Work Function Difference Research Articles

Electronic Redistribution Through the Interface: A Prodigy that Enhances Electrocatalysis

AbstractEfficient design approaches have been developed to create electrocatalysts with the aim of enhancing both the number of active sites and the inherent activity of each individual active site. There is a requirement for more universally applicable approaches to thoroughly understand the activity of electrocatalysts. Particularly in this regard, heterointerfaces that exhibit a strong coupling effect have significantly improved the reaction kinetics of electrocatalysis. The electronic redistribution that takes place between the two phases through the interface is the cause of the increased catalytic activity that is exhibited by the heterostructures. Electrophilic and nucleophilic sites are generated on the surface of the catalyst as a result of the electronic redistribution that occurs from one phase to another phase. These sites have the ability to catalyze both the HER and the OER simultaneously. However, a comprehensive debate is required regarding the mechanistic route that is responsible for the acceleration of the reaction rate experienced by the reallocation of electrons.This review summarizes the electron redistribution phenomenon happening after the strong contact between two interfaces. We have explained the charge distribution phenomenon in semiconductor‐semiconductor heterojunctions and metal‐semiconductor heterojunctions.

A ballistic model for subthreshold current and threshold voltage of the dual-material-gate nanosheet MOSFET

— A ballistic model for subthreshold current of the dual-material-gate (DMG) nanosheet (NS) MOSFET is developed based on the Landauer approach, three-dimensional scaling equation, and the continuity of subthreshold current at the interface between the control gate and screen gate in the channel, The work function difference between the screen gate and control gate can be converted into the new interface-quasi-fermi-potential (IQFP) at the junction between different gate regions. Through the IQFP, the ballistic subthreshold current for DMG NS MOSFET is successfully developed. With the determined subthreshold current, the ballistic threshold voltage can also be achieved by the constant current method. Under the low and high drain voltage corresponding to their IQFPs, the subthreshold behavior is mainly governed by the contact potential and thermal voltage, respectively. Furthermore, Ohm's law regarding ballistic resistance for the DMG NS MOSFET can still be valid in the subthreshold conduction.

Electrical Tracking of the Mott Insulating Kitaev Magnet using Graphene/α‐RuCl3 Heterostructure

AbstractElectrical signatures for quantum magnetic phases of α‐RuCl3 sensed by an adjacent graphene field‐effect transistor (FET) are reported. The gate‐voltage dependence of the graphene FET reveals p‐type doping beneath α‐RuCl3 caused by the charge transfer due to the work function difference. Furthermore, the gate‐voltage hysteresis exhibits a marked change in the transport behavior with the temperature variation. The high‐T simple paramagnetic phase and the low‐T zigzag antiferromagnetic phase of α‐RuCl3 exhibit negligible hysteresis. In sharp contrast, a huge hysteresis of the graphene FET at intermediate temperatures is observed. The possibility that the observed conductance hysteresis is associated with the intriguing continuum excitations of the thermally induced Kitaev paramagnet state is discussed. The results show that the proximity effect‐based electric approach can be utilized for investigating charge‐neutral quasiparticles in quantum magnetic insulators.

Engineering a Z-Scheme Heterostructure on ZnIn2S4@NH2-MIL-125 Composites for Boosting the Photocatalytic Performance.

Constructing a Z-scheme heterostructure on a metal-organic framework (MOF) composite with an explicit charge transfer mechanism at the interface is considered to be an effective strategy for improving the photocatalytic performance of MOFs. Herein, an internal electric field (IEF)-induced Z-scheme heterostructure on the ZnIn2S4@NH2-MIL-125 composite is designed and fabricated by a facile electrostatic self-assembly process. Systematic investigations reveal that close interfacial contact and difference in work function between NH2-MIL-125 and ZnIn2S4 enable the formation of the IEF, which drives the Z-scheme charge transfer as revealed by the in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), photoirradiated Kelvin probe force microscope (KPFM) measurement, electron paramagnetic resonance (EPR) radical trapping experiment, as well as density functional theory (DFT) calculation; meanwhile, directions of the interfacial IEFs are determined. Benefiting from the unique merit of IEF-induced Z-scheme charge transfer, the optimized ZnIn2S4@NH2-MIL-125 composite exhibits significantly enhanced photocatalytic activity for the photoreduction of 4-nitroaniline (4-NA) to p-phenylenediamine (PPD) under visible light irradiation. This work not only provides in-depth insights for charge transfer in the IEF-induced Z scheme heterostructure but also affords useful inspirations on designing the Z-scheme MOF composite to boost the photocatalytic performance.

