CAREER: Deciphering 2-Dimensional, Crystal-Mediated, Surface-Enhanced Raman Scattering for Quantitative Analysis

分子可以通过它们吸收或发射不同波长的光来检测和识别。一种称为拉曼光谱的技术利用分子以其独特频率振动时散射的光来揭示分子结构的信息。40多年前，人们发现当分子粘附（吸附）在粗糙的金属表面时，拉曼散射信号可以显著增加（超过一百万倍）。这一发现改进了化学检测和分析，但是信号改善并不总是从一个表面到另一个表面可重现，并且增强的确切原因仍在激烈的争论中。在该项目中，由化学部的化学结构，动力学和机制-A（CSDM-A）计划资助，波士顿大学的Xi Ling教授正在研究拉曼光谱在定义明确的二维（2D）晶体表面上的信号增强（例如，硫化锡（SnS 2）和硒化钨（WSe 2））。这些晶体的结构和性质比粗糙的金属表面的结构和性质更好地定义和理解，因此，凌教授和她的学生可能会揭示拉曼信号在表面上增强的方式和原因。 预计这项研究项目将产生新技术，特别是在化学分析领域，在这一领域，检测一种物质的几个甚至一个分子可能成为常规。参与该项目的学生正在获得光谱学（光物质相互作用）以及分子和材料设计方面的高级培训，这两个领域都是科学和技术领域越来越受欢迎的专业领域。 凌教授将通过与波士顿大学的学习资源网络（LERNet）及其推广计划合作，为学生开发和实施激光光谱学经验。这一推广方案鼓励年轻妇女和高中生进入科学和工程领域。林博士还将通过开发交互式视频课程模块来增强高中教师和学生的开源教育资源。表面增强拉曼光谱（Sers）的机理还不完全清楚，特别是化学机理（CM），它与电磁（EM）机理相比仍然相对神秘。该项目的科学目标是更深入地了解化学机理，并探索二维晶体在克服Sers在实际应用中重现性的关键问题方面的潜力。从定义明确的样品（二维基板和吸附的分析物）的定量Sers数据用于测试在文献中的CM理论。Ling小组正在采用多种分析方法，如波长扫描拉曼测量，微吸收光谱，以及严格的群论分析，以定量的方式了解化学增强的起源。此外，为了发展革命性的SERS传感技术，正在研究2D晶体/金属系统，以了解2D晶体如何影响金属纳米结构的等离子体频率和电磁场分布，并证明该系统在微传感中的高灵敏度，选择性和再现性。总的来说，这些研究提供了对Sers中有争议的CM的更深入的理解，并指导了更好的Sers平台的创新设计。这项工作的更广泛的技术影响包括Sers中CM的新知识以及化学和生物传感新技术的发展。 该教育计划提高了STEM学生在科学和技术领域的质量、保留率和多样性。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Molecules can be detected and identified by how they absorb or emit light of different wavelengths. A technique called Raman spectroscopy reveals information about molecular structure using the light scattered by molecules as they vibrate at their unique frequencies. Over 40 years ago, it was discovered that the Raman scattering signals could be increased dramatically (more than a million times) when molecules were stuck to (adsorbed on) a roughened metal surface. That discovery improved chemical detection and analysis, however the signal improvements are not always reproducible from one surface to another and the precise reason for the enhancement is still under vigorous debate. In this project, funded by the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program of the Chemistry Division, Professor Xi Ling of Boston University is investigating signal enhancements in Raman spectroscopy on the surfaces of well-defined, two-dimensional (2D) crystals (e.g., tin sulfide (SnS2) and tungsten selenide (WSe2)). The structure and properties of these crystals are better defined and understood than those of roughened metal surfaces and thus, Professor Ling and her students may uncover how and why Raman signal are enhanced on surfaces. New technologies are expected to emerge from this research project, especially in the field of chemical analysis, where it may become routine to detect just a few or even a single molecule of a substance. The students engaged in this project are gaining advanced training in spectroscopy (light-matter interactions) and molecular and materials design, both of which are increasingly sought-after areas of expertise in the science and technology sector. Professor Ling will develop and implement a laser spectroscopy experience for students by collaborating with Boston University's Learning Resource Network (LERNet) and its outreach programs. This outreach program encourages young women and high schools students to enter science and engineering fields. Dr. Lin will also enhance open source education resources for high school teachers and students by developing interactive video lesson modules. The mechanisms of surface-enhanced Raman spectroscopy (SERS) are not fully understood, especially the chemical mechanism (CM), which remains relatively mysterious compared to the electromagnetic (EM) mechanism. The scientific objectives of this project are to gain a deeper understanding of chemical mechanism and explore the potential of 2D crystals to overcoming the key problem of reproducibility of SERS in practical applications. Quantitative SERS data from well-defined samples (both 2D substrate and adsorbed analytes) serve to test the CM theory in the literature. The Ling group is employing multiple analytical approaches, such as wavelength-scanned Raman measurements, micro-absorption spectroscopy, as well as rigorous group theory analysis to understand the origin of the chemical enhancement in a quantitative manner. Furthermore, toward the development of revolutionary SERS-sensing techniques, 2D crystal/metal systems are being investigated to understand how the 2D crystals influence the plasmon frequency and electromagnetic field distribution of metal nanostructures and demonstrate the high sensitivity, selectivity and reproducibility of the system in micro-sensing. Collectively, these investigations are providing a deeper understanding of the controversial CM in SERS and guide an innovative design of a better SERS platform. The broader technical impacts of this work include new knowledge of CM in SERS and the seeding of development of new technique for chemical and bio-sensing. The education plan improves the quality, retention, and diversity of STEM students in science and technology.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.