Search Results (82)

Y-branched TiO₂ nanotubes (NTs) were produced by anodizing titanium plates derived from aerospace production leftovers and subsequently engineered to develop an enhanced TiO₂-based photocatalytic system. The NTs were electrochemically reduced to obtain reduced TiO₂ nanotubes (rTN) with a narrowed bandgap, followed by surface modification with polydopamine (PD) and silk fibroin-derived quantum dots (QDs) to promote enhanced UV and visible-light photocatalysis for wastewater treatment. The QDs were hydrothermally synthesized from Bombyx mori silk fibroin. Scanning Electron Microscopy (SEM) revealed spherical QD agglomerates encapsulated within the PD layer, while Energy Dispersive X-ray Spectroscopy (EDX) confirmed the presence of carbon and nitrogen originating from both PD and QD. The resulting rNT/PD/QD photocatalyst exhibited a significantly reduced bandgap (1.03 eV), increased Urbach energy (1.35 eV), and moderate hydrophilicity. A high double-layer capacitance (C_dl) indicated an enlarged electrochemically active surface due to the combination of treatments. Electrochemical characterization demonstrated reduced electrical resistance, higher charge density, and lower electron–hole recombination, leading to improved interfacial charge transfer efficiency and electrochemical stability during multi-cycle cyclic voltammetry measurements. Preliminary photocatalytic tests show that the rNT/PD/QD photocatalyst achieved a degradation efficiency of 79.26% for methyl orange (MO) and 35% for tetracycline (TC). Full article

This study aims to address a major challenge and find solutions for developing less expensive, lighter, and more efficient energy storage materials while remaining environmentally friendly. This work combines the study of the structural, morphological, and optical properties of epoxy nanocomposites containing ZnO and SnO₂ and highlights the influence of oxide filler content on their energy storage performance. To this end, epoxy nanocomposites filled with metal oxides (ZnO and SnO₂) prepared by extrusion, a simple, economical, and reliable industrial method, were studied and compared. The materials obtained are inexpensive, lightweight, and highly efficient, and can replace traditional glass-based systems in the energy sector. The results of XRD, SEM, and FTIR analyses show the absence of impurities, the stability of the structures in humid environments, and the homogeneity of the prepared films. They also indicate that the nature and charge content of the oxide integrated into the polymer matrix play a significant role in the properties of the nanocomposites. Optical measurements were used to determine the film thickness, the type of electronic transition, the band gap energy, and the Urbach energy. Based on the results obtained, the prepared nanocomposite films appear to be promising materials for energy-based optical applications. Full article

The compounds LiCo_1−xMn_xO₂ (x = 0.5, 0.7) were synthesized via the solid-state method and exhibited crystallization in the cubic spinel structure (space group Fd-3m). UV–Vis spectroscopy reveals strong visible-light absorption and a reduction in the indirect optical band gap from 1.85 eV (x = 0.5) to 1.60 eV (x = 0.7) with increasing Mn content, which is consistent with semiconducting behavior. This narrowing arises from Mn³⁺/Mn⁴⁺ mixed valence, which introduces mid-gap states and enhances Co/Mn 3d–O 2p orbital hybridization within the spinel framework. In contrast, the Urbach energy increases from 0.55 eV to 0.65 eV, indicating greater structural and energetic disorder in the Mn-rich composition which is attributed to the Jahn–Teller distortions and valence heterogeneity associated with Mn³⁺. Impedance and dielectric modulus analyses confirm two distinct non-Debye relaxation processes related to grains and grain boundaries. AC conductivity is governed by the Correlated Barrier Hopping (CBH) model, with bipolaron hopping identified as the dominant conduction mechanism. The x = 0.7 sample displays significantly enhanced conductivity due to increased Mn³⁺/Mn⁴⁺ mixed valence, lattice expansion, efficient 3D electronic connectivity of the spinel lattice, and reduced interfacial resistance. These findings highlight the potential of these two spinels compounds as narrow-gap semiconductors for optoelectronic applications including visible-light photodetectors, photocatalysts, and solar absorber layers extending their utility beyond conventional battery cathodes. Full article

