Search Results (323)

A ternary CdS–MoS₂–rGO photocathode was developed to enhance visible light-driven hydrogen evolution through interfacial heterostructure engineering. The composite was fabricated via a solution-based deposition method followed by thermal conversion, resulting in crystalline CdS and MoS₂ phases that were uniformly integrated within a conductive reduced graphene oxide (rGO) framework. Structural and surface analyses (XRD and XPS) confirmed the coexistence of Cd²⁺, Mo⁴⁺, and S²⁻ chemical states without detectable secondary phases. Photoelectrochemical measurements revealed that the ternary architecture significantly improves charge separation efficiency and interfacial charge-transfer kinetics compared to binary and single-component films. The CdS–MoS₂–rGO photocathode exhibited the highest photocurrent density, reduced charge-transfer resistance, and favorable Tafel slope under visible-light irradiation (0.25 sun, neutral electrolyte). Gas chromatography measurements verified that these electrochemical enhancements translate into increased hydrogen production rates, following the trend: CdS–MoS₂–rGO > CdS–rGO > MoS₂–rGO >> rGO. Applied bias photon-to-current efficiency (ABPE) analysis further confirmed improved photon utilization efficiency in the ternary system. The enhanced performance is attributed to synergistic integration of CdS (light harvesting), rGO (rapid electron transport), and MoS₂ (catalytic edge sites), which suppresses recombination and accelerates proton reduction kinetics. These findings demonstrate that rational multi-component heterostructure design is an effective strategy for improving hydrogen evolution rate under mild operating conditions. Full article

In this work, Fe, Co, Ni, Cu, and Mo powders were used as starting materials to prepare high-entropy alloy (HEA) thin films by a coating and vacuum sintering process. Using the HEA thin film as the substrate, selenium was subsequently deposited by chemical vapor deposition (CVD) to obtain high-entropy alloy selenide thin films (HEASe). The phase structure, surface chemical states, morphology, and elemental distribution of the porous films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The electrocatalytic hydrogen evolution performance of the electrodes was evaluated using a three-electrode configuration in 0.5 M H₂SO₄, 1 M KOH, 1 M KOH + 0.5 M NaCl, and 1 M KOH + 0.5 M Na₂S solutions. The results indicate that the HEA selenide thin-film electrodes exhibit favorable electrocatalytic behavior in all four electrolytes. Among them, HEASe-450 shows the best overall performance. In 0.5 M H₂SO₄, it requires an overpotential of only 57.6 mV to reach a current density of 10 mA cm⁻², with a Tafel slope of 146.96 mV dec⁻¹. In 1 M KOH, the overpotential at 10 mA cm⁻² is 50.1 mV, and the corresponding Tafel slope is 142 mV dec⁻¹. In 1 M KOH + 0.5 M NaCl, the overpotential is 52.7 mV with a Tafel slope of 122.72 mV dec⁻¹. In 1 M KOH + 0.5 M Na₂S, an overpotential of 85 mV is required, and the Tafel slope increases to 236 mV dec⁻¹. Full article

Catalysis has entered everyday life through a range of technological processes that rely on different catalytic systems. The increasing demand for such systems requires rationalization of the use of their expensive components, such as noble-metal catalysts. As such, a catalyst with low noble-metal concentration, in which each one of the noble atoms is active, would reach the lowest price possible. Nevertheless, no clear reactivity descriptors have been outlined for this type of low-coordinated supported atom. Using DFT calculations, we consider three diverse systems as models of single-atom catalysts. We investigate monomers and bimetallic dimers of Ru, Rh, Pd, Ir, and Pt on MgO(001), Cu adatom on thin Mo(001)-supported films (NaF, MgO, and ScN), and single Pt adatoms on oxidized graphene surfaces. The reactivity of these metal atoms was probed by CO. In each case, we see the interaction through the donation–backdonation mechanism. In some cases, CO adsorption energies can be linked to the position of the d-band center and the adatom’s charge. A higher-lying d-band center and less-charged, supported single atoms bind CO more weakly. Also, in some cases, metal atoms that are less strongly bound to the substrate bind CO more strongly. The results suggest that the identification of common activity descriptor(s) for single metal atoms on foreign supports is a difficult task with no unique solution. However, it is also suggested that the stability of adatoms and strong anchoring to the support are prerequisites for the application of descriptor-based search to novel single-atom catalysts. Full article

