Highly oriented 3D-hexagonal silica thin films produced with cetyltrimethylammonium bromide

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 diff erent 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 theta-2 theta scan mode, a s well as in transmission mode using two different scattering geometries. T he films exhibit large and homogeneous domains organised in a 3D-hexagonal (P6(3)/mmc) structure with the c axis normal to the surface throughout thei r whole thickness. Numerical analysis of the TEM pictures confirms the spac e 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 w hich show such extended and highly mono-oriented 3D-hexagonal (P6(3)/mmc) d omains. The film thickness, porosity and refractive index were evaluated by ellipsometry for the various treated films.