Nitrate ions as cathodic alkalization promoters for the electro-assisted deposition of sol–gel thin films

Nitrate was used as a promoter to prepare dodecyltrimethoxysilane thin films on aluminum substrates. With the addition of nitrate into silane sol–gel precursors, the electro-assisted formation of silane films was facilitated, as indicated by electrochemical impedance spectroscopy, scanning electron microscopy and secondary-ion mass spectroscopy, due to the promotion in cathodic alkalization. However, an extra-high concentration of nitrate would be harmful because of the salting-out effect in precursors and the soluble nitrate remaining in silane films.