Band Structure Effects Research Articles

Effect of band structure on the photocatalytic performance of CsPbBr3/UiO-66 composites

Photocatalytic technology driven by sunlight is rapidly developing in response to energy shortage and environmental pollution. ABX3 perovskite materials have gained widespread attention in photocatalysis due to their narrow band gap, high quantum efficiency, and high carrier mobility. The energy band structure plays a critical role in carrier generation, separation and redox processes in photocatalytic reactions. In this paper, we modulated the energy band structures of CsPbBr3 and UiO-66 by changing the reaction parameters, and prepared CsPbBr3/UiO-66 composites with different energy band structures to investigate photocatalytic activities. Our results showed that the degradation rate of (Methyl Orange) MO by CsPbBr3/UiO-66 was significantly enhanced. The change in the CsPbBr3 energy band structure did not significantly affect the photocatalytic activity of the composites. This work provides a new opportunity to improve the photocatalytic performance of perovskite-based composites using the energy band structure regulation strategy. Our findings may contribute to the design and development of highly efficient and stable perovskite-based photocatalysts for environmental remediation and energy conversion.

Low-energy Compton scattering in materials

Low-energy Compton scattering is an important background for sub-GeV dark matter direct-detection and other experiments. Current Compton scattering calculations typically rely on assumptions that are not valid in the low-energy region of interest, beneath ∼50 eV. Here we relate the low-energy Compton scattering differential cross section to the dielectric response of the material. Our new approach can be used for a wide range of materials and includes all-electron, band-structure, and collective effects, which can be particularly relevant at low energies. We demonstrate the strength of our approach in several solid-state systems, in particular, Si, Ge, GaAs, and SiC, which are relevant for current and proposed experiments searching for dark matter, neutrinos, and millicharged particles. Published by the American Physical Society 2024

High-Mobility Compensated Semimetals, Orbital Magnetization, and Umklapp Scattering in Bilayer Graphene Moiré Superlattices.

Twist-controlled moiré superlattices (MSs) have emerged as a versatile platform for realizing artificial systems with complex electronic spectra. The combination of Bernal-stacked bilayer graphene (BLG) and hexagonal boron nitride (hBN) can give rise to an interesting MS, which has recently featured a set of unexpected behaviors, such as unconventional ferroelectricity and the electronic ratchet effect. Yet, the understanding of the electronic properties of BLG/hBN MS has, at present, remained fairly limited. Here, we combine magneto-transport and low-energy sub-THz excitation to gain insights into the properties of this MS. We demonstrate that the alignment between BLG and hBN crystal lattices results in the emergence of compensated semimetals at some integer fillings of the moiré bands, separated by van Hove singularities where the Lifshitz transition occurs. A particularly pronounced semimetal develops when eight holes reside in the moiré unit cell, where coexisting high-mobility electron and hole systems feature strong magnetoresistance reaching 2350% already at B = 0.25 T. Next, by measuring the THz-driven Nernst effect in remote bands, we observe valley splitting, indicating an orbital magnetization characterized by a strongly enhanced effective gv-factor of 340. Finally, using THz photoresistance measurements, we show that the high-temperature conductivity of the BLG/hBN MS is limited by electron-electron umklapp processes. Our multifaceted analysis introduces THz-driven magnetotransport as a convenient tool to probe the band structure and interaction effects in van der Waals materials and provides a comprehensive understanding of the BLG/hBN MS.

