Development of Novel-Scheme Tip-Enhanced Raman Spectroscopy and Its Application in Realistic Conditions -- Photochemistry of MoS2

扫描探针显微镜方法提供了物体表面的化学地图，有望揭示有助于提高化学反应效率和开发更快的电子和光学设备的信息。有一天，扫描探针显微镜可能会在各种环境中产生单个分子的化学图像，但由于与有效和简单地将探针元件集成到显微镜系统中相关的限制，这种可视化如此小对象的潜力受到了阻碍。在化学测量和成像计划的支持和化学系高分子、超分子和纳米化学计划的部分共同资助下，贝勒大学的张振荣教授和Howard Lee教授正在开发尖端增强拉曼光谱技术，该技术允许在其原始环境中对单个纳米尺寸的物体进行成像，这是通过复杂的微制造方法制造的新颖、集成的光纤探头尖端的结果。这种建立化学成像系统的新方法大大简化了显微镜操作，并产生了一种可视化微量样品的方法。贝勒团队很容易研究气体和液体环境中催化剂表面的化学反应。由于新的纳米级化学成像工具的实用性和可及性，这项研究可能会影响材料、生物医学和光电子科学的研究。张教授和李教授正在为本科生和技术学院的学生提供光学和扫描探针显微镜方面的新的学习和研究机会。这样的学生技能组合对学生未来的职业生涯很有价值。贝勒团队还通过在梅伯恩博物馆频繁的动手光学和光谱学活动，向韦科社区提供广泛的公共教育和外展。该项目开发了一种用户友好的、尖端增强的拉曼光谱纳米级化学成像系统，该系统基于无光学对准设计，即集成的等离子体光纤尖端组件。光纤尖端组件可以很容易地集成到现有的扫描探针显微镜设计中。这种独特的方法提供了一种简单的路径，可以独立地将激发光传递到样品和从样品收集光，从而提供高的光耦合效率和几乎不存在的远场背景干扰。因此，样品信号是高度敏感的，并提供接近单分子的检测下限。等离子体纳米结构光纤融合了等离子体激元和光纤光学领域，从而使尖端增强型拉曼光谱成像应用于多种气体和液体环境。这项提议的具体目标是展示使用光纤尖端增强拉曼光谱成像的纳米级映射，并在可控的环境压力环境中研究纳米级的硫化钼(MoS_2)的光化学。该团队还试图通过使用场可调等离子体材料在液体环境中展示光纤尖端增强拉曼光谱成像。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Scanning probe microscopy methods that provide chemical maps of the surface of objects hold promise for revealing information that is useful for making chemical reactions more efficient and developing faster electronic and optical devices. Scanning probe microscopes may one day yield chemical images of individual molecules in a variety of environments, but this potential to visualize such small objects has been stymied due to limitations associated with effectively and simply integrating the probe element into the microscope system. With support from the Chemical Measurement and Imaging Program and partial co-funding from the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professors Zhenrong Zhang and Howard Lee at Baylor University are developing tip-enhanced Raman spectroscopy techniques that allow for imaging of individual nanometer-sized objects in their native environments, as a result of novel, integrated fiber optic probe tips made by sophisticated microfabrication methods. This new approach to building chemical imaging systems significantly simplifies microscope operation and yields a method for visualizing tiny amounts of sample. The Baylor team readily investigates chemical reactions on catalyst surfaces in gas and liquid environments. Due to the practical and accessible nature of the new nanoscale chemical imaging tool, the research may impact research in materials, biomedical, and optoelectronic sciences. Professors Zhang and Lee are providing undergraduate and technical college students new learning and research opportunities in optics and scanning probe microscopy. Such student skill sets are valuable for the students' future careers. The Baylor team is also providing broad, public education and outreach to the Waco community through frequent hands-on optics and spectroscopy events at the Mayborn Museum. This project develops a user-friendly, tip-enhanced, Raman spectroscopy nanoscale chemical imaging system that is based on an optical alignment-free design, namely, an integrated plasmonic fiber-tip assembly. The fiber-tip assembly can be easily integrated into existing scanning probe microscope designs. This unique approach provides a simple path for independent delivery of excitation light to and collection of light from a sample, which offers high light coupling efficiency and virtually nonexistent far-field background interference. As a result, sample signals are highly sensitive and provide detection limits approaching that of single molecules. The plasmonic nanostructured optical fibers merge the fields of plasmonics and fiber optics, thereby enabling tip-enhanced Raman spectroscopy imaging applications in numerous gaseous and liquid environments. The specific objectives of this proposal are to demonstrate nanoscale mapping using fiber-tip-enhanced Raman spectroscopy imaging and study the photochemistry of molybdenum sulfide (MoS2) at the nanometer scale in a controlled ambient pressure environment. The team also seeks to demonstrate fiber-tip-enhanced Raman spectroscopy imaging in a liquid environment via the use of field-tunable plasmonic materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.