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Anatase mesoporous TiO films doped with Ca were prepared by sol-gel and deposited onto glass slides. The influence of the dopant in the textural and structural properties of the films was studied together with their photocatalytic activity. Titania sols w/o and with Ca were synthesised from titanium isopropoxide as TiO precursor, acetic acid as complexing agent, and polyethylene glycol hexadecyl ether (Brij58) as pore-generating agent. The TiO films were characterised by Fourier transform infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy. Environmental ellipsometric porosimetry was used to obtain the adsorption-desorption isotherms and the total pore volume, for determining the pore size distribution and specific surface area ( S ) of the films, crucial parameters that govern the photocatalytic behaviour. The photocatalytic activity was evaluated through the degradation of methyl orange (MO) in aqueous solution using a Xe lamp that simulates solar radiation. The photocatalytic activity depends on the dopant amount. The dopant creates levels within the band gap that improving the charge separation, and reduces the recombination e / h pairs. The best results of MO degradation were obtained for the films sintered at 450 °C for 90 min and doped with 3 % of Ca. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Hybrid silica coatings based on 3- glycidoxypropyltriethoxysilane (GPTES), tetraethylorthosilicate (TEOS) and colloidal silica were deposited on polycarbonate (PC) by the sol-gel method, in order to obtain a material with enhanced properties with respect to raw PC (mainly scratch resistance, hydrophobicity and density), and consequently reach increased durability. The necessity of performing a N-plasma treatment on PC (before coating deposition) was highlighted in order to obtain a good adherence between the coating and the substrate: XPS measurements showed that after treatment, nitrogenous radicals had formed on the PC surface and were able to link covalently with the sol during its deposition. Adherence was also higher when young sols (<8-day-old) were used. Different alkoxysilanes/colloidal silica ratios were tested to optimize the coating resistance: crack resistance of the coatings was found to be greater when the ratio was high. Scratch resistance of raw PC was enhanced as soon as PC was coated, irrespective of the alkoxysilanes/colloidal silica ratio or the sol ageing time. The density of the coatings was assessed by environmental ellipsometric porosimetry and found to be very high. Water contact angle measurements showed that the hydrophobicity of the coatings was inferior to raw PC. The addition in the sol of a small wt% of octyltriethoxysilane (OTES), 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FTES) and silicone surface additive (BYK-306) allowed a significant increase in hydrophobicity of the samples. [ABSTRACT FROM AUTHOR]

The review article provides an overview of the most important and popular techniques for evaluating the porosity of thin films developed for various applications. These methods include ellipsometric porosimetry (EP), positron annihilation (lifetime) spectroscopy (PAS/PALS), and grazing incidence small-angle x-ray scattering (GISAXS). Special attention is given to the challenges associated with interpreting the measured data and the inherent limitations of each method. It is demonstrated that EP, GISAXS, and PALS are all informative for studying the pore structure in thin films, with each method offering unique insights. GISAXS, in particular, allows for the evaluation of three-dimensional mesostructures, including pore arrangement, pore spacing, and structural order. On the other hand, PALS has a unique advantage in its capability to analyze extremely small isolated pores (free volume). The advantage of EP lies in its simplicity and the possibility to analyze multiple properties from the same set of measurements. The cross-evaluation of different methods offers important insights into the complex pore structure of materials, highlighting the significance of appropriate modeling and interpretation of data. [ABSTRACT FROM AUTHOR]

Ordered porous polyimide films were fabricated from (AB)m type of diblock copolymer polyimide-b-polystyrene (PI-b-PS). An increase in PS volume fraction (f VPS) is beneficial to decrease the relative dielectric constants and water contact angles of the obtained porous PI films: the relative dielectric constant decreases to 1.89 and water contact angle decreases to 43° when f VPS is 0.36, indicating porous PI films can be used as low-κ material and have good wettability. The solvent uptake of the porous PI films increases with increasing f VPS. A net-like morphology appears when f VPS reaches 0.36. The net-like porous PI film reaches equilibrium uptake of water within approximately 2.5 h, with a final equilibrium uptake ratio of 17.5%, and reaches equilibrium uptake of toluene within approximately 8 h, with a final equilibrium uptake ratio of 15.4%, displaying the highest and fastest solvent uptake compared with other microstructured porous PI films, which is ascribed to the specific characteristic of the interconnecting porous channels derived from the self-assembly of PI-b-PS with f VPS 0.36. Introducing thermally degradable segments to PI-based block copolymer is an effective method to prepare porous PI films and can enhance some of their properties. [ABSTRACT FROM AUTHOR]

We created a blend between a TiO2 sponge with bimodal porosity and a Methyl-Ammonium Lead Iodide (MAPbI3) perovskite. The interpenetration of the two materials is effective thanks to the peculiar sponge structure. During the early stages of the growth of the TiO2 sponge, the formation of 5–10 nm-large TiO2 auto-seeds is observed which set the micro-porosity (<5 nm) of the layer, maintained during further growth. In a second stage, the auto-seeds aggregate into hundreds-of-nm-large meso-structures by their mutual shadowing of the grazing Ti flux for local oxidation. This process generates meso-pores (10–100 nm) treading across the growing layer, as accessed by tomographic synchrotron radiation coherent X-ray imaging and environmental ellipsometric porosimetry. The distributions of pore size are extracted before (>47% V) and after MAPbI3 loading, and after blend ageing, unfolding a starting pore filling above 80% in volume. The degradation of the perovskite in the blend follows a standard path towards PbI2 accompanied by the concomitant release of volatile species, with an activation energy of 0.87 eV under humid air. The use of dry nitrogen as environmental condition has a positive impact in increasing this energy by ~0.1 eV that extends the half-life of the material to 7 months under continuous operation at 60 °C. [ABSTRACT FROM AUTHOR]

