Electron Accumulation Research Articles

Achieving Long-Lived Charge Separated State through Ultrafast Interfacial Hole Transfer in Redox Sites-Isolated CdS Nanorods for Enhanced Photocatalysis.

As opposed to natural photosynthesis, a significant challenge in a semiconductor-based photocatalyst is the limited hole extraction efficiency, which adversely affects solar-to-fuel efficiency. Recent studies have demonstrated that photocatalysts featuring spatially isolated dual catalytic oxidation/reduction sites can yield enhanced hole extraction efficiencies. However, the decay dynamics of excited states in such photocatalysts have not been explored. Here a ternary barbell-shaped CdS/MoS2/Cu2S heterostructure is prepared, comprising CdS nanorods (NRs) interfaced with MoS2 nanosheets at both ends and Cu2S nanoparticles on the sidewall. By using transient absorption (TA) spectra, highly efficient charge separation within the CdS/MoS2/Cu2S heterostructure are identified. This is achieved through directed electron transfer to the MoS2 tips at a rate constant of >8.3 × 109 s-1 and rapid hole transfer to the Cu2S nanoparticles on the sidewall at a rate of >6.1 × 1010 s-1, leading to an exceptional overall charge transfer constant of 2.3 × 1011 s-1 in CdS/MoS2/Cu2S. The enhanced hole transfer efficiency results in a remarkably prolonged charge-separated state, facilitating efficient electron accumulation within the MoS2 tips. Consequently, the ternary CdS/MoS2/Cu2S heterostructure demonstrates a 22-fold enhancement in visible-light-driven H2 generation compare to pure CdS nanorods. This work highlights the significance of efficient hole extraction in enhancing the solar-to-H2 performance of semiconductor-based heterostructure.

Plasmon induced hot carrier distribution in Ag20 -CO composite.

The interaction between plasmons and the molecules leads to the transfer of plasmon-induced hot carriers, presenting innovative opportunities for controlling chemical reactions on sub-femtosecond timescales. Through real-time time-dependent density functional theory simulations, we have investigated the enhancement of the electric field due to plasmon excitation and the subsequent generation and transfer of plasmon-induced hot carriers in a linear atomic chain of Ag20 and an Ag20 -CO composite system. By applying a Gaussian laser pulse tuned to align with the plasmon frequency, we observe a plasmon-induced transfer of hot electrons from the occupied states of Ag to the unoccupied molecular orbitals of CO. Remarkably, there is a pronounced accumulation of hot electrons and hot holes on the C and O atoms. This phenomenon arises from the electron migration from the inter-nuclear regions of the C-O bond towards the individual C and O atoms. The insights garnered from our study hold the potential to drive advancements in the development of more efficient systems for catalytic processes empowered by plasmonic interactions.

Enhanced charge carriers separation/transportation via S-scheme ZnCeS–ZnWO heterostructure nanocomposite for photodegradation of synthetic dyes under sunlight

Domestic wastage and liquid discharge from industries cause serious water pollution and severely damage the life cycle of living species. Therefore, it is necessary to construct efficient photocatalysts for the removal of toxic pollutants from water. Herein, a novel heterostructure ZnWO–ZnCeS nanocomposite was prepared by the sol-gel route and studied its physical and photocatalytic properties using various analytical techniques. Under sunlight irradiation, the ZnWO–ZnCeS photocatalyst eliminated 99.7, 99.1, 99.0 % rhodamine-B (RhB), methylene blue (MB), and safranin-O (SO) dyes within 70 min with excellent performance higher than individual ZnWO and ZnCeS catalysts. The optimization tests exhibit the catalyst loading = 30 mg, dye content = 25 ppm, solution pH = 8 of ZnWO–ZnCeS against MB dye for practical application. The heterojunction of coupled ZnWO and ZnCeS leads to a synergistic effect that facilitates the charge transport and hampers the recombination of photo-induced charge carriers thereby leading to boosted photocatalytic performance. Furthermore, based on the scavenging test, the hydroxyl and superoxide radicals were the reactive species during the photodegradation reaction. The designed photodegradation reaction mechanism has proposed the formation of an S-scheme in ZnWO–ZnCeS that led to the accumulation of electrons at ZnCeS and holes at ZnWO, favoring the formation of reactive species for dye degradation. Moreover, this work provides a novel direction to synthesize S-scheme heterostructure photocatalysts for application in wastewater treatment.

