MRI: Development of a Holographic Nanoscale Optics Instrument

非技术光学（或光）显微镜可以说是迄今为止对微观世界进行非侵入性检查的最成功的技术之一。罗伯特·胡克（Robert Hooke）在17世纪首次通过显微镜观察到软木塞的亚结构，他创造了“细胞”一词来描述软木塞的亚结构。在过去的一个世纪里，各种复杂的方法已经发展到今天，提供了观察迁移细胞的能力，检查亚细胞结构的分布，绘制基因的表达，或形成根据样本的分子结构编码的“化学图像”。尽管光学显微镜取得了巨大的成功，但从根本上说，它在分辨小于几百纳米的特征方面的能力有限。具体来说，衍射极限会使物体上的点发出的光在通过透镜传播时扩散，从而使图像在放大时变得模糊。近场显微镜克服了这些限制，将光学探针放置在距离物体几十纳米的地方，并在衍射之前对发射或散射的光进行采样。波士顿大学的研究人员正在建造一种多功能近场显微镜，为本地和区域用户提供10纳米量级的光学分辨率。该仪器正在实现一系列重要的研究重点，包括(i)蛋白质折叠行为的研究，可以阐明阿尔茨海默氏症等疾病；（二）激光源新材料的开发；（iii）设计用于下一代电子产品的单原子厚层（如石墨烯）性能的方法；（四）控制纳米尺度光流的方法，这对新的光学传感器和通信技术很重要。波士顿大学的项目还吸引了女性和少数族裔本科生参与前沿研究。由于在纳米尺度上“看到”物体的能力对年轻人来说是一种强大的动力，因此该团队正在与波士顿大学的“向上发展数学科学”大学预科项目合作，该项目面向城市高中生，为期7周。在夏季的每周三，学生们进行纳米技术实践实验，并使用新的显微镜观察纳米世界。光学显微镜可以说是迄今为止对微观世界进行非侵入性检查的最成功的技术之一，但由于衍射极限，基本上仅限于100纳米或更长的长度尺度。近场显微镜通过将光源或探针置于样品的近光学场中，将非传播或消失模式耦合到远场传播模式以进行收集，从而克服了这一问题。虽然有五六家公司出售近场显微镜，但它们的能力都有限。波士顿大学的研究人员正在建造一种多功能全息纳米级光学仪器，将其集成到原子力显微镜中，结合了近场弹性散射光谱、拉曼光谱和宽波长范围内的荧光光谱。该仪器具有传输和后向散射两种几何形状，并包括用于相位分辨近场成像的干涉测量，以绘制3D场响应，提供灵活性和灵活性，这对于推进复杂的研究问题至关重要。该仪器使波士顿大学和地区大学的研究人员能够研究等离子体、生物物理学、石墨烯和其他二维（2D）晶体膜物理学中的纳米级光学现象。等离子体研究正在探索热点，局部状态密度，特别是预测在金属和介电元件之间的界面上发生的相奇点。在石墨烯、MoS2和hBN的应变工程二维晶体中，波士顿大学的研究人员正在探索原子尺度的摩擦和绘制应变诱导伪磁场的令人兴奋的可能性。在锗半导体纳米膜的研究中，局部光响应可以确定和帮助设计具有直接带隙的纳米器件。在生物物理学中，长波尖端增强近场显微镜可以提供前所未有的内在振动模式图像，能够进行亚细胞分类和重要蛋白质的局部存在。

Non-technicalOptical (or light) microscopy is arguably one of the most successful techniques for the non-invasive examination of the microscopic world ever created. Robert Hooke coined the term "cells" to describe the substructure of cork he first observed through a microscope in the 17th century. Over the past century a variety of sophisticated methods have been developed that today provide the ability to observe migrating cells, examine the distribution of subcellular structures, map the expression of genes, or form "chemical images" coded according to the molecular structure of the sample. Despite its immense success, optical microscopy is fundamentally limited in its ability to resolve features less than a few hundred nanometers. Specifically, the diffraction limit causes light from points in an object to spread out as it propagates through a lens, thereby blurring images as they are magnified. Near-field microscopy overcomes these limitations by placing an optical probe a few tens of nanometers away from the object and sampling the emitted or scattered light before it experiences diffraction. Boston University researchers are building a versatile near-field microscope providing local and regional users with access to optical resolution on the order of 10 nanometers. The instrument is enabling a range of important research thrusts including (i) studies of protein folding behavior that can shed light on conditions such as Alzheimer's; (ii) the development of new materials for laser sources; (iii) methods for engineering the properties of single atomic thick layers like graphene for next-generation electronics and; (iv) methods for controlling the flow of light on nanometer length scales, important for new optical sensors and communications technologies. The BU project is also engaging women and underrepresented minority undergraduate students in cutting-edge research. Since the ability to "see" objects at the nanoscale can be a powerful motivator for a young mind, the team is working with BU's Upward Bound Math Science 7-week residency college prep program for urban high school students. Every Wednesday in the summer, students perform nanotechnology hands-on experiments and use the new microscope to observe the nano-world. Technical DescriptionOptical microscopy is arguably one of the most successful techniques for non-invasive examination of the microscopic world ever created, but is fundamentally limited to length scales of 100 nm or more by the diffraction limit. Near-field microscopy overcomes this by placing a source or probe into the near optical field of a sample to couple the non-propagating or evanescent modes into far-field propagating modes for collection. While there are 5 or 6 companies that sell near-field microscopes, all are limited in capability. Boston University researchers are building a versatile holographic nanoscale optics instrument integrated into an atomic force microscope, combining near-field spectroscopies of elastic scattering, Raman and fluorescence over a wide wavelength range. The instrument operates in both transmission and back-scattering geometries, and includes interferometry for phase-resolved near-field imaging to map 3D field response, providing the flexibility and dexterity that are critical to advance complex research problems. The instrument enables researchers at BU and regional universities to investigate nanoscale optical phenomena in plasmonics, biophysics, and graphene and other two-dimensional (2D) crystal membrane physics. Plasmonic studies are exploring hot spots, local density of states and in particular, phase singularities predicted to occur at the interface between metal and dielectric components. In strain engineered 2D crystals of graphene, MoS2 and hBN, researchers at BU are exploring atomic-scale friction and the exciting possibility of mapping strain-induced pseudo-magnetic fields. In studies of Germanium semiconductor nanomembranes, local optical response can confirm and help engineer nano-devices with direct bandgaps. And in biophysics, long-wavelength tip-enhanced near-field microscopy can provide unprecedented images of intrinsic vibrational modes capable of sub-cellular classification and local presence of important proteins.