Regulation of Bi2O3 phase structure improves the self-powered UV-blue dual‐band photoresponse of Bi2O3/TiO2 photodetectors and the imaging application

Bi2O3 semiconductors with excellent optical and electrical properties can be used in photodetectors (PDs). For different phase structures of Bi2O3 with corresponding optoelectronic properties in Bi2O3 due to differences in crystal structure and energy band structure, it is important to control the phase structure to obtain high-performance Bi2O3-based PDs. Herein, Bi2O3 nanosheet films with α and β phase structures controlled by the annealing temperature are deposited on the surface of TiO2 nanorod arrays (NRs) to construct ultraviolet (UV)-blue self-powered PDs. The effects of the energy band structure, Fermi level and carrier mobility of Bi2O3 films with different phase structures on the performance of Bi2O3/TiO2 PDs are investigated by combining theoretical calculations and experimental. The β-Bi2O3/TiO2 PDs with strong built-in electric field, large carrier mobility, small interfacial transfer resistance and long carrier lifetime exhibit excellent photoresponse characteristics. The PD demonstrates a responsivity of 26.7 mA W−1 and detectivity of 5.93 × 1011 Jones under 365 nm illumination. In addition, the imaging application of β-Bi2O3/TiO2 PD is explored by extending the photocurrent mapping values of a single PD unit to a complex array of optical information image processing in complex environments utilizing the UV-blue dual-band self-powered photoresponse properties of the PDs.

Electrochemiluminescence Properties and Sensing Application of Zn(II)-Metal-Organic Frameworks Constructed by Mixed Ligands of Para Dicarboxylic Acids and 1,10-Phenanthroline.

Four metal-organic frameworks (MOFs) were designed and prepared through a mixed-ligand strategy by controlling the combination of various dicarboxylic acid ligands with invariant center metal and o-phenanthroline heterocyclic ligand. The regulatory effects of ligand electronic band and crystal structure on the electrochemiluminescence (ECL) characteristics of MOFs were verified by experimental results and density functional theory (DFT) calculations. The flexible chain structure of MOF-2 promotes electron transfer between MOF electroactive free radicals and the co-reactant, making it show outstanding ECL characteristics among all of the four MOFs with the luminescence quantum efficiency 8.37 times that of tris(bipyridine)-ruthenium(II) ([Ru(bpy)3]2+). Meanwhile, a new ECL mechanism for MOF luminescent crystal materials with reactive oxygen species in solvents as a co-reactant in the aqueous aerobic environment has been proposed. MOF-2 was selected to construct an ECL sensor for the determination of glucose in human urine samples. This study provides a useful idea for the development and design of new luminescent molecular crystal materials.

Intercalation in 2H-TaSe[formula omitted] for modulation of electronic properties and electrochemical energy storage

Two-dimensional transition metal dichalcogenides (TMDs) exhibit an extensive variety of novel electronic properties, such as charge density wave quantum spin Hall phenomena, superconductivity, and Dirac and Weyl semi-metallic properties. The diverse properties of TMDs suggest that structural transformation can be employed to switch between different electronic properties. Intercalation and zero valence doping of molecules and atoms into the van der Waals gap of TMDs have emerged as effective approaches to modify the charge order states of the material. This eventually leads to phase transition or the formation of different phases, thus expanding the electronic, thermoelectric and optical applications of these materials. In this study, electronic and electrochemical energy storage properties of such an intercalated TMD, namely, 2H-TaSe2 via intercalation of lithium (Li), sodium (Na) and potassium (K) have been investigated. The intercalation of these ions into the dichalcogenide resulted in a modified band structure and novel structural effects, leading to the emergence of a 1 eV band gap. Possibility of electrochemical energy storage application is also explored in this study. Furthermore, the importance of multi orbital electron–electron correlations in intercalated TaSe2 is also investigated via dynamical-mean-field theory with local density approximation.

DFT study on ORR catalyzed by bimetallic Pt-skin metals over substrates of Ir, Pd and Au

Bimetallic Pt-skin catalyst is a class of near-surface alloy (NSA) that owns a high degree of control over composition. Herein, density functional theory (DFT) is used to calculate the energetics of oxygen reduction reaction (ORR) on Pt-skin over Ir, Pd and Au substrates. A Brønsted-Evans-Polanyi (BEP) relationship can be determined for the oxygen molecule dissociation. The binding energy of both atomic oxygen and hydroxyl radical is found to correlate well with the d band center of Pt-skin atoms. Their catalytic activities show the volcano relationship as the positions of each substrate in the periodic table. The effect of surface strain, band structure and charge transfer on the d band center is well studied, and it can be found that the surface strain effect plays a dominant role for all Pt-skin catalysts. Ir substrate makes the d band center of Pt-skin go far away from the Fermi level, while Au substrate makes it move towards the Fermi level. Being different from both Ir and Au, Pd substrate makes the d band center of Pt-skin comparable with the monometallic Pt.

