MRI: Development of a New Paradigm for Apertureless Near-field Scanning Optical Microscope

我们建议构建一种最先进的工具，用于高倍率材料的成像，例如，可视化分子基团并能够识别它们。传统的光学显微镜，例如放大镜，只允许微米级的可视化，即人类头发的一小部分。这是由于可见光的衍射限制造成的。原子力显微镜使用尖端在材料表面上的锐利扫描，使材料能够在纳米级(人类头发的一小部分)上成像，然而，原子力显微镜无法提供尖端下是什么材料(金属、聚合物或离子)的信息。材料科学界的一项使命是将原子力显微镜的高分辨率与光学显微镜所显示的识别材料的能力结合起来。这种新仪器被称为近场扫描光学显微镜。由于两个相互竞争的因素，这项任务并不是微不足道的，成像部位需要足够的光强度(例如使用大的探头)，以及要求探头变小/锐利以达到光学分辨率。这项提议将使用一种新的方法，该方法源于我们的发现，即当一个人将一束激光聚焦在顶端时，特定类型的尖锐探测器会发光。发光的尖端为成像和光谱分析提供了一个“点光源”。初步的结果证明了产生近场信号的可行性，我们计划完成这台仪器的构建，优化性能并展示其应用。与以往的方法相比，该方法具有光强大、操作简单、分辨率高等优点。我们计划通过对四类重要材料的表征来展示这种新仪器的应用和能力：含有有机(聚合物)和无机(半导体)成分的材料；具有多种成分的无机小颗粒；碳纳米纤维；以及活细胞中的纳米材料。这项新技术的发展将把学生和博士后带入扫描探针显微镜技术及其在材料科学中的应用的前沿。该仪器的建成将加强加州大学的光谱成像设施(由PI领导)。我们提出了一种新的近场扫描光学显微镜(NSOM)范式。这一想法源于一项发现，微制造的原子力显微镜(AFM)探针在聚焦的激光束激励下显示出光致发光(PL)。这个PL尖端为NSOM成像和光谱分析提供了一个“点光源”。激发光聚焦到偏振分量垂直于针尖轴线的表面上，实现了原子力显微镜针尖的横向局部化和增强。初步的结果证明了产生近场信号的可行性，我们计划完成这台仪器的构建，优化性能并展示其应用。这种方法的内在优势包括：(A)高光子吞吐量，能够调节波长；(B)近场光信号的简单检测，因为PL表现出与激发光束不同的波长；(C)由于无孔AFM平台具有尖锐的探头和有效的偏转反馈，因此具有高空间分辨率；以及(D)操作简单。任何AFM用户应该能够通过大约一周的快速培训来掌握这台NSOM的操作。发展计划包括：(A)设计和建造一个低机械噪声和高稳定性的AFM/NSOM扫描组件，以获得高空间分辨率(横向为10 nm，法向为2 nm)；以及(B)获得真实的NSOM信号和局部光谱信息，为此，我们计划修改AFM探针以提高发光效率，建立激发路径和配置，以实现高度近场增强，并建立对近场信号的高灵敏度和选择性检测。结合NSOM仪器(Liu)、纳米纤维与波导(Guo)、聚合物纳米复合材料(Patten)以及具有新应用的纳米颗粒(Kauzlarich)的专业知识，我们计划使用这种NSOM来：(A)揭示细胞内形成的蛋白质复合体与配体的纳米结构的粘附性；(B)研究聚合物-纳米颗粒复合材料的结构和光学性质；(C)测量纳米线和纳米线组件的结构和波导性能；以及表征单个磁核/金属壳粒子的结构和光学性质。NSOM的发展将把学生和博士后带入扫描探针显微镜技术的前沿。学生将有机会学习和掌握最先进的AFM仪器、光学和光学信号检测、低噪音和高稳定性的硬件设计、显微镜电子以及NSOM的软件宏的技能。此外，他们还将研究光学激发与AFM针尖之间的局域相互作用、针尖-样品相互作用以及各种材料的对比机制，作为NSOM在材料研究中应用的初步探索。NSOM的完成将加强UCD有组织的研究单位NEAT的光谱成像设施(由PI领导)。拟议的研究项目将促进利用NSOM进行材料表征的进一步应用，以揭示当地结构的地形和功能。

We propose to construct a state-of-the-art tool for imaging materials with high magnification, e.g. visualizing groups of molecules and being able to identify them. Conventional optical microscopes, e.g. a magnifying glass, only allow visualization at micrometer scale, i.e. a fraction of a human hair. This is due to the diffraction limit of visible lights. Using a sharp tip scanning over material surfaces, atomic force microscope enables imaging materials at nanometer level (a small fraction of a human hair), however, provides no information as to what kind of materials (metals, polymers or ions) are under the tip. One mission in the materials science community is to combine the strength of the high resolution in atomic force microscope with the ability to identify materials shown by optical microscope. The new instrument is referred to as a near-filed scanning optical microscope. The task is not trivial due to two competing factors, the need for sufficient light intensity at the imaging site (e.g. using a large probe) and the requirement to make the probe small/sharp to attain optical resolution. This proposal will use a new methods derived from our finding that specific kind of sharp probes glow when one focuses a laser beam at the top tips. The glowing tips provide a "point light source" for imaging and spectroscopy. Preliminary results have demonstrated the feasibility of generating near-filed signals, and we plan to complete the construction of this instrument, to optimize the performance and to demonstrate its applications. Compared with past approaches towards this technique, the proposed method exhibits advantages of high intensity of light, simple to operate, and high resolution. We plan to demonstrate the application and capability of this new instrument by characterization of four classes of important materials: materials containing organic (polymeric) and inorganic (semiconductive) compositions; small inorganic particles with multiple