Search Results (17)

Triethylamine (TEA) is a common industrial contaminant and an important indicator of seafood spoilage. Therefore, determination of rapid and selective TEA is of great significance. This review article critically compares tungsten oxide (WO₃)- and molybdenum oxide (MoO₃)-based chemiresistive sensors by relating their crystal structure, surface chemistry, defect states, morphology, and interfacial electronic properties to TEA-sensing performance. Pristine WO₃- and MoO₃-based sensors generally operate at approximately 133–325 °C and provide sub-ppm detection, whereas doping, noble-metal sensitization, heterojunction formation, and light activation can reduce the operating temperature to 100–180 °C and extend detection into the low-ppb range. WO₃-based sensors have exhibited a response of 1100 to 20 ppm TEA at 160 °C, with an estimated detection limit of 5 ppb, whereas modified MoO₃-based sensors have also achieved decent detection limit of 1.7 ppb. WO₃ is particularly responsive to phase, facet, work-function, and catalytic-interface engineering, whereas α-MoO₃ benefits from its anisotropic structure, variable Mo valence, and favorable Lewis acid–base interactions with amines. Noble metals enhance gas sensing through catalytic and electronic sensitization, dopants regulate adsorption and defect chemistry, and n-n or p-n heterojunctions amplify resistance changes through depletion-layer modulation. Despite considerable advances in sensitivity, humidity interference, high power consumption, slow recovery, baseline drift, and limited long term stability remain unresolved. Future advances may require standardized performance assessment, operando mechanistic studies, humidity-resistant low-power devices, and validation under realistic seafood-storage and industrial conditions. Full article

Facing the dual challenges of energy shortage and environmental degradation, photocatalysis and electrocatalysis have emerged as key technologies for converting small molecules into value-added chemicals, yet their conflicting requirements on the electronic structure of catalysts prevent a single material from freely switching between the two modes. Here, we demonstrate a feasible strategy for achieving on-demand switching between these catalytic functions in a single ferroelectric heterojunction, Pd-C₃N₄@In₂Se₃, through polarization engineering. Using first-principles density functional theory calculations, we show that reversing the polarization direction of the α-In2Se3 layer induces a nonvolatile electronic phase transition. The downward polarization (P↓) configuration exhibits metallic behavior, whereas the upward polarization (P↑) state becomes semiconducting with a type-II band alignment. This transition arises from polarization-dependent interfacial built-in electric fields and charge transfer differences. Notably, the metallicity of the P↓ configuration is localized predominantly within the In₂Se₃ layer rather than delocalized over the entire heterostructure. This arises because the enhanced interfacial charge transfer, driven by the larger work-function difference, selectively populates the conduction band of In₂Se₃, pushing its band edge across the Fermi level, while the Pd-C₃N₄ layer remains semiconducting due to charge depletion and the absence of gap-closing hybridization at the interface. In the P↑ state, the heterojunction acts as an efficient photocatalyst for overall water splitting, with band edges straddling the redox potentials. Under illumination, photogenerated electrons and holes make the hydrogen evolution reaction and oxygen evolution reaction thermodynamically spontaneous. In contrast, the metallic P↓ state serves as an excellent electrocatalyst for hydrogen evolution, delivering a limiting potential as low as −0.11 V, attributed to strengthened N 2p and H 1s orbital hybridization. These findings resolve the conflicting electronic requirements of photocatalysis and electrocatalysis and offer a new paradigm for designing smart, dual-functional catalysts adaptable to varying energy inputs, providing valuable theoretical guidance for future experimental realization of switchable catalytic systems. Full article