We investigate how grain growth, strain relaxation, and vacancy chemistry shape the near-edge optical response of nanocrystalline Ce${\mathrm{O}}_{2-\delta }$ prepared by a chymosin-assisted Pechini route from nitrate–citrate precursors. Rietveld line-profile analysis shows that phase-pure Ce${\mathrm{O}}_{2-\delta }$ forms after calcination between 400 and 1000 °C. Over this range, the average crystallite size increases from ≈3.4 to ≈57 nm, while the microstrain decreases from 0.79% to 0.05%, with size–strain scaling consistent with interface-controlled grain growth that follows a normal growth law with exponent $m=2$ and activation energy $Q\approx 155$ kJ ${\mathrm{mol}}^{-1}$. Raman spectroscopy tracks the sharpening of the $F_{2g}$ mode and the fading of defect-related bands, X-ray photoelectron spectroscopy reveals a nonmonotonic evolution of the surface ${\mathrm{Ce}}^{3+}$ fraction and separates lattice from adsorbed oxygen species, and electron paramagnetic resonance detects vacancy-bound ${\mathrm{Ce}}^{3+}$ polarons that weaken at high temperature. Diffuse-reflectance UV–Vis spectra show a modest blue shift of the apparent band gap from $E_g\approx 2.78$ to 2.95 eV as crystallites coarsen, while the Urbach energy $E_u$ follows the ${\mathrm{Ce}}^{3+}$ content and sub-gap tailing. The structural, spectroscopic, and optical results together map out a quantitative connection between grain growth, vacancy populations, and near-edge optical properties in ${\mathrm{CeO}}_{2-\delta }$ nanoparticles. Full article

Kapton-H type is an optical plastic with a UV-Vis-NIR spectrum characterized by abrupt absorbance change at a wavelength of ca. 550 nm. Such sharp optical discontinuity, known as the fundamental absorption edge, has been investigated using the Tauc plot method, and a band gap energy (E_g) of (2.22 ± 0.05) eV for an indirect allowed electron transition model has been found. The Cody plot has also been applied, and a slightly lower band gap energy value (i.e., E_g = 2.33 ± 0.05 eV) has been found. The Urbach rule applied to the spectrum tail has provided an Urbach energy value (E_U) of ca. (185 ± 2) meV, which is quite a high value that is fully compatible with the highly disordered structure of this sterically rigid semi-crystalline polymer. The cut-on wavelength (550 nm), visible transparency (T% of ca. 80), and other relevant optical characteristics of the Kapton-H type have been also evaluated and compared with corresponding values of polyetherimide. Full article

Nb₂O₅ (niobia) coatings were prepared by spin coating of niobium sol, synthesized using niobium chloride as the precursor and ethanol and water as solvents, followed by high-temperature annealing. Doping of the films was achieved by incorporating commercially available SiO₂ (Ludox) and noble metal nanoparticles (NPs) into the sol prior to its deposition. Various sizes of Pt (5 and 30 nm), Ag (10, 20, and 40 nm), and Au (5, 10, and 20 nm) NPs were used to enhance sensing behavior of coatings. After annealing, films were subjected to chemical etching to remove the silica phase. This process generated porosity within the films, which in turn enabled the tailoring of both their optical and sensing properties. It was demonstrated that both the type and size of the incorporated nanoparticles significantly influenced the sensing behavior. The most effective enhancement was observed with the addition of 10 nm AuNPs. Optical characterization indicated that 10 nm AuNPs had a minimal effect on the optical properties. In contrast, doping with 20 nm AuNPs led to a reduction in the refractive index and an increase in Urbach energy. No significant alteration in the optical band gap due to doping was observed. Full article

Commercial electricity is increasingly being generated by renewable energy sources, and the photovoltaic conversion of sunlight is the fastest-growing renewable source. In addition to its rapid growth, solar electricity generation has seen very dramatic reductions in cost, as well as continuing increases in its conversion efficiency and installation lifetime. The growth between 2014 and 2024 in the record cell-level performance of four commercial technologies based on Si, CdTe, CuInGaSe₂, and perovskites is compared with each other, with the highest achieved by GaAs, which is primarily used in space applications. Si, CdTe, and CuInGaSe₂ have each narrowed the gap with their ideal efficiencies by about 5%, whereas perovskites, starting from a much lower base, have improved by closer to 20%, and GaAs, already much closer to its ideal value, has advanced by only a modest additional amount. Other important comparisons such as costs, stability, and environmental impact are not addressed here. Full article

The aim of this study was to produce a coating for protective glass glued to touch displays with high antibacterial effectiveness. This paper presents the structural, mechanical, optical, and antibacterial properties of a TiO₂:Ag–Pt coating prepared by dual reactive DC and RF magnetron sputtering. Characterization techniques used include XRD, TEM with EDS, SEM, AFM, nanoindentation for hardness and Young’s modulus, wettability tests, and optical property analysis. The coating exhibited columnar crystals with a width of 30–50 nm. Crystals of anatase, rutile, silver, and platinum with a size of up to 3 nm were identified. The coating deposited on glass had a concentration of 5.0 ± 0.2% at. Ag and 4.4 ± 0.1% at. Pt. The value of the optical band gap energy, corresponding to the direct transition, was 3.36 eV, while Urbach’s energy was in the order of 500 meV. The hydrophilic coating had a roughness RMS = 1.8 ± 0.2 nm, hardness HV = 6.8 ± 0.5 GPa, and Young’s modulus E = 116 ± 8 GPa. A unique combination of the phase composition of the TiO₂:Ag–Pt coating, metallic Ag and Pt nanoparticles in a ceramic matrix of anatase and rutile crystallites resulted a >90% reduction of Staphylococcus aureus bacteria. This antibacterial effect was attributed to the activation of the doped semiconductor under visible light via plasmon resonance of the Ag and Pt nanoparticles, as well as a light-independent antibacterial action due to Ag⁺ ion release. In contrast, commercial antibacterial coatings typically achieve only around 60% bacterial reduction. Full article

