Tahar Touam

Undoped and Er-doped alumina nanostructures at concentrations of 0.5, 1 and 3 at.%. were synthesized via the sol-gel method under supercritical isopropanol drying. X-ray diffraction (XRD) analysis demonstrated that undoped alumina consists of two crystalline phases: α and θ. In contrast, the Er-doped samples exhibited only the θ phase of alumina. This suggests that the presence of Er ions in the alumina matrix delays the transformation temperature from the θ phase to the α phase. UV-visible analysis revealed that the doped samples showed absorption bands in the blue-near infrared (NIR) region, confirming the incorporation of Er ions into the alumina matrix. Fourier-transform infrared (FTIR) spectroscopy spectra displayed bands corresponding to O-Al-O and Al-O functional groups in both θ- and α-alumina. Scanning electron microscopy (SEM) analysis showed that pure alumina featured a smooth surface with large interconnected grains and a uniform microstructure. The photoluminescence (PL) spectra revealed that Er doping introduced luminescent centers associated with Er³ ⁺ 4f-4f transitions, while also influencing the density of oxygen vacancies. At higher Er concentrations, self-quenching effects became significant. Additionally, an excitation wavelength of 600 nm was identified as optimal for Er-doped alumina, as it aligned with the energy levels of Er³ ⁺ ions and minimized interference from the host material, thereby enhancing luminescent efficiency. Overall, this study establishes a systematic correlation between erbium concentration, θ-phase stabilization, defect formation, and photoluminescent response in sol–gel-derived alumina nanostructures, clearly distinguishing it from previous reports and providing new insights into the role of Er–host interactions during thermal evolution.

Undoped and Eu³⁺-doped TiO₂ aerogels (0.5 and 1 at %) were synthesized by a sol–gel method followed by supercritical drying in isopropanol. X-ray diffraction analysis shows direct crystallization of the anatase phase without additional heat treatment. Europium incorporation causes minor lattice parameter variation and a slight increase in crystallite size (6.12–6.86 nm), indicating substitutional incorporation into the TiO₂ framework. Infrared spectra reveal modifications of Ti–O vibrational modes associated with changes in the local bonding environment. Optical absorption measurements indicate a small widening of the band gap with increasing Eu content. Photoluminescence spectra exhibit an intense emission at 612 nm corresponding to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions, suggesting defect-assisted energy transfer from the TiO₂ host matrix. The results demonstrate the influence of rare-earth doping on the structural and electronic properties of TiO₂ aerogels.

ZnO nanostructures were synthesized via a hydrothermal method using four different zinc precursors (zinc acetate, zinc chloride, zinc nitrate, and zinc sulfate) to systematically investigate the influence of precursor chemistry on their structural, morphological, and vibrational properties. X-ray diffraction analysis confirmed the formation of the hexagonal wurtzite phase in all samples, with significant variations in crystallinity and lattice constants attributable to the nature of the precursor anions. ZnO synthesized from zinc chloride exhibited the highest degree of crystallinity, whereas the zinc sulfate–derived sample showed pronounced defect formation. Scanning electron microscopy revealed a strong dependence of morphology on the precursor type, yielding well-defined nanorod architectures for zinc acetate, nitrate, and chloride, while zinc sulfate produced irregular and highly agglomerated structures. Energy-dispersive X-ray analysis verified the elemental purity of the samples, with Zn/O ratios indicating varying defect concentrations. Further insights from FT-IR and Raman spectroscopy highlighted differences in surface functional groups, lattice order, and defect states. Overall, these results demonstrate that precursor selection plays a critical role in tailoring the structural quality and defect characteristics of ZnO nanostructures, providing an effective strategy for optimizing their properties for targeted applications.