In the present work, graphene-modified zinc oxide (ZnO-rGO) and fluorine-doped tin oxide (FTO) thin films were successfully fabricated using a simple, low-cost pulsed spray pyrolysis technique. The structural, morphological, optical, electrical, and surface electronic properties of the deposited films were systematically characterized. X-ray diffraction (XRD) analysis confirmed the formation of polycrystalline ZnO- and SnO₂-based phases with crystallite sizes in the nanometer range. The crystallographic parameters, microstrain, and dislocation density of the deposited films were found to be influenced by the incorporation of reduced graphene oxide (rGO) and fluorine dopants. Scanning electron microscopy (SEM) revealed compact and homogeneous surface morphologies with good film coverage and well-defined nanocrystalline features. Optical characterization demonstrated the wide-bandgap semiconducting behavior of the deposited films, with optical bandgap energies ranging from 3.262 to 3.312 eV for the ZnO-rGO films and from 3.91 to 4.01 eV for the FTO films. Kelvin probe measurements yielded work-function values in the range of approximately 5.0–5.2 eV, indicating favorable surface electronic characteristics suitable for optoelectronic applications. Furthermore, fluorine incorporation enhanced the dielectric response of the SnO₂ films, particularly in the low-frequency region owing to increased interfacial polarization effects. The obtained results demonstrate that pulsed spray pyrolysis provides a simple, cost-effective, and efficient route for fabricating ZnO-rGO and FTO thin films with desirable structural, optical, electrical, and surface electronic properties. These findings highlight the considerable potential of the developed materials for transparent electrodes and a wide range of optoelectronic applications. Full article

Hydrogen is a promising clean-energy carrier, but its low ignition energy, high diffusivity, and wide flammability range demand reliable leak detection. Chemiresistive sensors based on n-type metal oxide semiconductors are attractive owing to their simple architecture, low cost, large resistance modulation, thermal robustness, and compatibility with miniaturized devices. This review focuses on n-type metal oxide semiconductor nanomaterials for hydrogen sensing, particularly ZnO, SnO₂, In₂O₃, WO₃, TiO₂, and related mixed oxides. The fundamental sensing mechanisms are examined, including oxygen chemisorption, electron-depletion-layer modulation, grain-boundary barrier control, catalytic hydrogen spillover, and hydrogen-induced surface reduction or metallization, together with the way these mechanisms compete and cooperate under different operating conditions. Recent performance-enhancement strategies are organized around morphology and porosity control, noble-metal sensitization, defect and dopant engineering, n–n heterojunctions, molecular sieving, and low-temperature activation. Density functional theory is discussed as a design tool for evaluating adsorption energetics, vacancy formation, work-function shifts, band alignment, and interfacial charge transfer, along with its current limitations for modeling humid surfaces. Finally, key challenges and future directions, including humidity tolerance, standardized reporting, device integration, and emerging materials, are summarized to guide the development of high-performance hydrogen sensors. Full article

In this study, first-principles density functional theory (DFT) calculations were employed to investigate the effects of single and binary gas adsorption of NO, CO, CO₂, NO₂, H₂S, and O₃ on the ZnGa₂O₄(111) surface. For single-gas adsorption, O₃ adsorbed on surface Ga sites induces a pronounced work-function increase of 0.97 eV, whereas H₂S adsorption at surface O sites yields the strongest adsorption energy (−1.21 eV), highlighting their distinct electronic interactions with the surface. For binary co-adsorption, the NO₂-O₃ pair adsorbed at Ga-coordinated sites produces the largest work-function shift (1.88 eV), while adsorption at Zn sites results in the most stable configuration, with an adsorption energy reaching −3.98 eV. These results indicate that co-adsorption of highly electronegative gases can significantly enhance charge transfer and sensing response. In contrast, mixed oxidizing–reducing gas pairs, such as NO₂-H₂S, lead to a markedly suppressed work-function variation (−0.02 eV), suggesting reduced sensor sensitivity due to compensating charge-transfer effects. Overall, this work demonstrates that gas-sensing behavior on ZnGa₂O₄(111) is governed not only by individual gas–surface interactions but also by cooperative and competitive effects arising from binary co-adsorption, providing insights into realistic multi-gas sensing environments. Full article