The manipulation and understanding of molecular transport across functionalized nanopores will take us closer to mimicking biological membranes and thus to design high-performance permselective separation systems. In this work, Surface-initiated atom transfer radical polymerization (SI-ATRP) of (2-methacryloyloxy)-ethyltrimethylammonium chloride (METAC) was performed on both mesoporous silica and mesoporous titania thin films. Pores were proven to be filled using ellipsometry and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Furthermore, the employed method leads to a polymer overlayer, whose thickness could be discriminated using a double-layer ellipsometry model. Cyclic voltammetry experiments reveal that the transport of electrochemically active probes is affected by the PMETAC presence, both due to the polymer overlayer and the confined charge of the pore-tethered PMETAC. A more detailed study demonstrates that ion permeability depends on the combined role of the inorganic scaffolds' (titania and silica) surface chemistry and the steric and charge exclusion properties of the polyelectrolyte. Interestingly, highly charged negative walls with positively charged polymers may resemble zwitterionic polymer behavior in confined environments. [ABSTRACT FROM AUTHOR]

Here, a detailed mechanical characterization of five important anhydrous microporous aluminophosphate materials (VPI-5, ALPO-8, ALPO-5, ALPO-18, and ALPO-31) is performed using first principles methods based on periodic density functional theory. These materials are characterized by the presence of large empty structural channels expanding along several different crystallographic directions. The elasticity tensors, mechanical properties, and compressibility functions of these materials are determined and analyzed. All of these materials have a common elastic behavior and share many mechanical properties. They are largely incompressible at zero pressure, the compressibilities along the three crystallographic directions being frequently smaller than 5 TPa − 1 . Notably, the compressibilities of ALPO-5 and ALPO-31 along the three principal directions are smaller than this threshold. Likewise, the compressibilities of ALPO-18 along two directions are smaller than 5 TPa − 1 . All of the considered materials are shear resistant and ductile due to the large bulk to shear moduli ratio. Furthermore, all of these materials have very small mechanical anisotropies. ALPO-18 exhibits the negative linear compressibility (NLC) phenomenon for external pressures in the range P = 1.21 to P = 2.70 GPa. The minimum value of the compressibility along the [1 0 0] direction, k a = − 30.9 TPa − 1 , is encountered for P = 2.04 GPa. The NLC effect in this material can be rationalized using the empty channel structural mechanism. The effect of water molecule adsorption in the channels of ALPO-18 is assessed by studying the hydrated ALPO-18 material (ALPO-18W). ALPO-18W is much more compressible and less ductile than ALPO-18 and does not present NLC effects. Finally, the effect of aging and pressure polymorphism in the mechanical properties of VPI-5 and ALPO-5 is studied. As hydration, aging leads to significant variations in the elastic properties of VPI-5 and increases substantially its compressibility. For ALPO-5, pressure polymorphism has a small impact in its elasticity at zero pressure but a large influence at high pressure. [ABSTRACT FROM AUTHOR]

E-waste from the electric and electronics industry is an emerging threat due to the pollution caused by hazardous cations. Immobilization and confinement of these cations as nanoparticles (NPs) in porous materials provide a strategy for the recovery and recycling of hazardous cations. Therefore, we propose the use of mesoporous oxides (MPO) films where the pores act as nanoreactors for the precipitation of metal sulfides (MS) to achieve a process in which dissolved cations are removed and at the same time form a nanostructure to serve as a basis for future designs. In this work, we present a detailed study of the formation of metal sulfides (MS - M = Cd, Zn, Co, Ni) NPs controlling the NP growth in the pores of the MPO by a successive ionic layer adsorption and reaction (SILAR) process. By varying diverse variables of interest such as pH, matrix composition (SiO2, TiO2, ZrO2), isoelectric point (IP) of the inorganic pore surface by organic functionalizers, we show that precipitation is comparable for the different metal sulfides where transport in the mesoporosity and the electrical charge of the surface, as well as the solvent, control the physicochemical response of the system. Understanding the role of each variable allows the limitations of loading MPOs to be identified and the pore filling to be optimized, although ion transport limitations in aqueous solutions lead to inhomogeneous distributions. Through a thorough characterization study (SEM, TEM, UVVIS, EEP, XRR, XPS), it was concluded that MPO thin films are useful platforms for the efficient removal of cations dissolved in water and even in alcohols. Highlights: Diverse metal sulfides nanoparticles were confined in the pores of mesoporous thin films. Successive ionic layer adsorption and reaction (SILAR) gives precipitation in mesopores. Progressive pore filling and composite structure were exhaustively characterized by complementary techniques. Pore oxide surface, functionalization and geometry affect filling, clogging, and particle formation. Heterogeneous nucleation is controlled by the cation interaction with the oxide surface. [ABSTRACT FROM AUTHOR]

