Search Results (157)

South Dongting Lake is an essential aquatic ecosystem that receives substantial water inflows from the Xiangjiang and Zishui Rivers. However, it is significantly impacted by human activities, including mining, smelting, and farming. These activities have led to serious contamination of the lake’s sediments with heavy metals (HMs). This study investigated the distribution, mobility, and influencing factors of HMs at the sediment–water interface. To this end, sediment samples were analyzed from three key regions (Xiangjiang River estuary, Zishui River estuary, and northeastern South Dongting Lake) using traditional sampling methods and Diffusive Gradients in Thin Films (DGT) technology. Analysis of fifteen HMs (Pb, Bi, Ni, As, Se, Cd, Sb, Mn, Zn, V, Cr, Cu, Tl, Co, and Fe) revealed significant spatial heterogeneity. The results showed that Cr, Cu, Pb, Bi, Ni, As, Se, Cd, Sb, Mn, Zn, and Fe exhibited high variability (CV > 0.20), whereas V, Tl, and Co demonstrated stable concentrations (CV < 0.20). Concentrations were found to exceed background values of the upper continental crust of eastern China (UCC), Yangtze River sediments (YZ), and Dongting Lake sediments (DT), particularly at the Xiangjiang estuary (XE) and in the northeastern regions. Speciation analysis revealed that V, Cr, Cu, Ni, and As were predominantly found in the residual fraction (F4), while Pb and Co were concentrated in the oxidizable fraction (F3), Mn and Zn appeared primarily in the exchangeable fractions (F1 and F2), and Cd was notably dominant in the exchangeable fraction (F1), suggesting a high potential for mobility. Additionally, DGT results confirmed a significant potential for the release of Pb, Zn, and Cd. Contamination assessment using the Pollution Load Index (PLI) and Geoaccumulation Index (Igeo) identified Pb, Bi, Ni, As, Se, Cd, and Sb as major pollutants. Among these, Bi and Cd were found to pose the highest risks. Furthermore, the Risk Assessment Code (RAC) and the Potential Ecological Risk Index (PERI) highlighted Cd as the primary ecological risk contributor, especially in the XE. The study identified sediment grain size, pH, electrical conductivity, and nutrient levels as the primary influencing factors. The PMF modeling revealed HM sources as mixed smelting/natural inputs, agricultural activities, natural weathering, and mining/smelting operations, suggesting that remediation should prioritize Cd control in the XE with emphasis on external inputs. Full article

This study investigates the development and sensing profile of synthetic melanin nanoparticle-coated electrodes for the electrochemical detection of heavy metals, including lead (Pb), cadmium (Cd), cobalt (Co), zinc (Zn), nickel (Ni), and iron (Fe). Synthetic melanin films were prepared in situ by the deacetylation of diacetoxy indole (DAI) to dihydroxy indole (DHI), followed by the deposition of DHI monomers onto indium tin oxide (ITO) and glassy carbon electrodes (GCE) using cyclic voltammetry (CV), forming a thin layer of synthetic melanin film. The deposition process was characterized by electrochemical quartz crystal microbalance (EQCM) in combination with linear sweep voltammetry (LSV) and amperometry to determine the mass and thickness of the deposited film. Surface morphology and elemental composition were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). In contrast, Fourier-transform infrared (FTIR) and UV–Vis spectroscopy confirmed the melanin’s chemical structure and its polyphenolic functional groups. Differential pulse voltammetry (DPV) and amperometry were employed to evaluate the melanin films’ electrochemical activity and sensitivity for detecting heavy metal ions. Reproducibility and repeatability were rigorously assessed, showing consistent electrochemical performance across multiple electrodes and trials. A comparative analysis of ITO, GCE, and graphite electrodes was conducted to identify the most suitable substrate for melanin film preparation, focusing on stability, electrochemical response, and metal ion sensing efficiency. Finally, the applicability of melanin-coated electrodes was tested on in-house heavy metal water samples, exploring their potential for practical environmental monitoring of toxic heavy metals. The findings highlight synthetic melanin-coated electrodes as a promising platform for sensitive and reliable detection of iron with a sensitivity of 106 nA/ppm and a limit of quantification as low as 1 ppm. Full article