(Invited) Engineering Molecular Solids and Monolithic Thin Films from Chromophoric Building Blocks: Model Systems and Integration into Devices

Functioning devices exploiting the properties of organic chromophores, e.g. in the context of photovoltaics, organic electronics, light-emitting devices, and photodetectors, often rely on the assembly of the molecules into appropriate solids and their interfacing to electrodes. In this context, recently the MOF-based approach [1] is receiving increasing attention. In this case, the organic chromophores (anthracene, pentacene, naphthalene-diimides, perylene-diimides, porphyrins, phthalocyanines, ...) are equipped with at least two coupling units so as to yield ditopic linkers suited for the coupling to metal- or metal-oxo nodes, thus yielding metal-organic frameworks (MOFs). Although the standard form of MOFs, powders, are not well suited for the integration of the arrayed chromophores into devices, in the past decade a number of methods able to yield high quality, monolithic MOF thin films deposited on a variety of substrates have been developed. Sophisticated fabrication methods, including layer-by-layer approaches yield films of impressive optical quality.[2]Optical absorption properties of condensed chromophores are often strongly affected by inter-molecular interactions. The periodic structure of MOFs provides the basis for a rational design of such assemblies, and e.g. J-aggregates have been first simulated and then realized experimentally.[3] In addition, band-structure effects like indirect band gaps can be realized in such periodic arrangements.[4] Finally, the implementation of chiral linkers allows to realize chiroptical phenomena, including the emission of circular polarized light and helicity-sensitive photodetectors.[5]Lbl architectures also allow the fabrication of heterostructures with built-in interfaces,[6] with interesting application e.g. in the context of photon up-conversion. A particularly attractive option is to exploit the porous nature of the MOFs in connection with the lbl method. An interesting example is the loading of C60 into the pores of SURMOFs and the subsequent integration into devices, e.g. in the context of photoconductivity [7] or organic diodes.[8] In the context of nonlinear optical properties, using sophisticated assembly strategies were recently used to fabricate non-centrosymmetric SURMOFs with built-in electric fields and large SHG activity.[9]In this presentation we well present selected successful examples of integrating organic chromophores into SURMOFs and the subsequent fabrication of functioning devices. We will in particular highlight the close interaction with theory. Such an advanced in-silico conquering of chemical spaces is mandatory, since the number of known MOFs (> 100.000) is so large that experimental trial-and-error approaches are highly inefficient.

A Rational Strategy to Assemble Porphyrins and Phthalocyanins into Crystalline Arrays: The SURMOF Approach

Realizing molecular “Designer Solids” by programmed assembly of building units taken from libraries is a very appealing objective. Recently, metal-organic frameworks (MOFs), or porous coordination polymers (PCPs) have attracted a huge interest in this context. Here, we will focus on MOF-based electrochemical, photoelectro-chemical, photovoltaic, and sensor devices built using porphyrin- and phthalocyanine-containing linkers. Internal interfaces in MOF heterostructures are also of interest with regard to photon-upconversion and the fabrication of diodes.Since the fabrication of reliable and reproducible contacts to MOF-materials represent a major challenge, we have developed a layer-by-layer (lbl) deposition method to produce well-defined, highly oriented and monolithic MOF thin films on appropriately functionalized substrates. The resulting films are referred to as SURMOFs [1,2] and have very appealing properties in particular with regard to optical applications [3]. The fabrication of hetero-multilayers is rather straightforward with this lbl method. In this talk, we will describe the principles of SURMOF fabrication as well as the results of systematic investigations of electrical and photophysical properties exhibited by empty MOFs and after loading their pores with functional guests. Band structure effects occurring in crystalline porphyrin arrays assembled using the SURMOF approach will also be discussed. [5] We will close with discussing further applications [4] realized by loading MOFs with nanoparticles or quantum dots and by creating molecular solids lacking inversion symmetry for second harmonic generation (SHG).[5]In the last part of the presentation we will point out that SURMOFs are very well suited for unattended experimentation approaches. Using robot systems controlled by machine learning (ML) algorithms allows to efficiently optimize thin film properties (orientation, crystallinity, roughness). We will discuss this point in particular in connection with the fabrication of SURMOF-based sensor systems.