Upscaling perovskite solar cells and modules requires precise laser patterning for series interconnection and spatial characterization of cell parameters to understand laser–material interactions and their impact on performance. This study investigates the use of nanosecond (ns) and picosecond (ps) laser pulses at varying fluences for the P3 patterning step of perovskite solar cells. Hyperspectral photoluminescence (PL) imaging was employed to map key parameters such as optical bandgap energy, Urbach energy, and shunt resistance. The mappings were correlated with electrical measurements, revealing that both ns and ps lasers can be utilized for effective series interconnections with minimal performance losses at optimized fluences. Our findings provide a deeper understanding of fluence-dependent effects in P3 patterning. Moreover, the results demonstrate that the process window is robust, allowing for reasonable cell performance even with deviations from optimal parameters. This robustness, coupled with the scalability of the laser patterning process, emphasize its suitability for industrial module production. Full article

By leveraging machine learning insights from prior perovskite studies and employing the sol–gel method, we successfully synthesized two novel perovskite nanoceramics—M_0.5 Ca_0.25Mg_0.25MnO₃ (M = La, Pr)—as multifunctional nanomaterials. X-ray diffraction (XRD) confirmed their orthorhombic Pnma crystal structure. The Williamson–Hall method estimated average particle sizes of 59.5 nm for PCMMO and 21.8 nm for LCMMO, while the Scherrer method provided corresponding values of 32.59 nm and 20.43 nm. SEM, UV-Vis, and FTIR analyses validated the chemical composition, homogeneity, and optical properties of the synthesized compounds, revealing band gaps of 3.25 eV (LCMMO) and 3.71 eV (PCMMO) with Urbach energies of 0.29 eV and 0.26 eV, respectively. These findings provide valuable insights into the structural and optical properties of LCMMO and PCMMO, highlighting their potential as multifunctional materials for advanced device applications. Full article

Notwithstanding the success of SnO₂ as a fundamental material for gas sensing, it has often been criticized for its cross-sensitivity and high operational temperatures. Therefore, in this study, RF-sputtered SnO₂ thin films were subjected to a modification process through doping with a rare earth element, dysprosium (Dy), and subsequently deposited onto two different types of substrates: alumina and glass substrates. All thin films underwent a comprehensive series of characterizations aimed at ensuring their suitability as NO₂ sensors. The dysprosium doping levels ranged from 1 to 7 wt.% in increments of 2% (wt.%). X-ray patterns showed that all deposited films exhibited the tetragonal rutile structure of SnO₂. The optical band gap energy (Eg) increased with Dy doping, while the Urbach energy decreased with Dy doping. Field emission scanning electron microscopy (FESEM) revealed highly compacted grainy surfaces with high roughness for alumina substrate thin films, which also exhibited higher resistivity that increased with the levels of Dy doping. Energy-dispersive X-ray spectroscopy (EDX) analyses confirmed the stoichiometry of both types of thin films. Gas sensing tests were conducted at different operating temperatures, where the highest response to nitrogen dioxide, over 42%, was recorded for the higher dopant level at 250 °C. Moreover, the sensor’s selectivity toward nitrogen dioxide traces was evaluated by introducing interfering gases at higher concentrations. However, the sensors showed also significant responses when operated at room temperature. Also, we have demonstrated that higher stability is related to the temperature of the sensors and Dy ratio. Hence, a detailed discussion of the gas-sensing mechanisms was undertaken to gain a deeper insight into the NO₂ sensitivity exhibited by the Dy-doped SnO₂ layer. Full article

