Advanced Materials: TechConnect Briefs 2015Advanced Materials TechConnect Briefs 2015

Nanoparticle Synthesis & Applications Chapter 5

Insulator oxide film formation with acid catalyzed hydrolysis of alkoxides in supercritical fluid carbon dioxide

J.S. Wang, C.M. Wai, G.J. Brown, S.D. Apt, A.M. Campo, G.R. Landis
Air Force Research Laboratory, United States

pp. 286 - 289

Keywords: TEOS, SiO2, film, supercritical CO2

Insulator oxide films can be produced by hydrolysis of metal alkoxide precursors in the presence of an acid catalyst in supercritical fluid carbon dioxide(sc-CO2). In this study, a new process has been developed to cover PbS or Au nanoparticle arrays with SiO2. Using tetraethylorthosilicate (TEOS) as a precursor and acetic acid as a catalyst, thin SiO2 films can be formed on surfaces of different substrates in sc-CO2 at pressure 170 atm and temperatures above 50 oC. The chemical equation of the SiO2 film formation can be expressed as Si(OCH2CH3)4 + 2H2O --> SiO2 + 4CH3CH2OH. The deposition reaction actually started at room temperature but produces good quality films at high temperatures. In the absence of acetic acid, the chemical reaction proceeds very slowly.The acid catalytic reaction probably involves proton coordination to the oxygen atoms of TEOS molecules that facilitates the hydrolysis. Water involved in the reaction for hydrolysis is generated by the esterification process which can be written as CH3COOH + C2H5OH = CH3COOC2H5 + H2O. Cross sections of Au nanoparticle and SiO2 films were measured by SEM. ATR-FTIR spectroscopic and EDS data of PbS and Au nanoparticle arrays covered with SiO2 films are also given.