Tuning the work function of graphite nanoparticles via edge termination.

Graphite nanoparticles are important in energy materials applications such as lithium-ion batteries (LIBs), supercapacitors and as catalyst supports. Tuning the work function of the nanoparticles allows local control of lithiation behaviour in LIBs, and the potential of zero charge of electrocatalysts and supercapacitors. Using large scale density functional theory (DFT) calculations, we find that the surface termination of multilayer graphene nanoparticles can substantially modify the work function. Calculations in vacuum and in electrolyte show that manipulating the edge termination substantially modifies the potential not only around the edge, but also on the basal plane. Termination with hydrogen or oxygen completely reverses the potential distribution surrounding the basal plane and edges. The trends can be explained based on the work function differences of the edges dependent on termination, and that of the basal plane. Electronic equilibration between different surfaces at the nanoscale allows manipulation of the work function. We demonstrate a link between the area of the graphite basal plane via changing the nanoparticle size, and the work function. We expect that these insights can be utilised for local control of electrochemical functions of graphite nanoparticles prepared under oxidising or reducing conditions.

Mitigated front contact energy barrier for efficient and stable perovskite solar cells

A passivating contact structure was developed to mitigate the front contact energy barrier and hence reduce interface recombination losses in perovskite solar cells. This device structure achieved champion power conversion efficiencies of 25.7%.

Tunable polarization properties of charge, spin, and valley in Janus VSiGeZ4 (Z = N, P, As) monolayers.

Polarization, as an important characterization of the symmetry breaking systems, has attracted tremendous attention in two-dimensional (2D) materials. Due to their significant symmetry breaking, Janus 2D ferrovalley materials provide a desirable platform to investigate the charge, spin, and valley polarization, as well as their coupling effects. Herein, using first-principles calculations, the polarization properties of charge, spin, and valley in Janus VSiGeZ4 (Z = N, P, and As) monolayers are systematically studied. The mirror symmetry breaking leads to a non-zero dipole moment and surface work function difference, indicating the presence of out-of-plane charge polarization. Magnetic properties calculations demonstrate that VSiGeN4 is a 2D-XY magnet with a Berezinskii-Kosterlitz-Thouless temperature of 342 K, while VSiGeP4 and VSiGeAs4 have an out-of-plane magnetization with a Curie temperature below room temperature. The magnetization can be rotated by applying biaxial strain, allowing manipulation of the spin polarization via nonmagnetic means. The spontaneous valley polarization is predicted to be 46, 49, and 70 meV for VSiGeN4, VSiGeP4, and VSiGeAs4, respectively, whose physical origin can be elucidated by employing the model analysis. In particular, the biaxial strain can induce the valley polarization switching from the valence (conduction) band to conduction (valence) band, but it hardly changes the valley polarization strength. Meanwhile, the valley extremum is transformed from the K' (K) to K (K') points. The present work not only provides an underlying insight into the polarization properties of Janus VSiGeZ4 but also offers a class of promising materials for spintronic and valleytronic devices.

Work function induced electron rearrangement of Ru@Ir core-shell nanocatalysts for promoting pH-universal overall water splitting

Water splitting, one of the primary strategies for advancing the utilization of hydrogen production, necessitates the input of external energies to initiate the reaction due to its thermodynamically uphill nature. Nevertheless, Ru-based compounds, which were widely used as benchmark anodic catalysts, facing significant drawbacks such as their susceptibility to dissolution, significantly restrict the overall water splitting efficiency. In this work, we introduce an approach for functionalization through combining Ru nanospheres with Ir to form a Ru@Ir core–shell structure (denoted as Ru@Ir core–shell NSs), which can activate the superior oxygen evolution reaction (OER) catalytic activity, and simultaneously inherit the hydrogen evolution reaction (HER) performance in all-pH condition. The work function difference between Ru and Ir promotes the necessary energetic impetus for electron migration from Ru to Ir, resulting in the charge redistribution. Density functional theory (DFT) calculations confirmed that the Ir shell, acting as an electron acceptor, could effectively trigger electron rearrangement, augmenting the ligand affinity of hydrogen and oxygen intermediates to attain the most favorable energy states, thereby accelerating the kinetics of hydrogen and oxygen evolution. Our suggested core–shell structure approach for manipulating interface charge distribution might find utility in creating other electrocatalysts for water splitting.

