Vapor-Phase Synthesis of Mesoporous SiO2−P2O5Thin Films.

Mesoporous SiO2−P2O5films were synthesized from the vapor phase onto a silicon substrate. First, a precursor solution of cetyltrimethylammonium bromide (C16TAB), H3PO4, ethanol, and water was deposited on a silicon substrate by a spin-coating method. Then, the C16TAB−H3PO4composite film was treated with tetraethoxysilane (TEOS) vapor at 90−180 °C for 2.5 h. The H3PO4−C16TAB composite formed a hexagonal structure on the silicon substrate before vapor treatment. The TEOS molecules penetrated into the film without a phase transition. The periodic mesostructure of the SiO2−P2O5films was retained after calcination. The calcined films showed a high proton conductivity of about 0.55 S/cm at room temperature. The molar ratio of P/Si in the SiO2−P2O5film was as high as 0.43, a level that was not attained by a premixing sol−gel method. The high phosphate group content and the ordered periodic mesostructure contributed to the high proton conductivity. [ABSTRACT FROM AUTHOR]