treating said coated substrate to harden said solution into {HEAD ~ 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 compounds consisting of tetramethylammonium formate, tetramethylammonium nitrate, tetramethylammonium oxalate, tetramethylammonium acetate, tetramethylammonium hydroxide and other salt exhibiting complete decomposition to volatile species upon heating to {TAIL ~ a temperature} between 300 and 450° C 
treating said coated substrate to harden said solution into { HEAD ~ 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 compounds consisting of tetramethylammonium formate , tetramethylammonium nitrate , tetramethylammonium oxalate , tetramethylammonium acetate , tetramethylammonium hydroxide and other salt exhibiting complete decomposition to volatile species upon heating to { TAIL ~ a temperature } between 300 and 450 ° C
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