Water-Stable CsPbBr3/Reduced Graphene Oxide Nanoscrolls for High-Performance Photoelectrochemical Sensing

Perovskite quantum dots (PQDs) have attracted much attention in the field of photoelectrochemical (PEC) sensors owing to their superb optical properties and efficient charge transport, but the inherent poor stability severely hinders their PEC applications. Herein, hydrolysis-resistant CsPbBr₃/reduced graphene oxide nanoscrolls (CsPbBr₃/rGO NSs) are obtained by solvent-assisted self-rolling process toward water-stable PEC sensors. CsPbBr₃ QDs embedded in rGO nanosheets can be prevented from water since the multilayer rGO shell layers, which maintains excellent optical properties. On account of strong interfacial interactions, rGO nanosheets are crimped spontaneously with CsPbBr₃ QDs, which offer access to superb structural and long-term storage stability. Moreover, appropriate band alignment and ultrafast interfacial carrier transfer enable CsPbBr₃/rGO NSs to exhibit greatly enhanced anode photocurrent response for subsequent PEC sensing. As a demonstration, the molecular imprinted PEC sensors for two kinds of mycotoxins (aflatoxin B1 or ochratoxin A) presents an ultra-high sensitivity and good anti-interference ability. Significantly, this work provides an inspirable and convenient route for hydrolysis-resistant PQDs-based optoelectronic and photoelectrocatalytic applications in aqueous ambience.     

Tuning the Charge Transfer Dynamics of the Nanostructured GaN Photoelectrodes for Efficient Photoelectrochemical Detection in the Ultraviolet Band

The intriguing surface sensitivity of the single-crystalline semiconductor nanowires offers tremendous opportunity in tuning the physical properties of nanophotonic and nanoelectronic devices for versatile applications. Particularly, in the pursuit of emerging photoelectrochemical (PEC)-type devices, significant efforts have been devoted to understanding the charge transfer dynamics between the nanowires and the electrolyte. Here, a PEC-type ultraviolet photodetector consisting of GaN p-n junction nanowires as photoelectrodes is constructed. It is found that two competing charge transport processes at the nanowires’ surface as well as in the p-n junction co-determine the photoresponsive behavior of the device. Furthermore, the surface platinum (Pt) decoration has successfully tuned the charge transfer dynamics by enhancing the charge transport efficiency at the surface, resulting in a twenty-fold increase of the photocurrent compared to the pristine GaN nanowires. Theoretical calculations reveal that the newly formed electronic states at the Pt/GaN interface account for the improved charge transfer at the surface, and the optimal hydrogen adsorption energy contributes to the boosted PEC reaction rate. The synergy of these two effects uncover the underlying mechanism of the high photoresponse of the constructed Pt/GaN-nanowires-based PEC photodetectors.     

Hematite Photoanodes: Synergetic Enhancement of Light Harvesting and Charge Management by Sandwiched with Fe2TiO5/Fe2O3/Pt Structures

Efficient charge separation and transport as well as high light absorption are key factors that determine the efficiency of photoelectrochemical (PEC) water splitting devices. Here, a PEC device consisting of a hematite nanoporous film deposited on Pt nanopillars, followed by the decoration with an Fe₂TiO₅ passivation layer, is designed and fabricated. This structure can largely improve the light absorption in the composite materials, and significantly enhance the water oxidation performance of hematite photoanodes. The Fe₂TiO₅ thin shell and Pt underlayer significantly improve the interfacial charge transfer while minimizing the hole‐migration length in Fe₂O₃ photoanodes, leading to a drastically increased photocurrent density. Specially, the Fe₂TiO₅/Fe₂O₃/Pt photoanode yields an excellent photoresponse for PEC water splitting reactions with 1.0 and 2.4 mA cm^?2 obtained at 1.23 and 1.6 V_RHE under AM 1.5G illumination in 1 m KOH. The resulting photocurrents are 2.5 times enhanced compared to a pristine Fe₂O₃ photoanode of the same geometry. These results demonstrate a synergistic charge transfer effect of Fe₂TiO₅ and Pt layers on hematite for the improvement of PEC water oxidation.     