Selective photocatalytic oxidation of furfural to C4 compounds with metal-TS-1 zeolite

A series of metal-TS-1 zeolite catalysts were designed to selectively catalyze the photo oxidation of furfural to C4 carboxylic acid derivatives at ambient temperature and pressure. The photocatalytic preparation of malic acid from furfural was realized for the first time. The selective distribution of products could be controlled by adjusting the physical and chemical characteristics of the catalyst. Smaller pore size prevented the further conversion of maleic acid to malic acid; moderate acidity was beneficial for the preparation of malic acid; lower valence band was in favor of maleic acid production while higher valence band tended to form malic acid. The synergistic effect of pore structure, acidity and energy band structure of catalysts affected the product distribution. The yield of maleic acid reached as high as 40% over Fe-TS-1, meanwhile, the yield of malic acid reached as high as 63% over Ni-TS-1. The doping of metal was believed to be an effective procedure to adjust the structure and physicochemical properties of zeolite. Matel-TS-1 zeolite was also expected to be widely used in photocatalytic system to achieve more selective reactions.

Surface plasmon assisted high-performance photodetectors based on hybrid TiO2@GaOxNy-Ag heterostructure

In this work, we reported a high-performance-based ultraviolet-visible (UV-VIS) photodetector based on a TiO2@GaOxNy-Ag heterostructure. Ag particles were introduced into TiO2@GaOxNy to enhance the visible light detection performance of the heterojunction device. At 380 nm, the responsivity and detectivity of TiO2@GaOxNy-Ag were 0.94 A/W and 4.79 × 109 Jones, respectively, and they increased to 2.86 A/W and 7.96 × 1010 Jones at 580 nm. The rise and fall times of the response were 0.19/0.23 and 0.50/0.57 s, respectively. Uniquely, at 580 nm, the responsivity of fabricated devices is one to four orders of magnitude higher than that of the photodetectors based on TiO2, Ga2O3, and other heterojunctions. The excellent optoelectronic characteristics of the TiO2@GaOxNy-Ag heterojunction device could be mainly attributed to the synergistic effect of the type-Ⅱ band structure of the metal–semiconductor–metal heterojunction and the plasmon resonance effect of Ag, which not only effectively promotes the separation of photogenerated carriers but also reduces the recombination rate. It is further illuminated by finite difference time domain method (FDTD) simulation and photoelectric measurements. The TiO2@GaOxNy-Ag arrays with high-efficiency detection are suitable candidates for applications in energy-saving communication, imaging, and sensing networks.

Calculating the Electrons Distribution Function for Gallium Arsenide at Low Fields by Solving the Boltzmann Transport Equation.

The electron distribution function for gallium arsenide GaAs was calculated by using the Boltzmann transition equation in the central valley , for a range of low fields relative to the threshold field (E0 = 5.95Kv/cm) (0.3-1)E0. To obtain the distribution function, the Boltzmann transport equation was solved using a mechanism that combines the analytical and numerical methods. Analytical method involving extension of the Legendre polynomial was used and the effect of polar optical scattering was introduced as the dominant scattering mechanism in this research, as well as the effect of an asymmetric energy band structure with spherical energy surfaces in the central valley. After obtaining a partial differential equation of the second order, it is solved numerically after separation process for the variables using the direct matrix method in energy space by building a mathematical program using MATLAB. In this study, a system with dimensions of 360 × 360 was built, and the rate of change in energy was taken as 0.001.The computational system was tested by applying low electric fields, and the distribution function that was obtained had a Maxwellian distribution at very low fields, and it shifted from the Maxwellian distribution at higher fields close to the threshold field, and the results obtained were agree with previous results. While this system did not give accurate results at the high-electric fields.