Efficient Hydrogen Evolution Reaction in 2H-MoS2 Basal Planes Enhanced by Surface Electron Accumulation

An innovative strategy has been developed to activate the basal planes in molybdenum disulfide (MoS2) to improve their electrocatalytic activity by controlling surface electron accumulation (SEA) through aging, annealing, and nitrogen-plasma treatments. The optimal hydrogen evolution reaction (HER) performance was obtained on the surface treated with nitrogen-plasma for 120 s. An overpotential of 0.20 V and a Tafel slope of 120 mV dec−1 were achieved for the optimized condition. The angle-resolved photoemission spectroscopy measurement confirmed the HER efficiency enhanced by the SEA conjugated with the sulfur vacancy active sites in the MoS2 basal planes. This study provides new insight into optimizing MoS2 catalysts for energy applications.

High-performance palladium nanotube network as fast, high-resolution, and wide range hydrogen detector in atmosphere

Due to its high energy density, cleanliness, and renewable properties, hydrogen (H2) has found wide applications in aerospace, fuel cells, biomedicine, and chemical production. However, ensuring its safety is crucial, and a quick response time for H2 leakage detection is urgently needed for subsequent explosion-proof measures, requiring a limit of less than 5 s. So far, there is no reported device with both high-resolution and wide range capabilities. In this study, we propose a novel solution by designing and fabricating a hollow palladium nanotube network (HPNN) as a rapid leaking-sensing H2 detector. The HPNN sensor demonstrates excellent performance with a low detection limit of 10 parts per million (ppm) and a fast response time of less than 0.6 s in atmospheric environment. These impressive safety characteristics are attributed to the unique structure of the Pd nanotube network, where both the lattice volume expansion effect and electron accumulation under mechanical deformation affect the electrical resistance. The device is capable of effectively detecting a wide range from 4 % to 0.001 % of H2 concentrations. Compared to previous results, the response speed is improved by over 8 times at the minimum explosion concentration (4 %) and two orders of magnitude at low limit concentration. Such simple and cost-effective manufacturing method offers potential for the development of high-performance hydrogen leakage detectors.

Synergy between palladium single atoms and small nanoparticles co-anchored on carbon atom self-doped graphitic carbon nitride boosting photocatalytic H2 generation

Supramolecule self-assembly of dicyandiamide and uracil followed by thermal polymerization route is designed to prepare carbon atom self-doped g-C3N4 (CCNx), and then wet reduction is applied to fabricate Pd single atoms (Pd1) and nanoparticles (PdNPs) co-anchored CCNx heterojunctions (Pd1+NPs/CCNx). In Pd1+NPs/CCNx structure, interlayer Pd−N4 coordination is the most favorable for chemically stabilizing Pd1, while PdNPs accumulate on the in-plane of CCNx. Pd1+NPs/CCNx heterojunctions exhibit remarkably enhanced photocatalytic H2 evolution reaction (HER) activity, and HER rate and AQY value reach up to 24.1 mmol g−1 h−1 and 17.1% (400 nm) over the optimized Pd1+NPs/CCNx catalyst. Mechanism studies unveil that synergy of as-built interlayer N−Pd−N electron transfer channels at the atomic-scale and surface Mott–Schottky effect of small Pd nanoparticles notably accelerates migration of photogenerated electrons, which leads to plentiful electrons accumulation around Pd single atoms and small nanoparticles to decrease the energy barrier of H* activation and boost HER photodynamics significantly.

An ultra-sensitive colloidal quantum dot infrared photodiode exceeding 100 000% external quantum efficiency via photomultiplication.