This study investigates the green synthesis of zinc oxide nanoparticles (ZnO NPs) using leaf extract as a natural reducing agent, evaluating their antimicrobial and photocatalytic properties. The nanoparticles were annealed at 320 °C and 500 °C, and the effects of leaf extract concentration and annealing temperature on their structural, morphological, and electronic properties were systematically explored. X-ray diffraction (XRD) analysis confirmed the hexagonal wurtzite structure of ZnO, with crystallite size and defect density being influenced by the concentration of the extract. Scanning electron microscopy (SEM) revealed the formation of smaller, spherical particles, with increased aggregation observed at higher extract concentrations. Fourier-transform infrared spectroscopy (FTIR) identified key functional groups, such as hydroxyl groups, C–O bonds, and metal–oxygen vibrations. UV–Vis spectroscopy showed a reduction in band gap energy and an increase in Urbach energy as the extract concentration and annealing temperature were increased. The antimicrobial activity of the ZnO NPs was evaluated against Gram-positive and Gram-negative bacteria as well as Candida albicans, demonstrating significant antibacterial efficacy. Photocatalytic degradation studies of methylene blue dye revealed a superior efficiency of up to 74% for the annealed samples, particularly at 500 °C. This research highlights the potential of green-synthesized ZnO NPs for a wide range of applications, including antimicrobial agents, water purification, and environmental catalysis. It contributes to the advancement of sustainable nanotechnology, offering promising solutions for both technological and ecological challenges. Full article

Developing sustainable and green packaging products that protect foods and preserve their unique properties from UV radiation, which causes photochemical damage, is one of the extensive challenges in the food-packaging industry. Accordingly, carboxymethyl cellulose sodium (CMC)/graphene (G) nanocomposites that contained different weight percentages were prepared by a mechanical milling method. The influence of the G on the chemical composition and optical properties of the nanocomposites were studied by different techniques. SEM and FT-IR analyses confirmed the interaction between the CMC and G. The XRD spectrum showed that the crystallite size of the CMC decreased with G addition. The findings showed that changing the G concentration modified the CMC’s optical properties. The CMC’s transmittance decreased to 52%, 49%, and 57% in the UV-C (200–280), UV-B (280–320 nm), and UV-A (320–400) regions, respectively, with the addition of 2 wt.% of G. Moreover, the optical band gap decreased to 4.80 eV, while the Urbach energy increased from 0.34 to 0.94 eV as the G content increased. The density functional theory (DFT) assumption was followed to establish the electronic properties and vibrational spectrum of the CMC/G model. The theoretically determined IR and experimental FT-IR spectra of the CMC/G nanocomposites showed good agreement. The obtained results show that these nanocomposites are good candidates for food packaging. Full article

A series of AlGaN/GaN high-electron-mobility transistor (HEMT) structures, with an AlN thin buffer, GaN thick layer and Al_0.25Ga_0.75N layer (13–104 nm thick), is prepared by metal–organic chemical vapor deposition and investigated via multiple techniques. Spectroscopic ellipsometry (SE) and temperature-dependent measurements and penetrative analyses have achieved significant understanding of these HEMT structures. Bandgaps of AlGaN and GaN are acquired via SE-deduced relationships of refraction index n and extinguish coefficient k vs. wavelength λ in a simple but straightforward way. The optical constants of n and k, and the energy gap E_g of AlGaN layers, are found slightly altered with the variation in AlGaN layer thickness. The Urbach energy E_U at the AlGaN and GaN layers are deduced. High-resolution X-ray diffraction and calculations determined the extremely low screw dislocation density of 1.6 × 10⁸ cm⁻². The top AlGaN layer exhibits a tensile stress influenced by the under beneath GaN and its crystalline quality is improved with the increase in thickness. Comparative photoluminescence (PL) experiments using 266 nm and 325 nm two excitations reveal and confirm the 2DEG within the AlGaN-GaN HEMT structures. DUV (266 nm) excitation Raman scattering and calculations acquired carrier concentrations in compatible AlGaN and GaN layers. Full article

In this work, Fe³⁺- and Co²⁺-doped ZnO NPs (zinc oxide nanoparticles), Zn_0.9Fe_xCo_0.1−xO, with a hexagonal wurtzite phase (single-phase), were synthesized via a co-precipitation technique where the phase purity and elemental composition were confirmed by XRD and EDX, respectively. Due to the substitution of Fe by Co, the cell parameters ($a$ and c) were increased, alongside which a slight shift to higher diffracted angles appeared. FTIR was carried out to confirm the insertion of both the Fe³⁺ and Co²⁺ dopants into the ZnO hexagonal phase. Based on the experimental results, different numerical techniques were used to determine the optical gap and refractive index for the ZnO NP-doped samples, and when the concentration of Fe³⁺ ions was increased, the band gap value of ZnO decreased from 3.36 eV to 3.29 eV, accompanied by a decrease in the Urbach energy, while the refractive index increased. The doped ZnO NPs were later found to be effective UV photocatalysts which demonstrated a maximum reduction (84%) of methylene blue (MB) in a neutral environment for X = 0.05. The correlation between the Fe³⁺ concentration, structure, optical parameters, and photocatalytic efficacy is explained in detail. Full article