treating said coated substrate to harden said solution into a porous silicon oxide film, wherein said nonionic surfactant is first purified to remove alkali metal impurities; and wherein said ionic additive is a tetramethylammonium salt chosen from a group of {HEAD ~ compounds} consisting of tetramethylammonium formate, tetramethylammonium nitrate, tetramethylammonium oxalate, tetramethylammonium acetate, tetramethylammonium hydroxide and {TAIL ~ other salt} exhibiting complete decomposition to volatile species upon heating to a temperature between 300 and 450° C 
treating said coated substrate to harden said solution into a porous silicon oxide film , wherein said nonionic surfactant is first purified to remove alkali metal impurities ; and wherein said ionic additive is a tetramethylammonium salt chosen from a group of { HEAD ~ compounds } consisting of tetramethylammonium formate , tetramethylammonium nitrate , tetramethylammonium oxalate , tetramethylammonium acetate , tetramethylammonium hydroxide and { TAIL ~ other salt } exhibiting complete decomposition to volatile species upon heating to a temperature between 300 and 450 ° C
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