In this study, we present ultrasensitive infrared photodiodes based on PbS colloidal quantum dots (CQDs) using a double photomultiplication strategy that utilizes the accumulation of both electron and hole carriers. While electron accumulation was induced by ZnO trap states that were created by treatment in a humid atmosphere, hole accumulation was achieved using a long-chain ligand that increased the barrier to hole collection. Interestingly, we obtained the highest responsivity in photo-multiplicative devices with the long ligands, which contradicts the conventional belief that shorter ligands are more effective for optoelectronic devices. Using these two charge accumulation effects, we achieved an ultrasensitive detector with a responsivity above 7.84 × 102 A W-1 and an external quantum efficiency above 105% in the infrared region. We believe that the photomultiplication effect has great potential for surveillance systems, bioimaging, remote sensing, and quantum communication.

Carrier behavior of a carbon material assisted TIPS-pentacene composite film for improvement of electrical conductivity.

Organic semiconductor devices have a lower intrinsic carrier density than inorganic semiconductors, and improving their electrical conductivity is important for organic electronic devices. Further theoretical investigations and understanding the properties of these electronic devices are necessary to improve the electrical conductivity of organic devices. In this study, we demonstrate how two carbon-material-assisted organic semiconductor devices affect the electrical conductivity and charge mechanism by using electrical measurements (i.e., I-V and C-V measurements, and numerical simulations). To clearly demonstrate the enhancement of the charge injection into TIPS (6,13-bis(triisopropylsilylethynyl)-pentacene), we studied the blending effect of carbon materials (carbon nanotube and fullerene) in TIPS and discussed injection, transport and charge accumulation of hole and electron in relation to trapped charge. This study will be helpful for understanding charge mechanisms in composite organic semiconductor devices.

Electronic and Structural Analysis of TMD/BP Heterostructures: Insights from Raman Spectroscopy, SEM, and Correlative Probe Electron Microscopy

The current study was designed in order to study the electrical and structural properties of heterostructures of TMD and BP through Raman spectrum mapping technique, Scanning electron microscopy (SEM) and Correlative Probe electron microscopy (CPEM). Single and few layer heterostructures were prepared by mechanical exfoliation and transferred onto a silicon substrate by poly(methyl methacrylate) (PMMA) transfer method. Optical and CPD mapping manifested increased signal intensity at the edges of the flake, and Raman spectroscopy indicated definite electron density near the fringes of the flake. In this system, scanning electron microscopy (SEM) studies performed employing a range of accelerating voltages have supported the presence of electronic domains within the heterostructures especially at their borderlines. The CPEM analysis showed a significant correlation between the topographical and electronic contrast, where the former was attributed to an intense accumulation of electrons at the edge of the flake and not due to structural flaws. These results highlight the fact that TMD/BP heterostructures possess relatively unique electrical properties and may be suitable for future optoelectronic applications.

Unveiling photoinduced electron transfer in cobalt(iii)-R-pyridine complexes anchored to anatase nanocrystals: photoluminescence and magnetic studies.

In this study, we synthesized mixed ligand complexes of the cis-[Co(tn)2(Rpy)Br]Br2 type using a novel mechanochemical approach. Characterization involved spectral measurements and single crystal X-ray diffraction analysis, confirming the structure of the cis-[Co(tn)2(4-Mepy)Br]Br2 complex. The single crystal refinement data revealed a monoclinic crystal system with a distorted octahedral geometry. The choice of the sixth ligand influenced the emission and magnetic properties, showing a ferromagnetic character in the Co(iii)-complex environment. We investigated efficient electron transfer to the cobalt(iii) center using TiO2 nanoparticles under UV-light irradiation. The adsorption characteristics of cis-[Co(tn)2(Rpy)Br]Br2 in aqueous 2-propanol varied, leading to surface compound formation. Under UV irradiation, the anatase surface exhibited remarkable adsorption capabilities, facilitating efficient electron transfer to the Co(iii) center and resulting in a high photoefficiency for Co(ii) formation. Our study has put forward a model for interfacial electron transfer (IET), taking into account the overlap between the TiO2 conduction band and the acceptor level of the Co center, as well as the electronic coupling between the donor level of the Ti center and the acceptor level of the Co center. This model sheds light on the accumulation of electrons for reducing the adhered complex ion. The IET process was corroborated by the conversion of 2-propanol into acetone, as verified by 1H NMR technique. Overall, our findings provide novel insights into the role of the Rpy moiety in modifying the structure of the TiO2-cobalt(iii)-Rpy compound and propose a mechanism for IET reactions, thus advancing the field.