Revealing The Role of Electronic Asymmetricity on Supported Ru Nanoclusters for Alkaline Hydrogen Evolution Reaction

AbstractModulating the electronic asymmetricity of catalysts is an effective method for optimizating the elementary steps of water dissociation and hydrogen adsorption/desorption process for the alkaline hydrogen evolution reaction (HER). Herein, uniform Ru nanoclusters anchored on N doped ultrathin carbon nanosheets (Ru/NC) are synthesized to optimize the asymmetricity electronic properties of supported Ru for efficient HER. It is found that Ru and NC with a large work function difference (ΔΦ) leading to the formation of stronger asymmetrical charge distributions of Ru that electron‐deficient high‐valence Ru (Run+) coupling with low‐valence Ru (Ru0). Experimental and theoretical studies indicate the Run+ sites lowered the energy barrier for water dissociation and provided enough hydrogen proton to promote the hydrogen spillover from the Run+ to Ru0 sites, and Ru0 sites can enhance H desorption process, thus synergistically enhancing the hydrogen evolution activity. Notably, the Ru/NC catalyst exhibits a high alkaline HER activity (21.9 mV@10 mA cm−2, 29.03 mV dec−1). The role of electronic asymmetricity on supported Ru nanoclusters for the alkaline HER are demonstrated, which will provide guidelines for the rational design of high‐efficiency alkaline HER catalysts.

Graphene encapsulated MnO2 nanorods boosts interfacial polarization for microwave absorption

The lightweight and efficient electromagnetic wave (EMW) absorption materials have been a popular research topic. In this work, MnO2 @graphene (MnGr) nanofibers with core-shell structure were synthesized by a one-step hydrothermal method. This one-dimensional linear structure was further self-assembled into a three-dimensional hierarchical MnGr aerogel network structure due to the interlayer forces of graphene sheets. The addition of graphene greatly enhances the interfacial polarization. The significant differences in electronic structure and work function between the outer graphene layer and the inner MnO2 layer greatly enhance the interfacial polarization. The formation of 3D hierarchical MnGr aerogel network structure constructs more fast electron transport channels. With the addition of graphene oxide at 7.5 wt% of the theoretical yield of MnO2, MnGr-7.5 exhibits excellent wave absorption properties. The effective absorption bandwidth (EAB) can reach 6.40 GHz at 2.2 mm. And the minimum reflection loss (RLmin) is − 41.3 dB at 1.8 mm and 17.36 GHz. Finite element physical simulation is used to simulate the response of 3D conductive network to electromagnetic wave. Through calculation, it is found that the inter-lap network structure is beneficial to enhance the loss. The low-cost MnO2 compounded with a small amount of graphene has excellent wave absorption performance and a great application prospect.

Direct Observation of Contact Electrification Effects at Nanoscale Using Scanning Probe Microscopy

AbstractIn the last decade, contact electrification has gained attention for its potential in energy harvesting, addressing fundamental physics. Scanning probe microscopy (SPM) has evolved as a powerful platform, enabling the in situ characterization/manipulation of a sample's tribological/electrical properties at nanoscale. However, although both the sliding and tapping modes are available in the energy harvesting, the lateral sliding using contact mode SPM has predominantly been employed in triboelectric study. In this work, contact electrification on polydimethylsiloxane is investigated, using peak force tapping atomic force microscopy (PF‐AFM). As PF‐AFM quasi‐discretely offers vertical tapping motions of the probe with a regulated force amplitude, resembling a vertical‐type triboelectric nanogenerator, while minimizing lateral forces. The subsequent surface potential measurements reveal that the generated tribocharge is influenced by both the effective work function difference and energy dissipation at the interface. Furthermore, the accumulation of transferred charges is explored by measuring tip‐sample current during the PF‐AFM operation, showing the comparable results with the surface potential measurement. The results can be attributed to the contact potential difference assisted by the energy dissipation at the interface. This study offers an advanced opportunity to understand and study charge generation behavior based on surface properties without damaging the sample.