One of the current issues in the development of devices based on porous thin films synthesized by sol gel is the eventual failure of the structural integrity of these systems due to chemical or mechanical stresses. In order to design and build robust systems, it is necessary to evaluate the role that each material forming the device has over its mechanical performance and chemical stability, considering their individual properties, their spatial arrangement, and the interfaces between them. In this work, the structural and mechanical evaluation of multilayers based on silica and titania mesoporous films is presented, and the variables that affect the structural integrity of these multilayered devices are evaluated. In addition, the chemical and mechanical stability of these optical devices against flow stress is assessed, simulating operating conditions of the sensors in a liquid environment. Single layer, bilayers, and multilayered devices were synthesized using the sol–gel method in combination with surfactant self-assembly, and their mechanical and structural properties were evaluated with electron and optical microscopy, X-ray reflectometry, and instrumented indentation. After these studies, improvements to the materials forming the device are proposed to maximize the structural integrity of the system. Highlights: Silica mesoporous films present a ductile behavior while titania mesoporous films are more brittle. The spatial disposition of SiO2 and TiO2 layers in bilayer structures modifies the failure mode. The mesoporous SiO2–TiO2 multilayer mechanical behavior is modulated by the SiO2 layers. The optical and mechanical behavior of the photonic device changes after immersion in water at 40 °C. [ABSTRACT FROM AUTHOR]

Abstract: Swelling and sorption of water, from the vapour phase, by thin (100–1000nm) and ultra-thin (<100nm) Nafion nanomembranes deposited on several surfaces were determined using quartz crystal micro-balance and environmental ellipsometric porosimetry techniques. The water uptake at room temperature, measured as the number of water molecules per ionic group in the polymer, is much lower than that observed in bulky Nafion 117 membranes. Water sorption by supported nanofilms was found to be independent of film thickness, but it depends on substrate nature. Aging due to slow relaxation of the polymer microstructure is also discussed. Results are relevant for modelling the three-phase region of proton exchange membrane fuel cells, where a thin Nafion film covers the carbon supported catalyst nanoparticles. [Copyright &y& Elsevier]

Abstract: Porous TiO2-anatase thin films were prepared by the sol–gel route and used for the study of the influence of structural properties in their photocatalytic activity. Sols were prepared by using titanium isopropoxide with two types of modifier ligands, namely acetic acid and acetyl acetone, and pore generating agents such as polyethylene glycol, pluronic F-127 and polyethylene glycol hexadecyl ether (Brij 58). The photocatalytic activity for the degradation of trichloroethylene in air was evaluated under ultraviolet irradiation at different gas flows and water vapour contents. The photocatalytic activity depends on the nature of the pore generating agent which influences the TiO2 crystallite size and the textural properties of the final material. The samples obtained by using acetic acid as the modifier ligand and either Brij 58 or PEG as the pore generating agent exhibited the best photocatalytic behaviour even in the presence of high quantities of water vapour. The direct trichloroethylene oxidation pathway to CO2 is favoured at low water vapour contents, but an important generation of COCl2 is observed even at low water partial pressures. [Copyright &y& Elsevier]

Abstract: This work reports the influence of the meso-structure of TiO2 films in the photocatalytic oxidation of methyl ethyl ketone. Five types of TiO2 films were prepared combining the sol–gel route with the Evaporation Induced Self-Assembly (EISA) method. Sols were prepared from titanium tetrachloride (TiCl4) using different types of pore generating agents. Films characterisation was performed by Fourier Transform Infrared Spectroscopy (FTIR), Grazing X-ray diffraction (GXRD), X-ray diffraction of small angle and Transmission Electron Microscopy (FE-SEM). Environmental Ellipsometric Porosimetry (EEP) studies were performed to obtain the adsorption/desorption isotherms and calculate porous size distribution, pore volume and specific surface area (S s) of the films. Kinetic of MEK photocatalytic oxidation data were modelled by Langmuir–Hinshelwood equation and the adsorption and kinetics constants (k and K) were calculated. Better results of MEK degradation were obtained for the Brij58 films deposited at relative humidity (RH) of 20% and 50%. The results are correlated with the porosity properties of the films. [Copyright &y& Elsevier]

Ordered mesoporous oxides obtained by combining sol-gel and self-assembly exhibit high surface area, controlled porosity, monodisperse pores in the mesoscale and amorphous or crystalline inorganic framework. In the particular form of thin films, they have been widely studied for a diversity of applications. In this context, the mechanical stability of devices based on mesoporous thin films (MTF) is one of the critical factors to consider for assuring robustness and reliability. Measuring and understanding the mechanical and tribological behavior of these designed materials are therefore issues of crucial importance when large-scale applications are pursued, such as photovoltaic devices, catalysis, sensors, microfluidic systems, biocompatible films and microelectronics. In this review, two aspects are discussed and critically evaluated: the mechanical properties of ordered MTF and the experimental techniques used to measure them. The relationship between hardness and elastic modulus with structural features (porosity, pore ordering, crystalline phase, among others) are analyzed for several mesoporous systems. Tribological and fractomechanical features are also assessed. Besides, the experimental techniques dedicated to measure the mechanical properties of porous thin film, including surface acoustic waves, Brillouin light scattering, ellipsometric porosimetry, X-Rays and neutron-based techniques and nanoindentation are described in detail, discussing the possibilities and limitations of these techniques applied to a diversity of systems. Highlights: Several techniques can be used to evaluate the mechanical behavior of mesoporous thin films. Ordered mesoporous films are excellent systems to correlate structure and mechanical properties. For mesoporous films, elastic modulus and hardness values decrease as porosity increases. For titania films, the crystalline phase and the porosity determine their mechanical strength. Mechanical properties of hybrid films can be designed by changing the composition and porosity. [ABSTRACT FROM AUTHOR]

