Electric Field Tuning Research Articles

Cross‐Scale Process Intensification of Spindle CuO Supported Tungsten Single‐Atom Catalysts toward Enhanced Electrochemical Hydrogen Production

AbstractProcess intensification engineering of electrocatalysts is crucial to facilitate electrocatalytic reaction, while its cross‐scale modulation is of great challenge. Herein, the spindle CuO supported tungsten single‐atom catalysts (W SACs) with tunable mesoscale electric field and atomic‐scale coordination structure are reported toward enhanced electrochemical hydrogen evolution process. Finite element analysis indicates the mesoscale electric field can be enhanced by tailoring the tip angle of spindle configuration from 74° to 27°, enhancing hydrogen production rate by 5 times. Based on the density functional theory calculations, the configuration regulation also triggers the increase of coordination number of W–O, which increases charge transfer and downshifts d‐band center, stabilizing W sites and optimizing hydrogen desorption process. The optimized WSA/CuO‐27 exhibits much better hydrogen evolution activity (η100 = 94 mV) and stability (200 mA cm−2 for 120 h) than as‐prepared WSA/CuO‐56 and WSA/CuO‐74 analogues. Impressively, the anion exchange membrane electrolyzer fabricated with the WSA/CuO‐27 presents excellent activity comparable to that of commercial electrocatalysts, and also delivers an ultra‐low attenuation of 0.085 mA cm−2 h−1 at 300 mA cm−2 after continuous electrocatalysis for 120 h. This work inspires the design of high‐efficiency supported metal catalysts for electrochemical synthesis via the cross‐scale process intensification engineering.

Ultra Low Power Consumption Optoelectronic Logic Operation of CuO/BaTiO3 Heterojunction Photodetector with Tunable Internal Electric Field Based on Poling Effect

AbstractThe study presents a novel self‐powered ultraviolet (UV) photodetector harnessing both polarization fields and photovoltaic effects, enabling the realization of ultra‐low power, reconfigurable optoelectronic logic gates. The approach is demonstrated on a CuO/BaTiO3 heterojunction photodetector. The behavior of the photodetector is augmented by the poling effect, aligning the internal electric field of the BaTiO3 through the application of a robust external electric field, thereby facilitating the implementation of optoelectronic logic gates. In the unpoled state, the “XOR” and “OR” logic gates operated at voltages of 750 and −500 µV, respectively. However, upon poling up state, the “XOR” logic gate exhibits reduced operation voltage, operating at 500 µV, while the “OR” logic gate implements clarity at −500 µV. In the unpoled state the “AND” logic gate does not operate; however, upon poling in the downward direction, it operated at −500 µV. The achievement demonstrates successful ultra‐low‐power logic operations, utilizing voltages in the hundreds of micron scale, under a 310 nm wavelength and a light intensity of 0.52 mW·cm−2. Furthermore, controllable polarization electric fields in BaTiO3 enable the operation of “AND” logic gate in the unpoled state, presenting a promising avenue for future research in optoelectronic logic gate design.

Tunable Intracavity Coherent Up-Conversion with Giant Nonlinearity in a Polar Fluidic Medium.

The study has demonstrated a novel microcavity-based flexible photon up-conversion system using second harmonic generation (SHG) from a polar nematic fluidic medium doped with a laser dye. The idea is based on coherent light generation via stimulated emission (lasing) and simultaneous frequency doubling inside a microcavity. The polar nematic fluid equips very high even-order optical nonlinearity due to its polar symmetry and large dipole moment along the molecular long axis. At the same time, its inherent fluidic nature allows to easily functionalize the media just by doping, in the present case, with an emissive laser dye. The demonstrated system exhibits a giant nonlinear optical response to input light, while enabling spectral narrowing and multiple-signal output of up-converted light, which is not attainable through the simple SH-conversion of input light. Furthermore, the susceptibility of the liquid crystal offers dynamic modulation capabilities by an external stimulus, such as signal switching by the application of electric field or wavelength tuning through temperature variation. Such a brand-new type of simple coherent flexible up-conversion system must be promising as a new principle for easily accessible and down-scalable wavelength conversion devices.