A mixed-potential gas sensor with heterojunctions based on Co3O4/ZnO/Y2O3 nanocomposite for low concentration H2S detection

This study aimed to develop a H2S gas sensor based on gadolinia-doped ceria (GDC) solid electrolyte and Co3O4/ZnO/Y2O3 ternary nanocomposite. Heterojunctions were formed inside the Co3O4/ZnO/Y2O3 ternary nanocomposite sensing material due to the difference of work function, which effectively adjusted the oxygen vacancy concentration, improved the electrocatalytic activity of the material, and reduced the working temperature. The response showed a piecewise linear correlation with the concentration of H2S, and its sensitivity for 0.2–2 ppm and 2–10 ppm H2S was −6.4 and −36.35 mV/decade, respectively. Furthermore, the sensor exhibited good stability, repeatability, and selectivity to H2S. This study showed that the GDC-based mixed potential sensor with Co3O4/ZnO/Y2O3-SE could be used as a potential sensor for detecting low concentration of H2S.

The role of oxide supports in constructing plasma-treated gold nanocatalysts for visible light photocatalytic oxidation of CO

Supported Au nanocatalysts are highly attractive plasmonic nanostructures for visible light (VL) photocatalysis due to their significant promise in direct conversion of solar to chemical energy. A promising strategy to prepare high-performance supported plasmonic Au nanocatalysts is treating the catalysts with plasma, where the support holds the key to constructing active Au-support interfaces by interacting with Au nanoparticles. Herein the role of oxide supports in constructing plasma-treated plasmonic Au nanocatalysts for VL photocatalytic oxidation of CO is studied by comparing effect of plasma treatment on typical oxides of TiO2, CeO2 and Al2O3 supported Au nanocatalysts. After O2 plasma treatment, CeO2 supported Au nanocatalyst obtains the highest intrinsic catalytic activity due to its high dispersion of Au nanoparticles induced by strong interaction between CeO2 and Au and strong oxygen activation ability. The O2 plasma treatment enables TiO2 supported Au nanocatalyst to exhibit the largest enhancement in catalytic activity under VL irradiation, which originates from the favorable hot-electron transfer process. This process is not only attributed to the strong surface plasmon resonance of Au nanoparticles and large numbers of Au-TiO2 interfacial sites that result from moderate interaction between TiO2 and Au, but also depends on the low Schottky barrier height at Au-TiO2 interface due to the small work function difference between TiO2 and metallic Au. This investigation deepens the understanding of the role of oxide supports in constructing plasma-treated supported Au nanocatalysts, and can be instructive for the design and optimization of plasmonic Au nanocatalysts for VL photocatalytic reactions.

In-Depth Analysis on Self Alignment Effect of the Fermi-Level Using Graphene on Both n- and p-Type Semiconductors.

Optimizing the contact structure while reducing the contact resistance in advanced transistors has become an extremely challenging problem. Because the existing techniques are limited to controlling only one semiconductor type, either n- or p-type, owing to their work function differences, significant challenges are encountered in the integration of a contact structure and metal suitable for both n- and p-type semiconductors. This is a formidable drawback of the complementary metal-oxide-semiconductor (CMOS) technology. In this paper, we demonstrate the effectiveness of a metal/graphene/semiconductor (MGrS) as a universal source/drain contact structure for both n- and p-type transistors. The MGrS contact structure significantly enhanced the reverse current density (JR) and reduced the Schottky barrier height (SBH) for both semiconductor types. From the analysis of the SBH values and their relationship with the metal work function, which refers to the S-parameter, the van der Waals contact of graphene (Gr) effectively alleviated the Fermi level (FL) pinning for both semiconductor types, reducing the metal-induced gap states (MIGS) at the Gr/semiconductor interface. Furthermore, Gr effectively modulated the work function of the contact metal to yield a position favorable for each semiconductor type. Consequently, a single MGrS contact structure on a Si substrate resulted in excellent Ohmic contacts in both n- and p-type Si, with SBH values reduced to 0.012 and 0.024 eV for n- and p-type Si, respectively. This new approach for integrating the contact structures of semiconductor types will lead to extended capabilities for high-performance device applications and CMOS logical circuitry.