Understanding the interactions between ionic liquid ions and lithium-metal surfaces is critical for designing safer and more efficient lithium metal batteries. In this work, we use density functional theory to investigate the electronic structure, binding energies, work-function shifts and interfacial charge redistribution of several ionic liquid ions, including FSI⁻, TFSI⁻, ${\mathrm{P}\mathrm{F}}_6^{-}$, ${\mathrm{B}\mathrm{F}}_4^{-}$, DFOB⁻, Pyr14⁺, and EMIM⁺, on a Li-metal anode (Li_m). Absorption orientation-dependent effects are examined for each molecule. Specifically, differences in charge density and electron localization function analyses revealed unique patterns of electron accumulation and delocalization that highlighted specific atomic roles in interfacial bonding. Interfacial charge transfer is analyzed through Bader charges, revealing a moderate charge redistribution for the cations (EMIM⁺, Pyr14⁺), and a more significant charge uptake for the reactive anions (FSI⁻, TFSI⁻, DFOB⁻). Among cations, EMIM⁺ was determined to have the most interfacial stability, while Pyr14⁺ displayed mid-level reactivity. For the anions, varying tendencies for bond formation with lithium metal and potential fragmentation could be determined. Overall, these discoveries detail an atomistic analysis of ionic liquid to Li_m interactions providing additional pathways for molecular design techniques to stabilize electrolytes performing not high-cost computational calculations. Full article

Organic hole transport materials (HTMs) have been frequently used to achieve high power conversion efficiencies (PCEs) in regular perovskite solar cells (PSCs). However, organic HTMs or their ingredients are costly and time-consuming to manufacture. Therefore, one of the hottest research topics in this area has been the quest for an efficient and economical inorganic HTM in PSCs. To promote efficient charge extraction and, hence, improve overall efficiency, it is crucial to look into the desirable properties of inorganic HTMs. In this context, a simulation investigation using a solar cell capacitance simulator (SCAPS) was carried out on the performance of regular PSCs using inorganic HTMs. Several inorganic HTMs, such as nickel oxide (NiO), cuprous oxide (Cu₂O), copper iodide (CuI), and cuprous thiocyanate (CuSCN), were incorporated in PSCs to explore matching HTMs that could add to the improvement in PCE. The simulation results revealed that Cu₂O stood out as the best alternative, with electron affinity, hole mobility, and acceptor density around 3.2 eV, 60 cm²V⁻¹s⁻¹, and 10¹⁸ cm⁻³, respectively. Additionally, the results showed that a back electrode with high work-function was required to establish a reduced barrier Ohmic and Schottky contact, which resulted in efficient charge collection. In the simulation findings, Cu₂O-based PSCs with an efficiency of more than 25% under optimal conditions were identified as the best alternative for other counterparts. This research offers guidelines for constructing highly efficient PSCs with inorganic HTMs. Full article

We have performed density functional VASP calculations of a pure and of a carbon-covered (100) tungsten surface under the presence of an electric field E directed away from the surface. Our aim is to answer the question of an increased penetrability of electrons at the collector side of a nanometric tunnel diode when covered by carbon atoms, a purely quantum mechanical effect related to the value of the workfunction Φ. To obtain Φ at a non-zero electric field we have extrapolated back to the electrical surface the straight line representing the linear increase in the potential energy with distance outside the metal-vacuum interface. We have found that under the presence of E the workfunction Φ = E_vac − E_F of the (100) pure tungsten surface has a minor dependence on E. However, the carbon-covered tungsten (100) surface workfunction Φ(C − W) has a stronger E dependence. Φ(C − W) decreases continuously with the electric field. This decrease is ΔΦ = 0.08 eV when E = 1 V/nm. This ΔΦ is explained by our calculated changes with electric field of the electronic density of both pure and carbon-covered tungsten. The observed phenomena may be relevant to other surfaces of carbon-covered tungsten and may explain the reported collector dependence of current in Scanning Field Emission Microscopy. Full article

