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In this work, we focused on the chemical and (micro)structural changes that occur during curing at different temperatures of geopolymers (GP) prepared with a mullite-based precursor obtained by sol-gel synthesis. Several factors, such as the Si-to-Al ratio in the precursors and the curing temperatures, affect geopolymerisation. While potassium, sodium and even lithium are the most commonly studied cations, for this study, we examined geopolymers with sodium cations only. The H 2 O:Na 2 O ratio was set high at 22.80 to allow good workability of the paste having in mind the intended thin film application, i.e. the water-to-geopolymer binder ratio was set at 0.64. We performed extensive structural (diffraction and vibrational spectroscopy), morphological (electron microscopy) and electrical (impedance spectroscopy) characterisation, to facilitate an understanding of the conditions behind the optimal geopolymerisation. Particular attention was paid to the study of the evolution of the GP system as a function of curing temperature using solid-state magic angle spinning nuclear magnetic resonance. This allowed us to better understand the influence of the chemical composition of the constituents and their homogeneity, on the evolution of the organizational domains and electrical properties of the GP samples. We have explored the feasibility of moving from a relatively porous bulk to a thin film configuration, highlighting the applicability of geopolymers as constituents in photovoltaic facade systems. [ABSTRACT FROM AUTHOR]

• CuCrO2 porous thin films prepared by spin coating and two-step annealing. • Use of polyvinylpyrrolidone in the precursor results in porous films. • High-purity CuCrO2 porous thin films with enhanced optical properties produced. In this study, CuCrO 2 thin films were fabricated by spin-coating technique on alkali-free glass substrates and a two-step annealing process. The copper-based delafossite CuCrO 2 is a p-type transparent conductive oxide that exhibits a wide energy bandgap and excellent stability. To improve the transmittance of CuCrO 2 thin films, polyvinylpyrrolidone (PVP) was used as a porogen for preparing thin films with high transmittance and high haze values. The highest transmittance of 73.75% was achieved with 0.5 g of PVP. The bandgaps of prepared CuCrO 2 thin films were estimated at 2.82 eV to 3.11 eV. The prepared CuCrO 2 thin films had a porous structure and high transmittance. The high potential transmittance of porous CuCrO 2 thin films makes them applicable to photovoltaic systems, transistors and touch screens or displays in the future. [ABSTRACT FROM AUTHOR]

A porosimetry technique that uses infrared-spectroscopic quantification of adsorbed probe molecules has been developed to characterize porous thin films. The amount of adsorbed probe molecules as a function of relative pressure of vapor is quantified via the absorbance of a characteristic signal of the probe molecule, to obtain adsorption isotherms. The pore size distributions of nanoporous thin films of SiO 2 -ZrO 2 , TiO 2 , and mesoporous silica MCM-41 are determined based on the Kelvin equation. In this technique, water and hexane are used as condensable vapors. Pore size distribution curves measured by infrared-spectroscopic porosimetry are in good agreement with those measured by the conventional gas/vapor adsorption technique, although the surface area per sample was less than 1 square meter. The results verify that the infrared-spectroscopic porosimetry technique is a simple methodology for characterizing the porous structures of thin films. • Porosimetry technique for characterizing micro- and mesoporous thin films. • The amount of adsorbed probe molecules is quantified by infrared spectroscopy. • Pore size distributions of thin films with thickness less than 1 μm are determined. • IR-porosimetry is compared with conventional porosimetry techniques. [ABSTRACT FROM AUTHOR]

Abstract We presented an optical fiber sensor based on dielectric film which is used to construct a Fabry–Perot structure. The Fabry–Perot resonant structure is consist of 11 porous thin films manufactured by electron beam physical vapor deposition. Since the films are porous material, the proposed fiber sensor structure is appropriate to detect the refractive index of liquid substances. In the refractive index detection experiments, the sensor probe possesses a refractive index sensitivity of 105 nm/RIU and a resolution of 2 × 10 −3 RIU. Cycling test results show that the prepared sensor probe has response time of 5 s and good repeatability. Highlights • We presented an optical fiber sensor based on dielectric film which is used to construct a Fabry–Perot structure. • The Fabry–Perot resonant structure is consist of 11 porous thin films manufactured by electron beam physical vapor deposition. • The proposed fiber sensor structure is appropriate to detect the refractive index of liquid substances. • The sensor probe possesses a refractive index sensitivity of 105 nm/RIU and a resolution of 2 × 1 0 − 3 RIU. • The prepared sensor probe has response time of 5 s and good repeatability. [ABSTRACT FROM AUTHOR]