An Integrated Metal-Free Modification Method to Construct Efficient and Durable Bulk Heterojunction Photocathode for Solar Hydrogen Production

Polymer semiconductor with bulk heterojunction (BHJ) structure has attracted increasing attention to fabricate highly efficient photoelectrode for converting solar energy and water into hydrogen, thanks to its high photocurrent output and positive onset potential beyond 0.6 V. However, BHJ-based photoelectrodes demonstrate poor anticorrosion against irradiation in aqueous environment, thus the photoelectrochemical (PEC) stability is a very intractable problem to solve. Herein, an inside and outside integrated modification method is developed to help BHJ-based photocathode withstand PEC erosion during hydrogen production in acidic solution. The obtained BHJ (PBDB-T:ITIC:PC₇₁BM)-based photocathode with surface carbon protective layer allows sustained and fast PEC hydrogen evolution (an average photocurrent density up to 13.5 mA cm⁻²) for a duration up to 15 h, which is among the best results of BHJ-based photocathodes. The internal modification with fullerene derivative of PC₇₁BM boosts the photogenerated electron transfer to balance against relative fast hole transfer, which largely alleviates electron accumulation and improves PEC intrinsic stability as a result. The surface carbon layer effectively resists the permeation of aqueous electrolyte without hindering interfacial charge transfer. This metal-free protective method is very promising toward construction of highly robust BHJ-based photoelectrodes for sustainable water splitting.     

Potential‐Specific Structure at the Hematite–Electrolyte Interface

The atomic‐scale structure of the interface between a transition metal oxide and aqueous electrolyte regulates the interfacial chemical reactions fundamental to (photo)electrochemical energy conversion and electrode degradation. Measurements that probe oxide–electrolyte interfaces in situ provide important details of ion and solvent arrangements, but atomically precise structural models do not exist for common oxide–electrolyte interfaces far from equilibrium. Using a novel cell, the structure of the hematite (α‐Fe₂O₃) ()–electrolyte interface is measured under controlled electrochemical bias using synchrotron crystal truncation rod X‐ray scattering. At increasingly cathodic potentials, charge‐compensating protonation of surface oxygen groups increases the coverage of specifically bound water while adjacent water layers displace outwardly and became disordered. Returning to open circuit potential leaves the surface in a persistent metastable state. Therefore, the flux of current and ions across the interface is regulated by multiple electrolyte layers whose specific structure and polarization change in response to the applied potential. The study reveals the complex environment underlying the simplified electrical double layer models used to interpret electrochemical measurements and emphasizes the importance of condition‐specific structural characterization for properly understanding catalytic processes at functional transition metal oxide–electrolyte interfaces.     

Quantitative Determination of Charge Transport Interface at Vertically Phase Separated Soluble Acene/Polymer Blends

Interfacial structure is critical for optimizing the electrical properties of organic field-effect transistors. In this study, the interfacial structures of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/polymer blends are nondestructively determined by the complementary neutron and X-ray reflectivity. The TIPS-pentacene/deuterated poly(methylmethacrylate) (d-PMMA) blends exhibit a vertically phase-separated structure with a molecularly sharp interface (interfacial roughness ≈5 Å), whereas the TIPS-pentacene/d-polystyrene (d-PS) blend intermix near the interface. Ultrahigh molecular weight d-PMMA leads to the formation of surface-segregated hexagonal spherulites of TIPS-pentacene owing to the thermodynamic factors (e.g., surface/interface energy, polarity, and viscosity) of the blending materials. The well-developed hexagonal spherulites of TIPS-pentacene on molecularly sharp d-PMMA interface result in higher field-effect mobility as compared to the dendritic crystals from d-PS blends because of the higher perfectness, coverage, and interfacial roughness of the TIPS-pentacene crystals. The approach used in this study facilitates the understanding of the charge transport mechanism at the phase-separated interfaces in soluble acene/polymer blends.     

