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We present comparative studies of sol–gel ITO multilayered films undoped and doped with Nb or Zn (4 at.%). The films were obtained by successive depositions of five layers using the dip-coating sol–gel method on microscopic glass, SiO2/glass, and Si substrates. The influence of the type of substrates and dopant atoms on the structure and optical properties of the sol–gel ITO thin films is examined and discussed in detail. XRD patterns of these layers showed a polycrystalline structure with an average crystallite size of <11 nm. Raman spectroscopy confirmed the chemical bonding of dopants with oxygen and showed the absence of crystallized Nb(Zn)-oxide particles, indicated by the XRD pattern. Spectroscopic Ellipsometry and AFM imaging revealed a clear dependence of the optical parameters and surface morphology of the ITO and ITO:Nb(Zn) thin films on the type of substrates and dopants. The analysis of the current-voltage and capacitance-voltage characteristics of the Al/ITO/Si structures revealed the presence of charge carrier traps in the ITO bulk and the ITO-Si interface. The densities of these traps are obtained and the character of the current transport mechanism is established. [ABSTRACT FROM AUTHOR]

Nanoscale oxides grown in c-silicon, implanted with low-energy (2 keV) H+ ions and fluences ranging from 1013 cm−2 to 1015 cm−2 by RF plasma immersion implantation (PII), have been investigated. The oxidation of the implanted Si layers proceeded in dry O2 at temperatures of 700 °C, 750 °C and 800 °C. The optical characterization of the formed Si/SiOx structures was conducted by electroreflectance (ER) and spectroscopic ellipsometric (SE) measurements. From the ER and SE spectra analysis, the characteristic energy bands of direct electron transitions in Si are elaborated. The stress in dependence on hydrogenation conditions is considered and related to the energy shifts of the Si interband transitions around 3.4 eV. Silicon oxides, grown on PII Si at a low H+ fluence, have a non-stoichiometric nature, as revealed by IR-SE spectra analysis, while with an increasing H+ fluence in the PII Si substrates and/or the subsequent oxidation temperature the stoichiometric Si-O4 units in the oxides become predominant. The development of surface morphology is studied by atomic force microscopy (AFM) imaging. Oxidation of the H+-implanted Si surface region flattens out the surface pits created on the Si surface by H+ implants. Based on the evaluation of the texture index and mean fractal dimension, the isotropic and self-similar character of the studied surfaces is emphasized. [ABSTRACT FROM AUTHOR]

Multilayered TiO2 films doped either with Niobium or Vanadium (1.2 at. %) were deposited by the sol-gel dip coating method on c-Si and glass substrates. The films on glass substrates were tested for CO sensing and photocatalytic degradation of methylene blue. X-ray diffraction data analysis showed that all the TiO2:Nb(V) films were nanocrystalline in the anatase phase, with a uniform and compact microstructure and a homogeneous superficial structure of small grains with diameters in the range of 13–19 nm. For the electrical characterization, the TiO2:Nb(V) films were incorporated in Metal-Insulator-Semiconductor (MIS) structures. The specific resistivity is of the order of 104 Ωcm and its value decreases with increasing the electrical field, which testifies to the injection of electrons into these layers. From the analysis of the current–voltage curves taken at different temperature- and frequency—dependent capacitance–voltage and conductance–voltage characteristics, the density and parameters of deep levels in these TiO2 films are evaluated and the electron charge transport mechanism is established. It was shown that the current in these TiO2:Nb(V)-Si MIS structures is mainly carried out by inter-trap tunneling via deep levels energetically distributed in the TiO2 bandgap. Testing these sol-gel TiO2:Nb(V) layers for gas sensing and photocatalytic capabilities proved that they could serve such purposes. In particular, the results of the V-doped sol-gel TiO2 film confirm its CO detection capability, which is rarely reported in the literature. For the photodegradation of methylene blue, the Nb-doped TiO2 samples were superior, with nearly double the photocatalytic efficiency of undoped TiO2. [ABSTRACT FROM AUTHOR]