The selective incorporation of deposition species with preferential directionality is analyzed during the growth of TiO 2 thin films by magnetron sputtering. Using wisely-designed collimators, tilted nanocolumnar morphologies are grown in a ballistic deposition regime, i.e. when most deposition species arrive at the film surface along well-defined preferential directions, and also in a thermalized deposition regime, when these species follow an isotropic momentum distribution in the plasma gas. The obtained results suggest that the use of particle collimators may promote the growth of porous thin films even in the classical magnetron sputtering configuration, when the target and the substrate are parallel. General insights are given on this approach and, as a proof of concept, its principles applied for the synthesis of nanostructured films in a laboratory-size reactor. [ABSTRACT FROM AUTHOR]

In this work, an innovative design was presented to fabricate ZnO nanostructured thin film-based sensor by thermal oxidation at low values of oxygen partial pressure using a buffer gas mixture of H 2 and H 2 O at different operating temperatures. Microstructural observations of the as-fabricated films prepared at different values of oxygen partial pressure showed significantly improved surface roughness and variations in porosity with reference to those obtained by thermal oxidation of sputtered Zn films in air and ZnO prepared by DC reactive sputtering followed by heated in argon. In low operating temperatures of oxygen partial pressure, ZnO nanostructures possessed larger grain sizes and higher porosity. ZnO film prepared by oxidization of sputtered Zn in low oxygen partial pressure possessed more oxygen vacancies that lead to the formation of more active sites to target gas and to be efficient gas sensor. As-fabricated ZnO nanostructures were characterized to be a platform for H 2 gas sensing. ZnO nanostructured films with substantially improved surface roughness and porosity were found to show better gas sensing performance toward low levels of H 2 (75–1200 ppm). This work paves a possibility for developing new porous metal oxides sensors with high computability and good repeatability toward different gases. [ABSTRACT FROM AUTHOR]

The mechanical properties of porous thin films and perforated layers are affected by pore content, shape and arrangement. The experimental determination of the in-plane mechanical properties of such materials is challenging, yet reliable data are essential for materials development and component design. Analytical and numerical approaches therefore provide valuable, supplementary tools for evaluating the effect of porosity on the mechanical properties of such materials. The applicability of both the classical self-consistent method and the Mori–Tanaka approach to the estimation of the effective elastic properties of porous thin films and perforated layers is investigated in this paper. For generic model microstructures with various arrangements of pores, variable pore content and varying matrix Poisson’s ratio, the effective elastic properties predicted by the classical self-consistent method and by the Mori–Tanaka approach are quantitatively compared with results obtained by numerical experiments. Based upon this comparison, the range of validity of both the classical self-consistent method and the Mori–Tanaka approach with regard to the different arrangements of pores investigated is defined, and the deviation to be expected if critical values of pore content or inter-pore distance are exceeded and interactions between adjacent pores are occurring is assessed. [ABSTRACT FROM AUTHOR]

Several mixed oxide thin film series of samples (Si–Co–O, Si–Ni–O, Si–W–O) have been prepared by reactive magnetron sputtering at oblique angle geometries. The paper focuses on the description of microstructure of the films as a function of their stoichiometry. It is found that for identical process parameters (gas mixture, pressure, magnetron-substrate distance, incidence angle of the vapour flux, etc.) the tilt angle of the developed columnar microstructure and the film porosity is strongly dependent on the stoichiometry of the films. The results are discussed in the framework of several theoretical models on this topic. [ABSTRACT FROM AUTHOR]

This paper is a short review about the principle, preparation, and applications of ultra-thin oxide films prepared by molecular layer deposition (MLD). Porous oxide films, with well-defined porous structures and precisely controlled thicknesses down to several angstroms, can be prepared from dense organic/inorganic hybrid polymer films grown by MLD. The organic constituents in the film can be removed either by calcination at elevated temperatures or mild water etching at room temperature. Because of the layer-by-layer growth process for MLD, the deposited polymer films have regular structures and the removal of organic components from MLD polymer films produces uniform interconnected highly porous structures with a high surface area. For example, porous aluminum oxide films prepared by such a method have both micropores and mesopores with a BET surface area as high as 1250 m 2 /g. Examples of the versatility of the technique for fabrication of novel functional materials for various applications are discussed, including thermally stable, highly selective metal nanoparticle catalysts, defect-free inorganic membranes for gas separation, and photocatalytic layers prepared from titanium alkoxide MLD films. [ABSTRACT FROM AUTHOR]