Interfacial Charge Transfer Bridge Prolongs Carrier Recombination Lifetimes of CoFe Metal-Thiolate Framework/Hematite Photoanode for Water Oxidation

Constructing heterostructural photoanodes is attractive for elevating the photoelectrochemical (PEC) performance, however, it is a long-standing challenge to achieve highly efficient interfacial charge transfer. Herein, a CoFe metal-thiolate framework (CoFe MTF)/Fe₂O₃ photoanode connected by an interfacial Fe─O─N/S bond is designed to modulate the behavior of charge carriers and improve water oxidation performance. It is disclosed that this interfacial bond functions as a direct charge transfer bridge between shallow trap states of Fe₂O₃ and CoFe MTF, leading to prolonged carrier recombination lifetimes (85 ns for CoFe MTF/Fe₂O₃ compared to 37 ns for Fe₂O₃) and enhanced charge transfer efficiency. Alternatively, a robust interfacial electric field is established in the CoFe MTF/Fe₂O₃ p–n heterojunction, facilitating efficient charge transfer. As expected, the CoFe MTF/Fe₂O₃ photoanode exhibits significant enhancement in water oxidation, resulting in a three-fold increase in photocurrent density compared to pristine Fe₂O₃. This study highlights the significance of designing interfacially bonded heterostructural photoelectrodes to regulate the transfer characters of charge carriers.     

Dirac Cone Spin Polarization of Graphene by Magnetic Insulator Proximity Effect Probed with Outermost Surface Spin Spectroscopy

The effects of the proximity contact with magnetic insulator on the spin‐dependent electronic structure of graphene are explored for the heterostructure of single‐layer graphene (SLG) and yttrium iron garnet Y₃Fe₅O₁₂ (YIG) by means of outermost surface spin spectroscopy using a spin‐polarized metastable He atom beam. In the SLG/YIG heterostructure, the Dirac cone electrons of graphene are found to be negatively spin polarized in parallel to the minority spins of YIG with a large polarization degree, without giving rise to significant changes in the π band structure. Theoretical calculations reveal the electrostatic interfacial interactions providing a strong physical adhesion and the indirect exchange interaction causing the spin polarization of SLG at the interface with YIG. The Hall device of the SLG/YIG heterostructure exhibits a nonlinear Hall resistance attributable to the anomalous Hall effect, implying the extrinsic spin–orbit interactions as another manifestation of the proximity effect.     

Constructing Conductive Interfaces between Nickel Oxide Nanocrystals and Polymer Carbon Nitride for Efficient Electrocatalytic Oxygen Evolution Reaction

Combining transition metal oxide catalysts with conductive carbonaceous material is a feasible way to improve the conductivity. However, the electrocatalytic performance is usually not distinctly improved because the interfacial resistance between metal oxides and carbon is still large and thereby hinders the charge transport in catalysis. Herein, the conductive interface between poorly conductive NiO nanoparticles and semi‐conductive carbon nitride (CN) is constructed. The NiO/CN exhibits much‐enhanced oxygen evolution reaction (OER) performance than corresponding NiO and CN in electrolytes of KOH solution and phosphate buffer saline, which is also remarkably superior over NiO/C, commercial RuO₂, and mostly reported NiO‐based catalysts. X‐ray photoelectron spectroscopy and extended X‐ray absorption fine structure spectrum reveal that a metallic Ni–N bond is formed between NiO and CN. Density functional theory calculations suggest that NiO and CN linked by a Ni–N bond possess a low Gibbs energy for OER intermediate adsorptions, which not only improves the transfer of charge but also promotes the transmission of mass in OER. The metal–nitrogen bonded conductive and highly active interface pervasively exists between CN and other transition metal oxides including Co₃O₄, CuO, and Fe₂O₃, making it promising as an inexpensive catalyst for efficient water splitting.     

Typical strategies to facilitate charge transfer for enhanced oxygen evolution reaction: Case studies on hematite

Hydrogen can be sustainably produced through photoelectrochemical (PEC) water splitting. The process of PEC water splitting is composed of two vital half-reactions: water oxidation to O₂ on photoanode, and proton reduction to H₂ on photocathode. Both in thermodynamics and kinetics, the oxidation of water on photoanode is much more challenging, because the formation of O₂ involves the four-holes reaction process that is more difficult than the two-protons reduction. Accordingly, the oxidation of water into O₂ is the rate-determining reaction for PEC water splitting, which is closely affected by the light harvesting, charge separation and transfer, as well as surface activity of photoanode. In principle, water oxidation is initiated by the photo-excited charge of photoanode. In this review, we took hematite photoanode as a typical example to illustrate the progress in modifying the charge separation and migration property of metal-oxide photoanodes for water oxidation. The typical strategies adopted to facilitate the charge transfer and separation of hematite photoanode were specifically summarized. In addition, the views designing and developing hematite photoanode with high-performance for water oxidation were presented. This review provides comprehensive information about the state-of-the-art progress of hematite-based photoanodes and forecast the developing directions of photoanode materials for solar water splitting.     