Tunable uniform field enhancement in a subwavelength air pillar by photonic doping in epsilon-near-zero medium

In this study, a novel electric field compressor is proposed by doping a metal-air-metal pillar in epsilon-near-zero medium within a metallic waveguide, which effectively enhances the background electric fields in a sub-wavelength air pillar with high uniformity. The field enhancement factor can be analytically determined through theoretical derivations from Maxwell’s equations, reaching its maximum value by appropriately selecting the size of the air pillar. Furthermore, the proposed compressor can achieve a tunable electric field enhancement effect within the deep sub-wavelength air pillar by adjusting the height of the air pillar through movement of two metal pillars inserted into the waveguide. Both theoretical analysis and numerical simulations are employed to validate the performance of the electric field compressor, which exhibits a wide range of tunable field enhancement effect (i.e., continuously adjustable enhancement factor between 20 and 800) with uniformity below 1.5 within the deep sub-wavelength air pillar (wherein the air volume is smaller than λ0/10 × λ0/10 × λ0/16). Finally, a practical model is proposed for the realization of the electric field compressor in the microwave range, where specially placed metal pillars and wires are incorporated into a rectangular metallic waveguide structure. The field enhancement and tunable effects of this practical model have been verified through simulations.

Controllable and reversible electric field tuning of photoluminescence response in lanthanide ions doped ferroelectric films

The rare-earth doped ferroelectric photoluminescence (PL) phosphors are attracting considerable interest because of their flexible structure, wide band gap and high-quality fluorescence signal emission. Although the change of PL performance in different samples have been solved to a certain extent, how to achieve the tuning of PL intensity in one sample sensitively and reversibly is still an issue. In this work, we present an "electric-elastic-optical" coupled structure of 0.94Bi0.5Na0.5TiO3–0.06BaTiO3:1 mol%Eu3+ (BNTBT:Eu)/ 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN-PT) heterostructures, which transfers strain from the PMN-PT to the BNTBT:Eu film via the converse piezoelectric effect and dynamically modulates the PL response of the epitaxial thin film. Our findings demonstrate that the PL response of the thin film can be effectively and linearly tuned under the influence of an external electric field. The relative change in the PL intensity (ΔI/I) of the BNTBT:Eu film was found to be linearly correlated with the lateral strain of the substrate. We also propose a novel design strategy for detecting strain, with significant implications for using BNTBT:Eu/PMN-PT heterostructures as sensors for integrating piezophotonic devices. This work provides valuable insights into the feasibility of electric field tuning of PL performance, which could inspire future research endeavors in the fields of nanophotonics, optical storage technology and photovoltaics.

Nanocurvature-induced field effects enable control over the activity of single-atom electrocatalysts

Tuning interfacial electric fields provides a powerful means to control electrocatalyst activity. Importantly, electric fields can modify adsorbate binding energies based on their polarizability and dipole moment, and hence operate independently of scaling relations that fundamentally limit performance. However, implementation of such a strategy remains challenging because typical methods modify the electric field non-uniformly and affects only a minority of active sites. Here we discover that uniformly tunable electric field modulation can be achieved using a model system of single-atom catalysts (SACs). These consist of M-N4 active sites hosted on a series of spherical carbon supports with varying degrees of nanocurvature. Using in-situ Raman spectroscopy with a Stark shift reporter, we demonstrate that a larger nanocurvature induces a stronger electric field. We show that this strategy is effective over a broad range of SAC systems and electrocatalytic reactions. For instance, Ni SACs with optimized nanocurvature achieved a high CO partial current density of ~400 mA cm−2 at >99% Faradaic efficiency for CO2 reduction in acidic media.

Symmetry-selective quasiparticle scattering and electric field tunability of the ZrSiS surface electronic structure

Three-dimensional Dirac semimetals with square-net non-symmorphic symmetry, such as ternary ZrXY (X = Si, Ge; Y = S, Se, Te) compounds, have attracted significant attention owing to the presence of topological nodal lines, loops, or networks in their bulk. Orbital symmetry plays a profound role in such materials as the different branches of the nodal dispersion can be distinguished by their distinct orbital symmetry eigenvalues. The presence of different eigenvalues suggests that scattering between states of different orbital symmetry may be strongly suppressed. Indeed, in ZrSiS, there has been no clear experimental evidence of quasiparticle scattering reported between states of different symmetry eigenvalues at small wave vector q⃗. Here we show, using quasiparticle interference, that atomic step-edges in the ZrSiS surface facilitate quasiparticle scattering between states of different symmetry eigenvalues. This symmetry eigenvalue mixing quasiparticle scattering is the first to be reported for ZrSiS and contrasts quasiparticle scattering with no mixing of symmetry eigenvalues, where the latter occurs with scatterers preserving the glide mirror symmetry of the crystal lattice, e.g. native point defects in ZrSiS. Finally, we show that the electronic structure of the ZrSiS surface, including its unique floating band surface state, can be tuned by a vertical electric field locally applied by the tip of a scanning tunneling microscope (STM), enabling control of a spin–orbit induced avoided crossing near the Fermi level by as much as 300%.