The poor magnetic and magneto-optical properties of BiFeO₃, along with its significant lattice mismatch with silicon, have limited its application in silicon-based integrated magneto-optical devices. In this study, co-doping with Sr²⁺ and Ti⁴⁺ ions effectively transformed the trigonal structure of BiFeO₃ into a cubic phase, thereby reducing the lattice mismatch with silicon to 2.8%. High-quality, highly oriented, silicon-based cubic Sr,Ti:BiFeO₃ thin films were successfully fabricated using radio frequency magnetron sputtering. Due to the induced lattice distortion, the characteristic periodic spiral spin antiferromagnetic structure of BiFeO₃ was suppressed, resulting in a significant enhancement of the saturation magnetization of cubic Bi_0.5Sr_0.5Fe_0.5Ti_0.5O₃ (48.0 emu/cm³), compared to that of pristine BiFeO₃ (5.0 emu/cm³). Furthermore, the incorporation of Sr²⁺ and Ti⁴⁺ ions eliminated the birefringence effect inherent in trigonal BiFeO₃, thereby inducing a pronounced magneto-optical effect in the cubic Sr,Ti:BiFeO₃ thin film. The magnetic circular dichroic ellipticity (ψ_F) of Bi_0.5Sr_0.5Fe_0.5Ti_0.5O₃ reached an impressive 2300 degrees/cm. Full article

The anisotropic magnetoresistance (AMR) effect is widely used in microscale and nanoscale magnetic sensors. In this study, we investigate the correlation between AMR and the crystal structure, epitaxial relationship, and magnetic properties of Co₅₀Fe₅₀ thin films deposited on rigid MgO and flexible mica substrates. The AMR ratio is approximately 1.6% for CoFe films on mica, lower than the 2.5% observed in epitaxially grown films on MgO substrates. The difference is likely due to the well-defined easy axis in the single domain epitaxial thin films on MgO, which enhances the AMR ratio. Microscopic strain induced by lattice mismatch and bending on flexible substrates were determined using grazing incidence X-ray diffraction and extended X-ray absorption fine structure techniques. These results showed that neither microscopic nor macroscopic strain (below 0.5%) affects the AMR ratio on mica, suggesting its suitability for magnetic sensors in flexible and wearable devices. Additionally, investigating M-H loops under various growth temperatures, lattice mismatch conditions, and bending strains could further benefit the fabrication and integration of the micro-scale magnetic sensors in the microelectronic industry. Full article

This study investigates the structural and catalytic properties of pure and Sr-doped LaCoO₃ and LaFeO₃ thin films for potential use as resistive gas sensors. Thin films were deposited via pulsed laser deposition (PLD) and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation, and scratch tests. XRD analysis confirmed the formation of the desired perovskite phases without secondary phases. XPS revealed the presence of La³⁺, Co³⁺/Co⁴⁺, Fe³⁺/Fe⁴⁺, and Sr²⁺ oxidation states. SEM and AFM imaging showed compact, nanostructured surfaces with varying morphologies (shape and size of surface irregularities) depending on the composition. Sr doping led to surface refinement and increased nanohardness and adhesion. Transmission electron microscopy (TEM) analysis confirmed the columnar growth of nanocrystalline films. Sr-doped LaCoO₃ demonstrated enhanced sensitivity and stability in the presence of NO₂ gas compared to pure LaCoO₃, as evidenced by electrical resistivity measurements within 230 ÷ 440 °C. At the same time, it was found that Sr doping stabilizes the catalytic activity of LaFeO₃ (in the range of 300 ÷ 350 °C), although its behavior in the presence of NO₂ differs from that of LaCo(Sr)O₃—especially in terms of response and recovery times. These findings highlight the potential of Sr-doped LaCoO₃ and LaFeO₃ thin films for NO₂ sensing applications. Full article

Flexible polymer-based piezoelectric nanogenerators (PENGs) have gained significant interest due to their ability to deliver clean and sustainable energy for self-powered electronics and wearable devices. Recently, the incorporation of fillers into the ferroelectric polymer matrix has been used to improve the relatively low piezoelectric properties of polymer-based PENGs. In this study, we investigated the effect of various nanofillers such as titania (TiO₂), zinc oxide (ZnO), reduced graphene oxide (rGO), and lead zirconate titanate (PZT) on the PENG performance of the nanocomposite thin films containing the nanofillers in poly(vinylidene fluoride-co-trifluoro ethylene) (P(VDF-TrFE)) matrix. The nanocomposite films were prepared by depositing molecularly thin films of P(VDF-TrFE) and nanofiller nanoparticles (NPs) spread at the air/water interface onto the indium tin oxide-coated polyethylene terephthalate (ITO-PET) substrate, and they were characterized by measuring their microstructures, crystallinity, β-phase contents, and piezoelectric coefficients (d₃₃) using SEM, FT-IR, XRD, and quasi-static meter, respectively. Multiple PENGs incorporating various nanofillers within the polymer matrix were developed by assembling thin film-coated substrates into a sandwich-like structure. Their piezoelectric properties, such as open-circuit output voltage (V_OC) and short-circuit current (I_SC), were analyzed. As a result, the PENG containing 4 wt% PZT, which was named P-PZT-4, showed the best performance of V_OC of 68.5 V with the d₃₃ value of 78.2 pC/N and β-phase content of 97%. The order of the maximum V_OC values for the PENGs of nanocomposite thin films containing various nanofillers was PZT (68.5 V) > rGO (64.0 V) > ZnO (50.9 V) > TiO₂ (48.1 V). When the best optimum PENG was integrated into a simple circuit comprising rectifiers and a capacitor, it demonstrated an excellent two-dimensional power density of 20.6 μW/cm² and an energy storage capacity of 531.4 μJ within 3 min. This piezoelectric performance of PENG with the optimized nanofiller type and content was found to be superior when it was compared with those in the literature. This PENG comprising nanocomposite thin film with optimized nanofiller type and content shows a potential application for a power source for low-powered electronics such as wearable devices. Full article