In this work, a self-powered, solar-blind photodetector, based on InZnSnO (IZTO) as a Schottky contact, was deposited on the top of Si-doped β-Ga₂O₃ by the sputtering of two-faced targets with InSnO (ITO) as an ohmic contact. A detailed numerical simulation was performed by using the measured J–V characteristics of IZTO/β-Ga₂O₃ Schottky barrier diodes (SBDs) in the dark. Good agreement between the simulation and the measurement was achieved by studying the effect of the IZTO workfunction, β-Ga₂O₃ interfacial layer (IL) electron affinity, and the concentrations of interfacial traps. The IZTO/β-Ga₂O₃ (SBDs) was tested at a wavelength of 255 nm with the photo power density of 1 mW/cm². A high photo-to-dark current ratio of $3.70\times {10}^5$ and a photoresponsivity of 0.64 mA/W were obtained at 0 V as self-powered operation. Finally, with increasing power density the photocurrent increased, and a 17.80 mA/W responsivity under 10 mW/cm² was obtained. Full article

Controlling the Schottky barrier height (${\varphi }_B$) and other parameters of Schottky barrier diodes (SBD) is critical for many applications. In this work, the effect of inserting a graphene interfacial monolayer between a Ni Schottky metal and a β-${\mathrm{Ga}}_2{\mathrm{O}}_3$ semiconductor was investigated using numerical simulation. We confirmed that the simulation-based on Ni workfunction, interfacial trap concentration, and surface electron affinity was well-matched with the actual device characterization. Insertion of the graphene layer achieved a remarkable decrease in the barrier height (${\varphi }_B$), from 1.32 to 0.43 eV, and in the series resistance ($R_S$), from 60.3 to 2.90$\mathrm{m}\Omega .{\mathrm{cm}}^2$. However, the saturation current ($J_S$) increased from $1.26\times {10}^{-11}$ to $8.3\times {10}^{-7}$(A/cm²). The effects of a graphene bandgap and workfunction were studied. With an increase in the graphene workfunction and bandgap, the Schottky barrier height and series resistance increased and the saturation current decreased. This behavior was related to the tunneling rate variations in the graphene layer. Therefore, control of Schottky barrier diode output parameters was achieved by monitoring the tunneling rate in the graphene layer (through the control of the bandgap) and by controlling the Schottky barrier height according to the Schottky–Mott role (through the control of the workfunction). Furthermore, a zero-bandgap and low-workfunction graphene layer behaves as an ohmic contact, which is in agreement with published results. Full article

In recent years, optical and electronic properties of metal–organic frameworks (MOFs) have increasingly shifted into the focus of interest of the scientific community. Here, we discuss a strategy for conveniently tuning these properties through electrostatic design. More specifically, based on quantum-mechanical simulations, we suggest an approach for creating a gradient of the electrostatic potential within a MOF thin film, exploiting collective electrostatic effects. With a suitable orientation of polar apical linkers, the resulting non-centrosymmetric packing results in an energy staircase of the frontier electronic states reminiscent of the situation in a pin-photodiode. The observed one dimensional gradient of the electrostatic potential causes a closure of the global energy gap and also shifts core-level energies by an amount equaling the size of the original band gap. The realization of such assemblies could be based on so-called pillared layer MOFs fabricated in an oriented fashion on a solid substrate employing layer by layer growth techniques. In this context, the simulations provide guidelines regarding the design of the polar apical linker molecules that would allow the realization of MOF thin films with the (vast majority of the) molecular dipole moments pointing in the same direction. Full article

A gallium nitride (GaN)-based normally off metal–oxide–semiconductor field-effect transistor (MOSFET) using a dual-metal-gate (DMG) structure was proposed and fabricated to improve current drivability. Normally off operation with a high V_th of 2.3 V was obtained using a Cl₂/BCl₃-based recess etching process. The DMG structure was employed to improve current characteristics, which can be degraded by recess etching. The I_D and g_m of a DMG-based device with nickel (Ni)-aluminum (Al) were improved by 42.1% and 30.9%, respectively, in comparison to the performances of a single-metal-gate-based device with Ni because the DMG structure increased electron velocity in the channel region. This demonstrates that the DMG structure with a large work-function difference significantly improves the carrier transport efficiency. GaN-based recessed-gate MOSFETs based on the DMG structure hold promising potentials for high-efficiency power devices. Full article

