MRI: Development of an Electron State Depletion Microscope at the University of Louisville

技术摘要：本提案的目标是开发一种远场光电显微镜，能够以亚衍射极限分辨率和三维成像缺陷密度，掺杂剂，成分变化和材料性质。远场亚衍射极限成像已被证明使用受激发射耗尽（STED），其中两个重叠的激光束被用来同时激发和耗尽纳米级粒子的荧光。一个规则形状的激发光束叠加在一个甜甜圈形状的漂白光束，使荧光被限制在甜甜圈零，与所有粒子在外围被耗尽。这使分辨率提高了一个数量级。目前，STED技术仅应用于生物系统中荧光标记的成像。然而，状态耗尽现象应该普遍适用于其他检测机制。通过将基于STED的技术与光激发电荷检测相结合，我们将开发一种能够将电荷激发成像到亚衍射极限精度的显微镜。该分辨率将比使用电子束感应电流（EBIC）或扫描深层瞬态光谱（dlt）所能达到的分辨率好一个数量级。此外，该技术不破坏材料结构（不像TEM），使其适用于原位器件表征。摘要高分辨率成像对于电子材料的表征非常重要，尤其是在纳米材料合成和器件制造的当今时代。本提案的目标是开发一种远场亚衍射分辨率光学显微镜，能够在三维空间中检测材料变化，缺陷状态，无序和杂质，而不会损坏被测材料。该显微镜将利用为荧光显微镜开发的高分辨率成像方案，但使用电荷位移而不是光致发光来产生可检测的信号。路易斯维尔大学（University of Louisville）的研究人员将利用3D亚衍射显微镜的电成像能力，研究光伏应用的纳米线组成、氧化和氢化石墨烯中间隙态的空间变化，以及有机和无机太阳能电池的组成变化。在三维、非破坏性和纳米尺度上研究材料变化和缺陷状态的能力是前所未有的，这将使研究人员有机会将材料特性与纳米尺度系统中的器件操作联系起来。

Technical AbstractThe goal of this proposal is to develop a far-field opto-electronic microscope capable of imaging defect densities, dopants, compositional variations, and material properties with sub-diffraction limited resolution and in three dimensions. Far-field sub-diffraction limited imaging has been demonstrated using stimulated emission depletion (STED) in which two overlapping laser beams are used to simultaneously excite and deplete the fluorescence of nanometer scale particles. A regularly shaped excitation beam is super-imposed on a donut shaped bleaching beam so that the fluorescence is confined to the donut zero, with all particles on the periphery being depleted. This produces an order of magnitude improvement in resolution. Up to now, the STED technique has only been applied for imaging of fluorescent tags in biological system. However, the state depletion phenomenon should be generally applicable to other detection mechanisms. By combining a STED based technique with photoexcited charge detection we will develop a microscope that has the ability to image charge excitation to sub-diffraction limited precision. The resolution will be an order of magnitude better than what is achievable using electron beam induced current (EBIC) or scanning deep level transient spectroscopy (DLTS). In addition, the technique is non-destructive to the material structure (unlike TEM), making it applicable for in-situ device characterization.Non-Technical AbstractHigh-resolution imaging is extremely important for electronic materials characterization, particularly in the present era of nanoscale material synthesis and device fabrication. The goal of this proposal is to develop a far-field sub-diffraction resolution optical microscope able to detect material variations, defect states, disorder, and impurities, in three dimensions without damaging the material under test. The microscope will utilize a high resolution imaging scheme developed for fluorescence microscopy, but using charge displacement rather than photoluminescence to generate a detectable signal. The electrical imaging capabilities of the 3D sub-diffraction microscope will be used by researchers at the University of Louisville to study nanowire composition for photovoltaic applications, spatial variations in midgap states in oxidized and hydrogenated graphene, and composition variations in organic and inorganic solar cells. The ability to study material variations and defect states in three dimensions, non-destructively, and on the nanometer scale is unprecedented, and will give researchers the opportunity to correlate material properties with device operation in nanoscale systems.