Enhancement of TOC removal efficiency of sulfamethoxazole using catalysts in the radiation treatment: Effects of band structure and electrical properties of radiocatalysts

Photocatalysts in AOP have been used for the decomposition of recalcitrant organic pollutants. However, several technical issues associated with energy band gap of catalysts still limit the practical application of photocatalysts with sunlight and UV. Some catalysts with large energy band gap have been successfully used in the radiocatalytic systems using gamma radiation and electron beam. However, there has been little systematic studies for band structure and electrical properties of an appropriate radiocatalyst in the radiation treatment. Kinetic studies were conducted to evaluate the properties (conduction band, valence band, energy band gap, electron mobility, and stability) of catalysts suitable for the radiocatalytic system using high energy sources and the radiocatalytic oxidation performance for sulfamethoxazole (SMX). The lower the CB potential and/or the higher the VB potential was, the higher the oxidation performance of a catalyst was. Unlike the photocatalytic process (activating the catalysts with energy band gaps lower than 6.2 eV), the radiation system using a gamma ray could activate the catalyst with a comparatively large energy band gap (<1,240 keV). TOC removal efficiency for SMX (30 mg/L) with Al2O3 (2 g/L) as a radiocatalyst was enhanced up to 83.9 % at an absorbed dose of 5 kGy, compared to the control (radiation treatment without catalysts) showing 6.6 % TOC removal efficiency at the same condition. The stabilities of metal oxide catalysts were much higher (low self-degradation of 0.0006–0.01 % at 50 kGy) than those (0.07–0.44 % at 50 kGy) of metal sulfide catalysts. Since S2− is less electronegative than O2−, the VB holes of metal sulfide catalyst are more prone to self-degradation. The radiation technology has a wide range of selection for catalysts, and can be an effective alternative-treatment system for the mineralization of recalcitrant organic chemicals.

Evaluation of the structural, electronic, optical, and mechanical properties of Sb2Se3 using density functional theory

This work investigates the effect of band structure, optical spectra, computed elastic coefficients, Bulk-to-Shear modulus ratio, Young’s modulus and Poisson’s ratio in metal selenide compounds and their influence on electronic, optical, and elastic properties of bulk crystals using density functional theory (DFT). By studying the structural and geometrical parameters, we show that the V–VI group compound has a direct bandgap of 0.887[Formula: see text]eV and the band structure can be explained by a partial density of states (PDOS) plot. By using Pugh’s formation, the bulk-to-shear ratio can be significant in precisely determining the ductility of a material. Poisson’s ratio can provide information to examine whether the lattice crystal is ionic or covalent. Our elastic data show that the orthorhombic system is found to be unstable. The optical spectra (high absorption coefficient of [Formula: see text][Formula: see text]cm[Formula: see text], dielectric coefficient of 8.61 and reflective index of 2.93) of our current work would be beneficial to explore the applications of optoelectronic devices, especially in light-harvesting materials, covering the UV region. Our findings advance the knowledge of the structural, electronic, optical, vibrational, and mechanical properties of Sb2Se3, the key to their use, and explained the potential applications in photovoltaics perspectives.

