Probing Molecular Dynamics Near Plasmonic Surfaces by Optical two-dimensional Coherent Spectroscopy

化学系的化学测量和成像计划与物理系的原子、分子和光学物理实验计划共同资助佛罗里达国际大学的李鹤斌和金河博士开发用于研究分子动力学的新型集成超快光谱和成像技术。在纳米尺度上探测分子和电子的超快化学行为的能力对于研究和理解材料至关重要，例如脱氧核糖核酸(DNA)分子、与光合作用有关的蛋白质、新型太阳能电池层和奇异的量子材料。先进的激光光谱学，如光学二维相干光谱学，在研究复杂体系中的化学行为方面表现出色，而空间分辨率通常限制在百万分之一米尺度。另一方面，扫描隧道显微镜(STM)为单分子研究提供纳米分辨率，而STM的测量仅限于毫秒级时间尺度。李鹤斌、金河博士和他们的研究团队将光学2DCS和基于扫描隧道显微镜的单分子技术相结合，以纳米分辨率、空间映射和飞秒时间分辨率获取表面的化学信息。这项新的成像技术使人们能够了解和改进众多的化学和材料系统。通过让学生参与积极的研究并与当地的科学教师建立联系，该项目也为FIU的目标做出了重要贡献，FIU是一家少数群体服务机构，旨在加强科学、技术、工程和数学(STEM)领域中未被充分代表的群体的教育，并促进南佛罗里达州公众对科学的兴趣。该项目的主要目标是发展表面增强光学二维相干光谱(2DCS)，通过在金属纳米电极(NE)上实施光学2DCS来探测等离子体表面的分子动力学，以达到高空间分辨率。该技术综合了扫描隧道显微镜和光学二维分散控制系统的优点，具有高空间分辨率、高探测灵敏度、飞秒时间分辨率和多维能力等优点。利用这项技术来研究金属NE表面的分子和两个金属纳米结构之间的纳米间隙中的分子结，这项研究使我们能够探测分子-金属和分子-分子界面的电荷转移动力学，小分子对中的分子间相互作用，以及蛋白质中金属-分子-金属结处的氢键模式和网络的动力学。这种方法的独特能力可能会在研究其他系统方面带来新的应用，如二维和钙钛矿材料、光合作用蛋白质和生物分子。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。

With this award, the Chemical Measurement and Imaging Program in the Chemistry Division, with co-funding from the Atomic, Molecular and Optical Physics - Experiment Program in the Physics Division, is funding Drs. Hebin Li and Jin He at Florida International University (FIU) to develop a novel integrated ultrafast spectroscopy and imaging technique for studying molecular dynamics. The ability to probe ultrafast chemical behavior of molecules and electrons at the nanometer scale is essential for studying and understanding materials, such as deoxyribonucleic acid (DNA) molecules, proteins linked to photosynthesis, novel solar cell layers, and exotic quantum materials. Advanced laser spectroscopy, such as optical two-dimensional coherent spectroscopy (2DCS), excels in studying chemical behavior in complex systems, while the spatial resolution is usually limited to the millionth of meter scale. On the other hand, the scanning tunneling microscope (STM) provides nanometer resolution for single-molecule studies, while the measurements in STM are limited to the millisecond timescale. Drs. Hebin Li and Jin He and their research team integrate optical 2DCS and STM-based single-molecule techniques to acquire chemical information about surfaces with nanometer resolution spatial mapping and femtosecond time resolution. The novel imaging technique enables understanding and improving numerous chemical and materials systems. By engaging students in active research and connecting to local science teachers, the project also makes an important contribution to the goal of FIU, a minority-serving institution, to strengthen the education of underrepresented groups in science, technology, engineering, and mathematics (STEM) fields, and to promote public interest in science in South Florida.The primary goal of this project is to develop surface-enhanced optical two-dimensional coherent spectroscopy (2DCS) to probe molecular dynamics on plasmonic surfaces by implementing optical 2DCS on a metal nanoelectrode (NE) to achieve a high spatial resolution. The developed technique has integrated advantages of both STM and optical 2DCS, including high spatial resolution, high detection sensitivity, femtosecond temporal resolution, and multidimensional capability. Using this technique to study molecules on the metal NE surface and molecular junctions in the nanogap between two metal nanostructures, the research enables new capabilities to probe charge transfer dynamics at molecule-metal and molecule-molecule interfaces, intermolecular interactions in small molecule pairs, and the dynamics of hydrogen-bonding patterns and networks in proteins at metal-molecule-metal junctions. The unique capabilities of this approach can potentially lead to novel applications in studying other systems such as two-dimensional and perovskite materials, photosynthetic proteins, and biological molecules.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.