Near Field Scanning Optical Microscopy(NSOM) of nano devices
Low, Chun Hong
Haegel, Nancy M.
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This thesis aims to investigate the optical properties of nano-devices using the technique of Near-Field Scanning Optical Microscopy (NSOM). A unique setup to perform Atomic Force Microscopy (AFM) and NSOM simultaneously in a scanning electron microscope (SEM) to collect spatially resolved luminescence and image transport on nano-scale structures, particularly nanowires, will allow direct determination of transport parameters, such as minority carrier mobility and diffusion length that are vital to the performance of optoelectronic devices. The work involves the development of a unique nano-scale imaging technique applicable to a wide range of structures. The main structures of interest in this thesis will be GaN nanowires. Instead of using a laser for generating charge for imaging, the e-beam from the SEM was used to generate localized charge for an NSOM probe to monitor the motion of the excess charge due to diffusion and/or drift via electron-hole recombination process. For the first time in this research, the author addressed numerous challenges such as the intricate NSOM technique to resolve sub-wavelength dimension measurements of the elements and determine optimized experimental parameters to compensate for the relatively low efficiency of NSOM optical collection. Of significance, transport imaging of 1-10 [micrometer] long GaN nanowires resulted in minority carrier diffusion lengths ranging from 1-2 [micrometer]. An initial experimental exploration was also conducted to determine the theoretical prediction of the unique transmission enhancement of Au nanobowties fabricated on luminescent GaAs heterostructure. The author will report the working principles, experimental procedures, optimal process parameters and the respective imaging results for assessing the properties of the nano-devices studied in this thesis work. Recommendations for future work pertaining to the augmentation of related NSOM work will also be made to ensure continued progress in this area of work.
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