potential. Evaluation of chemical potential shifts with half-blocking electrode is in progress.For the equivalent circuit approach, a model circuit was developed to simulate the linear and nonlinear responses of electrode/electrolyte systems. The circuit consisted of charged carrier transport lines connected by capacitors exhibiting the local defect equilibrium, as proposed by Jamnik and Maier[4]. Unlike an equivalent circuit for a regular impedance analysis, the circuit elements were defined using parameters that varied with local chemical potentials. The responses of the circuit were calculated by using a general-purpose circuit analyzer LT-SPICE that enabled analyses of transient response as well as linear impedance. It also enabled higher harmonic analyses which is useful for detecting electrolyte polarization. The developed model was tested with a simple symmetric cell with mixed conducting electrode. Qualitative correspondence was obtained regarding the oxygen potential dependence in the linear impedance and the second harmonic responses. In addition to the oxide ion conductors, proton conductor with hole and oxide ion as minor carriers were modeled. Calculations with different assumptions of the oxygen (and hydrogen) potential shift will be compared with the ongoing experiments to find the effect of polarization of a half-blocking electrode.

Second harmonic generation null angle polarization analysis for determining interfacial potential at charged interfaces.

Methods of quantifying the electrostatics of charged interfaces are important in a range of research areas. The surface-selective nonlinear optical technique second harmonic generation (SHG) is a sensitive probe of interfacial electrostatics. Recent work has shown that detection of the SHG phase in addition to its amplitude enables direct quantification of the interfacial potential. However, the experimental challenge of directly detecting the phase interferometrically with sufficient precision and stability has led to the proposal and development of alternative techniques to recover the same information, notably through wavelength scanning or angle scanning, each of which has their own associated experimental challenges. Here, we propose a new polarization-based approach to recover the required phase information, building upon the previously established nonlinear optical null ellipsometry (NONE) technique. Although NONE directly returns only relative phase information between different tensor elements of the second-order susceptibility, it is shown that a symmetry relation that connects the tensor elements of the potential-dependent third-order susceptibility can be used to generate the absolute phase reference required to calculate the interfacial potential. The sensitivity of the technique to potential at varying surface charge densities and ionic strengths is explored by means of simulated data of the silica:water interface. The error associated with the use of the linearized Poisson-Boltzmann approximation is discussed and compared to the error associated with the precision of the measured NONE null angles. Overall, the results suggest that NONE is a promising approach for performing phase-resolved SHG based quantification of interfacial potentials that experimentally requires only the addition of standard polarization optics to the basic single-wavelength, fixed-angle SHG apparatus.

Au‐Free Ti/Al/Ni/TiN Ohmic Contact to AlGaN/GaN Heterostructure: Ti/Al Thicknesses at an Optimized Ratio

Although a few studies report that tuning Ti/Al thicknesses at a fixed ratio can further improve the Ohmic contact to AlGaN/GaN heterostructure, systematic physical mechanisms have not been reported. In this work, after determining the optimal Ti/Al ratio of 1/4, two metal stacks with varying Ti/Al thicknesses and fixed Ni/TiN thicknesses are deposited to investigate how tuning Ti/Al thicknesses at an optimized ratio enhances the Ohmic contact performance. At the optimal annealing condition (950 °C, 45 s) of samples with Ti/Al thicknesses of 20/80 nm, samples with Ti/Al thicknesses of 35/140 nm exhibit a reduction of 48% in contact resistance and 70% in specific contact resistivity (ρc). By correlating the results from ρc–T measurements, time‐of‐flight secondary ion mass spectrometry, and high‐resolution X‐ray diffraction, it has been determined that this method effectively enables N‐vacancies doping into the heterostructure, thereby increasing the carrier concentration and reducing both the height and width of the interfacial potential barrier, achieving a more efficient carrier transport. By avoiding the use of Au with high solubility and ductility, this approach significantly improves contact performance without adversely affecting the electrode surface morphology, demonstrating good adaptability for optimizing Au‐free Ohmic contacts.

Ultrafast dynamics of two-dimensional electron gas at Al2O3/SrTiO3 interface studied by surface terahertz spectroscopy.