Design of 2D/2D heterojunction of Ti3C2/BiOClxBr1−x for enhancing photocatalytic performance

Newly emerged 2D metallic Ti3C2 is highly spotlighted for its unique properties and ubiquitous compounding compatibility. Herein we pioneeringly demonstrate a heterojunction photocatalyst of Ti3C2/BiOClxBr1−x. X-ray diffraction, scanning electron microscope, transmission electron scope, and X-ray photoelectron spectroscopy analysis indicates that BiOClxBr1−x is successfully in-situ grown upon Ti3C2 nanosheets. Visible light photocatalytic performance of 7 %-Ti3C2/BiOCl0.25Br0.75 is overwhelmingly superior to BiOClxBr1−x with an increment of 11.9 times in the reaction rate constant of RhB photodegradation, owing to the distinctive Schottky heterojunction between Ti3C2 and BiOClxBr1−x. UV–vis absorbance, photoluminescence, Fourier transform infrared spectra, Raman, electrochemical impedance spectra, and transient photocurrent response account for the improved utilization of visible light, effective separation of photogenerated carriers, and more photogenerated electron acceptors, which elucidate the superior photocatalytic performance and good stability of Ti3C2/BiOClxBr1−x. Trapping experiments and electron paramagnetic resonance tests verify that the dominant active species of·O2- and h+ are responsible for the rapid degradation of RhB. The reasonable photocatalytic mechanism of Ti3C2/BiOClxBr1−x is clarified based on the energy band structure and synergistic effect of the heterojunction. This work provides some novel insights into designing 2D layered heterojunction photocatalysts, boosting photocatalytic performance, and advancing Ti3C2 application.

Recent progress of transport theory in Dirac quantum materials

Dirac quantum materials comprise a broad category of condensed matter systems characterized by low-energy excitations described by the Dirac equation. These excitations, which can manifest as either collective states or band structure effects, have been identified in a wide range of systems, from exotic quantum fluids to crystalline materials. Over the past several decades, they have sparked extensive experimental and theoretical investigations in various materials, such as topological insulators and topological semimetals. The study of Dirac quantum materials has also opened up new possibilities for topological quantum computing, giving rise to a burgeoning field of physics and offering a novel platform for realizing rich topological phases, including various quantum Hall effects and topological superconducting phases. Furthermore, the topologically non-trivial band structures of Dirac quantum materials give rise to plentiful intriguing transport phenomena, including longitudinal negative magnetoresistance, quantum interference effects, helical magnetic effects, and others. Currently, numerous transport phenomena in Dirac quantum materials remain poorly understood from a theoretical standpoint, such as linear magnetoresistance in weak fields, anomalous Hall effects in nonmagnetic materials, and three-dimensional quantum Hall effects. Studying these transport properties will not only deepen our understanding of Dirac quantum materials, but also provide important insights for their potential applications in spintronics and quantum computing. In this paper, quantum transport theory and quantum anomaly effects related to the Dirac equation are summarized, with emphasis on massive Dirac fermions and quantum anomalous semimetals. Additionally, the realization of parity anomaly and half-quantized quantum Hall effects in semi-magnetic topological insulators are also put forward. Finally, the key scientific issues of interest in the field of quantum transport theory are reviewed and discussed.

Adsorption energies on transition metal surfaces: towards an accurate and balanced description

Density functional theory predictions of binding energies and reaction barriers provide invaluable data for analyzing chemical transformations in heterogeneous catalysis. For high accuracy, effects of band structure and coverage, as well as the local bond strength in both covalent and non-covalent interactions, must be reliably described and much focus has been put on improving functionals to this end. Here, we show that a correction from higher-level calculations on small metal clusters can be applied to improve periodic band structure adsorption energies and barriers. We benchmark against 38 reliable experimental covalent and non-covalent adsorption energies and five activation barriers with mean absolute errors of 2.2 kcal mol−1, 2.7 kcal mol−1, and 1.1 kcal mol−1, respectively, which are lower than for functionals widely used and tested for surface science evaluations, such as BEEF-vdW and RPBE.

Unveiling the Degradation Mechanism of High-Temperature Superconductor Bi2Sr2CaCu2O8+δ in Water-Bearing Environments.

