Chemical Vapor Deposition of Si-containing Thin Films and Si Nanostructures: From a molecular-level understanding to applications

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The technique of hot wire chemical vapor deposition (HWCVD) involves catalytic dissociation of source gases to form radicals on a heated metal wire and subsequent radical-radical and radical-molecule reactions in the gas phase to produce film growth precursors that react with the substrate, leading to thin film formation. These gas-phase growth precursors strongly affect the growth rate and properties of the deposited films. A lot of industrial efforts have been made to find the golden recipe for optimal and desired properties of final products, most often by trial-and-error methods. We have adopted a unique approach trying to understand the chemical and physical processes underpinning the thin film formation using HWCVD. For this, the technically demanding laser ionization mass spectrometric (LIMS) techniques will be employed as powerful diagnostic tools to identify the gas-phase film growth precursors and to study the chemical kinetics governing the production of these precursor species in the HWCVD processes of silicon nitride (SiNx) and carbonitride (SiCyNz) thin films with different source gas systems. This work on the underlying chemistry will help develop novel, environmentally benign precursors and rational improvement methods to find the best recipe in HWCVD of SiNx/SiCyNz films for industrial applications in optoelectronics and microelectronics.***We also aim at a fundamental understanding of the chemical reactions responsible for the formation of Si atoms in the CVD growth of Si nanowires (SiNWs) using the powerful LIMS diagnostic tools. This could help fill in some gaps in the current CVD growth models for SiNWs. Among a wide spectrum of applications of SiNWs, we focus on their use as anode materials in lithium ion batteries (LIB). Si is one of the most promising LIB anode materials due to its highest known theoretical charge capacity. To tackle the key challenge in using Si as LIB anode, which is the capacity fading due to the large volume expansion upon insertion and extraction of Li, we propose to fabricate an ordered array of SiNWs with pre-defined spacing and size by using organized metal nanoparticle arrays (MNAs) as catalysts in the CVD growth. The controlled formation of MNAs will be accomplished by the novel technique of pulsed laser-induced dewetting (PLiD) of metal films on pre-patterned substrates prepared by electrochemical methods. The developed protocol could provide an alternative method to the expensive lithography-based methods. Finally, the developed PLiD methods will be explored for the formation of Pt-based bimetallic MNAs as electrocatalysts for fuel cell reactions to limit the amount of expensive Pt and to obtain new catalysts with enhanced selectivity, activity and stability.***Overall, the proposed research will advance our current knowledge of the two CVD processes - HWCVD of SiNx/SiCyNz films and CVD growth of SiNWs. It will also contribute to the development of LIB anode materials and fuel cell catalysts. **