Dynamic physicochemical nanoscale imaging at the solid-liquid interface

拉曼光谱是材料表征的宝贵分析工具，使用振动光谱独特提供的诊断指纹提供有关分子结构、化学成分和局部环境的基本信息。它几乎无处不在地应用于工程、物理和生命科学，能够在没有标签或制备程序的情况下，以非侵入性和非破坏性的方式分析处于天然状态的分子材料(无论物质或环境的物理状态)。然而，它确实受到两个重大限制：(I)低灵敏度，这是由于拉曼效应的弱点，其中很少的入射光子可以被利用来产生关于振动结构的信息，以及(Ii)受光学绕射定律限制的空间分辨率。这从根本上限制了可以检查的材料的广度，以及在那些可以检查的材料中获取信息的绝对精度。由于认识到材料的主要功能是由纳米级分子结构中出现的特征和现象决定的，拉曼光谱技术的重大发展是必要的，因此建立了一种创新的方法-尖端增强拉曼光谱(TERS)。在TERS中，扫描探针显微镜(SPM)的尖端被激光以驻留在尖端的贵金属纳米颗粒的自然等离子体频率照射。这在SPM针尖附近产生了一个高强度的电磁场，从而为在纳米尺度上对分子材料进行高灵敏度成像提供了一种新的机制。然而，到目前为止，由于商业仪器先前技术上的不足，它的应用在很大程度上限制在标准温度和压力条件下对空气中固体表面的分析。因此，尽管TERS有效地解决了拉曼光谱学固有的根本缺陷，但它基本上未能转化母技术非常可取的方面，从而为其在重要材料科学发现中的应用设置了重大障碍。为了解决这一关键问题，我们的目标是开创一种创新的纳米级成像能力，包括光学耦合SPM和拉曼光谱，并首次独特地配置双光学接入、多种SPM功能以及用于环境控制的定制平台和液室。指定的DCI-ter，我们的尖端分析平台将使分子材料的化学指纹成像显著低于衍射极限(&lt；10 nm空间分辨率)，以采样液体和固体，具有近单分子级别的灵敏度，以及从单一位置同时获取的3D地形分析(尖端增强拉曼光谱)。全性能SPM模式的结合扩展了可从单个纳米级体积获得的表面物理特性的广度(相关成像)，而首次提供的环境控制条款将革命性地对气-固和液-固界面上的化学转化进行现场和操作研究，以响应光、热和电势(动态成像)。因此，DCI-ters为分子材料的时间分辨和位置相关成像提供了一种创新的方法，并将在相关条件下和纳米级提供关于表面物理化学(机械、电、热、结构组成)性质的新的基础知识，适用于从药物输送和医疗设备到光电子学和电池的广泛材料研究计划。

Raman spectroscopy is an invaluable analytical tool for materials characterisation, providing essential information on the structure, chemical composition and local environment of molecules using the diagnostic fingerprint that the vibrational spectrum uniquely delivers. It is applied almost ubiquitously across the engineering, physical and life sciences, enabling analysis of molecular materials in their native state (regardless of the physical state of matter or environment), in the absence of labels or preparation procedures, in a non-invasive and non-destructive fashion. It does, however, suffer from two significant limitations: (i) low sensitivity, a result of the weakness of the Raman effect, where very few incident photons can be harnessed to generate information on vibrational structure, and; (ii) spatial resolution limited by the laws of optical diffraction. This places fundamental restrictions on the breadth of materials that can be examined, and the absolute precision with which information can be obtained in those that can. Necessitated by the comprehension that the principle functions of materials are governed by characteristics and phenomena that arise in molecular structures at the nanoscale, significant developments in the technology of Raman spectroscopy was warranted and an innovative approach - termed tip-enhanced Raman spectroscopy (TERS) - was consequently established. In TERS, a scanning probe microscopy (SPM) tip is illuminated with a laser at the natural plasmon frequency of the noble metal nanoparticle that resides at the tip apex. This creates a high-intensity electromagnetic field in the immediate vicinity of the SPM tip, and as such provides a new mechanism for high-sensitivity imaging of molecular materials at the nanometre length scale. Yet, to date, and for reasons of prior technical inadequacies of commercial instrumentation, its application has been largely restricted to analysis of solid surfaces in air at standard conditions of temperature and pressure. Thus, whilst TERS has effectively solved the fundamental deficiencies inherent to Raman spectroscopy, it has essentially failed to translate the highly desirable aspects of the parent technique, thus placing a significant barrier to its application for important materials science discoveries. To address this critical issue, we aim to pioneer an innovative nanoscale imaging capability, comprising optically-coupled SPM and Raman spectroscopy, and uniquely configured for the first time with dual optical access, multiple SPM functionalities and custom-made stages and liquid cells for environmental control. Designated DCI-TERS, our cutting-edge analytical platform will enable chemical fingerprint imaging of molecular materials significantly below the diffraction limit (<10 nm spatial resolution) for sampling both liquids and solids, with near-single-molecule-level sensitivity, along with 3D topographical analysis, acquired simultaneously from a single location (Tip-Enhanced Raman Spectroscopy). The incorporation of full performance SPM modes extends the breadth of surface physical characteristics obtainable from a single nanoscale volume (Correlative Imaging), whilst first-time provisions for environmental control stands to revolutionise in situ and operando investigations of chemical transformations at the gas-solid and liquid-solid interfaces, in response to light, heat and electrical potential (Dynamic Imaging). Thus, DCI-TERS represents an innovative methodology for temporally-resolved and location-correlated imaging of molecular materials and will deliver new fundamental knowledge on surface physicochemical (mechanical, electrical, thermal, structural compositional) properties under relevant conditions and at the nanoscale level, applicable to a broad spectrum of material research programmes, from drug delivery and medical devices to optoelectronics and batteries.