Hydrophobic mesostructured organosilica-based thin films with tunable mesopore ordering

Hydrophobic mesostructured organosilica-based thin films with tunable mesoporosity offer promising opportunities for ultra low k applications. They are presently prepared by spin-on solutions and evaporation-induced self-assembly method (EISA) using polystyrene-b-polyethylene oxide block copolymers as structure-directing agents and methyltriethoxysilane (MTES) as organosilica precursor. With PS(1600)-b-PEO(1800) (between brackets is the molecular weights for blocks), different types of ordered mesostructures can be achieved by controlling the PS-b-PEO/MTES weight ratio, i.e. with Fm3m symmetry (evidenced for the first time in a organosilica film) and also with Im3m and P6mm space groups. Mesostructural ordering is characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and atomic force microscopy (AFM). The thin film porosity is analyzed using ellipsometric porosimetry (EP). Porogen removal and crosslinking of the organosilica network are followed by Fourier transform infrared spectroscopy (FTIR) and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR). The effect of the molecular weight and the hydrophilic lipophilic balance (HLB) of the used block copolymers on the mesostructure ordering is finally investigated using different types of polystyrene-b-polyethylene oxide block copolymers.

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► Mesoporous organosilica thin films exhibit FCC, BCC or 2D Hexagonal mesostructures.
► Negligible perturbation of the organosilica network crosslinking with the copolymers.
► Swelling and deflation of the mesostructure during calcination.
► Ordered mesostructures obtained for intermediate copolymer and HLB >10.