In this study, FeCoNiMoCu high-entropy alloy thin films were sulfided at different temperatures ranged from 250 °C to 450 °C by chemical vapor deposition, and the resultant sulfided Fe-Co-Ni-Mo-Cu-S alloys were characterized by means of XRD, SEM, XPS and EDS. HER performance tests were carried out in four electrolyte systems, namely 0.5 M H₂SO₄, 1 M KOH, 1 M KOH + 0.5 M NaCl and 1 M KOH + 1 M Na₂S. The results indicated that the as-prepared electrodes exhibited low HER overpotentials in all four electrolytes, with the optimal catalytic performance consistently achieved at a sulfidation temperature of 350 °C. Among the tested systems, the electrode delivered the best HER activity in 0.5 M H₂SO₄, showing an overpotential of merely 53 mV and a Tafel slope of 86.72 mV dec⁻¹ at a current density of 10 mA·cm⁻². In 1.0 M KOH, the overpotential required to reach the same current density was 98 mV with a Tafel slope of 72.43 mV dec⁻¹. For the mixed electrolyte of 1 M KOH and 0.5 M NaCl, the overpotential at 10 mA·cm⁻² was 142 mV accompanied by a Tafel slope of 49.51 mV dec⁻¹. In contrast, the 1 M KOH + 1 M Na₂S electrolyte yielded an overpotential of 77 mV and a Tafel slope of 84.01 mV dec⁻¹ at the identical current density. HER tests revealed that the sulfidation temperature exerts a significant influence on the formation and distribution of active phases of multi-metal sulfides (e.g., FeS_x, CoS_x, NiS_x, MoS₂) on the electrode surface. The electrodes prepared at an appropriate sulfidation temperature exhibit a larger specific surface area and enhanced hydrogen evolution reaction performance for water electrolysis. These findings may provide useful references for other researchers in the design and fabrication of high-entropy alloy-based HER catalysts. Full article

In this study, a highly crystalline 2H (hexagonal)-phase MoS₂ sensing layer with a precisely controlled crystal structure was realized through a combination of DC sputtering and sulfurization annealing processes, and subsequently integrated with a D-shaped optical fiber to develop a highly sensitive carbon dioxide (CO₂) sensor. Conventionally sputtered MoS₂ thin films often suffer from the presence of unstable metallic 1T (tetragonal) phases and a high density of sulfur vacancies, which significantly degrade sensor reversibility and long-term stability. Here, high-temperature annealing under a sulfur-rich atmosphere was employed to induce a complete phase transition from the metastable 1T phase to the stable semiconducting 2H phase, while simultaneously healing sulfur vacancies. Enhanced crystallinity was confirmed by Raman spectroscopy. The fabricated sensor exhibited excellent linearity (R² > 0.99) and markedly improved repeatability over a CO₂ concentration range of 1000–10,000 ppm. This significant performance enhancement is attributed to reversible charge transfer induced by sulfur vacancy passivation, which modulates the complex refractive index of the MoS₂ layer and optimizes optical interaction with the evanescent field of the D-shaped fiber. The phase engineering and defect-healing strategy presented in this work effectively addresses the drift issues commonly observed in conventional electrical gas sensors and provides a crucial pathway toward the realization of high-performance optical gas sensors. Full article

The photocatalytic efficacy of metallic silver nanoparticle/zinc oxide (Ag-NPs/ZnO) composite thin films, COMP-Ag_x, with varying silver concentrations (0 mol% ≤ x ≤ 100 mol%), is investigated for the degradation of methyl orange (MO). The films were spin-coated on a silica glass surface at 600 °C utilizing the molecular precursor method (MPM). The XRD spectra of these composite thin films revealed three significant peaks corresponding to the diffraction planes of (0 0 2), (1 0 0), and (1 0 1), indicative of the formation of ZnO crystallites in diverse orientations, in conjunction with an additional signal for cubic Ag crystals. The magnitude of the ZnO peaks diminishes as the mol% of silver increases. The images from the SEM confirm the integration of Ag-NPs into the ZnO matrix. The UV/Vis absorption spectra exhibit a 410 nm surface plasmon resonance (SPR) peak for composite Ag-NP/ZnO thin films. The absorption spectra of ZnO and Ag-NP/ZnO composite thin films demonstrate the band gap of ZnO to be 3.4 eV, while the band gaps of the composite thin films nearly approximate that of ZnO. The decomposition rates of the MO solution indicate that composite thin films function effectively under visible irradiation compared to pure ZnO. The optical properties indicated that the SPR of Ag-NPs contributed to the visible responsiveness of the composite thin films. The SPR demonstrate significant visible light responsiveness and essential characteristics during photoexcited electron transfer from the Ag-NPs to the ZnO conduction band. Full article