Yttrium-doped ZnO aerogel nanostructures with low Y concentrations (0.5 and 1 at.%) were synthesized through a modified sol–gel process coupled with supercritical isopropanol drying, yielding highly porous and crystalline materials. Structural and optical characteristics were investigated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Utraviolet–Visible (UV–Vis) spectroscopy, and photoluminescence (PL) spectroscopy. XRD results confirmed the formation of single-phase polycrystalline ZnO with a hexagonal wurtzite structure for all samples, along with lattice perturbations consistent with the substitution of Zn ²⁺ by Y ³⁺ ions. FTIR spectra further supported successful ZnO network formation, revealing a systematic shift of the Zn–O stretching band toward lower wavenumbers upon Y incorporation. UV–Vis measurements showed that yttrium doping enhances optical absorbance and induces a slight redshift of the absorption edge, indicating a modest narrowing of the band gap. PL analysis demonstrated a remarkable enhancement in UV and visible emission for the ZnO:Y (0.5 at.%) sample, which exhibited the highest overall PL intensity across the investigated spectral range. This enhancement is attributed to an increased radiative recombination rate of photogenerated carriers and the formation of additional defect-related states introduced by low-level Y doping. These findings highlight the strong potential of yttrium-modified ZnO aerogels for tunable optical and photonic applications.

Titanium dioxide thin films were synthesized by the sol–gel dip-coating technique under different acidic conditions (pH 5, 3, and 1) to investigate the influence of solution acidity on their structural, morphological, and optical properties. The deposited layers were annealed in air at 400°C for one hour and characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and ultraviolet–visible spectrophotometry. Structural analyses confirmed that all films crystallize in the anatase phase with a preferred orientation along the (101) plane, without any evidence of anatase–rutile transition. The diffraction and Raman peak intensities, as well as the crystallite size, increased with decreasing pH, indicating enhanced crystallinity under more acidic conditions. Surface imaging revealed that both the grain coarsening and surface roughness increased slightly with increasing sol acidity, in agreement with the observed structural evolution. All films exhibited high optical transparency, with average transmittance values exceeding 70% in the visible region, while the optical band gap slightly decreased with increasing acidity. These results demonstrate that controlled sol acidity effectively tailors the microstructure and optical response of sol–gel-derived titanium dioxide thin films for optoelectronic and photonic applications.

This study reports the synthesis and comprehensive characterization of aluminum-doped titanium dioxide nanostructures co-doped with yttrium at 0.5 and 1% levels prepared using a sol–gel method followed by supercritical ethanol drying. X-ray diffraction analysis confirmed the formation of a pure anatase phase with successful yttrium incorporation, causing slight lattice distortions and reduced crystallinity without significantly affecting the crystallite size. Yttrium doping modestly increased the specific surface area. Fourier transform infrared spectroscopy revealed titanium–oxygen lattice vibrations and surface hydroxyl groups, with a subtle redshift in the titanium–oxygen bands upon yttrium addition, corroborating the induced lattice distortion. Scanning electron microscopy images showed that yttrium incorporation densified the microstructure, reducing porosity and smoothing surface features. Optical reflectance measurements indicated a slight narrowing of the optical bandgap (from 3.25 to 3.22 eV), attributed to lattice strain and defect states, while maintaining the anatase structure. Photoluminescence spectroscopy displayed enhanced ultraviolet emission intensity with yttrium incorporation, reflecting a lower defect density and improved optical quality. Photocatalytic degradation experiments at alkaline pH demonstrated that undoped aluminum-doped titanium dioxide exhibited superior methylene blue degradation efficiency under both ultraviolet and visible light irradiation compared to yttrium-doped samples, where doping reduced activity likely due to enhanced charge recombination. Overall, yttrium co-doping modifies the structural and optical properties of aluminum-doped titanium dioxide but detrimentally affects its photocatalytic performance.