Exploring the low temperature fabrication and properties of barium strontium titanate tunable dielectric ceramics

Ba1−xSrxTiO3 compounds are widely recognized as leading dielectric materials for tunable electronic applications. To expand their applicability and enable integration with polymers and metals, there is a need for low-temperature processing. Here we show that Cold Sintering Process (CSP) enables the fabrication of Ba0.6Sr0.4TiO3 (BST) tunable dielectric ceramics, using Ba(OH)2·8 H2O as a flux, at a temperature as low as 350 ºC. A dielectric permittivity with a low magnitude of ∼ 340 at 10 kHz, an electric-field tunability of 11%, and a thermal stability of ±7.1% over the temperature range of −90 ºC to 85 ºC are obtained for CSP BST that thus outperforms conventionally sintered BST ceramics. Significant decrease in the sintering temperature and enhanced dielectric performance respond to the current sustainability concerns related to energy efficiency and tunable device requirements.

Epitaxial heterostructure of CdIn2S4/WO3 with the tunable built-in field for efficient photocathodic protection of 304SS and Q235

Photocathodic protection (PCP) can convert solar energy into protecting marine metallic structures from corrosion. However, the serious photocarrier recombination in the photoanode has hindered the development of the PCP technique. This study reported a feasible approach to construct the heterojunction with a tunable built-in electric field by epitaxially growing CdIn2S4(CIS) on the surface of WO3. The light absorbance, carrier separation, and transportation were found to be strongly dependent on the built-in field, and it would enable not only protection of the 304SS but also retard the corrosion of more vulnerable Q235. Accordingly, the OCP of coupled photoelectrode shifted to -950 and -880 mVAg/AgCl for 304SS and Q235, and their photocurrent density also reached 100 and 170 μA/cm2, respectively. Notably, the PCP performance of anti-corrosion on the 304SS and Q235 was visualized by microscopy, further proving the effectiveness of the photoanode. The underlying mechanisms and different protection capabilities were discussed in detail.

Infiltrated 2D/3D Heterojunction with Tunable Electric Field Landscape for Robust Inverted Perovskite Solar Cells with over 24% Efficiency.

In inverted perovskite solar cells, conventional planar 2D/3D perovskite heterojunctions typically exhibit a type-II band alignment, where the electric field tends to drive the electron motion in the opposite direction to the direction of electron transfer. Here, a 2D/3D gradient heterojunction is developed by allowing the 2D perovskite to infiltrate the 3D perovskite surface along the grain boundaries using the interaction between the organic cation of the 2D perovskite and the pseudohalogen thiocyanate ion (SCN-), which has the ability to diffuse downward. The infiltrated 2D perovskite not only fills the gaps of grain boundaries with improved structural stability, but it also reconstructs the original landscape of the electric field toward the n-doped surface to enable more rapid electron transfer and weaken the adverse type-II band alignment effect. Since 2D perovskite seals the GBs, the nonvolatile SCN- can accumulate at the top and bottom dual interfaces, releasing residual stress and significantly inhibiting nonradiative recombination. The device exhibits an excellent efficiency of 24.76% (certified 24.29%) and long-term stability that is >90% of the original PCE value after 800h of heating at 85°C or in high humidity (≈65%).

Full-spectrum Bi@SrTiO3 for bi-directional promotion effects on photocatalytic redox reaction: Insight into intermediates and mechanism

The development of full-spectrum photocatalysts active in the near-infrared (NIR) region has gained increasing attention for deleterious pollutant removal. The integration of plasmonic metals with semiconductors is an effective way to widen the light response range of photocatalysts due to the strong light absorption and fast plasmonic energy transfer of the localized surface plasmon resonance (LSPR). In this work, the full-spectrum responsive Bi@SrTiO3 was prepared via facile solvothermal chemical reduction. The optimal Bi@SrTiO3 achieves exceptional photocatalytic Cr(VI) reduction efficiency and tetracycline degradation, realizing bi-directional promotion effects on redox reaction. According to density functional theory (DFT) simulations, the extraordinary photocatalytic performance is attributed to the tunable built-in electric field (IEF) of the Ohmic contact. The favorable adaptability in real water and high stability of BSTO-25 were proved by experimental results. And the possible photocatalytic mechanism was proposed based on theoretical calculation and experimental results. Furthermore, the non-toxicity of the BSTO-25 was evaluated by E.coli cultivation, which further proves the feasibility of treating wastewater with BSTO-25. This work provides a new perspective on constructing full-spectrum-driven photocatalysts for applications dealing with environmental remediation.

