Silica thin films with a two-dimensional (2D) hexagonal structure were produced from TEOS and the F127 triblock copolymer PEO106PPO70PEO106. The structure of the films was deduced from transmission electron microscopy (TEM) performed on microtomed sections and from a 2D X-ray scattering technique adapted for film characterization. Both methods are complementary and allow for a detailed characterization of the film structure. The pore channels within the coatings are organized in domains, which spin and curve inside the film, but align with the surface plan at the air/film and film/substrate interfaces. The formation of the film was monitored by in situ time-resolved SAXS experiments to follow the structural evolution during the first minutes after deposition. Cylindrical micelles, which gives rise to a wormlike structure, form first at the air/film interface and extend toward the film/substrate interface via solvent evaporation. When most of the liquid phase is evaporated, the well-aligned domains located at both interfaces are obtained by a self-arrangement of the micelles parallel to the interfaces. This rearrangement occurs when the film is considered to be dry. The atom content profiles in the as-prepared films were obtained by Rutherford backscattering (RBS) and show homogeneous distribution of atoms throughout the film thickness. To stiffen the network and remove the surfactant, various postsynthesis treatments were applied to the coatings, that is, thermal treatment, base-catalyzed condensation, and solvent extraction. Each method induces shrinkage, leading to 2D-centered rectangular films through a contraction of the initial 2D hexagonal structure. As-prepared and treated films exhibit excellent optical transparency and high degree of organization. Ellipsometry measurements and N2 adsorption/desorption isotherms were thus used to estimate the refractive index and the porosity of the films. Refractive index down to 1.2 was obtained in the film that was pretreated under a NH3 atmosphere before solvent extraction of the surfactant. This shows the efficiency of this treatment to minimize the network shrinkage. N2 adsorption-desorption measurement performed on films calcined at 350 °C gives a surface area of 800 m2 g-1 and a porosity of 63%.@en

Since mesoporous materials can be prepared by combining the sol-gel chemistry and the structuring effect of surfactants, they have attracted attention for application in various high technology fields. The present work deals with the analyses of the mechanisms involved in the formation of SiO2 and TiO2 highly organised 2D-hexagonal meso-structured films using Brij 58 as surfactant. The preparation of such films by dip-coating involves rapid evaporation which makes the different steps difficult to control. Simultaneous in-situ SAXS (synchrotron) and interferometry analyses have been performed to get a first understanding of the self-assembly process. SiO2 and TiO2 materials have a different chemical reactivity (kinetics and coordination aspects). However, we show that the mechanisms involved during dip-coating are quite similar : The self-assembly leading to the organised phase takes place at a final stage of the drying process, involves the formation of a disorganised intermediate phase and depends also on the presence of micellar interfaces in addition to film/air and film/substrate interfaces.@en

The preparation and characterization of optically uniform mesoporous TiO thin films that present a high regularity in the pore mesostructure and orientation is reported. In addition, these films of optical quality are crack-free as confirmed on the nanometer and micrometer scales by electron microscopy. These films showed overall good optical quality as well as a high degree of organization before and after removal of the organic template and consolidation of the inorganic network.@en

The increasing interest in mesoporous materials in various fields of application has motivated the investigation of novel high-technology thin films with pore size, structure and organisation controlled by the presence of directing agents. The design of optical coatings made by this method is described in this work. Silica thin films with 1d-hexagonal mesoporous structure were deposited on silicon and glass substrates from a silicate precursor solution, containing a non-ionic triblock copolymer (EO106PO70EO106:F127) as structuring agent. 70 to 700 nm thick films, with an excellent optical quality, were prepared by single dipcoating at a constant withdrawal rate. The surfactant was removed from the coatings by various treatments (i.e. thermal treatment, washing, ultra-sonic bath or sohxlet extraction). XRD investigations showed that shrinkage or collapsing of the film network can take place upon removal of the surfactant. Profiles of the relative amounts of surfactant, present in the pores, were measured by Rutherford Back Scattering. Refractive index, thickness and porosity of untreated and treated coatings were deduced from ellipsometry measurements. Each treated film exhibits an uni-axial anisotropy. The highest porosity (46%) and the lowest structural degradation are obtained for samples pre-treated at 400 K before extraction of the surfactant by sohxlet technique, as a result of the rigidification of the silica matrix.@en

Silica thin films with ordered porosity can be prepared by dip coating, combining polycondensation of silicate species and organization of amphiphilic mesophases. This paper reports on the preparation of templated films using cetyltrimethylammonium bromide (CTAB) as the surfactant and tetraethoxysilane (TEOS) as the inorganic precursor. Depending on the CTAB/Si molar ratio, films with different porous networks - 3D hexagonal (P63/mmc), cubic (Pm3n), and columnar hexagonal (p6m) - were obtained. Identification of the structures was accomplished by coupling two-dimensional X-ray diffraction at grazing incidence and TEM investigations on film cross sections. Other experimental parameters (e.g., deposition rate and composition of the starting sol, including its aging time) appeared also to influence the degree of organization of the final films greatly. To obtain a better understanding of the self-assembly mechanism, the structural formation of the films was followed in real time by in situ SAXS. Because of the very fast self-assembly process ( <30 s), high-flux synchrotron radiation was used, which allows to record good quality X-ray patterns in 100 ms. For the first time, interferometry measurements were also combined with the SAXS experiments to correlate the organization steps detected during dip coating with the thickness profiles. A model has thus been proposed for the film formation: organization at the mesoscale (i) takes place at the final stage of liquid-phase evaporation; (ii) involves the formation of micelles at the film/air interface in the early stage of deposition and, in some cases, the formation of intermediate phases; and (iii) is influenced by the condensation degree of inorganic intermediates, the surfactant concentration, and the deposition external conditions.@en

Mesoporous silica thin films have been produced by sol-gel chemistry in the presence of cetyltrimethylammonium bromide (CTAB) template. The films were deposited on silicon or glass substrates by dip-coating and underwent different treatments to eliminate the CTAB and create porosity. As-prepared and treated coatings exhibit good optical quality. Their structures were fully characterised by transmission electron microscopy (TEM) performed on film cross-sections and by X-ray diffraction (XRD) in θ-2θ scan mode, as well as in transmission mode using two different scattering geometries. The films exhibit large and homogeneous domains organised in a 3D-hexagonal (P63/mmc) structure with the c axis normal to the surface throughout their whole thickness. Numerical analysis of the TEM pictures confirms the space group deduced from the XRD measurements. To our knowledge, these are the first reported thin films obtained by dip-coating in the presence of CTAB which show such extended and highly mono-oriented 3D-hexagonal (P63/mmc) domains. The film thickness, porosity and refractive index were evaluated by ellipsometry for the various treated films.@en

Highly oriented 3D-hexagonal silica thin films have been produced on silicon substrates by dip-coating technique, using cetyltrimethylammonium (CTAB) bromide as structuring agent. For the first time, time-resolved in situ X-ray diffraction experiments have been used to investigate the formation of such mesostructured films. Interestingly, the data shows that an intermediate mesophase appears just after film deposition (t<500 ms), characterized by one diffraction peak centered at a d spacing of 65 Å. Then after 20 s, another mesophase appears with a shorter d spacing (44 Å), which corresponds to the 3D-hexagonal structure found for the final dried film.@en