ADVANCE Fellow: Microscopy of Nanomaterials

这项研究的目的是开发一种新的表征技术来研究纳米材料的尺寸相关的磁性、光学和电子行为。了解这些新特性的起源对于它们在各种技术中的开发至关重要，这些技术包括高密度磁记录、高速光学计算、太阳能、环境毒理学、生物材料和生物传感器。即将开发的技术是电子能量损失谱(EELS)在透射电子显微镜(TEM)中的应用。鳗鱼能量分辨率(0.3 eV)的新发展将与电子显微镜的高空间分辨率相结合，以将单个纳米粒子的电子和光学性质与其尺寸、形状、组成和表面形态相关联。最初研究的具体材料将是由PI和她的合作者合成的氮化镓和硅纳米颗粒。单个纳米粒子的电子和光学特性将从EELS光谱的低能量损失和精细结构部分提取。结果将与从X射线吸收光谱学(XAS)和光学光谱学收集的信息以及建模工作进行比较。这些信息将反过来与单个纳米粒子的物理形态(大小和形状)、存在的特定表面重建(通过相差显微镜)以及元素组成和分布(例如掺杂、核/壳结构)相关。这项工作对理解依赖于尺寸的性质的起源的潜在影响预计将是巨大的，因为所提出的技术的能力是独特的，允许研究单个纳米颗粒，而不是纳米颗粒的集合。在过去的20年里，全球范围内的大量研究一直集中在了解当尺寸减小到大约10纳米(不到十亿分之一米)时对块状材料的磁、光学和电学性质的影响。对这些与尺寸有关的特性的行为和来源的研究对于它们在各种技术中的充分开发至关重要：高密度磁记录、高速光学计算、太阳能、环境毒理学(包括化学和生物武器检测)、生物材料(例如人造器官)和用于高级医学测试的生物传感器。由于所研究的材料尺寸很小，需要开发新的技术来了解它们的性质，因为传统的表征技术通常一次研究数百万个粒子，而不是只研究单个粒子。该项目的目标是利用电子显微镜的新发展，将单个纳米粒子的磁性、光学和电子行为与其特定的尺寸、形状、组成和表面结构相关联。这将通过充分利用电子显微镜对尺寸小于0.2纳米的特征成像的能力以及电子显微镜光谱方法的新发展来实现，这些方法将允许从单个纳米粒子收集光学和电子数据。了解纳米材料的性质如何受到这些不同因素的影响，将扩展对物质基本性质的知识，并指出新的合成策略，以优化这一重要类别材料的性能。该奖项由美国国家科学基金会高级研究员计划支持。高级方案的总体任务是通过增加妇女在学术、科学和工程职业中的代表性和地位，增加妇女在科学和工程工作中的参与度。

The purpose of the proposed research is to develop a new characterization technique for investigating the size-dependent magnetic, optical, and electronic behavior of nanomaterials. An understanding of the origin of these new properties is essential for their exploitation in a variety of technologies, including high-density magnetic recording, high-speed optical computing, solar energy, environmental toxicology, biomaterials, and biosensors. The technique that will be developed is electron energy-loss spectroscopy (EELS) in the transmission electron microscope (TEM). New developments in the energy-resolution of EELS (0.3 eV) will be used in concert with the high spatial-resolution of TEM to correlate the electronic and optical properties of individual nanoparticles to their size, shape, composition, and surface morphology. Specific materials for initial investigation will be gallium nitride and silicon nanoparticles, synthesized by the PI and her collaborators. The electronic and optical properties of individual nanoparticles will be extracted from the low energy-loss and fine structure portions of the EELS spectrum. Results will be compared to information collected from X-ray absorption spectroscopy (XAS) and optical spectroscopy, as well as modeling efforts. This information will in turn be related to the physical morphology (size and shape) of the individual nanoparticles, particular surface reconstructions present (via phase-contrast microscopy), and elemental composition and distribution (e.g. doping, core/shell structures). The potential impact of this work on understanding the origins of size-dependent properties is expected to be enormous, given that the capability of the proposed technique is unique in permitting the study of individual nanoparticles, rather than ensembles of nanoparticles.Intense worldwide research over the last twenty years has been focused on understanding the effect on the magnetic, optical, and electronic properties of a bulk material when size is reduced to less than about 10 nanometers (less than one in a hundred millionths of a meter). Investigation of the behavior and origin of these size-dependent properties is critical for their full exploitation in a broad range of technologies: high-density magnetic recording, high-speed optical computing, solar energy, environmental toxicology (including chemical and biological weapons detection), biomaterials (for example, artificial organs), and biosensors for advanced medical testing. The small size scale of the materials under investigation demands that new techniques be developed for understanding their properties, since traditional characterization techniques typically study millions of particles at a time, rather than single particles alone. The goal of this project is to use new developments in electron microscopy to correlate the magnetic, optical and electronic behavior of individual nanoparticles to their specific size, shape, composition and surface structure. This will be achieved by taking full advantage of the ability of electron microscopy to image features less than 0.2 nm in size, as well as new developments in spectroscopic methods in the electron microscope that will allow optical and electronic data to be collected from individual nanoparticles. An understanding of how the properties of nanomaterials are influenced by these various factors will extend knowledge of the basic properties of matter, as well as point to new synthesis strategies to optimize the performance of this important class of materials.This award is supported through the NSF ADVANCE Fellows Program. The overall mission of the ADVANCE Program is to increase the participation of women in the scientific and engineering workforce through the increased representation and advancement of women in academic science and engineering careers.