Development of Fabrication and Synthetic Protocols to Produce Substrate-Immobilized Plasmonic Nanomaterials

This dissertation serves to advance the fabrication techniques and synthesis protocols of plasmonic nanomaterials directly on substrate surfaces. The work presented here aimed, (i) to add novel pathways for obtaining plasmonic nanostructures with tunable properties that use substrate-immobilized seeds as a starting point and (ii) to provide further understanding of the nanoplate growth mechanism of seed-mediated approaches. The beginning segment aims to provide the required context for understanding what plasmonic nanomaterials are and express the importance of researching such structures and their properties. Plasmonic nanostructures composed of gold and silver are mentioned specifically due to the significant attention they have garnered within the field. A subclassification of plasmonic nanostructures, referred to as nanogap nanostructures, are then introduced and their desirable properties are described. The difficulties associated with their fabrication from multiple approaches are brought forth along with a novel pathway to overcome said limitations that are illustrated. The first of two syntheses is subsequently presented, defining a three-reagent liquid-phase gold nanotriangle synthesis with substantially higher yield than previously reported. The resulting structures are epitaxially aligned with atomically flat surfaces and sharp vertices. Their optical properties and topography are investigated through extensive characterization. The following section introduces an adapted silver nanoplate synthesis that greatly surpasses prior attempts to produce deterministically placed silver nanoplates on substrates. The prerequisites for plate formation are more thoroughly explained, and the importance of high-quality seeds is further emphasized. The penultimate chapter details an in-depth analysis of the growth mechanism that drives a gold hexagonal nanoplate synthesis by controlling light conditions through the use of a custom-made reflective chamber with interchangeable light emitting diodes. The results obtained through various illumination and reaction conditions support the existence of a never-before-seen growth mechanism. The final section summarizes the experimental data presented and reiterates the significance of the conclusions drawn.本论文旨在推进直接在衬底（substrate）表面制备等离子体纳米材料（plasmonic nanomaterials）的加工工艺与合成方案。本文所开展的研究工作具体达成两大目标：其一，开发以固定于衬底的晶种（seed）为起始位点的新型制备路径，以获得性能可调的等离子体纳米结构（plasmonic nanostructures）；其二，深化对晶种介导生长法（seed-mediated approaches）中纳米片生长机制的理解。开篇章节旨在为读者提供理解等离子体纳米材料的必要背景知识，并阐明研究此类结构及其性能的重要意义。由金、银构成的等离子体纳米结构因在该领域受到广泛关注而被重点提及。随后将介绍等离子体纳米材料的一个子类别——纳米间隙纳米结构（nanogap nanostructures），并阐述其优异性能。本文将阐述通过多种方法制备此类结构所面临的挑战，并介绍一种可克服上述局限的新型制备方案。随后将介绍两种合成方案中的第一种：一种基于三试剂液相体系的金纳米三角形（gold nanotriangle）合成法，其产率远高于此前已报道的同类方法。所制备得到的金纳米三角形具有原子级平整的表面与锐利的顶点，且呈外延取向排列。本文通过大量表征手段对其光学性能与表面形貌进行了研究。下一章节将介绍一种改进型银纳米片（silver nanoplate）合成法，该方法可在衬底上精准定位生长银纳米片，其性能远超此前的同类尝试。本章将更全面地阐释纳米片形成的先决条件，并进一步强调高质量晶种的重要性。倒数第二章详细阐述了一种生长机制的深度分析：该机制可通过定制反射腔（custom-made reflective chamber）搭配可更换发光二极管（light emitting diodes）调控光照条件，从而驱动金六方纳米片的合成。通过调控不同光照与反应条件得到的实验结果，证实了一种此前未被报道过的生长机制的存在。最后一章对本文呈现的实验数据进行了总结，并重申了所得结论的重要意义。