Mesoporous Thin Films: use of in-situ and ex-situ synchrotron techniques for materials characterization

G. J. A. A. SOLER ILLIA

Campinas. Brasil

Conferencia; 6th International Conference on Synchrotron Radiation in Materials Science; 2008

LNLS

Mesoporous Thin Films: use of in-situ and ex-situ synchrotron techniques for materials characterization Galo J. A. A. Soler-Illia Grupo de Nanomateriales, Gerencia de Química-Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes Av. Gral Paz 1499 (B1650KNA) San Martín, Buenos Aires, Argentina mail: gsoler@cnea.gov.ar Mesoporous thin films (MTF) present a fascinating variety of pore architectures, with controlled size, shapes and structures in the mesoscopic scale (2-100 nm). MTF can be used as functional building blocks of complex multilayer architectures. The possibility to control issues such as film or pore spatial ordering, surface modification and pore interconnection leads to promising applications, from selective membranes to environment-responsive photonic crystals. Synchrotron techniques are an essential tool to characterize these materials. The pore symmetry and orientation of MTF can be assessed by diffraction at low angles with 2D detection; film thickness, density and pore distribution can be accurately determined by using X-Ray Reflectometry (XRR). X-Ray absorption techniques (XAS, XANES, EXAFS) permit to assess the local environment of metallic centers, and their evolution upon chemical or thermal processing. In addition, in situ SAXS techniques can be used in order to understand the mechanisms of formation of these complex nanomaterials from an evaporation-induced self-assembly route. Synchrotron techniques constitute an essential tool in order to characterize complex nanostructured materials. In this presentation, we will focus in the use of 2D-SAXS, XRR and XANES in the characterization of mesoporous thin films (MTF), which are produced by a supramolecular templating method. The combination of self-assembly and sol-gel chemistry leads to produce a variety of inorganic or hybrid organic-inorganic matrices (oxides, functional oxides phosphates, carbon…) with perfectly defined cavities in the mesopore range (2-50 nm).[1] MTF can be produced by the Evaporation-Induced Self-Assembly (EISA) approach schematized in Figure 1.[2] Figure 1 – Left: Scheme of the EISA process [2]. Right: TEM image of CTAB-templated mesoporous titania presenting a hexagonal pore arrangement. Due to the presence of ordered pore arrays (“crystals of pores”), MTF present diffraction spots at low angle values. SAXS with bidimensional detection (2D-SAXS) permits to accurately determine the relative pore distance, and the symmetry and orientation of the whole pore arrays.[3] Examples are shown in Figure 2. The use of an intense SAXS beam permits to follow the EISA process in situ.[4] Figure 2 – Typical 2D-SAXS patterns of MTF with mesostructures derived from a cubic Im m (left), Pm3n (center) and 2D-hexagonal p6m (right). XRR permits to accurately characterize MTF thickness and density (i.e., pore volume can be obtained). Moreover, XRR measurements performed in controlled solvent atmosphere permit to determine pore size and surface area.[5] Apart from these mesostructural information, synchrotron XAS permits to quantitatively assess the local environment of the inorganic components. This is very advantageous in the case of MTF presenting partially nanocrystalline walls.[6] In conclusion, crossed synchrotron-based techniques are a powerful tool to characterize and understand completely complex materials with order at different length scales. References 1. G.J.A.A. Soler-Illia, P. Innocenzi Chem. Euro. J. 2006, 12, 4478. 2. C. J. Brinker, Y. Lu, A. Sellinger, H. Fan, Adv. Mater. 1999, 11, 579. 3. M. Klotz, P.-A. Albouy, et al. Chem. Mater. 2000, 12, 1721. 4. D. Grosso et al. Adv.Funct. Mater., 2004, 14, 309. 5. J.F. Bardeau et al, Thin Solid Films, 2006, 495, 191. 6. P.C. Angelomé et al. J. Phys. Chem C, 2007, 111, 10886.