Mesoporous thin films (MTFs) displaying high surface area and controlled porosity constitute interesting materials for a plethora of applications in optics and electronics. A critical aspect in MTF processing is template removal that usually consists in thermal treatment at 350 °C, which consolidates the oxide film but might change the pore features. In addition, the use of such high temperature must be avoided when organic functionalities are to be preserved, or in the case of film deposition on polymeric substrates. Here we present and compare five different methods to consolidate silica MTF (SMTF) in mild conditions, at a maximum processing temperature of 130 °C. Conditions, such as duration of the thermal treatment, vacuum conditions, exposure to acidic and alkaline media, were systematically explored and the resulting films were analyzed by optical microscopy, focused ion beam, scanning electron microscopy, ellipsometry, and infrared spectroscopy. The optimized conditions leading to accessible mesopores and a stable oxide structure that can be used as a mesoporous perm-selective electrode are discussed. Highlights: Soft template extraction methods from mesoporous silica thin films onto Si and Au were compared. These low-T treatments permit to extract ionic and non-ionic surfactants, keeping film integrity. A complete analysis on template extraction, film adhesion, and mesopore size is provided. Optimized 130 °C treatment followed by vacuum leads to robust frameworks with accessible mesopores. Mesoporous electrodes can be used for more than 90 consecutive electrochemical cycles in aqueous solutions. [ABSTRACT FROM AUTHOR]

For several decades, the sol–gel process allows the fabrication of functional materials through the strong coupling between materials chemistry and advanced processing. This branch of material's science is generally associated with the formation of oxide and hybrid materials obtained through a transition between a sol and a gel. Engineering the sol–gel process to extend same principles to other classes of materials is an emerging and promising research line. These aspects will be illustrated in this article by reviewing the successful case of optical materials with tunable structural colours. It will be shown that sol–gel transition from molecular or colloidal building blocks results in optical materials with great diversity in structure and composition such as oxide, hybrid, or metal–organic frameworks. Applicative examples will be provided including photocatalytic, "invisible" and anti-reflective coatings, graded photonic mirrors and 2D photonic sensors. Highlights: After 30 years from D. Ulrich's pionnering works, most of the key advantages of the sol-gel process are still valid today suppression or appearance of structural colours was obtained by controlling the interplay between intrinsic optical properties of the materials and their structure. Anti-reflective, invisible and photocatalytic coatings, graded Bragg mirros and diffraction gratings can be fabricated through engineering the sol-gel process to conventional and emerging materials. Taking advantage of the versatility of the sol-gel process by extending the composition threshold beyond oxides is an exciting future research line for the field. [ABSTRACT FROM AUTHOR]

Mesoporous TiO2 films doped with Ca2+, W6+ and nitrogen were obtained by sol-gel method using dip-coating procedure onto glass-slides in order to study the influence of dopants in their textural properties and photocatalytic activity. Titania sols were synthesized with and without dopants using titanium isopropoxide as titanium precursor, two complexing agents, acetic acid and acetyl acetone, and two pore generating agents, Pluronic F-127 (F127) and polyethylene glycol hexadecyl ether (Brij58). Films were characterised by Fourier Transform Infrared Spectroscopy (FTIR), Grazing X-ray diffraction (GXRD) and Transmission Electron Microscopy (TEM). Environmental Ellipsometric Porosimetry (EEP) permitted to obtain the adsorption/desorption isotherms and total pore volume, and to determine the porous size distribution and specific surface area (Ss) of the films. The photocatalytic activity was evaluated through the degradation of methyl orange (MO) in aqueous solution under UV light exposure. The photocatalytic activity depends on the nature of dopants, which affect the TiO2-anatase crystallite size and the textural properties of the final material. The best results of MO degradation were obtained for the films doped with Ca2+, this being correlated with the pore size and specific surface area of the films besides the dopant-effect on the photocatalytic mechanisms.

Abstract: Mesoporous films were synthesized by specific sol-gel route, including the use of surfactant molecules acting as templating agent through the evaporation induced self-assembly process. Controlled mesoporosity of the film is obtained by the thermal removal of the templating agent. In this work, the mesostructure of the sol-gel layer is used as reservoir for active enzymatic molecules providing antifingerprint coating. The mesopore size and their configuration were designed to assure a good impregnation by lipases. The coatings were applied on glass. The influence of the deposition process and the composition of the sol-gel on the structure of the mesoporous film was investigated. The film morphology was characterized by scanning electron microscopy and water adsorption/desorption isotherms recorded with a quartz crystal microbalance. The stability of the sol-gel solution was assessed by rheological measurements. The efficiency of the combination of mesoporous film and the enzymatic solution was determined in terms of antifingerprint properties using an artificial sebum.Mesoporous sol-gel film is used as reservoir for active enzymatic biomolecules to provide antifingerprint coating. Mesoporous structure is obtained by the sol-gel method using the evaporation induced self-assembly process. Different parameters (thickness of coating, concentration in templating agent, etc.) were studied to manage and adapt the size and the structure of the mesopores in order to obtain an active coating. Design of mesoporous sol-gel films using evaporation induced self-assembly process.Influence of the thickness, deposition method, and templating agent/precursor molar ratio on the mesoporosity.Evaluation of antifingerprint properties of the sol-gel films impregnated with enzymes. [ABSTRACT FROM AUTHOR]

