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

技术摘要本方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、成分变化和材料性质。利用受激辐射耗竭(STED)技术，利用两束重叠的激光同时激发和耗尽纳米粒子的荧光，实现了远场亚衍射极限成像。规则形状的激发光束叠加在甜甜圈形状的漂白光束上，使得荧光被限制在甜甜圈零点，外围的所有粒子都被耗尽。这使分辨率提高了一个数量级。到目前为止，STED技术仅应用于生物体系中荧光标记的成像。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的技术与光激电荷检测相结合，我们将开发出一种能够将电荷激发成像到亚衍射极限精度的显微镜。分辨率将比使用电子束感应电流(EBIC)或扫描深能级瞬变光谱(DLTS)获得的分辨率高一个数量级。此外，该技术对材料结构是非破坏性的(与透射电子显微镜不同)，使其适用于原位器件表征。非技术摘要高分辨率成像对于电子材料表征非常重要，特别是在当今纳米材料合成和器件制造的时代。该方案的目标是开发一种远场亚衍射分辨率光学显微镜，能够在不损害被测材料的情况下，在三维中检测材料的变化、缺陷状态、无序和杂质。该显微镜将利用为荧光显微镜开发的高分辨率成像方案，但使用电荷置换而不是光致发光来产生可检测的信号。路易斯维尔大学的研究人员将利用3D亚衍射显微镜的电子成像功能来研究光伏应用的纳米线组成、氧化和氢化石墨烯中能隙状态的空间变化，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系统中的设备操作相关联。

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.