Asymmetrical Schottky Junction Built by Metal/Conducting Polymer Targeting Efficient Flexible Direct Current Tribovoltaic Generator

Direct current (DC) from mechanical energy built on the tribovoltaic effect is promising for the development of self‐powered flexible electronics. A semiconductor triboelectric generator is one of the optimized solutions for DC output. However, it remains underutilized because of its low output power and insufficient insight into the fundamental principles of charge generation and transport at dynamic interfaces. Herein, a flexible fabric‐based DC generator that relies on a metal–semiconducting polymer interface constructed by an asymmetric Schottky junction between a poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS)‐coated fabric and an aluminum (Al) foil is reported. The dependence of the electrical output performance of the device on the doping carrier concentration using different types of PEDOT:PSS to modulate the Schottky barrier height, validating both the work function and conductivity of the triboelectric material, which plays a fundamental role in DC generation, is explored. A large work function difference is required to create a high built‐in electric field for efficient separation of electron–hole pairs. Decent conductivity also fulfills an integral role in the innate carrier‐transport capability. Accordingly, an open‐circuit voltage (Voc) of 800 mV, a short‐circuit current (Isc) of 80 μA, and a power density of 6.7 mW cm−2 are yielded simultaneously.

Optimization of SIS solar cells with ultra-thin silicon oxide layer

Due to the simple process, low energy consumption and stable performance, semiconductor/insulating layer/semiconductor (SIS) solar cells have attracted lots of research interests. However, the device physics of SIS solar cells needs further clarification and improvement. In this paper, the effects of TCO work function on the performance of TCO/SiO2/n-Si heterojunction solar cells were simulated by AFORS-HET and the physics mechanisms for these effects were clarified. It is found that for a work function of 5.2 eV or higher of TCO, the SIS devices possess high ƞ of 22.9% or higher, while the devices show the S-shape J-V curve with low FF when the work function work function of TCO is under 5.1 eV. Further analysis indicates that the work function difference between TCO and n-Si substrate is so small that there is an insufficient band bending at the interface leading to a lower built-in electric field that degrades the photogenerated carriers’ separation, which results in the deformation of J-V curve. Moreover, the simulation results show that the performances of TCO/SiOx/n-Si devices are significantly affected by the band offsets at the SiOx/n-Si interface. When the conduction band offset is higher than 0.4 eV, it can effectively prevent electrons from passing through the SiOx layer to reduce the recombination at the interface, resulting in the excellent output performances of the SIS device. But for a low conduction band order of 0.4 eV or less, the blocking effect of electrons weakens, leading to the large recombination at the interface. Finally, we propose two mechanisms of S-shape J-V curve of SIS solar cells: one is the built-in electric field is too small to separate photogenerated carriers, and the other one is that the carrier transmission is blocked by the thick tunneling layer or insulating layer. This work deepens the understanding of the device physics of SIS solar cells and paves the way for enhancing the output performance of industrial Si-based solar cells.

BiOI/AgI/Ag plasmonic heterostructure for efficient photoelectrochemical water splitting

BiOI-based photocathode has attracted much attention for photoelectrochemical (PEC) water splitting application. Here, we have designed a BiOI/AgI/Ag plasmonic heterostructure through a facile electrodeposition combined with ion-exchange and illumination approach. The work function difference between BiOI and AgI brings favorable interfacial band bending, and the Ag nanoparticle exhibits localized surface plasmonic effect to boost the carrier transfer. Thus, the BiOI/AgI/Ag photocathode achieves superior current density of −1.02 mA cm−2 at 0 V vs. RHE for 200 min, which is 50 times than that of pristine BiOI. These results pave a way for promising PEC water splitting using BiOI-based heterostructure photocathodes.