Global warming and environmental pollution due to the overuse and exploitation of fossil fuels are the main issues affecting humans’ well-being. Solar energy is considered to be one of the most promising candidates for providing human society with a clean and sustainable energy supply. Thin-film organic solar cells (TFOSCs) use organic semiconductors as light-absorbing layer materials. TFOSCs have attracted wide research interest due to several advantages, such as easy fabrication, affordability, light weight, and environmental friendliness. Over the years, TFOSCs have been dominated by donor–acceptor blends based on polymer donors and fullerene acceptors. However, a new class of non-fullerene acceptors (NFAs) has gained prominence in TFOSCs owing to their significant improvement in the power conversion efficiency (PCE) of non-fullerene-based devices. In this study, the One-Dimensional Solar Cell Capacitance Simulator (SCAPS-1D) numerical simulator was used to study the performance of a device with a configuration of FTO/PDINO/PBDB-T/ITIC/CFTS/Al. Here, the PBDB-T/ITIC polymer blend represents poly[(2,6-(4,8-bis(5-(2 ethylhexyl)thiophen-2-yl)benzo [1,2-b:4,5-b]dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo [1,2-c:4,5-c]dithiophene-4,8-dione)] (PBDB)/3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetraki(4-hexylphenyl)-dithieno[2,3-d:2,3-d]-s-indaceno [1,2-b:5,6-b]dithiophene) (ITIC) and the non-fullerene acceptor (NFA) and serves as the absorber layer. The electron transport layer (ETL) was 2,9-Bis[3-(dimethyloxidoamino)propyl]anthra[2,1,9-def:6,5,10-d’e’f’]diisoquinoline-1,3,8,10(2H,9H)-tetrone (PDINO), and Cu₂FeSnS₄ (CFTS) was used as a hole transport layer (HTL). This research article aims to address the global challenges of environmental pollution and global warming caused by the overuse of fossil fuels by exploring alternative energy solutions. Upon optimization, the device achieved a power conversion efficiency (PCE) of 16.86%, a fill factor (FF) of 79.12%, a short-circuit current density (J_SC) of 33.19 mA cm⁻², and an open-circuit voltage (V_OC) of 0.64 V. The results obtained can guide the fabrication of NFA-based TFOSCs in the near future. Full article

The modulation of the magneto-optical signal is a crucial research focus in the field of magneto-optics. Micron arrays of varying shapes were fabricated using the UV exposure technique, and their effects were tested on the magneto-optical Kerr response of CoFeB thin films. The influence of the organic–inorganic interface on the magneto-optical Kerr effect (MOKE) was investigated by utilizing organic materials to fabricate arrays. The results indicate that the micron-scale metal array exhibits a limited enhancement of the magneto-optical Kerr signal, but it can change the ferromagnetic strength and the magnetization speed of the magnetic layer. This is because the electron orbit coupling at the organic–inorganic interface enhances the performance of the magnetic film. When a photoresist is used as the array material, the longitudinal magneto-optical Kerr signal of the CoFeB film increases by at least two-fold. The enhancement effect of different shapes of arrays is different because of the different contact area with the CoFeB film. Full article