Role of Charge Density Wave in Monatomic Assembly in Transition Metal Dichalcogenides

The charge density wave (CDW) in transition metal dichalcogenides (TMDs) has drawn tremendous interest due to its potential for tailoring their surface electronic and chemical properties. Due to technical challenges, however, how the CDW could modulate the chemical behavior of TMDs is still not clear. Here, this work presents a study of applying the CDW of NbTe₂, with a high transition temperature above room temperature, to generate the assembling adsorption of Sn adatoms on the surface. It is shown that highly ordered monatomic Sn adatoms with a quasi‐1D structure can be obtained under regulation by the single‐axis CDW of the substrate. In addition, the CDW modulated superlattices could in turn change the surface electronic properties from semimetallic to metallic. These results demonstrate an effective approach for tuning the surface chemical properties of TMDs by their CDWs, which could be applied in exploring them for various practical applications, such as heterogeneous catalysis, epitaxial growth of low‐dimensional materials, and future nanoelectronics.     

Rational Design of Colloidal Core/Shell Quantum Dots for Optoelectronic Applications

Colloidal core/shell quantum dots (QDs) are promising for solar technologies because of their excellent optoelectronic properties including tunable light absorption/emission spectra, high photoluminescence quantum yield (PLQY), suppressed Auger recombination, efficient charge separation/transfer, and outstanding photo-/thermal-/chemical stability. In this review, engineered core/shell QDs with various types of band structures and corresponding device performance in luminescent solar concentrators (LSCs), light-emitting diodes (LEDs), solar-driven photoelectrochemical (PEC) devices, and QDs-sensitized solar cells (QDSCs) are summarized. In particular, the applications of interfacial layer engineering and eco-friendly, heavy metal-free core/shell QDs in optoelectronic devices are highlighted. Finally, strategies towards the developments and practical perspectives of core/shell QDs are briefly mentioned to offer guidelines for achieving prospective high-efficiency and long-term stable QD devices.     

Electronic Modulation of Metal–Organic Frameworks by Interfacial Bridging for Efficient pH-Universal Hydrogen Evolution

Designing well-defined interfacial chemical bond bridges is an effective strategy to optimize the catalytic activity of metal–organic frameworks (MOFs), but it remains challenging. Herein, a facile in situ growth strategy is reported for the synthesis of tightly connected 2D/2D heterostructures by coupling MXene with CoBDC nanosheets. The multifunctional MXene nanosheets with high conductivity and ideal hydrophilicity as bridging carriers can ensure structural stability and sufficient exposure to active sites. Moreover, the Co–O–Ti bond bridging formed at the interface effectively triggers the charge transfer and modulates the electronic structure of the Co-active site, which enhances the reaction kinetics. As a result, the optimized CoBDC/MXene exhibits superior hydrogen evolution reaction (HER) activity with low overpotentials of 29, 41, and 76 mV at 10 mA cm⁻² in alkaline, acidic, and neutral electrolytes, respectively, which is comparable to commercial Pt/C. Theoretical calculation demonstrates that the interfacial bridging-induced electron redistribution optimizes the free energy of water dissociation and hydrogen adsorption, resulting in improved hydrogen evolution. This study not only provides a novel electrocatalyst for efficient HER at all pH conditions but also opens up a new avenue for designing highly active catalytic systems.     

Intrinsic Polarization of Self-Assembled Guanosine Supramolecules in GaN-Based Metal–Semiconductor–Metal Nano-Structures

The transport properties of self-assembled guanosine supramolecules (SAGS) confined within nanoscale metal electrodes on transparent GaN semiconductor substrates have been studied. The modified guanosine molecules have been used as self-assembled nanowires to realize nanoscale UV-Visible photodetectors with self-assembly length ranging from 30 to 450 nm. The ribbon-like guanosine supramolecules exhibit semiconductor properties and have polarization along its axis due to the strong intrinsic dipole moment of guanosine molecules. The charge transport through the SAGS wire with nanoscale metal-semiconductor-metal structure on passivated Ga-terminated GaN surface can be explained by Schottky type conductivity and near-surface-states. The intrinsic polarization in SAGS nano-wires changes the band-offset at the metal-semiconductor interface similar to semiconductor photodiodes.      