Two-dimensional electron gas (2DEG) confined at the interface of SrTiO3-based heterostructure exhibits intriguing electronic and optoelectronic properties. In this work, we study the ultrafast dynamics of 2DEG at the Al2O3/SrTiO3 interface using surface-specific terahertz difference-frequency spectroscopy. Through proper polarization selection, we have resolved simultaneously the evolution of 2DEG confined in the quantum well and the surface potential after optical pump with different photon energies. The hot electrons excited from 2DEG with pump photon energy below the band gap relax to the ground state through two processes, a fast interfacial process associated with electron-electron and electron-phonon scattering on the order of tens of picoseconds and a slow surface-to-bulk transport on the order of hundreds of picoseconds. When the pump photon energy exceeds the bandgap, electrons are directly injected from the valence band to 2DEG at the interface and relax via electron-hole recombination in 3ps. The recorded dynamic change of interfacial potential provides the key information to identify the drift and diffusion of photocarriers at the interface. Our results broaden the horizon of investigation on the comprehension of complex oxide interfaces and their photonics capabilities.

Preparation, characterization and mechanism of SiO2@SiO2 core-shell microspheres through polymerization-induced colloid aggregation for fast separation using ultra performance liquid chromatography

The polymerization-induced colloid aggregation (PICA) method is commonly used to create SiO2@SiO2 core–shell silica microspheres (CSSMs), but it often encounters challenges such as incomplete shell coating and poor reproducibility. In this paper, the formation mechanism of the silica shell layer during the preparation of SiO2@SiO2 CSSMs using the PICA method was investigated. It was found that ureido modification can reduce the Zeta potential of the silica core surface, facilitating the deposition of coacervates formed by urea-formaldehyde resin (UF) and silica nanoparticles on the silica core surface to form the SiO2 shell layer when the Zeta potential of the surface is in the range of −20.1 mV to −4.8 mV. By controlling the interfacial state and surface potential of the SiO2 core, the issue of inconsistent reproducibility in preparing SiO2@SiO2 CSSMs can be overcome. Furthermore, optimization of experimental parameters such as pH, reaction temperature, water content, and reaction time can enhance the formation process. The thickness of the shell and pore size of CSSMs can be successfully adjusted by varying the reaction time and the particle size of colloidal silica sol, respectively. With optimal conditions, the semi-scale production yield of SiO2@SiO2 CSSMs can be increased to 50 g. The SiO2@SiO2 CSSMs were modified with octadecyltrichlorosilane (ODS) to be used as stationary phases in reversed phase liquid chromatography (RPLC) for fast separation of small solutes, peptides, and proteins. The superior separation efficiency indicates that the improved PICA method has the potential to be utilized as an alternative to the layer-by-layer method for large-scale production of SiO2@SiO2 CSSMs.

Chiral Electrokinetic Phenomena in Single Nanopores

AbstractThe arrangement of solvent molecules and ions at solid–liquid interfaces determines electrochemical properties that are important in separations platforms, sensing technologies, and energy‐storage systems. Here we show that single glass and polymer pores in contact with propylene carbonate (PC) solutions of LiClO4 exhibit an effective surface potential that is modulated by the enantiomeric excess of the solvent. In particular, electrochemical and electrokinetic measurements of ionic transport through glass pipettes and polymer pores reveal that the effective surface potential is significantly lower in solutions prepared using enantiomerically pure PC than in solutions prepared using racemic PC. Both pore systems became positively charged in all racemic solutions examined in the range of LiClO4 concentrations between 1 mM and 100 mM, whereas solutions in (R)‐(+)‐PC induced a positive surface potential only at concentrations above ~5 mM. The effective surface potential is quantified through asymmetry in current–voltage curves and zeta‐potential measurements. Vibrational sum‐frequency‐generation experiments on LiClO4 solutions in racemic and enantiomerically pure PC indicate that the surface lipid‐bilayer‐like region in the former is more strongly organized than in the latter, dictating the favorable positions for lithium and perchlorate ions in each case. The more ordered molecular packing in the racemic liquid leads to accumulation of lithium ions on the outside of the bilayer, creating a higher effective positive charge. Our results highlight the extreme sensitivity of the interfacial potential on molecular organization of the solvent, and the relatively unexplored role that chirality can play in electrokinetic phenomena.