Design of Dual-Material Gate Junctionless FinFET based on the Properties of Materials Forming Gate Electrode

This work elaborately investigates the electrical behaviour and short channel performance of Dual-Material Gate Junctionless Fin Field Effect Transistors (DMG-JLFinFETs) with multiple-gate metal pairs and varying gate metal length ratios. Rigorous analysis on the nature of DMG-JLFinFET with gate length as low as 10 nm is done using a device simulator by Silvaco, Inc. The gate material closer to the source, namely M1, has a dominating influence on the threshold voltage (V th) and tunnelling current (I tunn) than the gate material closer to the drain (named M2) in a DMG-JLFinFET. I tunn is lower when the work function of M1 (Φ M1) is greater than the work function of M2 (Φ M2). The relative change in threshold voltage is minimum for Platinum–Gold (PtAu)-DMG-JLFinFET (0.68%). Titanium–Aluminium (TiAl) and Nickel–Titanium (NiTi) gate material pairs, having the same work function difference of 0.38 eV, have the least Drain-Induced Barrier Lowering (DIBL) of 12.88 mV/V. A better Sub-threshold Swing (SS) is observed for DMG-JLFinFET having Φ M1 < Φ M2. For devices with Φ M1 > Φ M2, SS can be improved by making a length of M1 (L M1) greater than 70% of the total gate length (L g).

Dielectric and ferroelectric photovoltaic properties of epitaxial BiFeO3 film with La0.5Sr0.5CoO3 bottom electrode

In order to deeply investigate the dielectric and ferroelectric photovoltaic properties of BiFeO3 (BFO) thin films, the Pt/BFO/La[Formula: see text]Sr[Formula: see text]CoO3 (LSCO) heterostructure ferroelectric capacitor grown on (001) SrTiO3 (STO) substrate is successfully fabricated by off-axis magnetron sputtering. The X-ray diffraction (XRD) and Phi scanning results show that the STO-based BFO and LSCO films are both (001) epitaxial structure. Although the BFO ferroelectric film exhibits an obvious dielectric dispersion phenomenon, a remarkable ferroelectric photovoltaic performance is obtained with open circuit voltage ([Formula: see text]) of 0.38[Formula: see text]V and short-circuit current ([Formula: see text]) of 0.23[Formula: see text]mA/cm2, respectively. With increasing test temperatures, [Formula: see text] decreases slowly and then rapidly, while [Formula: see text] increases rapidly and then decreases. At a critical temperature of 80∘C, the BFO ferroelectric film exhibits a faster photovoltaic response, in which the values of [Formula: see text] and [Formula: see text] are about 0.19[Formula: see text]V and 0.28[Formula: see text]mA/cm2, respectively. Moreover, the energy band analysis indicates that a large work function difference ([Formula: see text][Formula: see text]eV) between LSCO and Pt leads to a strong built-in electric field in the BFO film, which is beneficial to separate the photo-generated carriers and improve ferroelectric photovoltaic effect. In all, this study not only shows that BFO is an excellent and environmentally friendly photovoltaic candidate material, but also provides a practical strategy for improving the performance of BFO ferroelectric photovoltaic devices.

The Superaerophobic N-Doped Carbon Nanocage with Hydrogen Spillover Effort for Enhanced Hydrogen Evolution.

Under the high current density, the excessive strong adsorption of H* intermediates and H2 accumulation the catalysts are the major obstacle to the industrial application of hydrogen evolation reaction (HER) catalysts. Herein, through experimental exploration, it is found that the superaerophobic Nitrogen (N)-doped carbon material can promote the rapid release of H2 and provide H* desorption site for the hydrogen spillover process, which makes it have great potential as the catalysts support for hydrogen spillover. Based on this discovery, this work develops the hydrogen spillover catalyst with electron-rich Pt sites loaded on N-doped carbon nanocage (N-CNC) with adjustable work function. Through a series of comprehensive electrochemical tests, the existence of hydrogen spillover effort has been proved. Moreover, the in situ tests showed that pyrrolic-N can activate adjacent carbon sites as the desorption sites for hydrogen spillover. The Pt@N-1-CNC with the minimum work function difference (ΔΦ) between Pt NPs and support shows superior hydrogen evolution performance, only needs overpotential of 12.2mV to reach current density of 10mA cm-2 , outstanding turnover frequency (TOF) (44.7 s-1 @100mV) and superior durability under the 360h durability tests at current density of 50mA cm-2 .