Large-pore three-dimensional (3D) mesoporous silicas are among the most interesting mesoporous materials discovered in recent years, and they have attracted much attention for potential applications requiring easily accessible, uniform, large pores. Examples of these are SBA-15 (p6mm) and SBA-16 (Im3 ¯m), which have cylindrical-and cage-type structures, respectively. It has been reported that hexagonally ordered large-pore mesoporous SBA-15 silica made by using a block copolymer contains complementary pores, while such pores were not found in MCM-41 with the same 2D hexagonal p6mm symmetry. [1] These complementary pores are arranged in a disordered way between the hexagonally ordered largepore channels.
Recently, large-pore mesoporous silicas with a cubic Ia3 ¯d structure were synthesized by using triblock copolymers as structure-directing agent under various synthesis conditions. [2] The mesoporous silica with a bicontinuous cubic structure of Ia3 ¯d symmetry is composed of an enantiomeric pair of 3D mesoporous networks that are interwoven, as observed in the MCM-48 structure.
The structures of these highly ordered mesoporous materials can hardly be determined from powder XRD patterns alone, because the few reflections that are observed at low scattering angles are especially broad and overlap. Electron microscopy is the main tool for characterization of such structures. The advantage over XRD is the stronger interaction of electrons with matter, which enables us to obtain structural information from a single crystal with only a few hundred unit cells. In electron crystallography (EC) the phases and amplitudes of the structure factors are obtained by Fourier transformation of high-resolution TEM (HRTEM)