High sensitivity and selectivity of h-BN/WO3 n-n heterojunction to triethylamine at low-temperature

Due to the unique properties of heterojunction interfaces, heterojunction materials have broad application prospects in gas sensors. In this work, a facile and economical two-step synthesis method was employed to fabricate h-BN/WO3 heterojunctions, exhibiting excellent performance in triethylamine (TEA) detection. The results indicate that compared to pure WO3 sensors, h-BN/WO3 sensors exhibit superior TEA sensing capabilities, with an excellent response of 281.45 to 20 ppm TEA at 100 °C, which is 3.4 times higher. Moreover, h-BN/WO3 sensors demonstrate favorable response times, low detection limits, and good stability. These significant enhancements are attributed to the increase in oxygen vacancies and the establishment of heterojunctions between h-BN and WO3. Heterojunctions can regulate the concentration and transport rate of charge carriers, as well as the interface potential barrier, thereby affecting the gas sensing processes. This work may promote the further development of sensing materials and the practical application of WO3 sensors in TEA detection.

Free Vibration of Graphene Nanoplatelet-Reinforced Porous Double-Curved Shells of Revolution with a General Radius of Curvature Based on a Semi-Analytical Method

Based on domain decomposition, a semi-analytical method (SAM) is applied to analyze the free vibration of double-curved shells of revolution with a general curvature radius made from graphene nanoplatelet (GPL)-reinforced porous composites. The mechanical properties of the GPL-reinforced composition are assessed with the Halpin–Tsai model. The double-curvature shell of revolution is broken down into segments along its axis in accordance with first-order shear deformation theory (FSDT) and the multi-segment partitioning technique, to derive the shell’s functional energy. At the same time, interfacial potential is used to ensure the continuity of the contact surface between neighboring segments. By applying the least-squares weighted residual method (LWRM) and modified variational principle (MVP) to relax and achieve interface compatibility conditions, a theoretical framework for analyzing vibrations is developed. The displacements and rotations are described through Fourier series and Chebyshev polynomials, accordingly, converting a two-dimensional issue into a suite of decoupled one-dimensional problems. The obtained solutions are contrasted with those achieved using the finite element method (FEM) and other existing results, and the current formulation’s validity and precision are confirmed. Example cases are presented to demonstrate the free vibration of GPL-reinforced porous composite double-curved paraboloidal, elliptical, and hyperbolical shells of revolution. The findings demonstrate that the natural frequency of the shell is related to pore coefficients, porosity, the mass fraction of the GPLs, and the distribution patterns of the GPLs.

Electron surface scattering kernel for a plasma facing a semiconductor.

Employing the invariant embedding principle for the electron backscattering function, we present a scheme for constructing an electron surface scattering kernel to be used in the boundary condition for the electron Boltzmann equationof a plasma facing a semiconducting solid. The scheme takes the solid's microphysics responsible for electron emission and backscattering from the interface within a randium-jellium model into account and is applicable to dielectrics and metals as well. As an illustration, we consider silicon and germanium, describing the interface potential by a Schottky barrier and including impact ionization across the energy gap as well as scattering on phonons and ion cores. The emission yields deduced from the kernel agree well enough with measured data to support its use in the electron boundary condition of a plasma facing silicon or germanium.

Model-free chemomechanical interfaces: History-dependent damage under transient mass diffusion

This paper presents a data-driven framework based on distance functional for chemo-mechanical cohesive interfaces to capture transient diffusion and resulting interfacial damage evolution. The framework eliminates reliance on complex constitutive models and phenomenological assumptions, especially avoiding the coupling tangent terms with a given material database. The interfacial chemical potential and its jumps are used to expand the phase space for describing the chemical states of interfaces. Subsequently, a novel chemo-mechanical distance norm, including traction-separation pair, interfacial chemical potential-concentration pair and corresponding chemical potential jump-flux pair, is presented. Momentum conservation law for interfacial tractions and mass conservation law for interfacial concentration are enforced via Lagrange multipliers. For tracking the history-dependent state of the interface damage, an internal variable, termed interface integrity, is introduced to condition the interfacial database and manage the subsets mapping strategies, following physically motivated evolution constraints. Numerical examples are conducted to investigate the efficiency and capability of the present framework. A monotonic loading test validates a good numerical convergence relative to the number of data points. Subsequent cyclic loading simulations, compared with the reference solutions, show that the algorithm is well suitable to predict the history-dependent interface damage evolution under complex loading paths. Finally, the chemo-mechanically coupled examples capture phenomena such as interfacial swelling and interface degradation induced by transient diffusion and stress-driven diffusion. The current work provides a promising tool for understanding chemo-mechanical behaviors of interfaces within heterogeneous composites.