The physical properties of copper oxide high-temperature superconductors have been studied extensively, such as the band structure and doping effects of Bi2Sr2CaCu2O8+δ (Bi-2212). However, some chemical-related properties of these superconductors are rarely reported, such as their stability in water-bearing environments. Herein, we report experiments combined with ab initio calculations that address the effects of water in contact with Bi-2212. The evolution of Bi-2212 flakes with exposure to water for different time intervals was tested and characterized by optical microscopy (OM), atomic force microscopy (AFM), Raman spectroscopy, transmission electron microscopy (TEM), and electrical measurements. The thickness of Bi-2212 flakes is gradually decreased in water, and some thin flakes can be completely etched away after a few days. The stability of Bi-2212 in other solvents is also evaluated, including alcohol, acetone, HCl, and KOH. The morphology of Bi-2212 flakes is relatively stable in organic solvents. However, the flakes are etched relatively quick in HCl and KOH, especially in an acidic environment. Our results imply that hydrogen ions are primarily responsible for the deterioration of their properties. Both TEM and calculation results demonstrate that the atoms in the Bi-O plane are relatively stable when compared to the inner atoms in Sr-O, Ca-O, and Cu-O planes. This work contributes toward understanding the chemical stability of a Bi-2212 superconducting device in environmental medium, which is important for both fundamental studies and practical applications of copper oxide high-temperature superconductors.

Simulation analysis of high-field carrier transport in wide-bandgap semiconductors considering tunable band structures and scattering processes

Though the high breakdown electric field of wide-bandgap semiconductors is usually attributed to their large bandgap, the impacts of other band structure parameters and scattering processes on impact ionization phenomena have not been clarified yet. This study computationally analyzes the effects of band structures and scattering rates on the high-field carrier transport properties such as impact ionization coefficients and drift velocity in wide-bandgap semiconductors. For that purpose, this study adopts Monte Carlo simulations in which the E–k dispersion and scattering rates are directly tuned. Simulations with varied band structures indicate that an average of the group velocity in the whole Brillouin zone is a dominant factor determining the impact ionization coefficients rather than the effective mass at the band edge. In addition, the Brillouin zone width has critical impacts when Bloch oscillations occur, which significantly suppress impact ionization. As for scattering mechanisms, the roles of inelastic scattering processes including impact ionization in energy relaxation are discussed. It is also revealed that elastic scattering contributes to energy relaxation processes through transitions of electrons to higher bands. This mechanism leads to the unintuitive positive temperature dependence of impact ionization coefficients when Bloch oscillations occur. These results obtained by the theoretical analyses in this study can serve as basic physical insight to understand the behaviors of impact ionization coefficients in wide-bandgap semiconductors.

CuO Nanozymes as Multifunctional Signal Labels for Efficiently Quenching the Photocurrent of ZnO/Au/AgSbS2 Hybrids and Initiating a Strong Fluorescent Signal in a Dual-Mode Microfluidic Sensing Platform.

A novel dual-mode microfluidic sensing platform based on CuO nanozymes as a photoelectrochemical (PEC)-fluorescent (FL) multifunctional signal label was developed for ultrasensitive neuron specific enolase (NSE) detection. Herein, ZnO/Au/AgSbS2 hybrids, possessing excellent PEC properties, were first exploited as a sensing matrix to provide a stable photocurrent. The controlled synthesis of photoactive ZnO nanoflowers (NFs) was successfully conducted using a microfluidic reactor in the scale of seconds. Furthermore, the photocurrent of ZnO NFs decorated by Au and AgSbS2 nanoparticles significantly improved, owing to the local surface plasma resonance effect of Au and matching band structure between ZnO and AgSbS2. A strategy of catalytic oxidation ascorbic acid (AA) by CuO nanozymes was proposed to quench the PEC signals and initiate FL signals. CuO nanoparticles growing on conductive carbon spheres (CuO@CSs) as secondary antibodies' labels could efficiently catalyze the oxidation of AA to achieve a PEC "signal-off" state. Then, the produced dehydroascorbic acid reacting with o-phenylenediamine opportunely generated a strong FL signal. Importantly, wide linear ranges of 0.0001-150 ng/mL for the PEC technique and 0.001-150 ng/mL for the FL method with a low detection limit of 0.028 and 0.25 pg/mL, respectively, could guarantee the sensitive detection of NSE.