Nature as the ultimate inspiration can direct, gate, and selectively transport species across channels to fulfil a specific targeted function. Harnessing such precision over local structure and functionality at the nanoscale is expected to lead to indispensable developments in synthetic channels for application in catalysis, filtration and sensing, and in drug delivery. By combining mesoporous materials with localised charge-switchable poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes, precisely controlling pore filling and exploring the possibility of incorporating two different responsive polymers, we hope to approach the precision control of natural systems in the absence of an external force. Here, we report a simple one-step approach to prepare a mesoporous silica thin film with ~8 nm pores functionalised with a photoiniferter by combining sol-gel chemistry and evaporation-induced self-assembly (EISA). We show that surface-initiated photoiniferter-mediated polymerisation (SI-PIMP) allows the incorporation of a high polymer content up to geometrical pore blocking by the simple application of UV light in the presence of a monomer and solvent, proceeding in a controlled manner in pore sizes below 10 nm, with the potential to tune the material properties through the formation of surface-grafted block copolymers. [ABSTRACT FROM AUTHOR]

As an extension of spectral ellipsometry, ellipsometric porosimetry has gained considerable importance for the characterization of porous thin films. The in-situ measurement of sorption facilitates the evaluation of open porosity, pore radius distribution, film backbone refractive index and even elastic properties. Multilayer assemblies and gradients within films can be characterized. These features are especially interesting for sol-gel derived thin films that are commonly composed of aggregated nanoparticles and thus may retain significant porosity after thermal treatment. In this paper the general features of Ellipsometric Porosimetry are highlighted and related to the characterization of selected sol-gel films. The examples range from simple assessments of porosity and pore radius distribution, film backbone analysis to the characterization of multilayer assemblies and systematic changes induced by thermal treatment or leaching phenomena. Graphical abstract: Besides optical properties Ellipsometric Porosimetry can reveal structural features such as open porosity and pore radius distribution of sol-gel derived thin films. [ABSTRACT FROM AUTHOR]

Mesoporous thin films were prepared by dip-coating with a purely aqueous method, as a substitute for the alcohol-based evaporation-induced self-assembly route. Unlike other aqueous routes that require a very slow pulling rate possible only using high performance dip-coaters, as a result of the high surface tension of water, this new process works with standard dip-coaters and at similar pulling rates as are used for the evaporation-induced self-assembly route. This unique asset is the result of the synthesis of prefabricated self-assembled silicate/organic hybrid micelles. These building blocks are concentrated before use, which provides a gelling edge after moderate evaporation. As a result, defect-free continuous mesoporous films with well-organized hexagonally packed pores were prepared after optimization of both the evaporation rate of the solution of hybrid micelles and the dip-coater pulling rate. Graphic Abstract: The transmission electron microscopy observation reveals the hexagonally packed structure of mesoporous silica film. This nanostructure has already been observed on films prepared with the evaporation-induced self-assembly process, but it is the first time it is obtained with a pure aqueous method, based on prefabricated hybrid micelles, not on controlled evaporation of mesophases. [ABSTRACT FROM AUTHOR]

In this work, we report a new generation of sol-gel photonic vapor sensor based on water-repellent methyl-functionalized mesoporous silica thin films for the detection of alcohol vapors. Relative humidity, generally accountable for sensor performance deterioration, was demonstrated as a key parameter to detect and enhance sensor sensitivity concerning ethanol. The ethanol-assisted water vapor capillary condensation into hydrophobic mesopores was observed and investigated as an innovative sensing mechanism. We showed that water condensation was triggered by the surfactant-like behavior of alcohol molecules whose alkyl moieties preferentially interact with the hydrophobic walls and reversibly switch the surface energy from hydrophobic to hydrophilic. Influence of the ethanol and water pressure conditions for which the capillary condensation occurs were studied by in situ ellipsometry. This study revealed a synergic mechanism of co-adsorption where the minimum ethanol concentration allowing water capillary adsorption decreases when humidity increases. Nanopatterned diffraction gratings films, fabricated via a nanoimprinting process, were demonstrated to be efficient transductor to transform the capillary-induced nanoscale variations of refractive index of the porous materials into optical signals easily measurable by conventional camera. Sensing results exhibited an ethanol vapor pressure threshold limit of detection of P/ P = 0.07 at 100 % relative humidity and typical response and regeneration times are below one minute. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Resin films based on polyurethane dispersions (PUDs) have recently gained substantial interest as surface protective coatings. However, defects in the resin films such as micro-cracks may induce high permeability to moisture, thereby compromising the coatings' performance. In this contribution, we report on a simple electrochemical method for characterization of the micro-cracks in a resin film deposited on a copper surface. Electrochemical measurements are facilitated in a two-electrode cell where the resin-coated copper electrode serves as the anode. The ionic current flow due to electrolyte penetration within the micro-cracks of the resin film is measured and quantified. The ionic current ( I) exhibits an inverse exponential dependence on the film thickness ( x): I ∝ e. The physical basis for this dependence is discussed using a mathematical model that incorporates the surface fraction of micro-cracks in a layered resin film. While the analysis presented herein is for the specific case of PUD resins, the overall methodology is applicable to the characterization of many metallic and non-metallic surface coatings used in corrosion protection and surface functionalization applications. Graphical abstract: [ABSTRACT FROM AUTHOR]