Metal gate technology is one of the most important methods used to increase the low on-current of tunnel field-effect transistors (TFETs). However, metal gates have different work-functions for each grain during the deposition process, resulting in work-function variation (WFV) effects, which means that the electrical characteristics vary from device to device. The WFV of a planar TFET, double-gate (DG) TFET, and electron-hole bilayer TFET (EHBTFET) were examined by technology computer-aided design (TCAD) simulations to analyze the influences of device structure and to find strategies for suppressing the WFV effects in TFET. Comparing the WFV effects through the turn-on voltage (V_turn-on) distribution, the planar TFET showed the largest standard deviation (σV_turn-on) of 20.1 mV, and it was reduced by −26.4% for the DG TFET and −80.1% for the EHBTFET. Based on the analyses regarding metal grain distribution and energy band diagrams, the WFV of TFETs was determined by the number of metal grains involved in the tunneling current. Therefore, the EHBTFET, which can determine the tunneling current by all of the metal grains where the main gate and the sub gate overlap, is considered to be a promising structure that can reduce the WFV effect of TFETs. Full article

In this short commentary, we discuss a fundamental reason why two different semiconductor technologies are needed for complementary thin-film transistor (TFT) operations. It is mainly related to an energy-level matching between the band edge of the semiconductor and the work-function energy of the metal, which is used for the source and drain electrodes. The reference energy level is determined by the energy range of work-functions of typical metals for the source and drain electrodes. With the exception of silicon, both the conduction band edge (E_C) and valence band edge (E_V) of a single organic or inorganic material are unlikely to match the metal work-function energy whose range is typically from −4 to −6 eV. For example, typical inorganic materials, e.g., Zn–O, have the E_C of around −4.5 eV (i.e., electron affinity), so the conduction band edge is within the range of the metal work-function energy, suggesting its suitability for n-channel TFTs. On the other hand, p-type inorganic materials, such as Cu–O, have an E_V of around −5.5 eV, so the valence band edge is aligned with metal work-function energy, thus the usage for p-channel TFTs. In the case of p-type and n-type organic materials, their highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) should be aligned with metal work-function energy. For example, p-type organic material, e.g., pentacene, has a HOMO level around −5 eV, which is within the range of the metal work-function energy, implying usage for p-channel TFTs. However, its LUMO level is around −3 eV, not being aligned with the metals’ work-function energy. So it is hard to use pentacene for n-channel TFTs. Along with this, n-type organic materials (e.g., C60) should have HOMO levels within the typical metals’ work-function energy for the usage of n-channel TFT. To support this, we provide a qualitative and comparative study on electronic material properties, such as the electron affinity and band-gap of representative organic and inorganic materials, and the work-function energy of typical metals. Full article

This paper reports low temperature solution processed ZnO thin film transistors (TFTs), and the effects of interfacial passivation of a 4-chlorobenzoic acid (PCBA) layer on device performance. It was found that the ZnO TFTs with PCBA interfacial modification layers exhibited a higher electron mobility of 4.50 cm² V⁻¹ s⁻¹ compared to the pristine ZnO TFTs with a charge carrier mobility of 2.70 cm² V⁻¹ s⁻¹. Moreover, the ZnO TFTs with interfacial modification layers could significantly improve device shelf-life stability and bias stress stability compared to the pristine ZnO TFTs. Most importantly, interfacial modification layers could also decrease the contact potential barrier between the source/drain electrodes and the ZnO films when using high work-function metals such as Ag and Au. These results indicate that high performance TFTs can be obtained with a low temperature solution process with interfacial modification layers, which strongly implies further potential for their applications. Full article