components; carbon nanofibers; and nanomaterials in living cells. The development of this new technique should bring students and postdocs to the forefront of scanning probe microscopy technology and its applications in materials science. The completion of this instrument will enhance the Spectral Imaging Facility (led by the PI) at UCD. We propose a new paradigm for near-field scanning optical microscopy (NSOM). The idea derives from a finding that microfabricated atomic force microscopy (AFM) probes exhibit photoluminescence (PL) upon excitation by a focused laser beam. This PL tip provides a "point light source" for NSOM imaging and spectroscopy. The excitation beam will be focused onto the surface with polarization component perpendicular to the tip axe, as at such we attain laterally localization and enhancement by the AFM tip. Preliminary results have demonstrated the feasibility of generating near-filed signals, and we plan to complete the construction of this instrument, to optimize the performance and to demonstrate its applications. The intrinsic advantages of this approach include: (a) high photon throughput with the ability to tune wavelength; (b) simplicity in detection of near-field optical signals because the PL exhibits different wavelength from the excitation beam; (c) high spatial resolution due to the apertureless AFM platform with sharp probes and effective deflection feedback; and (d) simplicity in operation. Any AFM users should be able to master the operation of this NSOM with a quick training of ca. one week. Development plan includes: (a) design and construction of a low mechanical noise and high stability AFM/NSOM scanning assembly to attain high spatial resolution (10 nm in lateral and 2 nm in normal directions); and (b) attaining true NSOM signal and local spectroscopy information, for which we plan to modify AFM probes to improve the PL efficiency, to build the excitation path and configuration for high near-field enhancement, and to build a high sensitivity and selectivity detection of near field signals. Combining expertise of NSOM instrumentation (Liu), nanofibers and wave guides (Guo), polymer nanocomposite materials (Patten) and nanoparticles with novel applications (Kauzlarich), we plan to use this NSOM for: (a) revealing the protein complex formed at the cell focal adhesion on nanostructures of ligands; (b) investigating the structure and optical property of polymer-nanoparticle composite materials; (c) measuring the structure and wave-guide property of nanowires and nanowire assemblies; and characterizing the structure and optical property of single magnetic core / metal shell particles. The development of this NSOM should bring students and postdocs to the forefront of scanning probe microscopy technology. Students will have a chance to learn and master the skills for the instrumentation of state-of-the-art AFM, optics and detections of optical signals, hardware design for low noise and high stability, electronics for microscopy, and software macros for NSOM. In addition, they will also investigate local interactions between optical excitation and AFM tip, tip-sample interaction, and contrast mechanism for a variety of materials as the initial exploration for NSOM applications in materials research. The completion of this NSOM will enhance the Spectral Imaging Facility (led by the PI) at UCD's organized research unit known as NEAT. The proposed research projects will facilitate further applications of using NSOM for material characterization to reveal the topographic as well as the functionality of the local structures.