Study on Structural, Mechanical, and Optical Properties of Al₂O₃–TiO₂ Nanolaminates Prepared by Atomic Layer Deposition

Structural, optical, and mechanical properties of Al₂O₃/TiO₂ nanolaminates fabricated by atomic layer deposition (ALD) were investigated. We performed transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray reflectivity (XRR), energy dispersive X-ray spectroscopy (EDX), ellipsometry, UV–vis spectroscopy, photoluminescence (PL) spectroscopy, and nanointendation to characterize the Al₂O₃/TiO₂ nanolaminates. The main structural, optical, and mechanical parameters of Al₂O₃/TiO₂ nanolaminates (thickness, grain size, refractive index, extinction coefficient, band gap, hardness, and Young’s module) were calculated. It was established that with decreasing of the layer thickness, the value of band gap energy increases due to the quantum size effect related to the reduction of the nanograins size. On the other hand, the decreasing of nanograins size leads to generation of interface defects and, as a consequence, to the increasing of Urbach energy. It was also shown that there is an interdiffusion layer at the Al₂O₃–TiO₂ interface, which plays a crucial role in explaining mechanical and optical properties of Al₂O₃/TiO₂ nanolaminates. The correlation between structural, optical, and mechanical parameters was discussed

Structural, Spectroscopic, and Magnetic Properties of Eu³⁺-Doped GdVO₄ Nanocrystals Synthesized by a Hydrothermal Method

New interesting aspects of the spectroscopic properties, magnetism, and method of synthesis of gadolinium orthovanadates doped with Eu³⁺ ions are discussed. Gd_1–<i>x</i>Eu_<i>x</i>VO₄ (<i>x</i> = 0, 0.05, 0.2) bifunctional luminescent materials with complex magnetic properties were synthesized by a microwave-assisted hydrothermal method. Products were formed in situ without previous precipitation. The crystal structures and morphologies of the obtained nanomaterials were analyzed by X-ray diffraction and transmission and scanning electron microscopy. Crystallographic data were analyzed using Rietveld refinement. The products obtained were nanocrystalline with average grain sizes of 70–80 nm. The qualitative and quantitative elemental composition as well as mapping of the nanocrystals was proved using energy-dispersive X-ray spectroscopy. The spectroscopic properties of red-emitting nanophosphors were characterized by their excitation and emission spectra and luminescence decays. Magnetic measurements were performed by means of vibrating sample magnetometry. GdVO₄ and Gd_0.8Eu_0.2VO₄ exhibited paramagnetic behavior with a weak influence of antiferromagnetic couplings between rare-earth ions. In the substituted sample, an additional magnetic contribution connected with the population of low-lying excited states of europium was observed

Structural, Spectroscopic, and Magnetic Properties of Eu³⁺-Doped GdVO₄ Nanocrystals Synthesized by a Hydrothermal Method

New interesting aspects of the spectroscopic properties, magnetism, and method of synthesis of gadolinium orthovanadates doped with Eu³⁺ ions are discussed. Gd_1–<i>x</i>Eu_<i>x</i>VO₄ (<i>x</i> = 0, 0.05, 0.2) bifunctional luminescent materials with complex magnetic properties were synthesized by a microwave-assisted hydrothermal method. Products were formed in situ without previous precipitation. The crystal structures and morphologies of the obtained nanomaterials were analyzed by X-ray diffraction and transmission and scanning electron microscopy. Crystallographic data were analyzed using Rietveld refinement. The products obtained were nanocrystalline with average grain sizes of 70–80 nm. The qualitative and quantitative elemental composition as well as mapping of the nanocrystals was proved using energy-dispersive X-ray spectroscopy. The spectroscopic properties of red-emitting nanophosphors were characterized by their excitation and emission spectra and luminescence decays. Magnetic measurements were performed by means of vibrating sample magnetometry. GdVO₄ and Gd_0.8Eu_0.2VO₄ exhibited paramagnetic behavior with a weak influence of antiferromagnetic couplings between rare-earth ions. In the substituted sample, an additional magnetic contribution connected with the population of low-lying excited states of europium was observed

Tailoring the Structural, Optical, and Photoluminescence Properties of Porous Silicon/TiO₂ Nanostructures

The structural, optical, and photoluminescence properties of porous silicon (PSi)/titanium dioxide (TiO₂) nanostructures were investigated. PSi structures consisting of macro- and mesoporous layers were fabricated by metal-assisted chemical etching, and then TiO₂ was introduced inside the PSi matrix using the atomic layer deposition technique. We performed scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction, energy dispersive X-ray spectroscopy, Raman spectroscopy, ellipsometry, and photoluminescence (PL) spectroscopy to characterize the prepared and annealed PSi/TiO₂ nanostructures. TEM and Raman analyses revealed that TiO₂ had a crystalline anatase structure. PL measurements of the PSi/TiO₂ composite system showed two broad peaks at approximately 2.4–3 eV (blue PL) and 1.7–1.9 eV (red PL). The mechanisms of the emissions were discussed, and it was found that two main competing recombination mechanisms take place, including radiative recombination through the surface states (surface recombination) and through oxygen vacancies and self-trapped excitons (volume recombination)