A novel ternary tungsten disulfide (WS 2 )/copper oxide (CuO)/single-wall carbon nanotubes (SWCNT) porous laminated hybrids are fabricated with the aid of electrostatic interaction and vacuum filtration. In which, the layered WS 2 sheets are spaced by high electrochemical active CuO nanosheets and conductive SWCNT and form a unique sandwich-like porous structures. When used as a lithium ion batteries anode, it demonstrates high reversible specific capacity of 962.4 mA h g −1 at 0.1 A g −1 after 100 cycles and excellent rate capability, a reversible specific capacity of 418.1 mA h g −1 even at a high rate current density of 2 A g −1 . The unique assembled WS 2 /CuO/SWCNT porous hybrids not only show the improved electrical conductivity, but also provide efficient charge transport channels for electrolyte penetration and sustain for the volume variation during the lithiation and delithiation. These synergistic effects significantly improve the electrochemical performances. The synthesis approach presented here would be extended to the other layered-based composites for energy applications. [ABSTRACT FROM AUTHOR]

Abstract: Porous thin films of Ir oxide were prepared by reactive dc magnetron sputtering onto unheated substrates. The crystallite size was ~5nm, and a small amount of unoxidized Ir was present. The electrochromic performance was studied by optical transmittance measurements and cyclic voltammetry applied to films in aqueous and non-aqueous electrolytes, specifically being 1M propionic acid, 1M potassium hydroxide (KOH), and 1M lithium perchlorate in propylene carbonate (Li–PC). Cyclic voltammetry measurements indicated that the films had a fractal surface structure. Good electrochromism, with mid-luminous transmittance modulation between ~55 and ~90% in ~100-nm-thick films, was documented in all of the electrolytes. [Copyright &y& Elsevier]

It is demonstrated that, besides classical nanocolumnar arrays, the oblique angle geometry induces the growth of singular structures in the nanoscale when using wisely designed patterned substrates. Well-ordered array of crosses, cylindrical nanorods or hole structures arranged in square or hexagonal regular geometries are reported as examples, among others. The fundamental framework connecting substrate topography and film growth at oblique angles is presented, allowing the use of substrate patterning as a feasible thin film nanostructuring technique. A systematic analysis of the growth of TiO 2 thin films on 4 different lithographic patterned substrates in 4 different scale lengths is also presented. A first conclusion is the existence of a height-based selective growth in the initial stages of the deposition, by which the film preferentially develops on top of the tallest substrate features. This behavior is maintained until the film reaches a critical thickness, the so-called Oblivion Thickness, above which the film topography becomes gradually independent of the substrate features. A general formula relating the spatial features of the pattern, the coarsening exponent and the Oblivion Thickness has been deduced. [Display omitted] • Thin film nanostructuring by substrate patterning at oblique angle is demonstrated. • A height-based selective growth principle is deduced for the first stages of growth. • A relation between growth modes, pattern wavelengths and growth exponent is found. • The growth on 16 different patterned substrates corroborates the theory. • Films made of well-ordered arrays of nanorods with thickness up to ~1 μm are shown. [ABSTRACT FROM AUTHOR]

Abstract: We have studied low refractive index fluorine doped silica thin films prepared by reactive magnetron sputtering. Two experimental parameters were varied to increase the porosity of the films, the geometry of the deposition process (i.e., the use of glancing angle deposition) and the presence of chemical etching agents (fluorine species) at the plasma discharge during film growth. The microstructure, chemistry, optical properties, and porosity of the films have been characterized by scanning electron and atomic force microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV–vis, and spectroscopic ellipsometry. It is found that either the deposition at glancing angles or the incorporation of CFx species in the plasma discharge during film growth produces a decrease in the refractive index of the deposited films. The combined effect of the two experimental approaches further enhances the porosity of the films. Finally, the films prepared in a glancing geometry exhibit negative uniaxial birefringence. [Copyright &y& Elsevier]