In the present study, as-prepared silver nanoparticles have been incorporated into SiO and TiO sols. The characterisation of the silver nanoparticles was performed through transmission electron microscopy, grazing X-ray diffraction, and UV-visible spectroscopy, before and after mixing with the different sols. Multilayer coatings doped with silver nanoparticles were also prepared by combining different compositions and analysed by TEM and GXRD. The photocatalytic activity was studied through the degradation of methyl orange in aqueous solution under UV light exposure. High photocatalytic efficiency was observed for all the multilayer coatings. The highest efficiency was obtained for the Ag-SiO/TiO mesoporous system that reached a degradation percentage of methyl orange up to 94 % after 2.5 h of irradiation, near the complete elimination of the pollutant. The mechanism that explains the high photocatalytic efficiency of this multilayer coating is associated with the high porosity of the mesoporous coatings and with the increase in the local electric field, associated with the effect of plasmon resonance surface produced for the presence of metallic silver nanoparticles in the SiO film. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We report on the direct consequences of reversible water adsorption on the optical performance of silica-based nanoporous antireflective (AR) coatings as they are applied on glass in photovoltaic and solar thermal energy conversion systems. In situ UV-VIS transmission spectroscopy and path length measurements through high-resolution interferometric microscopy were conducted on model films during exposure to different levels of humidity and temperature. We show that water adsorption in the pores of the film results in a notable increase of the effective refractive index of the coating. As a consequence, the AR effect is strongly reduced. The temperature regime in which the major part of the water can be driven-out rapidly lies in the range of 55°C and 135°C. Such thermal desorption was found to increase the overall transmission of a coated glass by ~ 1%-point. As the activation energy of isothermal desorption, we find a value of about 18 kJ/mol. Within the experimental range of our data, the sorption and desorption process is fully reversible, resulting in optical breathing of the film. Nanoporous AR films with closed pore structure or high hydrophobicity may be of advantage for maintaining AR performance under air exposure. [ABSTRACT FROM AUTHOR]

The correlation between the textural properties and the photocatalytic activity of nanocrystalline Titanium dioxide (TiO)-anatase films obtained by sol-gel has been investigated. Mesoporous and mesostructured TiO-anatase films were prepared using different titanium precursors and Pluronic (F127) and polyethylene glycol hexadecyl ether P5884 (Brij58) surfactants via acid catalysis. Ca(NO) and WCl were incorporated to TiO sols to investigate the effect of the doping on the photocatalytic behaviour. The microstructure and textural properties were characterised by X-ray diffraction, spectral ellipsometry and transmission electronic microscopy. The photocatalytic properties were evaluated in aqueous solution (methyl orange) and in gas phase (trichloroethylene, sulphide acid and methyl-ethyl-ketone) using multilayer films deposited on glass-slides. TiO-B-Brij-58 films exhibited the most efficient photocatalytic activity either in aqueous or gas medium. The Ca doping strongly enhances the photocatalytic activity associated with the reduced recombination of electrons and holes in the catalyst. [ABSTRACT FROM AUTHOR]

In this work, we prepared oriented mesoporous thin films of silica on various solid substrates using the pluronic block copolymer P123 as a template. We attempted to insert guest iron oxide (FexOy) nanoparticles into these films by two different methods: (a) by co-precipitation—where iron precursors are introduced in the synthesis sol before deposition of the silica film—and subsequent oxide production during the film calcination step; (b) by preparing and calcining the silica films first then impregnating them with the iron precursor, obtaining the iron oxide nanoparticles by a second calcination step. We have examined the structural effects of the guest nanoparticles on the silica film structures using grazing incidence X-ray scattering (GISAXS), high-resolution transmission electron spectroscopy (HRTEM), spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), and Raman microscopy. Formation of nanoparticles by co-precipitation may induce substantial changes in the film structure leading, in our adopted process, to the appearance of lamellar ordering in the calcination stage. On the contrary, impregnation-based approaches perturb the film structures much more weakly, but are also less efficient in filling the pores with nanoparticles. [ABSTRACT FROM AUTHOR]

Electrochemistry can be used for fabrication and characterization of mesoporous oxide films. First, this review provides insight into the methods used to prepare templated mesoporous thin films on an electrode surface, i.e., evaporation-induced self-assembly (EISA) and electrochemically assisted self-assembly (EASA). Electrochemical characterization of mass transport processes in pure and organically functionalized mesoporous oxide films is then discussed. The electrochemical response can be basically restricted by the electron/mass transfer reaction at the electrode-film interface and diffusion through mesopore channels. The contributions of cyclic voltammetry, hydrodynamic voltammetry, electrochemical impedance spectroscopy, and scanning electrochemical microscopy to the characterization of films with distinct mesostructures are finally described, with special emphasis on identification of conditions that can affect the electrochemical response recorded with such modified electrodes. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract  Ellipsometry porosimetry (EP) is an emerging technique that is well adapted to porous thin films analysis; it is non contact and non destructive. EP tools developed at SOPRA, allows us to obtain adsorption isotherms with many different adsorptives at an ambient temperature. EP leads to the same results as classical adsorption experiments (e.g. porosity, pore size distribution …), but it also has some particular features leading to new information. For instance, our optical setup (Spectroscopic Ellipsometry) allows us to determine the variation of the thickness of the samples during the adsorption experiment. It is also very sensitive to interfaces; it is thus possible to detect a porosity gradient or to study a bi-layer sample and plot the two corresponding adsorption isotherms at the same time (Bourgeois et al. 2004). For porous thin films with a non porous barrier layer deposited on top, it is also possible to study the lateral diffusion phenomenon in the film (see figure below). In this paper, we will demonstrate a part of the different features of EP for adsorption on porous thin films. [ABSTRACT FROM AUTHOR]

