Platinum/silica Thin Films by Chemical Vapor Deposition

Composite thin films consisting of platinum and silica (SiO)2 have been fabricated by chemical vapor deposition (CVD). These films were studied for possible future use in enhancing the selectivity of sensors for the chemical warfare agent sarin. Chemical vapor deposition is a thin film growth technique in which precursor molecules are carried into a reactor and decomposed, often at high temperature, to produce a thin solid film. A new cold wall CVD reactor was built for this work. The platinum precursor used in this work was platinum acetylacetonate [Pt(acac)2] and the silica precursor was tetraethoxysilane (TEOS). It was found that by simultaneously decomposing the two together, the decomposition temperature of TEOS was lowered from an expected 973K to as low as 593K. In addition, the composition of the films was found to be self limiting at one silicon atom per platinum atom over a wide range of deposition conditions and growth rates. X-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) were used to characterize the films. An in situ fourier transform infrared spectroscopy (FTIR) study was undertaken to gain further insight into this phenomena. The equipment had to be significantly modified to combine the CVD system with the spectrometer. Striking spectral evidence for the decomposition of TEOS at low temperatures is presented. A reaction is proposed based on the results of this work and the work of others. This work has implications for the use of catalysis in CVD to reduce the deposition temperature. A lower deposition temperature is desirable because a wider range of substrates can be used and it results in less film stress upon cooling. There are also implications for the production of composite films by CVD and the use of in situ FTIR spectroscopy for studying CVD systems.