The transition to clean and renewable energy sources is of prime importance in addressing environmental challenges related to the consumption of fossil fuels. Hydrogen, being a clean fuel with a high energy density, has huge potential, especially when it can be obtained through solar-driven PEC water splitting. Herein, $Mo{S}_2$ photocatalysts were synthesized by sulfurizing $Mo{O}_3$ thin films, using a CVD technique. The deposited $Mo{O}_3$ films by thermal evaporation at 450 °C were further sulfurized at 500 °C, 550 °C, and 600 °C. XRD results confirmed the successful conversion of $Mo{O}_3$ into $Mo{S}_2$. The optical properties showed a bandgap reduction from 2.50 eV to 1.30 eV, which leads to better absorption of light in the visible region.The photoelectrochemical experiment shows that the S-$Mo{O}_3$-600 °C thin film has the best performance, and the solar-to-hydrogen conversion efficiency reaches 0.11385% at an applied bias of 1.0 V versus Ag/AgCl, which is about 189 times higher than that of the pristine $Mo{O}_3$ thin film. Full article

Ultrathin two-dimensional (2D) coatings exhibit functional properties that are strongly defined by morphological features such as sheet edges, fracture sites, overlaps, folds, and local thickness variations, which are often difficult to resolve using conventional scanning electron microscopy (SEM) configurations. Here, we introduce a grazing-incidence SEM approach based on controlled sample tilting close to 90° for enhancing surface sensitivity and morphological feature detectability in ultrathin coatings. The method is proved on colloidal MoS₂ nanosheet coatings prepared by liquid-phase exfoliation. Optical absorption spectroscopy confirms the presence of mono- and few-layer MoS₂ nanosheets in the dispersion, confirming the ultrathin nature of the deposited coating. Compared to standard 0° imaging, grazing-incidence SEM reveals clearer boundaries and discontinuities. Quantitative Sobel-based image analysis supports these observations, showing an increase in edge density from 5.9% to 7.6% and in average gradient magnitude from 0.151 to 0.172 a.u. under grazing incidence, indicating a higher amount of retrievable morphological information. The proposed approach relies only on standard stage tilting and provides a broadly applicable framework for the surface-sensitive morphological characterization of ultrathin 2D coatings and thin films. Full article

Liquefied petroleum gas (LPG) is a widely used clean and efficient fuel across domestic and industrial sectors. However, the highly flammable nature of LPG poses serious safety risks. Therefore, the advancement of dependable and effective LPG sensors is vital. This work produced a cost-effective and extremely sensitive LPG thin film sensor that operates at room temperature using hydrothermally generated MoTe₂. The synthesized MoTe₂ was comprehensively characterized to investigate its phase purity, crystal structure, phase formation, and morphology employing powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), and Raman spectroscopy. The PXRD and Raman results confirmed the formation of a single-phase hexagonal 2H-MoTe₂ structure, while FE-SEM analysis revealed elongated, sheet-like morphologies. The LPG sensing properties were evaluated across concentrations ranging from 0.5 to 2.0 vol%. The sensor exhibited a maximum response of 1.50 at 2.0 vol% LPG, while the fastest response and recovery times of 11 s and 23 s, respectively, were observed at 0.5 vol% LPG. Additionally, the sensor demonstrated excellent repeatability, reaching 99.55%. The mechanism involving the adsorption and desorption of LPG is also explained. Full article