This study investigates the effect of polyvinylidene fluoride–CoFe₂O₄ (PVDF-CFO) composite film thickness on their supramolecular structure, phase composition, and dielectric properties. The composites were synthesized from PVDF with CFO nanoparticles using the Dr. Blade method to obtain film thicknesses ranging from 15 to 58 μm. The data obtained show that the thinner film (15 μm) has a higher β-phase content compared to the thicker films (58 μm), as confirmed by FTIR and Raman spectroscopy. Scanning electron microscopy (SEM) showed that increasing film thickness within the studied range leads to the development of larger spherulitic structures and increased porosity. Atomic force microscopy (AFM) analysis also showed that thicker films have higher tensile strength due to their larger cross-sectional area, while thinner films exhibit lower elasticity. A more uniform microstructure and an increased electroactive phase in thin films result in increased permittivity, which is critical for PVDF-based sensors and energy devices. Full article

Laser ablation was used to successfully fabricate multiferroic bilayer thin films, composed of BaTiO₃ (BTO) and CoFe₂O₄ (CFO), on highly doped (100) Si substrates. This study investigates the influence of BaTiO₃ layer thickness (50–220 nm) on the films’ structural, magnetic, and dielectric properties. The dense, polycrystalline films exhibited a tetragonal BaTiO₃ phase and a cubic spinel CoFe₂O₄ layer. Structural analysis revealed compression of the CoFe₂O₄ unit cell along the growth direction, while the BaTiO₃ layer showed a tetragonal distortion, more pronounced in thinner BTO layers. These strain effects, attributed to the mechanical interaction between both layers, induced strain-dependent wasp-waisted behavior in the films’ magnetic hysteresis cycles. The strain effects gradually relaxed with increasing BaTiO₃ thickness. Raman spectroscopy and second harmonic generation studies confirmed BTO’s non-centrosymmetric ferroelectric structure at room temperature. The displayed dielectric permittivity dispersion was modeled using the Havriliak–Negami function combined with a conductivity term. This analysis yielded relaxation times, DC conductivities, and activation energies. The observed BTO relaxation time behavior, indicative of small-polaron transport, changed significantly at the BTO ferroelectric Curie temperature (Tc), presenting activation energies E_τ in the 0.1–0.3 eV range for T < Tc and E_τ > 0.3 eV for T > Tc. The BTO thickness-dependent Tc behavior exhibited critical exponents ν ~ 0.82 consistent with the 3D random Ising universality class, suggesting local disorder and inhomogeneities in the films. This was attributed to the composite structure of BTO grains, comprising an inner bulk-like structure, a gradient strained layer, and a disordered surface layer. DC conductivity analysis indicated that CoFe₂O₄ conduction primarily occurred through hopping in octahedral sites. These findings provide crucial insights into the dynamic dielectric behavior of multiferroic bilayer thin films at the nanoscale, enhancing their potential for application in emerging Si electronics-compatible magneto-electric technologies. Full article

The pyroelectric nanogenerator (PyNG) has gained increasing attention due to its capability of converting ambient or waste thermal energy into electrical energy. In recent years, nanocomposite films of poly(vinylidene fluoride-co-trifluoro ethylene) (P(VDF-TrFE)) and nanofillers such as reduced graphene oxide (rGO) have been employed due to their high flexibility, good dielectric properties, and high charge mobility for the application of wearable devices. This work investigated the effect of rGO reduction on pyroelectric nanogenerator performance. To prepare rGO, GO was reduced with different reducing agents at various conditions. The resulting rGO samples were characterized by XPS, FT-IR, XRD, and electrical conductivity measurements to obtain quantitative and qualitative information on the change in surface functionalities. Molecularly thin nanocomposite films of P(VDF-TrFE)/rGO were deposited on an ITO-glass substrate by the Langmuir–Schaefer (LS) technique. A PyNG sandwich-like structure was fabricated by arranging the thin films facing each other, and it was subjected to the pyroelectric current test. For various PyNGs of the thin films containing rGO prepared by different methods, the average pyroelectric peak-to-peak current (APC) and the pyroelectric coefficient (p) values were measured. It was found that a more reduced rGO resulted in higher electrical conductivity, and the thin films containing rGO of higher conductivity yielded higher APC and p values and, thus, better energy-harvesting performance. However, the thin films having rGO of too high conductivity produced slightly reduced performance. The Maxwell–Wagner effect in the two-phase system successfully explained these optimization results. In addition, the APC and p values for the thin film with the best performance increased with increasing temperature range. The current PyNG’s performance with an energy density of 3.85 mW/cm² and a p value of 334 μC/(m²∙K) for ΔT = 20 °C was found to be superior to that reported in other studies in the literature. Since the present PyNG showed excellent performance, it is expected to be promising for the application to microelectronics including wearable devices. Full article