For many years, TiO2-based materials and improving their properties in order to expand their application areas have been the focus of numerous research groups. Various innovative approaches have been proposed to improve the photocatalytic and gas-sensing properties of TiO2 nanostructures. In this review, we aim to synthesize the available information in the literature, paying special attention to the sol–gel technology, which is one of the most frequently used methods for TiO2 synthesis. The influence of dopants on the structural, morphological, optical, and electrical properties of TiO2 and the way to modify them in a controlled manner are briefly discussed. The role of shallow and/or deep energy levels within the TiO2 bandgap in the electron transport behavior of doped TiO2 is emphasized. Selected research on photocatalytic applications in water disinfection, wastewater treatment, and self-sterilizing coatings that contribute to improving the quality of human life and environmental preservation is highlighted. A survey of biosensors that are closely related to medical applications such as cancer detection, implantology, and osteogenesis is also provided. Finally, the pressing problems that need to be solved in view of the future development of TiO2-based nanostructures are listed. [ABSTRACT FROM AUTHOR]

Wastewater treatment targeting reuse may limit water scarcity. Photocatalysis is an advanced oxidation process that may be employed in the removal of traces of organic pollutants, where the material choice is important. Titanium dioxide (TiO2) is a highly efficient photocatalyst with good aqueous stability. TiO2 powder has a high surface area, thus allowing good pollutant adsorption, but it is difficult to filter for reuse. Thin films have a significantly lower surface area but are easier to regenerate and reuse. In this paper, we report on obtaining sol-gel TiO2 thin films on spherical beads (2 mm diameter) with high surface area and easy recovery from wastewater. The complex influence of the substrate morphology (etched up to 48 h in concentrated H2SO4), of the sol dilution with ethanol (1:0 or 1:1), and the number of layers (1 or 2) on the structure, morphology, chemical composition, and photocatalytic performance of the TiO2 thin films is investigated. Etching the substrate for 2 h in H2SO4 leads to uniform, smooth surfaces on which crystalline, homogeneous TiO2 thin films are grown. Films deposited using an undiluted sol are stable in water, with some surface reorganization of the TiO2 aggregates occurring, while the films obtained using diluted sol are partially washed out. By increasing the film thickness through the deposition of a second layer, the roughness increases (from ~50 nm to ~100 nm), but this increase is not high enough to promote higher adsorption or overall photocatalytic efficiency in methylene blue photodegradation (both about 40% after 8 h of UV-Vis irradiation at 55 W/m2). The most promising thin film, deposited on spherical bead substrates (etched for 2 h in H2SO4) using the undiluted sol, with one layer, is highly crystalline, uniform, water-stable, and proves to have good photocatalytic activity. [ABSTRACT FROM AUTHOR]

The development of a facile method to obtain materials with piezoelectric properties, through a green synthesis, as an alternative to lead-free materials, was the main objective of this work. Piezo active materials were grown by chemical methods on two types of metal substrates: Pt/Ti/SiO2/Si and the Ti foil. Ag and Li-doped ZnO nanostructures were prepared by hydrothermal method at low temperature on metallic substrates which were previously covered with ZnO seed layer deposited by spin coating sol-gel method. The newly prepared materials were covered with a polymer layer and were morphological characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The piezoelectric properties were estimated by measuring the direct piezoelectric coefficient d33. The test results show that the doped ZnO nanostructures synthesized using a green route exhibit a piezoelectric response so the established method can be considered a promising approach for obtaining piezoelectric materials on large surfaces. Piezo active nanostructures could be of interest for integration into piezoelectric devices. [ABSTRACT FROM AUTHOR]