ZnO and CuO thin films were deposited separately using the radio frequency (RF) sputtering technique, and the effect of annealing in nitrogen and oxygen ambient environments was investigated. In this article, structural, optical, vibrational, and electrical characterizations were sequentially performed using techniques such as X-ray diffraction (XRD), UV–visible spectroscopy (UV-vis), Raman spectroscopy, photoluminescence (PL) spectroscopy, and current-voltage measurements using a DC four-probe station. XRD confirmed a high-crystallinity and wurtzite structure for ZnO, with the preferred orientation being along the c-axis (0001), and a monoclinic structure for CuO, with preferential orientation along the (002) axis. The absorption edges of the ZnO and CuO thin films were determined to be 3.24 eV and 2.89 eV, respectively. However, Urbach tails were observed only in the ZnO thin films, confirming the presence of localized Zn interstitials and oxygen vacancies. The absorption of CuO showed weak Urbach tails, suggesting that the defects were not localized. Raman spectroscopy performed on the ZnO and CuO thin films showed the appearance of weak E₂(high) and prominent A_g/B_2g modes, confirming the presence of ZnO and CuO bonding states, respectively. PL studies revealed room temperature emission for both the CuO and ZnO thin films, which is crucial for thin film solar cells and photodetectors. Two thin film heterostructures were fabricated with and without MoS₂ (a hole transport layer) on FTO substrates. The Al/FTO/CuO/ZnO/Al heterostructure revealed a rectifying behavior with a photo current of 2 mA in the dark, whereas light-induced characteristics resulted in a photocurrent of 5 mA. The Al/FTO/MoS₂/CuO/ZnO/Al heterostructure exhibited a similar rectifying behavior, with improved photo currents of 5 mA in the dark and 9 mA in the light. Full article

Hydrogen is a key energy carrier for fuel cell vehicles and hydrogen energy systems. However, its colorless and odorless nature, combined with a wide flammability range, poses significant safety risks in the event of leakage. Accordingly, compact and reliable hydrogen sensors capable of low-ppm detection at moderate operating temperatures are essential for early-stage safety monitoring. In this study, a bias-optimized hydrogen gas sensor based on a Pd-functionalized SnO₂ thin film with Mo electrodes and an integrated microheater is designed, fabricated, and systematically characterized. The sensor employs a Mo-based vertical microheater and a multilayer thermal insulation stack, enabling thermally efficient and stable operation at 250–280 °C with low power consumption. The electrical and sensing properties of the SnO₂ layer are optimized by controlling the oxygen partial pressure during reactive sputtering and post-deposition annealing. The Pd catalytic layer promotes hydrogen dissociation and spillover, resulting in pronounced resistance modulation through surface redox reactions and interfacial charge transport effects. By systematically optimizing the sensing bias voltage, a clear trade-off between sensitivity enhancement and electrical noise is identified, which allows stable and repeatable operation in the low-ppm regime. The sensor response follows a power-law dependence on hydrogen concentration, and an automated measurement platform is employed to evaluate repeatability and statistical performance. Based on baseline noise analysis and concentration-dependent resistance variation, a limit of detection of approximately 6.4 ppm is achieved. Furthermore, a concentration-normalized figure of merit that combines response magnitude and concentration dependence is introduced to quantitatively assess low-concentration hydrogen sensing performance. These results demonstrate that the proposed Mo-electrode Pd/SnO₂ thin-film sensor, enabled by bias-optimized operation and integrated thermal control, provides a robust and scalable platform for safety-critical hydrogen leak detection. Full article

The structure and composition of a refractory Ni-containing CrMoNbTaVW high-entropy-alloy (HEA) thin film were investigated. The HEA thin film with a thickness of 5 μm was grown via conventional direct current magnetron sputtering from a multiple-elemental compound target. The Ni-containing HEA thin film with a Ni concentration of 3.6 at. % exhibits a single-phase body-centered cubic (BCC) crystal structure with a lattice parameter of a = 0.316 nm. The grains in the HEA thin film are columns, extended in the growth direction. They are not aligned exactly perpendicular to the substrate surface. The thin film grows in a polycrystalline structure with a tendency to preferred orientation or texture. Energy-dispersive X-ray analyses of the HEA thin film show near-equal atomic concentrations of Cr, Mo, Nb, Ta, V, and W elements in the range 15–17 at. % with almost uniform distribution. In contrast, Ni is not uniformly distributed in the film, and grains with a different Ni concentrations were observed. The defects observed in the HEA thin film are mainly single dislocations or an assembly of dislocations, which could be caused by residual stresses in the layer forming during the growth of the HEA thin film. Full article

Amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) have emerged as promising candidates for next-generation large-area and low-power electronics due to their high mobility, low leakage current, and compatibility with low-temperature fabrication on flexible or transparent substrates. In this work, we report the fabrication of bottom-gate a-IGZO NMOS TFTs using HfO₂ as high-k gate dielectric and Mo top contacts. The devices were electrically characterized through capacitance–voltage (C–V) and current–voltage (I–V) measurements, from which key parameters were extracted. Based on these transistors, we designed, fabricated, and characterized inverters employing four different load configurations: resistive, diode, depletion, and pseudo-CMOS. A comparative analysis was performed in terms of voltage transfer characteristics (VTCs), gain, and noise margins, highlighting that depletion-load inverters offer the highest gain and robust noise margins. Finally, a two-channel multiplexer was designed and fabricated. The multiplexer was characterized under both square and sinusoidal input signals up to 1 kHz, demonstrating correct channel selection and robust switching behavior. These results confirm the potential of a-IGZO TFT-based circuits as building blocks for low-power and high-reliability digital and mixed-signal electronics. Full article

With the discovery of amorphous oxide semiconductors, a new era of electronics opened. Indium gallium zinc oxide (IGZO) overcame the problems of amorphous and poly-silicon by reaching mobilities of ~10 cm²/Vs and demonstrating thin-film transistors (TFTs) are easy to manufacture on transparent and flexible substrates. However, mobilities over 30 cm²/Vs have been difficult to reach and other materials have been introduced. Recently, polycrystalline In₂O₃ has demonstrated breakthroughs in the field. In₂O₃ TFTs have attracted attention because of their high mobility of over 100 cm²/Vs, which has been achieved multiple times, and because of their use in scaled devices with channel lengths down to 10 nm for high integration in back-end-of-the-line (BEOL) applications and others. The present review focuses first on the material properties with the understanding of the bandgap value, the importance of the position of the charge neutrality level (CNL), the doping effect of various atoms (Zr, Ge, Mo, Ti, Sn, or H) on the carrier concentration, the optical properties, the effective mass, and the mobility. We introduce the effects of the non-parabolicity of the conduction band and how to assess them. We also introduce ways to evaluate the CNL position (usually at ~E_C + 0.4 eV). Then, we describe TFTs’ general properties and parameters, like the field effect mobility, the subthreshold swing, the measurements necessary to assess the TFT stability through positive and negative bias temperature stress, and the negative bias illumination stress (NBIS), to finally introduce In₂O₃ TFTs. Then, we will introduce vacuum and non-vacuum processes like spin-coating and liquid metal printing. We will introduce the various dopants and their applications, from mobility and crystal size improvements with H to NBIS improvements with lanthanides. We will also discuss the importance of device engineering, introducing how to choose the passivation layer, the source and drain, the gate insulator, the substrate, but also the possibility of advanced engineering by introducing the use of dual gate and 2 DEG devices on the mobility improvement. Finally, we will introduce the recent breakthroughs where In₂O₃ TFTs are integrated in neuromorphic applications and 3D integration. Full article

This study investigates how molybdenum oxide (MoO_x) rear interface passivation—specifically its thickness and deposition conditions—affects CIGS thin-film solar cells. The MoO_x layer effectively suppresses selenium/sulfur diffusion into the molybdenum back contact during high-temperature processing, while improving the absorber’s microstructure by reducing interfacial voids. These modifications enhance electrical properties, yielding lower series resistance, higher shunt resistance, and improved fill factor and current density. Although recombination increases slightly, the reduction in voltage-related fill factor loss ultimately boosts hole extraction and suppresses electron recombination at the back contact. Consequently, MoO_x-passivated cells achieve superior performance, with industrial-scale modules (1650 mm × 658 mm) reaching 152.41 W output power and 14.0% efficiency. This work provides valuable insights for optimizing MoO_x-based interface engineering to improve CIGS solar cell efficiency and manufacturability. Full article