In this work, TiO₂ and Anderson-type polyoxometalates (Ni, Co, and Fe) thin-film composites were fabricated. The composites were characterized by FTIR and Raman spectroscopy, diffuse reflectance, and scanning electronic microscopy. The methylene blue (MB) photocatalytic degradation on the composites under UV irradiation was studied. Spectroscopic results verified the modification of TiO₂ thin films. Optical and morphological properties changed after TiO₂ modification. The largest change in the optical band gap was observed for the FePOM/TiO₂ system, which reported a value of 3.05 eV. The POM/TiO₂ systems were more efficient in methylene blue (MB) adsorption than bare TiO₂. Furthermore, the modified films were more efficient than bare TiO₂ during MB photodegradation tests. The NiPOM/TiO₂ and the CoPOM/TiO₂ were the most efficient in the MB adsorption, reaching ~20%. The NiPOM/TiO₂ and the CoPOM/TiO₂ composites were the most efficient in the photodegradation process, reaching ~50% of MB removal. The stability tests indicated that composite films were moderately stable after the three performed reusability cycles. Thus, these results suggest that POM modification of TiO₂ can improve the adsorption and photodegradation capacity of semiconductors. Full article

Hematite (α-Fe₂O₃) is one of the most promising and widely used semiconductors for application in photoelectrochemical (PEC) water splitting, owing to its moderate bandgap in the visible spectrum and earth abundance. However, α-Fe₂O₃ is limited by short hole-diffusion lengths. Ultrathin α-Fe₂O₃ films are often used to limit the distance required for hole transport, therefore mitigating the impact of this property. The development of highly controllable and scalable ultrathin film deposition techniques is therefore crucial to the application of α-Fe₂O₃. Here, a plasma-enhanced atomic layer deposition (PEALD) process for the deposition of homogenous, conformal, and thickness-controlled α-Fe₂O₃ thin films (<100 nm) is developed. A readily available iron precursor, dimethyl(aminomethyl)ferrocene, was used in tandem with an O₂ plasma co-reactant at relatively low reactor temperatures, ranging from 200 to 300 °C. Optimisation of deposition protocols was performed using the thin film growth per cycle and the duration of each cycle as optimisation metrics. Linear growth rates (constant growth per cycle) were measured for the optimised protocol, even at high cycle counts (up to 1200), confirming that all deposition is ‘true’ atomic layer deposition (ALD). Photoelectrochemical water splitting performance was measured under solar simulated irradiation for pristine α-Fe₂O₃ deposited onto FTO, and with a α-Fe₂O₃-coated TiO₂ nanorod photoanode. Full article

Cobalt-doped lead ferrite (Pb₂Fe₂O₅) thin films were deposited by reactive magnetron sputtering. The influence of the cobalt concentration and synthesis temperature on the structure, phase composition and ferroelectric properties of Pb₂Fe₂O₅ thin films was investigated. It was determined that the increase in deposition temperature increased the grain size and density of the Co-doped PFO thin films. The XRD data demonstrated that the Co-doped Pb₂Fe₂O₅ thin films consisted of Pb₂Fe₂O₅ and PbO phases with a low amount of CoO and Co₃O₄ phases. The increase in the cobalt concentration in the Pb₂Fe₂O₅ films slightly enhanced the cobalt oxide phase content. Polarization dependence on electric field measurement demonstrated that the highest ferroelectric properties of the Co-doped Pb₂Fe₂O₅ films were obtained when the synthesis was performed at 550 °C temperatures. The increase in the cobalt concentration in the films enhanced the remnant polarization and coercive field values. It was found that the Co-doped Pb₂Fe₂O₅ film deposited at 550 °C temperature and containing 10% cobalt had the highest remnant polarization (72 µC/cm²) and coercive electric field (105 kV/cm). Full article

This research introduces a hydrogen sensor made from a thin film of magnesium zinc oxide (MgZnO) deposited using a technique called radiofrequency co-sputtering (RF co-sputtering). Separate magnesium oxide (MgO) and zinc oxide (ZnO) targets were used to deposit the MgZnO film, experimenting with different deposition times and power levels. The sensor performed best (reaching a sensing response of 2.46) when exposed to hydrogen at a concentration of 1000 parts per million (ppm). This peak performance occurred with a MgZnO film thickness of 432 nanometers (nm) at a temperature of 300 °C. Initially, the sensor’s responsiveness increased as the film thickness grew. This is because thicker films tend to have more oxygen vacancies, which are imperfections that play a role in the sensor’s function. However, further increases in film thickness beyond the optimal point harmed performance. This is attributed to the growth of grains within the film, which hindered its effectiveness. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were employed to thoroughly characterize the quality of the MgZnO thin film. These techniques provided valuable insights into the film’s crystal structure and morphology, crucial factors influencing its performance as a hydrogen sensor. Full article