This study investigates the AZO/Cu/Ag/AZO multilayer thin films deposited on PET substrates via RF confocal magnetron sputtering, focusing on the influence of Cu and Ag interlayer thickness ratios, while maintaining a constant total metal thickness of 10 nm, on their microstructural, optical, and electrical properties. X-ray diffraction (XRD) analysis combined with Rietveld refinement revealed that Ag-rich configurations enhance crystallinity, reduce residual stress, and promote a pronounced (002) preferential orientation in the AZO layers, which is attributed to improved nucleation behavior and reduced interfacial disorder. Atomic force microscopy (AFM) analysis demonstrated that the Cu/Ag thickness ratio effectively modulates nanoparticle coalescence and surface roughness. Optical characterization revealed that Ag-rich films exhibit higher visible transmittance owing to improved film continuity and constructive interference effects, whereas Cu-rich structures favor enhanced near-infrared (NIR) transparency. Electrical properties, evaluated using Hall effect measurements, indicated that a balanced Cu/Ag configuration (5/5 nm) delivers optimal charge transport, achieving the lowest resistivity (1.22 × 10 ⁻³ Ω.cm), the highest carrier mobility (7.08 cm ² .V ⁻¹ .s ⁻¹ ), and the maximum figure of merit (6.88 × 10 ⁻⁵ Ω ⁻¹ ). These results demonstrate that rational Cu/Ag interlayer engineering enables an effective balance between transparency and conductivity in flexible transparent electrodes, opening viable pathways for applications in wearable electronics, flexible photovoltaics, and foldable display technologies.

ZnO thin films were deposited on borosilicate glass substrates by confocal radio frequency (RF) magnetron sputtering and subsequently annealed in air at 300 °C and 500 °C for 60 min. The influence of thermal treatment on the structural, morphological, optical, and electrical properties was systematically investigated. X-ray diffraction (XRD) confirmed the formation of a hexagonal wurtzite phase with a pronounced (002) preferential orientation. Rietveld refinement analysis revealed that annealing led to a decrease in the lattice parameter c from 5.344 Å to 5.220 Å, an increase in crystallite size from 9.3 nm to 34.1 nm, and a reduction in microstrain from 0.0265 to 0.0027. Raman spectroscopy exhibited a sharper E ₂ ^high mode at 438 cm ^-1 and a suppressed defect-related A₁(LO) mode (583 cm ^-1 ), evidencing enhanced crystallinity and defect passivation. Scanning electron microscopy (SEM) observations revealed grain coalescence and densification with increasing annealing temperature. The average optical transmittance improved from 70.8% to 82.2%, accompanied by a slight widening of the optical band gap from 3.22 eV to 3.27 eV. Hall measurements indicated a marked decrease in resistivity from 2.7 × 10 ^-2 Ω·cm to 5 × 10 ^-3 Ω·cm, yielding a maximum figure of merit of 1.68 × 10 ^-3 Ω ^-1 at 500 °C. Overall, post-deposition annealing is shown to significantly enhance crystallinity, reduce structural defects, and improve the optoelectronic performance of ZnO thin films, confirming their suitability for transparent electronics and photovoltaic applications.

The current study offers a path toward the reliable and affordable manufacturing of high-performance dielectric surfaces consisting of tantalum pentoxide (Ta2O5) functional in the visible to near-infrared (NIR) spectrum. The article reports an in-depth analysis of its fabrication method and characterization for flat optical and photonic applications. Despite the inherent broadband gap of Ta2O5, films formed by conventional magnetron sputtering may unavoidably include flaws and show sub-bandgap absorption. The e-beam physical vapor deposition deposited Ta2O5 films show a high refractive index of nearly 2.2 to 2.1 across the visible wavelengths and a minimal absorption coefficient of k ≈ 0 down to λ0 ≈ 400 nm at an O2 flow rate and evaporation rate of 5 SCCM and 2.5 Å/s, respectively. In this work, Ta2O5 coating had a broadband gap of 3.87–3.91 eV, which permits low-loss and high-transmission functionality over the whole visible-NIR (400–1000 nm) and a portion of the near-ultraviolet (λ ∼ 320 nm) region. Complete oxidation of the annealed film was revealed by x-ray photoelectron spectroscopy, giving a stoichiometric ratio of Ta:O ∼ 2:5, a crucial parameter for lower optical absorbance. Moreover, optical investigations found high transparency (∼85%) in 350 nm ˂ λ ˂ 1000 nm, while the surface morphology exhibited uniform deposition with fairly flakelike grains having a size of 10–25 nm. As the developed coating resolves the issue of dust particle deposition on the solar-facing surface of photovoltaic components through the improved hydrophobic traits (water contact angle ∼ 114°), the coating has practical utility to realize self-cleaning ability of solar cells.