The possibility to gradually increase the porosity of thin films facilitates a variety of applications, such as anti-reflective coatings, diffusion membranes, and the herein investigated tailored nanostructuring of a substrate for subsequent self-assembly processes. A low-temperature (<160 °C) preparation route for porous silicon oxide (porSiO2) thin films with porosities of about 60% and effective refractive indices down to 1.20 is tailored for bulk as well as free-standing membranes. Subsequently, both substrate types are successfully employed for the catalyst-assisted growth of nanowire-like zinc oxide (ZnO) field emitters by metal organic chemical vapor deposition. ZnO nanowires can be grown with a large aspect ratio and exhibit a good thermal and chemical stability, which makes them excellent candidates for field emitter arrays. We present a method that allows for the direct synthesis of nanowire-like ZnO field emitters on free-standing membranes using a porSiO2 template. Besides the application of porSiO2 for the catalyst-assisted growth of nanostructures and their use as field emission devices, the herein presented general synthesis route for the preparation of low refractive index films on other than bulk substrates—such as on free-standing, ultra-thin membranes—may pave the way for the employment of porSiO2 in micro-electro-mechanical systems. [ABSTRACT FROM AUTHOR]

Nanoporous ultrathin films, constituted by a slab less than 100 nm thick and a certain void volume fraction provided by nanopores, are emerging as a new class of systems with a wide range of possible applications, including electrochemistry, energy storage, gas sensing and supercapacitors. The film porosity and morphology strongly affect nanoporous films mechanical properties, the knowledge of which is fundamental for designing films for specific applications. To unveil the relationships among the morphology, structure and mechanical response, a comprehensive and non-destructive investigation of a model system was sought. In this review, we examined the paradigmatic case of a nanoporous, granular, metallic ultrathin film with comprehensive bottom-up and top-down approaches, both experimentals and theoreticals. The granular film was made of Ag nanoparticles deposited by gas-phase synthesis, thus providing a solvent-free and ultrapure nanoporous system at room temperature. The results, bearing generality beyond the specific model system, are discussed for several applications specific to the morphological and mechanical properties of the investigated films, including bendable electronics, membrane separation and nanofluidic sensing. [ABSTRACT FROM AUTHOR]

Mesoporous materials bear great potential for biotechnological applications due to their biocompatibility and versatility. Their high surface area and pore interconnection allow the immobilization of molecules and their subsequent controlled delivery. Modifications of the mesoporous material with the addition of different chemical species, make them particularly suitable for the production of bioactive coatings. Functionalized thin films of mesoporous silica and titania can be used as scaffolds with properties as diverse as promotion of cell growth, inhibition of biofilms formation, or development of sensors based on immobilized enzymes. The possibility to pattern them increase their appeal as they can be incorporated into devices and can be tailored both with respect to architecture and functionalization. In fact, selective surface manipulation is the ground for the fabrication of advanced micro devices that combine standard micro/nanofluids with functional materials. In this review, we will present the advantages of the functionalization of silica and titania mesoporous materials deposited in thin film. Different functional groups used to modify their properties will be summarized, as well as functionalization methods and some examples of applications of modified materials, thus giving an overview of the essential role of functionalization to improve the performance of such innovative materials. [ABSTRACT FROM AUTHOR]

Sensitive and selective personal exposure monitors are needed to assess ozone (O3) concentrations in the workplace atmosphere in real time for the analysis and prevention of health risks. Here, a cumulative gas sensor using visible spectroscopy for real-time O3 determination is described. The sensing chip is a mesoporous silica thin film deposited on transparent glass and impregnated with methylene blue (MB). The sensor is reproducible, stable for at least 50 days, sensitive to 10 ppb O3 (one-tenth of the occupational exposure limit value in France, Swiss, Canada, U.K., Japan, and the USA) with a measurement range tested up to 500 ppb, and insensitive to NO2 and to large variation in relative humidity. A model and its derivative as a function of time are proposed to convert in real time the sensor response to concentrations, and an excellent correlation was obtained between those data and reference O3 concentrations. This sensor is based on a relatively cheap sensing material and a robust detection system, and its analytical performance makes it suitable for monitoring real-time O3 concentrations in workplaces to promote a safer environment for workers. [ABSTRACT FROM AUTHOR]

