Fabrication of Two Dimensional Array of Silica Nanospheres on GaN Using Spin Coating Method and Nomarski Image Processin
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1207-N10-43
Fabrication of Two Dimensional Array of Silica Nanospheres on GaN using Spin Coating Method and Nomarski Image Processing
K. Lee1, H. Yalamanchili1, J. Dawson1, and D. Korakakis1 1 Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, WV 26506, USA
ABSTRACT Large-scale two dimensional ordering of silica nanospheres on GaN substrates was fabricated using spin-coating and observed using Matlab-based Nomarski image processing, which was developed to calculate the surface coverage of 2D and 3D ordering of silica nanospheres on GaN substrates. Optimal spin coating condition and SDS concentration were investigated with Nomarski image processing and an SEM. The details on spin coating process parameters or SDS concentration vs. surface coverage of silica nanospheres on GaN substrate are discussed, along with a theoretical exploration of the effects of nanosphere patterning on photonic crystals fabricated using this method. INTRODUCTION Large-scale fabrication of 2D ordering of nanospheres on GaN substrate or surface of GaN-based LEDs’ structures is demanded for enhancement of light extraction efficiency of GaNbased LEDs and reduction of dislocation density in GaN because of widespread application of highly efficient GaN-based LEDs, such as flat panel display, traffic lights, solid-state lighting, and liquid crystal display back lightings. However, nano-fabrication methods for a photonic crystal, such as e-beam and nanoimprint lithography, are expensive, time consuming, and are only suitable for small areas. For example, small area photonic crystal, 300 x 300 µm2 in size, is fabricated using e-beam lithography.[1] A simple, scalable spin-coating technique has been employed for large-scale self assembling of silica nanospheres on a glass slide or silicon substrate [2] but surface hydrophobicity of GaN substrates hampers the large-scale fabrication of 2D orderings of nanospheres on GaN using spin-coating technique. Moreover, many groups have reported the fabrication of 2D ordered arrays of silica nanospheres on GaN substrates but most of reports show the small-area observation of 2D ordering by SEM. [3,4,5] Thus, we have developed an image processing method using Nomarski micrograph and MATLAB software program for large-scale observation of 2D or 3D self assembly of silica nanospheres on GaN substrates. This technique can be applied to other substrates as well. The relationship between each spin parameter and surface coverage of silica nanospheres on GaN substrates will be investigated using both image processing and direct microscopic observations. Also, the effects of SDS as a surfactant on the processes of array formation will be discussed. With image processing and precise control of spin coater, we achieved a large area, ~ 70% of 2 inch GaN substrate, monolayer of silica nanospheres on GaN substrates.
EXPERIMENT Silica nanospheres, suspended in deionized water with mean diamenters of 490 nm ± 20 nm (Duke Scientific), were used for nanopatterning GaN substra
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