Search Results (77)

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

Ultrawide bandgap (UWBG) AlN c- and m-face crystals have been prepared using the physical vapor transport (PVT) method and studied penetratively using temperature-dependent (TD) Raman scattering (RS) measurements under both visible (457 nm) and DUV (266 nm) excitations in 80–870 K, plus correlative atomic force microscopy (AFM) and variable-angle (VA) spectroscopic ellipsometry (SE). VASE identified their band gap energy as 6.2 eV, indicating excellent AlN characteristics and revealing Urbach energy levels of about 85 meV. Raman analyses revealed the residual tensile stress. TDRS shows that the E₂(high) phonon lifetime decayed gradually in the 80–600 K range. Temperature has the greater influence on the stress of m-face grown AlN crystal. The influence of low temperature on the E₂(high) phonon lifetime of m-plane AlN crystal is greater than that of the high-temperature region. By way of the LO-phonon and plasma coupling (LOPC), simulations of A₁(LO) modes and carrier concentrations along different faces and depths in AlN crystals are determined. These unique and significant findings provide useful references for the AlN crystal growth and deepen our understanding on the UWBG AlN materials. Full article

One of the key parameters characterizing the microstructure of a layer is its degree of order. It can be determined from optical studies or X-ray diffraction. However, both of these methods applied to the same layer may give different results because, for example, aggregates may contribute to the amorphous background in XRD studies, while in optical studies, they may already show order. Because we are usually interested in the optical and/or electrical properties of the layers, which in turn are closely related to their dielectric properties, determining the optical order of the layers is particularly important. In this work, the microstructure, optical properties and electrical conductivity of poly(3-hexyl)thiophene layers were investigated, and a model describing the electrical conductivity of these layers was proposed. The model is based on the generalized theory of the effective medium and uses the equation from the percolation theory of electrical conductivity for the effective medium of a mixture of two materials. The results indicate a key role of the aggregate size and limited conductivity of charge carriers, mainly due to structural imperfections that manifest themselves as an increase in the number of localized states visible in the subgap absorption near the optical absorption edge. The critical value of the order parameter and the corresponding values of the Urbach energy, excitonic linewidth and band gap energy are determined. Full article

We have studied the variations in the temperature-dependent absorption edge of a bulk InSe-layered semiconductor using photoconductivity (PC) measurements. From both the X-ray diffraction (XRD) and Raman experimental results, the structural phase of the as-prepared InSe sample was confirmed to be γ-polytype. Upon heating from 15 K to 300 K, the absorption edge of PC spectra was found to shift significantly toward lower energy, and the absorption edge as a function of temperature was further analyzed by the Varshni’s relationship and Bose–Einstein empirical equation. The Urbach energy as a function of temperature was obtained by fitting the absorption tail below the absorption coefficient of the PC spectrum, and the effective phonon energy can be derived from the temperature-dependent steepness parameter associated with Urbach energy. Our study indicates that the broadening of the absorption edge in the as-synthesized bulk γ-InSe is caused by a combination of electron/exciton–phonon interactions and thermal/structural disorder. Full article

An approach to derive the below-bandgap absorption in GaSb/GaAs self-assembled quantum dot devices using room-temperature external quantum efficiency measurement results is presented. Devices with five layers of delta-doped quantum dots placed in the intrinsic, n- and p-regions of a GaAs solar cell are studied. The importance of incorporating an extended Urbach tail absorption in analyzing the absorption strength of quantum dots and the transition states is demonstrated. The theoretically integrated absorbance via quantum dot ground states is calculated as 1.04 × 10¹⁵ cm⁻¹s⁻¹, which is in reasonable agreement with the experimentally derived value 8.1 × 10¹⁵ cm⁻¹s⁻¹. The wetting layer and quantum dot absorption contributions are separated from the tail absorption and their transition energies are calculated. Using these transition energies and the GaAs energy gap of 1.42 eV, the heavy hole confinement energies for the quantum dots (320 meV) and for the wetting layer (120 meV) are estimated. Full article

Materials engineering based on metal oxides for manipulating the solar spectrum and producing solar energy have been under intense investigation over the last years. In this work, we present NiO thin films double doped with niobium (Nb) and nitrogen (N) as cation and anion dopants (NiO:(Nb,N)) to be used as p-type layers in all oxide transparent solar cells. The films were grown by sputtering a composite Ni-Nb target on room-temperature substrates in plasma containing 50% Ar, 25% O₂, and 25% N₂gases. The existence of Nb and N dopants in the NiO structure was confirmed by the Energy Dispersive X-Ray and X-Ray Photoelectron Spectroscopy techniques. The nominally undoped NiO film, which was deposited by sputtering a Ni target and used as the reference film, was oxygen-rich, single-phase cubic NiO, having a visible transmittance of less than 20%. Upon double doping with Nb and N the visible transmittance of NiO:(Nb,N) film increased to 60%, which was further improved after thermal treatment to around 85%. The respective values of the direct band gap in the undoped and double-doped films were 3.28 eV and 3.73 eV just after deposition, and 3.67 eV and 3.76 eV after thermal treatment. The changes in the properties of the films such as structural disorder, direct and indirect energy band gaps, Urbach tail states, and resistivity were correlated with the incorporation of Nb and N in their structure. The thermally treated NiO:(Nb,N) film was used to form a diode with a spin-coated two-layer, mesoporous on top of a compact, TiO₂ film. The NiO:(Nb,N)/TiO₂heterojunction exhibited visible transparency of around 80%, showed rectifying characteristics and the diode’s parameters were deduced using the I-V method. The diode revealed photovoltaic behavior upon illumination with UV light exhibiting a short circuit current density of 0.2 mA/cm² and open-circuit voltage of 500 mV. Improvements of the output characteristics of the NiO:(Nb,N)/TiO₂ UV-photovoltaic by proper engineering of the individual layers and device processing procedures are addressed. Transparent NiO:(Nb,N) films can be potential candidates in all-oxide ultraviolet photovoltaics for tandem solar cells, smart windows, and other optoelectronic devices. Full article