Gold Films by Atomic Layer Deposition: Precursor Design, Synthesis, Evaluation and Optimization in Deposition

金薄膜在薄膜领域引起了极大的兴趣。金薄膜的应用范围从传感器界面(由于金的化学惰性和增强的表面等离子激元)到超材料(金在可见光波长的负渗透性)。金通常是通过溅射或蒸发制成薄膜的，但这些技术遇到了视线沉积问题：阴影屏蔽和无法控制纳米厚度的沉积速度。*化学气相沉积(CVD)和原子层沉积(ALD)是我所在团队十年来研究的主要主题。我们已经成功地设计了用于沉积氧化物(铝、镓和铟)以及金属(特别是铜)的配体系统。我的团队在第11族化合物的合成及其热分解途径方面的经验使我们有机会了解类似化合物的化学吸附和分解的机理。我们不断开发的配体目录使我们有机会探索一些新的金前体及其热化学和表面化学，并对现有的金化合物进行研究，这些化合物是为气相沉积以外的目的而开发的。例如，催化化学富含Au(I)卡宾络合物，类似于我们已知的金前体的配方。*一个研究项目将对以前合成的和已知的Au(I)化合物进行测试。例如，我们的研究定义了一类N-杂环卡宾(NHC)化合物：R2-NHC-M-N(SiMe3)2，其中“R”基团与NHC的氮相连。研究发现，化合物iPr2-NHC-Au-N(SiMe3)2在Ar气氛中的氢等离子体中沉积金膜，其生长速率为每周0.10ó。这种沉积的问题是，前驱体在110℃时只为沉积过程提供足够的蒸气压力，但在140℃时开始进行热分解(分解为金金属)，这使得CVD前驱体相当好，但作为ALD前驱体，前驱体的“热窗口”需要改进。由于我们的金沉积研究的局限性，我们无法系统地研究改变这个R基团对热稳定性和沉积条件的影响。这笔赠款将使我们能够进行这样的研究。*类似地，我们以前合成了一系列亚胺基吡咯烷酸盐(IP)配体(R-IP，其中R是任何丙基或丁基)，通过阻止两种已知的热分解途径来限制热分解：碳二亚胺消除和伯氢消除。这在扩展Al(III)和Cu(I)化合物的热稳定性方面已被证明是非常成功的。为了测试Au(I)的热稳定性和沉积条件，有必要制备这一系列Au(I)化合物。该项目还将研究加入配位配体(产生单体化合物)或允许IP桥联以产生更高阶低聚物的效果。*最终，研究计划将有更大的范围，设想Au(I)和Au(III)前体。对于阴离子配体，重点将放在氮基基团上，如酰胺、酰胺、胍酸盐和亚氨基吡咯烷酸酯。金的配位范围(2个用于Au(I)，4个用于Au(III))也将需要包括配位配体。这里，重点将放在膦、NHCs和无环氨基卡宾上。该计划将包括这些前体化合物的合成和热测试，以及沉积工艺和薄膜表征的开发。这项研究计划的目标将是实现在高度复杂的几何结构上稳定和可重复地沉积纳米厚的金膜。

Gold films are of significant interest in the thin film community. Applications for gold thin films range from sensor interfaces (due to gold's chemical inertness and enhanced surface plasmon) to metamaterials (gold's negative permeability at visible wavelengths). Gold is typically produced as a thin film by sputtering or evaporation, but these techniques suffer line-of-sight deposition issues: shadow masking and lack of control over the deposition rate at nanometre thicknesses.* Chemical vapour deposition (CVD) and atomic layer deposition (ALD) have been main themes of research in my group for a decade. We have had great success designing ligand systems for the deposition of oxides (aluminium, gallium, and indium) as well as metals (particularly copper). My group's experience with synthesis of group 11 compounds and their thermolysis pathways gives us the occasion to understand the mechanistic chemisorption and decomposition of similar compounds. Our ever-developing catalogue of ligands gives us an opportunity to explore some novel gold precursors and their thermal and surface chemistries, as well as to undertake the study of existing gold compounds that have been developed for purposes other than vapour deposition. For example, catalysis chemistry is rich with Au(I) carbene complexes, similar to the formulation our known gold precursor.* One research project will undertake the testing of previously-synthesized and known compounds of Au(I). As an example, our research has defined a class of N-heterocyclic carbene (NHC) compounds: R2-NHC-M-N(SiMe3)2, where the "R" group is bound to the nitrogen of the NHC. The compound iPr2-NHC-Au-N(SiMe3)2 was found to deposit a gold film with a growth rate of 0.10 Å per cycle when subjected to a plasma of hydrogen in argon. The problem with this deposition is that the precursor only provides sufficient vapour pressure for the deposition process at 110°C, but starts to undergo thermal decomposition (to gold metal) at 140°C. This makes a reasonably good CVD precursor, but the precursor's "thermal window" needs to be improved as an ALD precursor. Limitations to our gold deposition research have prevented a systematic study of the effect of altering this R-group on thermal stability and deposition conditions. This grant will allow us to undertake such a study.* Similarly, we have previously synthesized a series of iminopyrrolidinate (IP) ligands (R-IP, where R is any propyl or butyl group) that limit the thermal decomposition by preventing two known thermal decomposition pathways: carbodiimide elimination and ß-hydrogen elimination. This has proven to be very successful at extending the thermal stability of both Al(III) and Cu(I) compounds. It is necessary to make this series of compounds with Au(I) to test both thermal stability and deposition conditions. This project will also study the effect of incorporating a coordinating ligand (producing a monomeric compound) or allowing the IP to bridge to produce higher-order oligomers. * Ultimately, the research program will have a larger scope, envisioning both Au(I) and Au(III) precursors. For anionic ligands, focus will be on nitrogen-based groups such as amides, amidinates, guanidinates, and iminopyrrolidinates. The coordination sphere of gold (2 for Au(I) and 4 for Au(III)) will also necessitate the inclusion of coordinating ligands. Here, the focus will be on phosphines, NHCs, and acyclic aminocarbenes. The program will include the synthesis and thermal testing of these precursor compounds, as well as development of deposition processes and film characterization. The goal of this research program will be to enable the robust and repeatable deposition of nanometre-thick films of gold over highly complex geometries.