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Antireflective silicon nanostructures
Published in Klaus D. Sattler, Silicon Nanomaterials Sourcebook, 2017
Young J. Yoo, Eun K. Kang, Yong T. Lee, Young M. Song
Many techniques based on top-down lithography, such as electron-beam lithography [53,54], focused ion beam [55], interference lithography [56–58], and nanoimprint lithography [59], have been applied to fabricated AR structured surfaces. To avoid scattering from the optical interface, its structure dimension has to be smaller than the wavelength of the incident light [11,60]. For UV and visible light applications, the feature size should always be below 200 nm. In such a small size range, conventional top-down lithographic technologies (electron-beam etching and fast atom beam) require sophisticated equipment and are time-consuming and expensive for large-area fabrication for practical applications. To overcome the limitations of electron-beam etching, nanoimprint lithography is introduced to fabricate various functional polymer nanopillar arrays with a high throughput [61,62]. Moreover, by using such polymer arrays as masks, many functional material nanopillar arrays can be prepared by utilizing reactive ion etching (RIE).
Exotic Solar Technologies
Published in Anco S. Blazev, Solar Technologies for the 21st Century, 2021
Owing to their single-crystalline nature, nanopillars have the potential to produce high-performance solar modules. Although nanowires can be grown non-epitaxially on amorphous substrates, their random orientation on the growth substrates could limit the explored device structures.
Fabrication of 3D nano-hemispherical cavity array plasmonic substrate for SERS applications
Published in International Journal of Optomechatronics, 2018
Chu-Yu Huang, Ming-Shiuan Tsai
Surface-enhanced Raman scattering (SERS) is a promising technique for molecule recognition in analytical chemistry, biochemistry, and environmental science. Its high sensitivity and unique molecular “fingerprint” spectra makes it a powerful tool for rapid chemical and biomolecular detection applications. However, a major drawback of the SERS detection technique is that the measured spectra intensity varies from substrate to substrate, or even worse from points to points over the same sample substrate. It is mainly due to the failure of current fabrication methods to provide a good control of the nanostructure geometry and the nanoparticle distribution on SERS substrates. Therefore, the hot spots (Hot spots are of intense local field enhancement caused by local surface plasmon resonances[1]) are not uniformly distributed across the SERS substrate, and the reproducibility of the SERS substrates are not good. As a result, the SERS detection is not good for quantitative measurements. To overcome this drawback of the SERS detection, many studies used the sophisticated microfabrication process, in order to fabricate a substrate with uniform nanostructure and high density hot spots. For example, Schmidt[2] and his colleagues fabricated silver-coated silicon nanopillars array as a Raman active substrate by using reactive ion etching process to fabricate silicon nanopillars, and electron beam evaporation deposition to coat silver on the silicon nanopillars. Zhang[3] and his colleague made nanoarrays of silver nanoparticles decorated silicon nanowires through wet etching and galvanic redox reaction processes. Kandjani[4] and his colleagues synthesized ZnO/Ag nanorod arrays using hydrothermal technique and electroless plating method. Zhao[5] et al. fabricated Au–graphene–Ag sandwiched hybrid structures through plasma sputtering Ag nanoparticles, wet-transferring CVD grown monolayer graphene film onto Ag nanoparticles, and another sputtering for Au film deposition. However, the relatively complicated microfabrication processes limit the capability of mass production, and leads to these SERS active substrates becoming economically unthroughble to be widely used.
Modulation of surface physics and chemistry in triboelectric energy harvesting technologies
Published in Science and Technology of Advanced Materials, 2019
Bo-Yeon Lee, Dong Hyun Kim, Jiseul Park, Kwi-Il Park, Keon Jae Lee, Chang Kyu Jeong
Even though bottom-up nanopatterning technologies have notable nanoscale controllability, they encumber the compatibility to the practical device fabrication because most of commercialized processes are based on top-down processes. To overcome the processing impracticality of most developments in triboelectric energy harvesting devices, the commercialized semiconducting process was adopted to achieve wafer-scale and defect-free nanoscale patterning on both rigid and flexible substrates, as presented in Figure 4(b) [79]. The polycrystalline Si nanograting patterns were fabricated by the conventional optical lithography on an 8-in Si wafer using alternative deposition of spacers and Si layers. Subsequently, the spacer sidewalls were reciprocally formed by spacer deposition and dry etching processes until the polycrystalline Si nanograting patterns were revealed. This modified spacer lithography method is called the multi-spacer pattern downscaling (MS-PaD) method. The uniform nanograting patterns can become much narrower by consuming underneath spacers and Si pattern receivers, which are the core constituents of MS-Pad method. Finally, the large-area sub-50 nm grating nanopattern was well transferred to the flexible plastic film as a replica. The scanning electron microscopy (SEM) image and the iridescent diffraction of optical photograph guarantee the uniform and well-aligned nanopatterned surface (the right panel of Figure 4(b)). The nanograting-based TEG accomplished the performance enhancement of triboelectric energy harvesting, up to 200 times higher power level, compared to the TEG of non-patterned flat surface. Moreover, they systemically demonstrated that the thickness of metal thin film on the nanopatterns can affect the triboelectric energy harvesting performance, firstly indicating the trade-off phenomena in the modulation between electrode conducting and nanopattern flattening effects. Choi et al. fabricated the nature-inspired nanopillar arrays by using the nano-imprint lithography and the electrodeposition [95]. Figure 4(c) presents the structure of nanopillar arrays-based TEG. Through the well-tailored interlocked interfaces, the contact surface area was effectively increased, resulting in the enhanced output voltage and current. Note that the fabrication of surface texturing by micro/nano- patterning and structuring have been utilized as the basis of all surface modulation approaches, which will be introduced as following sections, because the modification of surface morphology and architecture is the basic techniques in the TEGs.