Photonic Crystals Fabricated Using Patterned Nanorod Arrays

Abstract

Two-dimensional (2D) photonic crystal (PC) slabs have attracted much research interest due to the relative ease of achieving a full photonic bandgap. [1,2] A wide variety of applications in optoelectronics have been explored using 2D PCs, such as waveguides, [3] superprisms, [4] laser diodes, [5] and photonic integrated circuits. [6] Traditionally, 2D PCs are fabricated by electron-beam lithography, which is a top±down process that is expensive and limited to relatively small areas; [7] these factors possibly hinder the application and commercialization of 2D PCs. A combination of top±down and bottom± up processes has been attempted, in which a 2D pattern is created by lithography followed by a self-assembly process to achieve the final structure.[8] Recently, by using monolayer self-assembly (MSA) of polystyrene (PS) submicrometer spheres to define a pattern, a catalyst-controlled selective growth technique has been applied to make 2D periodic arrays, such as hexagonal-patterned carbon nanotubes [9] and ZnO nanorods. [10] This is a simple and cost-effective approach for growing quasi-one-dimensional (quasi-1D) nanostructure arrays on a relatively large scale. However, these as-synthesized 1D nanostructures have a large percentage of air space and a vanishing photonic bandgap, and are not suitable for photonic applications. We present here a bottom±up process for fabricating 2D PC slabs starting with patterned ZnO nanorod arrays that were conformally coated with TiO 2 by template-assisted atomic layer deposition (ALD), a powerful technique for fabricating a variety of nanostructures, such as inverse opals, [11,12] one-dimensional nanostructures, [13] and nanobowl arrays. [14] The space between the ZnO nanorods was partially filled with TiO 2 , thus forming a continuous ZnO/ TiO 2 matrix with a highly ordered air-hole array. This periodic structure showed a reflection peak at the theoretically predicted bandgap region, while the near-UV emission of ZnO was unaffected by the TiO 2 coating. This technique demonstrates an effective and economical bottom±up process for 2D PC fabrication. Our objective was to make a photonic crystal with high refractive-index contrast, which was achieved by a two-step process: growth of patterned nanorod arrays with large air holes, then infiltration of the nanorod arrays with TiO 2 to form an air/TiO 2 /nanorod photonic crystal. In the first step, a continuous hexagonal gold nanoparticle pattern was formed on a sapphire substrate. The aligned ZnO nanorods were then grown using the gold pattern as a catalyst in a tube furnace at elevated temperature.[10] A honeycomb-like pattern of dense and well-aligned ZnO nanorod arrays was produced, as shown by the scanning electron microscopy (SEM) image in Figure 1a. The diameter and length of the ZnO nanorods were controlled by the thickness of the gold catalyst layer and the growth time. For a growth time of 15 min, the length of the ZnO nanorods was~500 nm and their diameters ranged from 20±30 nm.

In Situ Field Emission of Density‐Controlled ZnO Nanowire Arrays

“…Owing to their unique semiconducting properties, ZnO nanowires (NWs) have received intensive research interests in optics, [1,2] electronics, [3,4] piezoelectrics, [5] and mechanics. [6] The vertically aligned morphology has already shown great advantages in manipulation and device assembly within the nanometer regime.…”

“…The FE I-V curves are shown in Figure 3b. The counter electrode (the W needle tip) has an area of only 0.03 mm 2 , which was much smaller than the size of the sample. However, considering the density of the aligned NWs, the number of NWs covered under the counter electrode was of the order of 10 6 to 10 7 , which is big enough to show a representative universal property.…”

Interfacial Reaction Growth: Morphology, Composition, and Structure Controls in Preparation of Crystalline ZnxAlyOz Nanonets

“…[6] For example, zinc oxide has been demonstrated to be quite effective in lasing, [7] dye-sensitized solar cells, [8] photonic crystals, [9,10] and even biodevices because of its biocompatibility. [11] It belongs to the wurtzite family of structures with preferential directions of growth that can be utilized to prepare, in a controlled manner, a variety of high-purity nanostructures.…”

Optimized Distribution and Morphology of Carbon Nanofibers for a Field Emitter Grown by Nickel and Chromium Cosputtering

“…In the formation of a catalyst microstructure separated by a noncatalyst, a eutectic alloy allows for phase separation with grains of the catalyst layer controlling of contents of catalyst and noncatalyst. Nickel (Ni) was used as a catalyst to synthesize stable CNFs [22][23][24][25][26][27] which form catalyst patterns with small grains at low temperature. Chromium (Cr), which is used as the electrode in flat panel displays and is known for its excellent rigidity and durability, was used as the nonmetal catalyst for the separation of Ni grains.…”

“…When the distance between adjacent patterns of synthesizing CNFs is at least twice the CNF length, they found that the field strength focused on those CNFs was almost the same as a CNF standing alone. There are many reports on the optimization of FE properties with CNF array patterning that followed the reports of Nilsson et al [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. In some these reports, the patterning of CNFs by lithography, which commonly uses semiconductor process technology, was explained.…”