Heterostructures constructed by NiMoO4 functionalized 2D MoO3 nanosheets for ultrasensitive trimethylamine detection with ppb level detection

Trimethylamine (TMA) serves as an indicator for assessing seafood spoilage and a biomarker for kidney disease. Achieving this dual functionality necessitates the detection of TMA with a low detection limit and exceptional selectivity. Here, NiMoO4 functionalized MoO3 heterostructures were constructed and subjected to a systematic investigation of their sensing properties towards TMA. The 7 %-NiMoO4/MoO3 sensor could detect trace TMA at 200°C with a response value of 3.93 (0.1 ppm) and achieve detecting thresholds as low as 2.48 ppb (theoretical limit). Additionally, the sensor exhibits remarkable selectivity to TMA, an expansive adjustable concentration on detection range, and excellent long-term stability. The enhanced sensing properties may be ascribed to the forming p-n heterojunctions at the NiMoO4/MoO3 interface, effectively modulating the interfacial potential. Moreover, the NiMoO4/MoO3 heterostructures demonstrate excellent charge-transfer capability, high charge carrier density, and a substantial active surface area in electrochemical measurements, thereby enhancing the sensing ability of TMA. Additionally, the thin nanosheet structure facilitates efficient charge transportation along the length of the nanosheets, further enhancing the sensing response. These results indicate the potential of NiMoO4/MoO3 as a promising sensing material for TMA gas sensors.

Development of SnO2 functionalized In2O3 porous microrods for trace level detection of formaldehyde at room temperature

Room temperature detection is a crucial objective in semiconductor sensor research, given its inherent benefits including reduced energy consumption, extended sensor lifespan, and significant reduction of safety hazards. Herein, novel room temperature sensing materials, SnO2-modified In2O3 porous microrods were synthesized, which exhibited exceptional sensing capability towards formaldehyde at room temperature. Specifically, the 5%-SnO2/In2O3 porous microrods demonstrate an impressive sensing response across varying formaldehyde concentrations, even at sub-ppm levels (0.1 ppm, 5.22), with a theoretical detection limit of 5.47 ppb, thereby enabling the detection of trace amounts of formaldehyde. Moreover, the sensors exhibit superior formaldehyde selectivity, rapid response characteristic, as well as good stability and reproducibility. The exceptional formaldehyde sensing ability of the SnO2/In2O3 sensor primarily arises from the creation of n-n heterojunctions at the SnO2/In2O3 interface, effectively modulating the interfacial potential. Additionally, the presence of SnO2 enhances the amount of surface-adsorbed oxygen species and active sites, thereby boosting sensing response. The porous rod-like structures further facilitate gas adsorption and diffusion, enhancing gas sensing capabilities. This work presents a novel strategy for constructing SnO2-In2O3 heterojunctions to achieve room-temperature formaldehyde detection.

Electro-Thermo-Magnetic Effect-Induced Large Thermoelectric Performance of Calcium Cobaltite Nanocomposites.

As attractive thermoelectric oxides, Ca3Co4O9-based materials have been intensively studied for their applications in recent years. However, their thermoelectric performance is enormously limited due to the contradiction of electrical resistivity and thermal conductivity. Herein, BaFe12O19 nanospheres were introduced into the Ca3Co4O9 matrix. The metallic Ag, ferrites, and matrix phase survived together, and a high density of nanoscale BaFe12O19 precipitation was observed. The reduction of work function could lead to band bending and form an interface potential due to the electro-thermo-magnetic effect contributing to the hole migration. As a result, a huge ZT value of 0.51 for the 8 wt % BaFe12O19/Ca3Co4O9 nanocomposites was obtained at 1073 K, accompanied by a low electrical resistivity of 6.7 mΩ·cm and a high Seebeck coefficient of 217.5 μV/K. In addition, a significant reduction of thermal conductivity (1.11 W/(m·K)) occurred, which was due to the nanoscale ferromagnetic phase effectively scattering the mid- and short-wavelength heat-carrying phonons. The synergistic enhancement of thermoelectric performance confirmed that the electro-thermo-magnetic effect is an effective way to solve the challenging problem of performance deterioration in oxide thermoelectric materials.