Enhanced light driven CO2 conversion based on silver bismuth sulfide hollow octahedrons coated with amorphous metal–organic frameworks

AgBiS2 hollow octahedrons coated with ZIF-67 outer layers formed a core–shell heterostructure with more favorable charge transfer kinetics, which conduced to electron accumulation and photosensitizer adsorption for CO2 photoreduction.

Improving built-in electric fields for effective photocatalytic activity in the rationally designed electron transfer pathway of TiO2@MoS2/Bi2S3

An augmented built-in electric field was successfully fabricated within TiO2@MoS2/Bi2S3. DFT calculations reveal electron accumulation and depletion at the heterointerface, demonstrating unique electron transfer pathway directed towards MoS2.

Noval carrier accumulation reverse-conducting lateral insulated gate bipolar transistor

Reverse-conducting lateral insulated gate bipolar transistor (RC-LIGBT) with freewheeling diode integrated in the body by introducing n<sup>+</sup> anode can realize the reverse conduction and optimize the turn-off characteristics of the device, which is a promising device in a power integrated circuit. In this work, a novel RC-LIGBT with electron-controlled gate (EG) and separated short-anode (SSA) is proposed and investigated by TCAD simulation, which can achieve low on-state voltage drop (<i>V</i><sub>on</sub>) and low turn-off loss (<i>E</i><sub>off</sub>) at the same time. The EG structure of p-n-n<sup>+</sup>-p (p<sup>+</sup> region/n-type silicon region/n-type barrier layer/p<sup>+</sup> region) is adopted, the gate electrode and anode electrode are connected by the EG structure. In the forward conduction state, a high-density electron accumulation layer is formed on the surface of the drift region by EG structure, which greatly reduces the <i>V</i><sub>on</sub> of the device. At the same time, the use of the SSA structure can also optimize the <i>E</i><sub>off</sub> of the device by forming an additional electron extraction channel. In addition, based on the EG structure, a low-doping p-drift can be combined with the SSA structure to simply achieve reverse-conduction and snapback-free characteristics. Furthermore, the EG structure and the SSA structure can complement each other. On the one hand, the high-density electron accumulation layer formed by EG structure compensates for the weakened conductance modulation effect caused by the SSA structure. On the other hand, the electron extraction channel of the SSA structure enables a large number of accumulated electrons to be removed quickly. The simulation results show that the proposed device has an excellent trade-off relationship between <i>V</i><sub>on</sub> and <i>E</i><sub>off</sub>, specifically, <i>V</i><sub>on</sub> is 1.16V, which is 55% lower than that of SSA LIGBT, and <i>E</i><sub>off</sub> is 0.099 mJ/cm<sup>2</sup>, which is 38.5% and 94.7% lower than that of SSA LIGBT and conventional LIGBT, respectively.

Interfacial properties of a ZnO/PTFE composite from density functional tight-binding simulations.

Metal-oxide-reinforced plastic nanocomposites are widely used in high-tech industries, but the reinforcement mechanism of the metal oxide is not fully understood. Here we investigate the interfacial properties of a zinc-oxide-reinforced amorphous polytetrafluoroethylene (a-PTFE) composite as a prototype for such composites using superlattice modeling and density functional tight-binding molecular dynamics simulations. To study the ZnO/a-PTFE composites, the superlattice supercells are built using a ZnO (112̄0) surface supercell and a-PTFE layer with an experimental density of 1.8 g cm-3 and various thicknesses. Our calculations demonstrate that the binding energy between ZnO and a-PTFE is negative, indicating their attractive binding, and electron accumulation occurs in the middle space between ZnO and a-PTFE, as well as around ZnO, evidencing that the newly formed interfacial chemical bonds are partially covalent. We further reveal that the tensile stress and elastic moduli of the ZnO/a-PTFE superlattice increases with increasing ZnO fraction, with values placed between those of ZnO and a-PTFE, which confirms the enhancement of the mechanical strength of the composites by incorporating ZnO into the a-PTFE matrix. This work provides a design guideline for developing high-performance metal-oxide-reinforced plastic composites.

