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Mesoporous silicas fabricated using organic surfactant molecules or block copolymers as structural directing agents has attracted much attention as catalysts and adsorbents using their large surface areas and uniform mesopores. Micropatterning of ordered mesoporous films has been considered as a key technology in order to apply them to sensors and electronic or optical devices. Considering such device applications, it is of primary importance to eliminate surfactants at low temperature because thermal treatment causes not only cracking or peeling due to substantial shrinkage, but also damages to substrate and device elements. Thus, an alternative method without thermal treatment has been required persistently. In order to satisfy this requirement, we have previously reported a novel calcination technique, namely, photocalcination, using an excimer lamp radiating vacuum ultraviolet light of 172 nm in wavelength. This method is advantageous compared with conventional thermal treatment, since it may be conducted at room temperature. However, it requires relatively long time for complete removal of surfactant molecules. In this study, we demonstrated rapid elimination of surfactant molecules at low temperature through electron beam irradiation. First, mesostructured film was spin-cast on Si substrates from a precursor solution prepared through the reaction of tetramethoxysilane in acidic aqueous solution (pH=2) of hexadecyltrimethylammonium chloride (C16TMACl). The mesostructured film was then annealed for several hours at 100 °C. Next, electron beam was irradiated on the film with a thickness of approximately 200 nm under various pressures at 10, 103 and 105 Pa. As confirmed by FT-IR, XRD and TEM, the well-ordered mesopores with an average pore diameter of 3.8 nm was formed. It took for only 5 min in order to completely remove C16TMACl molecules at 103 Pa without distorting its periodic mesostructures. This removal rate was found to be about 3 times faster than that demonstrated by the previously reported photocalcination. On the other hand, in the case of 105 Pa, the elimination of C16TMACl molecules did not proceed completely.
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