Collaborative Research: A Mechanistic Study of Chemical Enhancement in Surface Enhanced Raman Spectroscopy and Graphene Enhanced Raman Spectroscopy

在化学系化学测量和成像计划的支持下，南加州大学的克罗宁教授和宾夕法尼亚州立大学的詹森教授研究了拉曼光谱作为测量特定键延伸能量的强大工具的使用。该技术为化学鉴定提供了唯一的指纹图谱。因此，拉曼光谱在化学、环境和威胁检测监测中的许多应用中都非常有用。虽然这是一项非常有用的技术，但大多数分子的拉曼散射截面都非常小，这通常限制了它的潜在用途。本研究项目中研究的表面增强拉曼散射(SERS)和石墨烯增强拉曼散射(GERS)技术可以用来提高小信号强度，从而使拉曼光谱的相关应用更加实用。在更广泛的影响方面，克罗宁博士为洛杉矶的高中化学教师开设了研讨会。他利用南加州大学与邻近高中之间的现有关系(例如，南加州大学的好邻居运动、联合教育项目和服务学习计划)来增加贫困学校(即洛杉矶市中心的学校)为代表不足的少数族裔群体提供服务的出勤率。研讨会的内容进行了重新制定，使未被充分代表的学生接触到结果，更重要的是，让他们接触到研究的兴奋。本科生的研究项目让他们了解基础科学研究，并给他们在科学和工程领域追求职业生涯的信心。为南加州大学纳米科学和纳米技术的一门新课程开发了一个专门讨论表面增强拉曼光谱的新模块，并在课堂上讨论了他们的研究成果，并将其纳入课程。詹森教授使用一个名为NanHub.org的网站，与他实验室之外的科学家分享他们的计算工具。在这次合作中，Cronin教授和Jensen教授研究了在两种基于表面的光谱技术中观察到的强烈光谱响应背后的机制：表面增强拉曼散射(SERS)和石墨烯增强拉曼散射(GERS)。他们使用实验和计算工具仔细地将化学增强(CE)引起的增强拉曼信号与电磁增强(EM)引起的信号分离，以了解化学增强(CE)的机制。具体地说，南加州大学的Cronin教授的团队在各种SERS衬底上对单分子进行了拉曼光谱分析，这使得能够直接与PSU的Jensen团队进行的理论计算进行比较。在不同的电化学条件下采集了拉曼光谱，以探索分子-金属能级排列的作用，并将振动模特定的化学增强与均匀的化学增强解耦。Jensen教授的第一性原理计算为解释SERS和GERS光谱中的化学增强提供了详细的理论框架，从而有助于更好地理解化学增强机制。这两个组的学生都体验到了跨学科的培训机会。这两个团体都积极参与了面向当地高中教师和普通公众的外展活动。

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Cronin at University of Southern California and Professor Jensen at Pennsylvania State University investigate the use of Raman spectroscopy as a powerful tool that measures the energies of specific bond stretches. This technique provide the unique fingerprint for chemical identification. As such, Raman spectroscopy is extremely useful for a number of applications in chemical, environmental and threat detection monitoring. While a highly useful technique, the Raman scattering cross-section of most molecules is extremely small, and this generally limits its potential uses. Surface Enhanced Raman Scattering (SERS) and Graphene Enhanced Raman Scattering (GERS), the techniques investigated in this research project, can be used to improve the small signal intensities, thus making Raman spectroscopy-related applications more practical. In terms of broader impacts Dr. Cronin creates workshops for Los Angeles high school chemistry teachers. He leverages existing relationships between USC and its neighboring high schools (e.g., USC's Good Neighbors Campaign, Joint Education Project, and the Service Learning Program) to increase the attendance from disadvantaged schools (i.e., central Los Angeles inner city schools) serving underrepresented minority groups. The content of the workshop is reformulated to expose underrepresented students to the results and, more importantly, the excitement of research. Research projects for undergraduate students introduce them to fundamental scientific research and give them confidence to pursue careers in science and engineering. A new module devoted to SERS is developed for a new course at USC on nanoscience and nanotechnology, and their research accomplishments are discussed in class and integrated into the curriculum. Professor Jansen uses a website, nanoHub.org, to share their computational tools with scientists outside of his labs. In this collaboration, Professors Cronin and Jensen investigate the mechanism behind the strong spectroscopic responses observed in two surface-based spectroscopic techniques: Surface Enhanced Raman Scattering (SERS) and Graphene Enhanced Raman Scattering (GERS). They use both experimental and computational tools to carefully isolate the enhanced Raman signals caused by Chemical Enhancement (CE) from those signals caused by ElectroMagnetic Enhancement (EM) in order to understand the CE mechanism. Specifically, Professor Cronin's group at USC performs Raman spectroscopy of single molecules on various SERS substrates, which enables a direct comparison with the theoretical calculations preformed at the Jensen's group at PSU. The Raman spectra are collected under various electrochemical conditions in order to explore the role of the molecule-metal energy level alignment and decouple the vibrational-mode-specific chemical enhancement from the uniform chemical enhancement. Professor Jensen's first principles calculations provide a detailed theoretical framework for interpreting chemical enhancement in SERS and GERS spectra to facilitate a better understanding of the chemical enhancement mechanism. Students in both groups experience the interdisciplinary training opportunities. Both groups' are actively engaged in outreach activities to local high school teachers and general public.