Microwave Quasi‐Solid State to Construct Strong Metal‐Support Interactions with Interfacial Electron‐Enriched Ru for Anion Exchange Membrane Electrolysis

AbstractRegulating the metal‐support interaction of the anchored metal nanoclusters is recognized as valid approach to optimize the electrocatalytic performance through tuning the interfacial electronic structure. However, developing novel support and understanding the interfacial electron accumulation on modulating the reaction kinetics are still elusive. Herein, highly‐dispersed Ruthenium (Ru) nanoclusters anchored onto phosphorous doped molybdenum boride (Ru/P‐MoB) is developed through ultrafast microwave‐plasma (60 s) approach. The synthesized Ru/P‐MoB impressively promote the hydrogen evolution with low overpotentials of 34, 45, and 40 mV to drive 10 mA cm−2 in alkaline freshwater, alkaline seawater and acid media. Specially, it presents superior turnover frequency and mass/specific activity relative to Pt/C, Ru/C, and Ru/MoB. Moreover, the anion exchange membrane (AEM) electrolyzer cell based on Ru/P‐MoB can achieve 500 and 1000 mA cm−2 with small voltages of 1.71 and 1.78 V with good durability. Experimental and density functional theoretical (DFT) analysis reveal that the strong metal‐support interactions (Ru─Mo and Ru─P bonds) with generated interfacial electron‐enriched Ru, and then favoring the water‐molecule adsorption/dissociation and optimal H intermediate adsorption free energy. This work provides novel designing avenue to exploit electrocatalysts with outstanding catalytic performance under high current density at practical high‐temperature.

Reliability of enhancement-mode p-GaN gate GaN HEMT with multiple field plates

In this paper, we fabricate enhancement-mode p-GaN gate GaN HEMTs with multiple field plates (MFPs) and analyze the reliability of the devices by means of simulation and experiment. Simulations of the electric-field distribution indicate that the MFPs effectively weaken the electric field peak near the gate to below the theoretical breakdown value and smooth the electric field between the gate edge and drain-side field plate edge. The simulated electric field peak leading to the breakdown of the device with MFPs at high drain voltage is located at the drain edge, which is validated by experimental results. The GaN HEMTs with MFPs exhibit excellent long-term reliability under high temperature and drain voltage, while deviations from threshold voltage and on-resistance were observed in the device subjected to drain stress. We attribute these deviations to electron accumulation and high field-assisted detrapping processes in the p-GaN layer. This investigation provides new insight into the mechanism of variations in threshold voltage and on-resistance under off-state drain stress.

Revealing the mechanism of oxygen vacancy defect for CO2 adsorption and diffusion on CaO: DFT and experimental study

The calcium looping is a promising technology to achieve industrial CO2 capture, and the introduction of oxygen vacancy can promote the CO2 capture reactivity of CaO-based sorbents. In this work, DFT calculations were performed to investigate the CO2 adsorption by CaO in the presence of oxygen vacancy defect. The presence of oxygen vacancy reduces the band gap of CaO surface, which results from the delocalization of Ca 2p orbital. Besides, the electron accumulation at the oxygen vacancy occurs due to the unsaturated Ca-O bonds, and the reaction possibility is promoted neighbouring the defect. The top site of oxygen vacancy defect of CaO is favourable for CO2 adsorption. The adsorption energy of CO2 on CaO with oxygen vacancy achieves − 2.52 eV, which is 1.81 times as high as that on pristine CaO. Due to strong interaction between CO2 and CaO with oxygen vacancy, CO2 migration from this site is more difficult, while the following diffusion is more prone to occur. In the presence of steam, CO2 adsorption energy is enhanced to − 2.70 eV on CaO with oxygen vacancy, and the distance from CO2 radical to surface is intuitively reduced, which results from the electrons donated from defect and neighbouring Ca atoms, while CO2 diffusion difficulty is increased. This work provides an incisive investigation for structural, electronic, and thermodynamic characteristics of CO2 adsorption and diffusion on CaO in the presence of oxygen vacancy defect, and it can shed light on rational synthesis and functional design of surface-active sites of CaO-based sorbents.

