Plasmonically Enhanced Stimulated Coherent Spectroscopy

在化学系的化学测量和成像计划以及化学、生物工程、环境和运输系统系的纳米生物传感计划的支持下，波士顿大学的Ziegler和Reinhard教授合并了两个非常活跃的研究领域，这两个领域已经独立地影响了我们生活的许多方面：纳米材料和激光技术。该项目的目标是利用这两个学科相结合所提供的特殊能力，以推动针对一些重要社会需求的技术解决方案。更具体地说，这些研究人员探索了如何利用超快脉冲激光与金属纳米材料相互作用来增强和控制金属表面的化学作用，以应用于化学催化、减轻污染、能量转换、化学成像和传感应用。正在进行的实验详细描述了分子如何与纳米结构的金属表面相互作用。已经有了成熟的方法，可以用精细的控制来设计纳米级的表面。这些实验的结果揭示了这些材料如何与分子相互作用的分子水平的细节，从而为上述应用提供了优化纳米结构设计策略的信息。这项研究工作的合作性质为参与的学生提供了在材料和超快科学的界面上的独特体验，从而促进了波士顿大学的跨学科科学和技术活动。与这项研究相配合，这笔赠款支持一个实质性的教育和推广计划，包括当地社区大学的学生和教职员工、市中心和大波士顿地区的高中学生和高中教师的参与，以及新授予的NSF本科生研究经验(REU)现场计划，以及其他以波士顿大学为基础的推广计划。超快光谱学和纳米技术的结合正被用于通过三种超快激光技术研究等离子体活性表面上分子的动力学和相互作用。等离子体增强(PE)光外差探测拉曼光谱(PE-OHD-RIKES)为观察等离子体表面的拉曼响应，特别是分子表面物理吸附产生的低频模式提供了灵敏度优势，并为理解振动和等离子体对非线性响应的贡献提供了一种相位敏感的方法。对PE三脉冲光子回波峰移测量(PE3PEPS)的分析给出了分子在等离子体表面上的光学退相或等效溶剂化(能量不均匀分布、光谱扩散和涨落时间)的动力学描述。最后，PE飞秒受激拉曼光谱(PE-FSRs)的成功实施，作为一种新的表面化学探针，可能会产生巨大的影响，使振动特定的标记能够跟踪等离子体表面短寿命中间体的演化和激发分子的快速构象变化。所确定的等离子体基质上分析物的动力学和结构性质与液体溶液的动力学和结构性质进行了对比，并与观察到的等离子体增强因子等基于等离子体的现象相关联。基片是通过模板引导的自组装过程制备的，这导致了电磁强耦合纳米颗粒簇阵列，其中光场通过纳米颗粒之间的近场耦合和团簇之间的衍射耦合来增强。关于分子如何与工程等离子体表面相互作用的详细分子水平信息为最大限度地提高等离子体增强光学响应和化学结果提供了合理的设计策略。这一方法的实施在以下方面对光学成像能力产生了影响：提高了灵敏度和更快的采集时间，实时监测光诱导的表面化学反应，增强了化学和生物传感能力，并改进了后续自发SERS和其他基于等离子体的技术的策略。

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry and the NanoBiosensing Program in the Division of Chemical, Bioengineering, Environmental, and Transport Systems, Professors Ziegler and Reinhard at Boston University merge two very active research areas that have independently already impacted many aspects of our lives; nanomaterials and laser technology. The goal of the project is to exploit the special capabilities afforded by the combination of these two disciplines to advance a technical solution to some important societal needs. More specifically, these researchers explore how ultrafast pulsed laser light interacting with metal nano-materials can be used to enhance and control chemistry on metal surfaces for applications such as chemical catalysis, pollution mitigation, energy conversion, chemical imaging and sensing applications. The on-going experiments develop a detailed description of how molecules interact with nanostructured metal surfaces. Well-established methodologies are already in place that allow the design of nanoscale surfaces with exquisite control. The results of these experiments reveal molecular level details of how these materials interact with molecules and thus provide information on optimizing nanostructures design strategies for the applications cited above. The collaborative nature of this research effort provides participating students with unique experience at the interface of materials and ultrafast science, and thus promote cross-disciplinary activities in science and technology at Boston University. In synergy with the research, this grant supports a substantial education and outreach program to include participation of local Community College students and faculty, inner city and greater Boston area High School students, and High School teachers in conjunction with a newly awarded NSF research experience for undergraduates (REU) site program, as well as other BU based outreach programs.The merger of ultrafast spectroscopy and nanotechnology is being used to study the dynamics and interactions of molecules on plasmonically active surfaces via three ultrafast laser techniques. Plasmonically enhanced (PE) optical heterodyne detected Raman spectroscopy (PE-OHD-RIKES) offers sensitivity advantages for viewing Raman responses on plasmonic surfaces, especially for low frequency modes resulting from molecular-surface physi-adsorption, and a phase sensitive methodology for understanding vibrational and plasmon contributions to nonlinear responses. Analysis of PE three-pulse photon echo peak shift measurements (PE 3PEPS) yields a dynamical description of optical dephasing, or equivalently solvation, of molecules on plasmonic surfaces (inhomogeneous energy distributions, spectral diffusion and fluctuation timescales). Finally, the successful implementation of PE femtosecond stimulated Raman spectroscopy (PE-FSRS), could have enormous impact as a new probe of surface chemistry allowing vibrationally-specific labels to follow the evolution of short-lived intermediates and rapid conformation changes of excited molecules on plasmonic surfaces. Determined dynamical and structural properties of analytes on plasmonic substrates is being contrasted with those of liquid solutions and correlated with observed plasmonic based phenomenon such as SERS enhancement factors. Substrates are being fabricated by a template-guided self-assembly procedure which results in electromagnetically strongly coupled nanoparticle cluster arrays where optical fields are enhanced by both near field coupling between nanoparticles, and diffractive coupling between clusters. Detailed molecular level information about how molecules interact with engineered plasmonic surfaces is providing rational design strategies for maximizing plasmon enhancement of optical responses and chemical outcomes. The implementation of this methodology is impactful upon optical imaging capabilities in terms of improved sensitivity and faster acquisition times, real time monitoring of photoinduced surface chemical reactivity, enhanced chemical and biological sensing capabilities, and improved strategies for subsequent spontaneous SERS and other plasmonic based techniques.