Metal oxide films can be produced by hydrolysis of metal alkoxide precursors in the presence of an acid catalyst in supercritical fluid carbon dioxide. In this study, a new process has been developed to encapsulate PbS films with SiO2. Tetraethylorthosilicate (TEOS) as a precursor and acetic acid as a catalyst are used to form SiO2 films on surfaces of different substrates. The SiO2 film formation may be expressed by the following equation:Si(OCH2CH3)4 + 2H2O acid� > SiO2 + 4CH3CH2OH (1)Without the acid catalyst and at room temperature, hydrolysis of TEOS is very slow. When acetic acid is used as the catalyst, a smooth silicon dioxide film with reasonable thickness can be formed in supercritical fluid CO2 at temperatures above 100 oC. The deposition reaction actually started at room temperature but produces good quality thick films at 100 oC. In the absence of acetic acid, only uneven and thin silicon dioxide films can be formed. The acid catalytic reaction probably involves proton coordination to the oxygen atoms of TEOS molecules that facilitates the hydrolysis. Water for hydrolysis is generated by the esterification process which can be written asH3C-COOH + C2H5OH = H3C-COOC2H5 + H2O (2)Preliminary spectroscopic data of lead sulfide (PbS) nanoparticle arrays covered with SiO2 films are given in this presentation.

Formation of insulator oxide films by acid catalyzed hydrolysis of metal alkoxides in supercritical fluid carbon dioxide

248th National Meeting (2014)

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