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

热线化学气相沉积(HWCVD)技术包括源气体的催化解离，在加热的金属丝上形成自由基，然后在气相中发生自由基-自由基和自由基-分子反应，生成与衬底反应的薄膜生长前体，从而形成薄膜。这些气相生长前驱体对薄膜的生长速度和性能有很大的影响。工业上已经做出了许多努力，以寻找最终产品的最佳和所需性能的黄金配方，最常见的是反复试验的方法。我们采用了一种独特的方法，试图了解使用HWCVD形成薄膜的化学和物理过程。为此，技术要求高的激光电离质谱学(LIMS)技术将被用作强有力的诊断工具来鉴定气相薄膜生长前体，并研究在不同源气体系统的氮化硅(SiNx)和碳氮化物(SiCyNz)薄膜的HWCVD过程中控制这些前体物种产生的化学动力学。这项基础化学方面的工作将有助于开发新的、环境友好的前驱体和合理的改进方法，以找到用于光电子和微电子工业应用的SiNx/SiCyNz薄膜的HWCVD的最佳配方。*我们还旨在利用强大的LIMS诊断工具，从根本上了解在CVD生长硅纳米线(SiNW)中导致硅原子形成的化学反应。这可能有助于填补当前SiNW的CVD增长模型中的一些空白。在SiNW的广泛应用中，我们重点介绍了它们作为锂离子电池(Lib)负极材料的应用。由于其最高的理论充电容量，硅是最有前途的锂离子电池正极材料之一。为了解决用硅作为LiB阳极的关键挑战，即由于Li的插入和提取而导致的大体积膨胀导致的容量衰减，我们提出了在CVD生长中使用有组织的金属纳米颗粒阵列(MNAs)来制备预定间距和尺寸的有序SiNW阵列。MNAs的可控形成将通过脉冲激光诱导去湿(PLiD)的新技术来实现，该技术是通过电化学方法在预图案化的衬底上制备金属薄膜。开发的协议可以为昂贵的基于光刻的方法提供一种替代方法。最后，我们将探索所开发的PLiD方法来形成铂基双金属MNAs作为燃料电池反应的电催化剂，以限制昂贵的铂的用量，并获得具有更高选择性、活性和稳定性的新型催化剂。*总的来说，该研究将促进我们对两种CVD过程--SiNx/SiCyNz薄膜的HWCVD和SiNWs的CVD生长的了解。这也将有助于锂离子电池负极材料和燃料电池催化剂的发展。**

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. **