Gas-assisted liquid phase deposition of crystalline ceria films

Abstract

A modified liquid phase deposition process named “gas-assisted liquid phase deposition (G-LPD)” was developed to fabricate oxide films at a synthesis temperature below 100 °C and atmospheric pressure using readily available metal salts such as nitrates and chlorides. One of the major points of this process was that a moderately low initial pH of the aqueous metal salt solution was required. In addition, a slight increase of the hydroxide ion concentration was required to facilitate oxide deposition through an equilibrium reaction between metal ions and oxides. Gaseous ammonia generated from aqueous hexamethylenetetramine solution slightly increased the hydroxide ion concentration of the metal salt solution. This process required only one sealed vessel and two beakers, one of which contained an aqueous solution of metal salts and the other hexamethylenetetramine solution. The slow rate of the equilibrium reaction induced heterogeneous nucleation at solid–liquid interfaces, resulting in film formation. Crystalline ceria films were fabricated at 60 °C by keeping the pH almost constant in the range from 4.6 to 5.2. The thickness of ceria films fabricated on polyether sulfone substrates from aqueous 0.05 M cerium nitrate solutions after 3, 7, and 14 days were about 120, 210, and 380 nm, respectively.