Electric field tuning of multistate and nonvolatile resistance variation in amorphous Fe75Si25/PMN-0.3PT (0 0 1) heterostructures

The multistate resistance states in the amorphous Fe75Si25/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN − 0.3PT) (001) heterostructure were modulated by electric fields (E). Based on the in-plane nonvolatile stress changes associated with ferroelectric domain switching in PMN-0.3PT, the widening and narrowing of surface gaps, and the fact that magnetism generally tracks the strain variation in amorphous Fe75Si25 films, the distinct four-state and nonvolatile resistance tuning near the coercive E-field are observed. Then, combining the converse magnetoelectric coupling and magnetoresistive effect, we quantify the coaction effect and equivalence relation between the E-field and magnetic fields (H) on the resistance modification. Meanwhile, another four-state resistance is obtained under the coaction of the E-fields and H-fields. All eight resistive states exhibit excellent E-field switchable behavior and stability performance at room temperature. These results provide a promising approach for exploring and designing multistate and multifield controlled spintronic memory devices.

Interband transition physics from the absorption edge in GaN: New prospects from numerical analysis

The strong polarization effects and abundant surface states in III-nitrides result in a tunable electric field, modifying the absorption/emission by changing the band structure. Thus, the mechanism of the electric field and the absorption/emission is crucial for future optical logic devices. Here, we propose to extract the information from the absorption/emission edge by numerical simulations. The simulations show that the increase in the field strength would red-shift the spectrum as well as decrease the slope of the edge for both the uniform and non-uniform field. For numerical simulations, we also provide the lower limit of the quantum states to be simulated from Wentzel–Kramers–Brillouin approximation. Then three GaN samples with different n values are analyzed, and the results validate our methods in two ways. On the one hand, the nonuniform field is shown to fit the experimental absorption better at higher n, which is in accordance with previous studies. On the other hand, the reasonable bandgap Eg at zero doping level and the bandgap-renormalization coefficient are obtained. This work would deepen the understanding of the absorption/emission influenced by the electric field and pave the way for numerical analysis of the edge.

Precise Interstitial Built-In Electric Field Tuning for Hydrogen Evolution Electrocatalysis.

The built-in electric field (BEF) has become an effective means of adjusting the electronic structure and hydrogen spillover to influence the adsorption of intermediates. However, the previously reported BEF cannot be tuned continuously and precisely. Herein, a series of nanocatalysts with interstitial BEF were successfully synthesized, and the effect of precisely tuned interstitial BEF on the intermediate's adsorption and hydrogen spillover was systematically investigated using changing the insertion of interstitial B. Three catalysts with different BEF strengths were obtained by changing the interstitial content (B0.22-Cu/NC, B0.30-Cu/NC, B0.41-Cu/NC), and it was demonstrated that B0.30-Cu/NC gave the best catalytic performance for hydrogen evolution reactions (HERs). The turnover frequency (TOF) value is shown to reach 0.36 s-1 at just -0.1 V vs. RHE, which is about 3 times that of Cu (0.12 s-1). For the HER, it is one of the best Cu-based catalysts reported to date (Table S3). Besides, when the catalyst was applied to the cathode of the PEM water electrolyzer, B0.30-Cu/NC exhibited long-time stability at a water-splitting current density of 500 mA cm-2. Density functional theory and in situ Raman spectroscopy suggest that a suitable interstitial BEF can not only optimize the intermediate's adsorption but also promote hydrogen spillover.

Electric field tuning of a nickel zinc ferrite resonator by non-linear magnetoelectric effects

The nature of nonlinear magnetoelectric (NLME) effect has been investigated at room-temperature in a single-crystal Zn substituted nickel ferrite. Tuning of the frequency of magnetostatic surface wave (MSSW) modes under an applied pulsed DC electric field/current has been utilized to probe the effect. The frequencies of the modes at 8–20 GHz were found to decrease by ~ 400 MHz for an applied DC power P of ~ 100 mW and the frequency shift was the same for all of the MSSW modes and linearly proportional to P. A model is proposed for the effect and the NLME phenomenon was interpreted in terms of a reduction in the saturation magnetization due to the DC current. The decrease of magnetization with applied electric power, estimated from data on mode frequency versus P, was − 2.50 G/mW. The frequency tuning efficiency of the MSSW modes due to NLME effects in the ferrite resonator was found to be 4.1 MHz/mW which is an order of magnitude higher than the shift reported for M-type strontium and barium hexaferrite resonators investigated earlier. The spinel ferrite resonator discussed here has the potential for miniature, electric field tunable, planar microwave devices for the 8–20 GHz frequency range.