Modulation of internal electric field in S-scheme heterojunction towards efficient photocatalytic CO2 conversion

The internal electric field (IEF) inherent within a composite photocatalyst plays a pivotal role in orchestrating the photogenerated charge carrier separation. Consequently, achieving precise regulation of the IEF emerges as the keystone for optimizing photocatalytic performance. Herein, we present a demonstrative study centered around the deliberate manipulation of the IEF within a g-C3N4/In2S3 step-scheme (S-scheme) heterojunction. This manipulation is deftly accomplished through the introduction of sulfur doping (S-doping) into the g-C3N4. Employing advanced techniques such as Kelvin probe force microscopy and density functional theory calculations, we substantiate that S-doping precipitates a reinforcement in IEF existing between g-C3N4 and In2S3. The soundness of this proposition is fortified through in situ X-ray photoelectron spectroscopy, which unveils a pronounced augmentation in the accumulation of photogenerated electrons on the surface of g-C3N4 subsequent to S-doping. This empirically substantiates the enhanced charge carrier dynamics made possible by the manipulation of the IEF within S-scheme heterojunction.

Enhanced tunneling electroresistance through interfacial charge-modulated barrier in α-In2Se3-based ferroelectric tunnel junction

The manipulation of tunneling resistance is critical for ferroelectric tunnel junction (FTJ) devices. In this work, we propose a mechanism to manipulate tunneling resistance through interfacial charge-modulated barrier in two-dimensional (2D) n-type semiconductor/ferroelectric FTJs. Driven by ferroelectric reversal, different effective tunneling barriers are realized by the depletion or accumulation of electrons near the n-type semiconductor surface in such devices. Thus, the tunneling resistance in FTJs undergoes significant changes for different polarization orientations, resulting in a giant tunneling electroresistance (TER) effect. To illustrate this idea, we construct 2D FTJs based on n-InSe/α-In2Se3 van der Waals (vdW) heterostructures. Based on the electronic transport calculations, it is found that TER ratio can reach 4.20 × 103% in the designed FTJs. The physical origin of the giant TER effect is verified through analysis of the effective potential energy of the n-InSe/α-In2Se3 vdW heterostructures and the real-space transmission eigenstates of the designed FTJs. This work contributes to the knowledge of carrier tunneling mechanisms at the interface of semiconductor/In2Se3 vdW heterostructures, and providing a significant insight into the TER effect of this FTJ systems, also presenting an alternative approach for the design of FTJ-based devices.

The role of metal-doping on the enhanced electrocatalytic properties of α-MnO2 during oxygen reduction reaction

Metal-doping is a common strategy for improving the performance of α-MnO2 during oxygen reduction reaction (ORR) in metal-air batteries (MABs). Understanding the role of dopants in an atomic level is crucial to develop this cathode's performance, which is required to study. This work presents the insight effects of metal-doping (Co, Ni, and Pd) in α-MnO2 during ORR, investigated through density functional theory and computational hydrogen electrode calculations. As a result, all dopants enhance the adsorption strength of surface species during ORR due to the induction of electron accumulation at the Mn site, modifying the d-band center of the doping site. Unfortunately, Ni doping had an inhibiting effect on specific ORR elementary steps, leading to lower activity. In the volcano plot of theoretical overpotential, Co and Pd doping play as the promoter, where enhanced ORR activity is found on the Mn-site. The insight information reveals that the enhanced α-MnO2 catalysts are achieved by Co and Pd doping at interstitial sites rather than substitution on Mn sites. These findings emphasize the critical role of both well-controlled dopant concentration and the atomic dispersion of a dopant at the interstitial sites on the electrocatalytic activity for MABs.