Photocatalytically Active TiO₂/Ag₂O Nanotube Arrays Interlaced with Silver Nanoparticles Obtained from the One-Step Anodic Oxidation of Ti–Ag Alloys

The development of a photocatalyst with remarkable activity to degrade pollutants in aqueous and gas phase requires visible light-responsive stable materials, easily organized in the form of a thin layer (to exclude the highly expensive separation step). In this work, we present a one-step strategy for synthesizing material in the form of a self-organized TiO₂/Ag₂O nanotube (NT) array interlaced with silver nanoparticles (as in a cake with raisins) that exhibited photoactivity significantly enhanced compared to that of pristine TiO₂ NTs under both ultraviolet (UV) and visible (vis) irradiation. An NT array composed of a mixture of TiO₂ and Ag₂O and spiked with Ag nanoparticles was formed via the anodization of a Ti–Ag alloy in a one-step reaction. Silver NPs have been formed during the <i>in situ</i> generation of Ag ions and were (i) embedded in the NT walls, (ii) stuck on the external NT walls, and (iii) placed inside the NTs. The enhancement of photocatalytic efficiency can be ascribed to the existence of an optimal content of Ag₂O and Ag NPs, which are responsible for decreasing the number of recombination centers. In contrast to UV–vis light, performance improvement under vis irradiation occurs with increasing Ag₂O and Ag⁰ contents in the TiO₂/Ag₂O/Ag NTs as a result of the utilization of larger amounts of incident photons. The optimized samples reached phenol degradation rates of 0.50 and 2.89 μmol dm^–3 min^–1 under visible and UV light, respectively, which means degradation activities 3.8- and 2-fold greater than that of the reference sample, respectively, remained after four photodegradation cycles under UV light

Enhancement of Electronic and Optical Properties of ZnO/Al₂O₃ Nanolaminate Coated Electrospun Nanofibers

Nanolaminates are new class of promising nanomaterials with outstanding properties. Here we explored on the tuning of structural properties and the enhancement of electronic and optical properties of 1D PAN ZnO/Al₂O₃ nanolaminates designed by atomic layer deposition (ALD) and electrospinning. The influence of ZnO/Al₂O₃ bilayer thicknesses on the fundamental properties of 1D PAN ZnO/Al₂O₃ nanolaminates has been investigated. Due to the quantum confinement effect, the shift of XPS peaks to higher energies has been observed. Work function of Al₂O₃ was mostly independent of the bilayers number, whereas the ZnO work function decreased with an increase of the bilayer number. Photoluminescence of the 1D PAN ZnO/Al₂O₃ nanolaminates corresponded to emission bands in ZnO nanolayers. Due to quantum confinement and surface band bending, no excitonic peaks were observed. The defect emission band was affected by the band bending and defect concentration. The enhanced photoluminescence of the 1D PAN ZnO/Al₂O₃ nanolaminates allows applications in optical (bio)­sensing field

Acetate-Induced Disassembly of Spherical Iron Oxide Nanoparticle Clusters into Monodispersed Core–Shell Structures upon Nanoemulsion Fusion

It has been long known that the physical encapsulation of oleic acid-capped iron oxide nanoparticles (OA–IONPs) with the cetyltrimethylammonium (CTA⁺) surfactant induces the formation of spherical iron oxide nanoparticle clusters (IONPCs). However, the behavior and functional properties of IONPCs in chemical reactions have been largely neglected and are still not well-understood. Herein, we report an unconventional ligand-exchange function of IONPCs activated when dispersed in an ethyl acetate/acetate buffer system. The ligand exchange can successfully transform hydrophobic OA–IONP building blocks of IONPCs into highly hydrophilic, acetate-capped iron oxide nanoparticles (Ac–IONPs). More importantly, we demonstrate that the addition of silica precursors (tetraethyl orthosilicate and 3-aminopropyltriethoxysilane) to the acetate/oleate ligand-exchange reaction of the IONPs induces the disassembly of the IONPCs into monodispersed iron oxide–acetate–silica core–shell–shell (IONPs@acetate@SiO₂) nanoparticles. Our observations evidence that the formation of IONPs@acetate@SiO₂ nanoparticles is initiated by a unique micellar fusion mechanism between the Pickering-type emulsions of IONPCs and nanoemulsions of silica precursors formed under ethyl acetate buffered conditions. A dynamic rearrangement of the CTA⁺–oleate bilayer on the IONPC surfaces is proposed to be responsible for the templating process of the silica shells around the individual IONPs. In comparison to previously reported methods in the literature, our work provides a much more detailed experimental evidence of the silica-coating mechanism in a nanoemulsion system. Overall, ethyl acetate is proven to be a very efficient agent for an effortless preparation of monodispersed IONPs@acetate@SiO₂ and hydrophilic Ac–IONPs from IONPCs