Tetraethoxysilane (TEOS) and polyethoxysiloxanes (PEOSs; prepared by the acid-catalyzed hydrolytic polycondensation of TEOS) were subjected to the sol-gel process in the presence of cetyltrimethylammonium bromide (CTAB), respectively. The PEOSs with M-w 700-26,000, as prepared by sol-gel coating of TEOS and PEOS under various conditions, were used. Uniform and crack-free thin films of thickness 276613 nm were prepared by spin-coating of a PEOS solution containing CTAB. When the coating films were sintered at 400 degrees C, the combustion of ethoxy groups and CTAB took place to provide porous silica thin films. The structure of the thin films was found to be dependent on the molecular weight of PEOS and the molar ratio of CTAB/Si: lamellar or hexagonal phase was observed for M-w less than 15,000 and for CTAB/Si molar ratios greater than 0.10. Honeycomb structures were observed for M-w less than 5000 and for CTAB/Si molar ratios of 0.15. The honeycomb structure was also observed by atomic force microscopy and transmission electron microscope. (c) 2006 Wiley Periodicals, Inc.