(Invited) Understanding Carrier-Selective Catalyst/Semiconductor Contacts in Water-Splitting Photoelectrodes and Photocatalyst Particles

Heterogeneous electrochemical processes, including photoelectrochemical water splitting to evolve hydrogen and oxygen using electrocatalyst-coated semiconductors, are driven by the accumulation of charge carriers and thus the interfacial electrochemical potential gradients that promote charge transfer. Conventional electrochemical techniques measure/control potentials at the conductive substrate or semiconductor ohmic contact, but are unable to isolate processes and electrochemical potentials at the surface during operation. I will discuss how the nanoelectrode tip of an atomic-force-microscope cantilever can effectively sense the surface electrochemical potential of electrocatalysts coating semiconductor photoelectrodes during operation. This data can be combined with ex-situ electrical measurements, spectroscopy, and materials characterization approaches to provide a comprehensive physical picture of how excited electrons and holes can be effectively separated and catalyst/semiconductor contacts. This new understanding is particularly important for the design of photocatalyst particles where direct electrical measurements of catalyst/semiconductor interface properties is not possible. In these systems we are applying spectroscopic techniques, for example ambient pressure x-ray photoelectron spectroscopy and Stark-effect spectroscopy to understand electric and electrochemical potential distribution and how nanoscale, adaptive, heterogeneous contacts can be controlled to design higher performance photochemical systems.

Experimental Investigations and MD Simulation on Nanoparticle-Enhanced CO2-Responsive Foam (NECRF): Implications on CO2-EOR.

CO2-responsive foam (CRF) is a highly promising candidate for CO2-enhanced oil recovery (CO2-EOR) because it displays higher stability than the surfactant-stabilized foam owing to the formation of robust wormlike micelles (WLMs) upon exposure to CO2. In this work, the nanoparticle-enhanced CO2-responsive foam (NECRF) was properly prepared using lauryl ether sulfate sodium (LES)/diethylenetriamine/nano-SiO2, and its interfacial properties and EOR potential were experimentally and numerically assessed, aiming to explore the feasibility and effectiveness of NECRF as a novel CO2-EOR technique. It was found that the interfacial expansion elastic modulus increased 6-fold after CO2 stimulation. The modulus continued to increase with the introduction of nano-SiO2 owing to the pronounced synergistic effect of WLMs and nanoparticles. In addition to increasing the viscosity of the foaming liquid, WLMs and nano-SiO2 enhanced the shearing resistance of the NECRF as well. Calculations demonstrated that both the coarsening rate and the size distribution uniformity coefficient of NECRF were markedly lower than that of the LES foam, which subsequently inhibited NECRF decay and greatly improved its dynamic stability. Besides, molecular dynamics simulation revealed that adding inorganic salts to NECRF could notably enhance the foaming performance due to the intensified hydration of surfactant head groups and reduced binding energy of neighboring molecules. Nuclear magnetic resonance-assisted core flooding experiments validated the exceptional capacity of NECRF to sweep the low-permeability region and improve the conformance profile. Overall, these findings may provide valuable insights into the development and application of novel materials and strategies for the CO2-EOR.

Organic-Inorganic Rubrene/WS2 Heterostructure for Broadband Detection and Polarization Imaging.

Organic single crystals exhibit improved carrier mobility, longer exciton diffusion length, anisotropic charge transport, and unique linear dichroism, while its high exciton binding energy seriously limits the free-carrier generation and photoelectric conversion efficiency. Layered van der Waals heterostructures, which integrate organic crystals with high mobility two-dimensional (2D) inorganic semiconductors, are promising for promoting exciton dissociation and boosting sensitivity by utilizing the interfacial potential and photogating effect. In this work, organic single-crystal rubrene is integrated with a few-layer WS2 to design the high-performance photodetector. The device exhibits an excellent responsivity of 1000 A W-1, and a fast speed of 180 μs, which is far superior to the individual WS2 device. Equally importantly, this device provides excellent polarization detection performance by virtue of the anisotropic properties of rubrene, and the dichroic ratios are 1.56, 1.5, and 1.7 for 375, 405, and 658 nm irradiation, respectively. Finally, several high-resolution single-pixel broadband polarization imaging was demonstrated. Our work shows that organic-inorganic heterostructure is an essential candidate for improving optoelectronics performance and has potential for polarization imaging.