Nanostructured materials represent a breakthrough in many fields of application. Above all for sensing, the use of nanostructures with a high surface/volume ratio is strategic to raise the sensitivity towards dangerous environmental gas species. A new Dc-Reactive sputtering Deposition method has been applied to grow highly porous p-type nitrogen-doped titanium oxide layers by modifying the previously developed reactive sputtering method called gig-lox. The doping of the films was achieved at room temperature by progressive incorporation of nitrogen species during the deposition process. Two different amounts of N2 were introduced into the deposition chamber at flow rates of 2 and 5 standard cubic centimeter per minutes (sccm) for doping. It has been found that the N2 uptake reduces the deposition rate of the TiO2 film whilst the porosity and the roughness of the grown layer are not penalized. Despite the low amount of N2, using 2 sccm of gas resulted in proper doping of the TiO2 film as revealed by XPS Analyses. In this case, nitrogen atoms are mainly arranged in substitutional positions with respect to the oxygen atoms inside the lattice, and this defines the p-type character of the growing layer. Above this strategic structural modification, the multibranched spongy porosity, peculiar of the gig-lox growth, is still maintained. As proof of concept of the achievements, a sensing device was prepared by combining this modified gig-lox deposition method with state-of-the-art hot-plate technology to monitor the electrical response to ethanol gas species. The sensor exhibited a sensitivity of a factor of ≈2 to 44 ppm of ethanol at ≈200 °C as measured by a rise in the layer resistivity according to the p-type character of the material. At the higher temperature of ≈350 °C, the sensor turned to n-type as without doping. This behavior was related to a loss of nitrogen content inside the film during the annealing. It was indeed proved that p-type doping of a gig-lox sponge during growth is feasible, even at room temperature, without losing the layer porosity and the capability to host and detect environmental species. Moreover, the material integration on a device is simply done as the last production step. Easy TiO2 doping procedures, combined with porosity, are of general purpose and interest for several applications even on flexible substrates. [ABSTRACT FROM AUTHOR]

The porosity and pore-size distribution in the glass play an important role in glass corrosion; however, such information is difficult to be obtained non-destructively. Here we report the use of spectroscopic ellipsometry (SE) under controlled humidity environments to determine those structural parameters in the alteration layers formed on international simple glass (ISG), a model nuclear waste glass, in aqueous corrosion conditions. The SE results show that the ISG sample corroded for nearly 4.5 years develops pores larger than 2 nm in diameter, while the alteration layers formed initially in less than 1 month do not have such large pores. The development of larger pores over a long period of corrosion time, while the overall thickness remains relatively constant, implies structural rearrangements of the silicate network occurring within the alteration layer, which could eventually affect the transport of reactants and products as well as the structural stability. Gel layers: Scrutinized by spectroscopy Spectroscopy has been used to study the interfacial silica gel layer created during the corrosion of a model nuclear-waste glass. Understanding the way in which such materials degrade is of great importance because they are used to store radioactive waste. When international simple glass (ISG) corrodes an 'alteration' layer forms on its surface and now Seong H. Kim, from The Pennsylvania State University, and co-workers have used spectroscopic ellipsometry to characterize the thickness, porosity, and pore-size distribution of this layer after exposing it to different corrosive experimental conditions. Their data show that, although their alteration layers are of similar depths, the pore diameters in ISG samples corroded for 7 or 28 days are smaller than 2 nm whereas those corroded for 1625 days are larger, implying some restructuring of the layer over this time. [ABSTRACT FROM AUTHOR]

Concentrator photovoltaic (CPV) systems, where incident direct solar radiation is tightly concentrated onto high-efficiency multi-junction solar cells by geometric optical elements, exhibit the highest efficiencies in converting the sun’s energy into electric power. Their energy conversion efficiencies are greatly limited, however, due to Fresnel reflection losses occurring at three air/optics interfaces in the most sophisticated dual-stage CPV platforms. This paper describes a facile one-step wet-etching process to create a nanoporous surface with a graded-index profile on both flat and curved glasses, with capabilities of achieving ~99% average transmission efficiency in a wide wavelength range from 380 nm to 1.3 µm and for a wide range of incident angles up to ±40° regardless of the polarization state of incident sunlight. The simplicity of the etching process remarkably increases their versatility in various optical elements that require unconventional form factors such as Fresnel lenses and microlens arrays, and/or demanding curvatures along with much reduced dimensions such as ball lenses. Etched glass surfaces on two-stage optical concentrating systems yield enhancements in total optical transmission efficiencies by 13.8% and in the photocurrent by 14.3%, as experimentally determined by measurements on microscale triple-junction solar cells. The presented strategy can be widely adapted in a variety of applications such as image sensors, display systems, and other optoelectronic devices. [ABSTRACT FROM AUTHOR]

We created a blend between a TiO 2 sponge with bimodal porosity and a Methyl-Ammonium Lead Iodide (MAPbI 3 ) perovskite. The interpenetration of the two materials is effective thanks to the peculiar sponge structure. During the early stages of the growth of the TiO 2 sponge, the formation of 5-10 nm-large TiO 2 auto-seeds is observed which set the micro-porosity (<5 nm) of the layer, maintained during further growth. In a second stage, the auto-seeds aggregate into hundreds-of-nm-large meso-structures by their mutual shadowing of the grazing Ti flux for local oxidation. This process generates meso-pores (10-100 nm) treading across the growing layer, as accessed by tomographic synchrotron radiation coherent X-ray imaging and environmental ellipsometric porosimetry. The distributions of pore size are extracted before (>47% V) and after MAPbI 3 loading, and after blend ageing, unfolding a starting pore filling above 80% in volume. The degradation of the perovskite in the blend follows a standard path towards PbI 2 accompanied by the concomitant release of volatile species, with an activation energy of 0.87 eV under humid air. The use of dry nitrogen as environmental condition has a positive impact in increasing this energy by ~0.1 eV that extends the half-life of the material to 7 months under continuous operation at 60 °C.