Transparent and antireflective coatings were prepared by deposition of modified silica materials onto polyvinyl chloride (PVC) substrates. These materials were obtained by the sol-gel route in acidic medium, at room temperature (25 °C), using different alkoxysilanes with various functional groups (methyl, vinyl, octyl or hexadecyl). Physicochemical and microstructural properties of resulted silica materials and of thin coatings were investigated through Fourier Transforms Infrared Spectroscopy (FTIR), UV-Vis spectroscopy, Thermal Gravimetric Analysis (TGA), Dynamic Mechanical Analysis (DMA), Atomic Force Microscopy (AFM) and ellipsometric measurements. Wetting behaviors of the silica coatings were evaluated by measurement of static contact angle against water. FTIR spectra of materials confirmed the high degree of cross-linking that result from the formation of the inorganic backbone through the hydrolysis and polycondensation reactions together with the formation of the organic network. These sol-gel silica coatings showed a reduction in the reflectance (10%) compared with uncoated PVC substrate. AFM reveals that the films are uniform, and adherent to the substrate, but their morphology is strongly influenced by the chemical composition of the coating matrices. These silica coatings can be useful for potential electronic and optical devices. [ABSTRACT FROM AUTHOR]

Zn, Fe modified SnO2 powders were prepared by sol-gel method using Tripropylamine as chelating agent and Polyvinylpyrrolidone K90 as dispersant and stabilizer. Two compositions were taken into account: Zn, Fe modified SnO2 – 20 mol% Zn, 10 mol% Fe and Zn, Fe modified SnO2 – 20 mol% Zn, 30 mol% Fe, denoted further as SZFe1and SZFe2 respectively. The properties and the influence of Fe amount on structure, morphology and surface chemistry, electrical and magnetic properties have been investigated. The X-ray diffraction analysis showed the formation of a polycrystalline mixture of cassiterite – SnO2, hematite – Fe2O3, franklinite – ZnFe2O4 and zincite – ZnO for the samples with different Fe content. The magnetization of SZFe2 sample was found to be composed of a ferromagnetic and a paramagnetic phase. The presence of Fe in the powders composition improved the electrical properties, demonstrating performant features in sensing characteristics (tested in CO gas concentrations varied from 50 to 1000 ppm). The magnetic investigations suggest their possible future applications as soft magnetic materials. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid thin films, silica–titanium oxides and silica–aluminum oxides, designed based on the sol–gel process are evaluated as catalysts in the photo-degradation of the cationic dyes. Silica matrices from different precursors with various organic functional groups and cross-linked with titanium or aluminum agents (tetraisopropyl orthotitanate and aluminum sec-butoxide) allow the surface property tailoring related to the high capacity of the dye adsorption respective, high photo-degradation activity. The cationic dyes (methylene blue, rhodamine B, crystal violet, malachite green) embedded on the hybrid silica matrix, under ultraviolet light, have a first order kinetics of photodegradation. The cross-linking agents play a key role in the photocatalytic degradation and silica matrix as dye absorbent. The photo-degradation rate for the binary system derived from methyltriethoxysilane/vinyltriethoxysilane precursors with both cross linkers showed a significant improvement by comparison with other hybrid materials. The significant increasing in the photodecomposition rate is related to the capacity to generate additional oxidizing species by each silica hybrid compounds. [Copyright &y& Elsevier]

The development of short-wave infrared (SWIR) photonics based on GeSn alloys is of high technological interest for many application fields, such as the Internet of things or pollution monitoring. The manufacture of crystalline GeSn is a major challenge, mainly because of the low miscibility of Ge and Sn. The use of embedded GeSn nanocrystals (NCs) by magnetron sputtering is a cost-effective and efficient method to relax the growth conditions. We report on the use of GeSn/SiO 2 multilayer deposition as a way to control the NC size and their insulation. The in situ prenucleation of NCs during deposition was followed by ex situ rapid thermal annealing. The nanocrystallization of 20×(11nm&#95;Ge 0.865 Sn 0.135 /1.5nm&#95;SiO 2 ) multilayers leads to formation of GeSn NCs with ∼16% Sn concentration and ∼9 nm size. Formation of GeSn domes that are vertically correlated contributes to the nanocrystallization process. The absorption limit of ∼0.4 eV in SWIR found by ellipsometry is in agreement with the spectral photosensitivity. The ITO/20×(GeSn NC/SiO 2 )/p-Si/Al diodes show a maximum value of the SWIR photosensitivity at a reverse voltage of 0.5 V, with extended sensitivity to wavelengths longer than 2200 nm. The multilayer diodes have higher photocurrent efficiency compared to diodes based on a thick monolayer of GeSn NCs.