Abstract: ZnO thin films containing nano-sized pores were synthesized on solid substrates through a sol–gel process by accommodating cetyl-trimethyl-ammonium bromide (CTAB) as an organic template in the precursor solution. By X-ray diffraction the resultant ZnO films were found to possess ordered pore arrays forming lamellar structure with the spacing between two adjacent pores being ∼3.0nm. Photoluminescence measurements indicated that the surfactants effectively passivated the surface defects of the ZnO films responsible for the green emission. Al doping was found to improve not only the lamellar structure of the pore arrays but also the near-band-gap emission intensity while the suppression effect of CTAB on the green emission remained undisturbed. With a proper control of doping level, the optical property as well as the structural integrity can be tailored to augment the potential of ZnO films for the optoelectronics and sensor applications. [Copyright &y& Elsevier]

Abstract: The deposition of samaria-doped ceria (SDC, Sm0.2Ce0.8O x ) and NiO-SDC thin films on a SDC substrate was studied using the electrostatic spray deposition (ESD) technique. The precursor solution was prepared by dissolving the correct amount of Sm(NO3)3·6H2O, Ce(NO3)3·6H2O and Ni(NO3)2·6H2O into a mixture of ethanol (C2H5OH) and butyl carbitol (C4H9OC2H4OC2H4OH). The surface microstructure of as-deposited thin films was strongly influenced by the substrate temperature, solvent composition and precursor solution. The reticular film of SDC with high porosity could be successfully prepared at the deposition temperature ranging from 300 to 350°C, a precursor solution of 0.005mol/dm3 and a 50vol.% of butyl carbital. The correlations between the surface morphology of as-deposited thin films and the physical properties of precursor solution could be approximately explained by the following equation :where d is the size of sprayed droplet, Q the flow rate of liquid pushed through the jet, ɛ the dielectric constant of liquid, ɛ 0 the electrical permittivity of vacuum, and G(ɛ) is the function of ɛ. The as-deposited thin films were amorphous at the used deposition temperature (350°C). Subsequently, the thermal treatments were done for ranging from 700 to 900°C in air. As the result, the crystal structure transformed into the desired cubic fluorite one after the sample was annealed over 700°C in the as-deposited SDC thin films and 900°C in the as-deposited NiO-SDC thin films, respectively. To confirm the composition of the as-sintered SDC thin films, ICP-OES analysis was studied for the films annealed at 900°C in air for 2h. The observed chemical composition was found to be close to that of the precursor solution within experimental errors. [Copyright &y& Elsevier]

Abstract: Amorphous carbon is an interesting material and its properties can be varied by tuning its diamond-like (sp3) fractions. The diamond-like fractions in an amorphous carbon films depends on the kinetic energy of the deposited carbon ions. Porous amorphous carbon thin films were deposited onto silicon substrates at room temperature in a vacuum chamber by Glancing Angle Pulsed Laser Deposition (GAPLD). Krypton fluoride (248nm) laser pulses with duration of 15ns and intensities of 1–20GW/cm2 were used. In GAPLD, the angles between the substrate normal and the trajectory of the incident deposition flux are set to be almost 90°. Porous thin films consisting of carbon nanowires with diameters less than 100nm were formed due to a self-shadowing effect. The kinetic energies of the deposited ions, the deposition rate of the films and the size of the nanowires were investigated. The sp3 fraction of the porous carbon films produced at intensity around 20GW/cm2 were estimated from their Raman spectra. [Copyright &y& Elsevier]

Abstract: The sol–gel deposition method has been successfully applied to obtain Pb(Zr0.2Ti0.8)O3 thin films on platinized silicon wafers. Addition of different amounts (7–15 wt.%) of organic macromolecular polyvinylpyrrolidone in the precursor solution prior to spin coating proves to be an excellent method for obtaining porous films. The crystal structure of as deposited films was analyzed by X-ray diffraction. The porous films show perovskite phase after annealing at 650 °C. The surface morphology has been studied by Atomic Force Microscopy and Scanning Electron Microscopy. The surface profile indicates a roughness of the film of 5 nm and no microcracks on the surface. The ferroelectric behavior was proved for each film, by hysteresis loops and by the “butterfly” shape of the capacitance–voltage characteristics. The remnant polarization and the coercive field decrease while the amount of added PVP increases. [Copyright &y& Elsevier]