Nanogenerators with Superwetting Surfaces for Harvesting Water/Liquid Energy

Water covers about 70% of the earth's surface and contains tremendous energy that remains untapped. Despite success in harvesting hydrodynamic energy based on heavy‐weight and bulky electromagnetic generators, a great deal of water energies stored in the low‐frequency flow of water such as in the form of raindrops, river/ocean waves, and the tide, remain largely untapped. In spite of diversity in development strategies and working mechanisms, engineering efficient water energy harvesting devices, especially nanogenerators, requires the elegant control of interfacial properties of substrates for rapid liquid mass and momentum transfer and effective electron generation/transfer. In particular, inspired by various special wetting phenomena in nature, the design of superwetting surfaces offers a new dimension to fundamentally mediate the way the liquid, as well as the charge, interact with the substrate. Herein, the latest progress in the development of nanogenerators with three distinctive interface types—solid/liquid, solid/solid, and liquid/liquid interfaces—are summarized and their representative applications, challenges, and future perspectives are highlighted.     

过渡层和界面电荷对金属硅化物/硅肖特基接触特性的影响

针对金属硅化物／硅接触存在过渡层，提出了分析这种结构的肖特基接触特性的模型；讨论了过渡层厚度、界面电行及有关参数的影响，分析了不同退火条件下PtSi／Si肖特基二极管的特性。     

Effect of heat treatment on WO3-loaded TiO2 nanotubes for hydrogen generation via enhanced water splitting

We determined the optimum phase structure of WO₃-loaded TiO₂ nanotubes (WTNs) for hydrogen generation via photoelectrochemical (PEC) water splitting by controlling the annealing temperature. The surface morphology of WTNs was closely related to crystal growth and phase transformation. The nanotubular structure completely collapsed at 700 °C due to the anatase–rutile phase transformation. In PEC studies, high-crystallinity anatase-phase WTNs exhibited a higher photocurrent density (2.4 mA/cm²) than WTNs of amorphous or polycrystalline (anatase+rutile) phases. This can mainly be attributed to better charge carrier separation and transportation in PEC water splitting by providing an effective way to address recombination losses.     

Metal/Metal‐Oxide Interfaces: How Metal Contacts Affect the Work Function and Band Structure of MoO3

When transition metal oxides are used in practical applications, such as organic electronics or heterogeneous catalysis, they often must be in contact with a metal. Metal contacts can affect an oxide's chemical and electronic properties within the first few nanometers of the contact, resulting in changes to an oxide's chemical reactivity, conductivity, and energy‐level alignment properties. These effects can alter an oxide's ability to perform its intended function. Thus, the choice of contacting metal becomes an important design consideration when tailoring the properties of transition‐metal oxide thin films or nanoparticles. Here, metal/metal‐oxide interfaces involving a widely used oxide in organic electronics, MoO₃, are examined. It is demonstrated that metal contacts tend to reduce the Mo⁶⁺ cation to lower oxidation states and, consequently, alter MoO₃’s valence electronic structure and work function when the oxide layer is very thin (less than 10 nm). MoO₃ becomes semimetallic and has a lower work function near metal contacts. The observed behavior is attributed to two causes: 1) charge transfer from the metal Fermi level into MoO₃’s low‐lying conduction band and 2) an oxidation‐reduction reaction between the metal and MoO₃ that results in oxidation of the metal and reduction of MoO₃. These results illustrate how interfaces are important to an oxide's ability to provide energy‐level alignment.     

Impacts of gate electrode materials on threshold voltage (V/sub th/) instability in nMOS HfO/sub 2/ gate stacks under DC and AC stressing

Ultrathin nMOSFET hafnium oxide (HfO/sub 2/) gate stacks with TiN metal gate and poly-Si gate electrodes are compared to study the impact of the gate electrode on long term threshold instability reliability for both dc and ac stress conditions. The poly-Si/high-/spl kappa/ interface exhibits more traps due to interfacial reaction than the TiN/high-/spl kappa/ interface, resulting in significantly worse dc V/sub th/ instability. However, the V/sub th/ instability difference between these two stacks decreases and eventually diminishes as ac stress frequency increases, which suggests the top interface plays a minor role in charge trapping at high operating frequency. In addition, ac stress induced interface states (Nit) can be effectively recovered, resulting in negligible G/sub m/ degradation.