Computational Design of a Split Cavity with Localized Independent Electric Field Tunability

Computational Design of a Split Cavity with Localized Independent Electric Field Tunability

Interfacial Electric Field Tuning Carbon-Catalyzed Persulfate Activation toward a Maneuverable Oxidation Pathway for Enhanced Removal of Bisphenol A

Interfacial Electric Field Tuning Carbon-Catalyzed Persulfate Activation toward a Maneuverable Oxidation Pathway for Enhanced Removal of Bisphenol A

Magnetic ε-Phosphorene for Sensing Greenhouse Gas Molecules.

It is critical for gas sensors that sense greenhouse gas molecules to have both good sensitivity and selectivity for water molecules in the ambient environment. Here, we study the charge transfer, IV curves, and electric field tuning of vanadium-doped monolayer ϵ-phosphorene as a sensor for NO, NO2, and H2O gas molecules via first-principle and transport calculations. We find that the paramagnetic toxic molecules of NO and NO2 have a high adsorption energy on V-ϵ-phosphorene, which originates from a large amount of charge transfer driven by the hybridisation of the localised spin states of the host with the molecular frontier orbital. Using the non-equilibrium Green's function, we investigate the IV responses with respect to the adsorption of different molecules to study the performance of gas molecule sensors. Our IV curves show a larger amount of changes in resistance of the paramagnetic NO and NO2 than nonmagnetic H2O gas molecules, suggesting both sensitivity and selectivity. Moreover, our calculations show that an applied external electric field (gate voltage) can effectively tune the amount of charge transfer. More charge transfer makes the sensor more sensitive to the molecule, while less charge transfer can reduce the adsorption energy and remove the adsorbed molecules, allowing for the repeated use of the sensor.

Tunable Interfacial Charge Transfer in a 2D-2D Composite for Efficient Visible-Light-Driven CO2 Conversion.

Photocatalytic CO2 conversion for hydrocarbon fuel production has been known as one of the most promising strategies for achieving carbon neutrality. Yet, its conversion efficiency remains unsatisfactory mainly due to its severe charge-transfer resistance and slow charge kinetics. Herein, a tunable interfacial charge transfer on an oxygen-vacancies-modified bismuth molybdate nanoflower assembled by 2D nanosheets (BMOVs) and 2D bismuthene composite (Bi/BMOVs) is demonstrated for photocatalytic CO2 conversion. Specifically, the meticulous design of the Ohmic contact formed between BMOVs and bismuthene can allow the modulation of the interfacial charge-transfer resistance. According to density functional theory (DFT) simulations, it is ascertained that such exceptional charge kinetics is attributed to the tunable built-in electric field (IEF) of the Ohmic contact. As such, the photocatalytic CO2 reduction performance of the optimized Bi/BMOVs (CO and CH4 productions rate of 169.93 and 4.65µmol g-1 h-1 , respectively) is ca. 10 times higher than that of the pristine BMO (CO and CH4 production rates of 16.06 and 0.51µmol g-1 h-1 , respectively). The tunable interfacial resistance of the Ohmic contact reported in this work can shed some important light on the design of highly efficient photocatalysts for both energy and environmental applications.

Magnetoelectric tuning of spin, valley, and layer-resolved anomalous Nernst effect in transition-metal dichalcogenides bilayers

The anomalous Nernst coefficient (ANC) for transition-metal dichalcogenide (TMD) bilayers is studied with a focus on the interplay between layer pseudospin, spin, and valley degrees of freedom when electric and exchange fields are present. Breaking the inversion and time reversal symmetries via respectively electric and exchange fields results for bilayer TMDs in a spin-valley-layer polarized total ANC. Conditions are determined for controlling the spin, valley, and layer-resolved contributions via electric field tuning. Our results demonstrate the control of layer degree of freedom in bilayer TMDs magnetoelectrically which is of relevance for possible applications in spin/valley caloritronics.