Abstract: TiO2 materials possessing not only photocatalytic but also electrochromic properties have attracted many research and development interests. Though WO3 exhibits excellent electrochromic properties, the much higher cost and water-sensitivity of WO3 as compared with the TiO2 may restrict the practical application of WO3 materials. In the present study, the feasibility of preparing nanocrystalline porous TiO2/WO3 composite thin films was investigated. Precursors of sols TiO2 and/or WO3 and polystyrene microspheres were used to prepare nanocrystalline pure TiO2, WO3, and composite TiO2/WO3 thin films by spin coating. The spin-coated thin films were amorphous and, after heat treating at a temperature of 500 °C, nanocrystalline TiO2, TiO2/WO3, and WO3 thin films with or without pores were prepared successfully. The heat-treated thin films were colorless and coloration-bleaching phenomena can be observed during cyclic voltammetry tests. The heat-treated thin films exhibited good reversible electrochromic behavior while the porous TiO2/WO3 composite film exhibited improved electrochromic properties. [Copyright &y& Elsevier]

Titanium dioxide porous films have been deposited on glass slides by sol–gel technology. Tetrabutylorthotitanate and polyethylene glycol were used as a precursor and template, respectively. The chemical mechanism is discussed in relation to the sol–gel transition, which provides a possible theoretic explanation to the formation of TiO2 porous films. The morphology of porous TiO2 thin films strongly depends on the amount of water, the types of solvents and complexing agents, and the concentration and molecular weight of the template. It was shown that the diameter of pores is tunable in the range of 10–500 nm and the maximum of BET specific area of the films is 72 m2/g. [Copyright &y& Elsevier]

Porous thin films have various application fields, e.g., for energy conversion in fuel cells, energy storage in lithium ion batteries or supercapacitors as well for catalysis, filtration and sensing. We synthesized porous thin films by co-evaporating a low-vapor-pressure material (e.g., Si, Ni or C) together with zinc and depositing a compact layer of resulting composite. High-rate deposition process up to 100 nm/s was realized by electron beam physical vapor deposition (EB-PVD) of the materials from two graphite crucibles with a fast deflected electron beam in high vacuum. Immediately after deposition, the coated substrates were heated up in vacuum to a temperature above 500 °C and thereby zinc is removed selectively. Due to its higher vapor pressure against that of remaining component, zinc is expelled from the layer and vacancies are generated by so called vapor phase dealloying (VPD). We investigated the feasibility of VPD process for the elements silicon, nickel and carbon. The elemental composition and the morphology of the layers prior and after thermal annealing were analyzed by scanning electron microscopy, by energy-dispersive X-ray spectrometry and by X-ray diffraction. [Display omitted] • High-rate deposition of compact multiphase layers by co-evaporation of Zn together with Si/Ni/C • Layer morphology can be adjusted by deposition parameters. • Subsequent thermal annealing in vacuum for expelling zinc and generating pores • Porous structure can be adjusted by layer morphology and annealing parameters. [ABSTRACT FROM AUTHOR]

• Aluminum thin films were successfully deposited by DC magnetron sputtering in different He/Ar mixtures. • The cooling process by He gas could explain the decrease of Al crystallite size for Γ He ≤ 70%. Then, as Γ He increased to 95%, helium started to be ionized in the plasma and the concentration of He atoms increased in the film. • Helium incorporation induced the formation of open or closed pores (filled with He). • Fiberform porous nanostructures coated by nanoparticles were obtained by sputtering Al in pure He plasma for hydrothermal hydrogen production. [ABSTRACT FROM AUTHOR]

Abstract: Porous and dense nanocrystalline TiO2 films grown on F:SnO substrates used in vertical geometry ultraviolet photodetectors are investigated. Compared with a detector with a dense nanocrystalline TiO2 film (D-detector), a detector with a porous nanocrystalline TiO2 film (P-detector) exhibits one order of magnitude higher responsivity due to a light scattering effect. In addition, the vertical geometry detectors show a fast response time. The rise time and decay time of the P-detector and D-detector are 19 and 136ns, and 14 and 100ns, respectively, which are six orders of magnitude faster than those of lateral geometry detectors based on dense nanocrystalline TiO2 films. It is a result of a decreased mobility fluctuation. [Copyright &y& Elsevier]