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

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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.