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项目的支持下，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拉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非常有用。虽然是一种非常有用的技术，但大多数分子的拉曼散射截面非常小，这通常限制了它的潜在用途。本研究项目研究的表面增强拉曼散射（SERS）和石墨烯增强拉曼散射（GERS）技术可用于提高小信号强度，从而使拉曼光谱相关应用更加实用。就更广泛的影响而言，克罗宁博士为洛杉矶的高中化学教师开设了讲习班。他利用南加州大学与其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）来增加弱势学校（即洛杉矶市中心的学校）的出勤率，这些学校服务于代表性不足的少数群体。研讨会的内容被重新制定，以使未被充分代表的学生接触到结果，更重要的是，研究的兴奋。面向本科生的研究项目，使他们了解基础科学研究，增强他们从事理工科职业的信心。南加州大学的纳米科学和纳米技术新课程开发了一个专门用于SERS的新模块，他们的研究成果在课堂上讨论并整合到课程中。詹森教授使用nanoHub.org网站与实验室以外的科学家分享他们的计算工具。在这次合作中，Cronin和Jensen教授研究了两种基于表面的光谱技术：表面增强拉曼散射（SERS）和石墨烯增强拉曼散射（GERS）中观察到的强光谱响应背后的机制。他们使用实验和计算工具仔细分离由化学增强（CE）引起的增强拉曼信号和由电磁增强（EM）引起的信号，以了解CE机制。具体来说，南加州大学的Cronin教授小组在各种SERS底物上对单分子进行拉曼光谱分析，这可以与PSU的Jensen小组进行的理论计算进行直接比较。在不同的电化学条件下收集拉曼光谱，以探索分子-金属能级排列的作用，并将振动模式特异性化学增强与均匀化学增强解耦。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，以促进对化学增强机制的更好理解。两个组的学生都有跨学科的培训机会。这两个组织都积极地向当地的高中教师和公众开展宣传活动。

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.