The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

In materials science, “green” synthesis has gained extensive attention as a reliable, sustainable, and eco-friendly protocol for synthesizing a wide range of materials/nanomaterials including
 metal/metal oxides nanomaterials, hybrid materials, and bioinspired materials. As such, green synthesis is regarded as an important tool to reduce the destructive effects associated with the traditional methods of synthesis for nanoparticles commonly utilized in laboratory and industry. In this review, we summarized the fundamental processes and mechanisms of “green” synthesis approaches, especially for metal and metal oxide [e.g., gold (Au), silver (Ag), copper oxide (CuO), and zinc oxide (ZnO)] nanoparticles using natural extracts. Importantly, we explored the role of biological components, essential phytochemicals (e.g., flavonoids, alkaloids, terpenoids, amides, and aldehydes) as reducing agents and solvent systems. The stability/toxicity of nanoparticles and the associated surface engineering techniques for achieving biocompatibility are also discussed. Finally, we covered applications of such synthesized products to environmental remediation in terms of antimicrobial activity, catalytic activity, removal of pollutants dyes, and heavy metal ion sensing.

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‘Green’ synthesis of metals and their oxide nanoparticles: applications for environmental remediation

Even though the mesoporous-type perovskite solar cell (PSC) is known for high efficiency, its planar-type counterpart exhibits lower efficiency and hysteretic response. Herein, we report success in suppressing hysteresis and record efficiency for planar-type devices using EDTA-complexed tin oxide (SnO2) electron-transport layer. The Fermi level of EDTA-complexed SnO2 is better matched with the conduction band of perovskite, leading to high open-circuit voltage. Its electron mobility is about three times larger than that of the SnO2. The record power conversion efficiency of planar-type PSCs with EDTA-complexed SnO2 increases to 21.60% (certified at 21.52% by Newport) with negligible hysteresis. Meanwhile, the low-temperature processed EDTA-complexed SnO2 enables 18.28% efficiency for a flexible device. Moreover, the unsealed PSCs with EDTA-complexed SnO2 degrade only by 8% exposed in an ambient atmosphere after 2880 h, and only by 14% after 120 h under irradiation at 100 mW cm−2. The development of high efficiency planar-type perovskite solar cell has been lagging behind the mesoporous-type counterpart. Here Yang et al. modify the oxide based electron transporting layer with organic acid and obtain planar-type cells with high certified efficiency of 21.5% and decent stability.

/pdf/high-efficiency-planar-type-perovskite-solar-cells-with-473dsp8iad.pdf

High efficiency planar-type perovskite solar cells with negligible hysteresis using EDTA-complexed SnO2

Silicon nanowire possesses great potential as the material for renewable energy harvesting and conversion. The significantly reduced spectral reflectivity of silicon nanowire to visible light makes it even more attractive in solar energy applications. However, the benefit of its use for solar thermal energy harvesting remains to be investigated and has so far not been clearly reported. The purpose of this study is to provide practical information and insight into the performance of silicon nanowires in solar thermal energy conversion systems. Spectral hemispherical reflectivity and transmissivity of the black silicon nanowire array on silicon wafer substrate were measured. It was observed that the reflectivity is lower in the visible range but higher in the infrared range compared to the plain silicon wafer. A drying experiment and a theoretical calculation were carried out to directly evaluate the effects of the trade-off between scattering properties at different wavelengths. It is clearly seen that silicon nanowires can improve the solar thermal energy harnessing. The results showed that a 17.8 % increase in the harvest and utilization of solar thermal energy could be achieved using a silicon nanowire array on silicon substrate as compared to that obtained with a plain silicon wafer.

/pdf/silicon-nanowires-for-solar-thermal-energy-harvesting-an-35qf4w71op.pdf

Silicon Nanowires for Solar Thermal Energy Harvesting: an Experimental Evaluation on the Trade-off Effects of the Spectral Optical Properties

Contents: Variety and Quality. Variability loss and tolerance. Determining tolerances. Tolerance design and experimental design. Offline and online quality control. Parameter design and tolerance design: case study. Experimental design for smaller is better characteristics. Experimental design for larger is better characteristics. Bypassing the S/N ratio: spring experiment. Experimental design for dynamic characteristics.

Introduction to quality engineering. designing quality into products a

Fast depleting reserves of conventional energy sources has resulted in an urgent need for increasing energy conversion efficiencies and recycling of waste heat. One of the potential candidates for fulfilling these requirements is thermophotovoltaic (TPV) devices. TPV devices generate electricity from either the complete combustion of different fuels or the waste heat of other energy sources, thereby saving energy. The thermal radiation from the emitter is incident on a TPV cell, which generates electrical currents. Applications of such devices range from hybrid electric vehicles to power sources for microelectronic systems. Absence of any moving parts and versatile fuel usage has made TPV devices very appealing for military and space applications. However, the presently available TPV systems suffer from low conversion efficiency. A viable solution to increase their efficiency is to apply microscale radiation principles in the design of different components to utilize the characteristics of thermal radiation at small distances and in microstructures. In order to have a clear understanding of microscale radiation and its role in TPV devices, several critical issues are reviewed in the present work. Emphasis is given to the development of wavelength-selective emitters and filters and the aspects of microscale heat transfer as applied to TPV systems. Recent progress, along with challenges and opportunities for future development of TPV systems are also outlined. Copyright © 2006 John Wiley & Sons, Ltd.

Microscale radiation in thermophotovoltaic devices- : A review

Design of tungsten complex gratings for thermophotovoltaic radiators

A wavelength-selective but polarization-insensitive thermophotovoltaic emitter was numerically developed with a binary tungsten grating and its appealing emittance spectra were demonstrated with analysis. Ranges of emitter dimensions were preliminarily confined with the excitation of the surface plasmon polariton, cavity resonance, and Wood's anomaly at specified wavelengths. Then, a hybrid scheme (the rigorous coupled wave analysis together with a genetic algorithm) was able to finely tailor the grating profile such that emittance could be significantly enhanced in the near infrared region. The peak emittance at the transverse electric and transverse magnetic polarizations was 0.997 and 0.935, respectively. The emittance was actually almost twice that from a plain tungsten plate at short wavelengths but significantly reduced at long wavelengths. Moreover, such spectral emittance is insensitive to the polarization and 5% dimension modification, making the emitter ideal for thermophotovoltaic applications. Patterns of electromagnetic fields and Poynting vectors were able to confirm the excitation of physical mechanisms.

Development of a polarization-insensitive thermophotovoltaic emitter with a binary grating

Biomedical and chemical sensors utilizing surface plasmon resonance (SPR) in the mid-infrared range were developed with the aid of highly doped silicon owing to its tailored optical constants. SPR may be excited by light incident on a periodic doping profile embedded in an intrinsic silicon film without constraints on the flow of chemical solutions or activities of biomedical samples. General guidance for tuning SPR wavelengths based on dispersion curves to catch different target materials in free space or water was also provided. The feasibility of sensors was demonstrated with a sharp spectral-directional reflectance dip, which shifted with optical constants variation. The effects of doping concentration, doping profile, and angle of incidence on sensor performance were numerically studied with a rigorous coupled-wave analysis algorithm. Developed sensors could work well for a real target and show superiority in sensitivity over existing sensors.

Yu-Bin Chen

Papers

Silicon Nanowires for Solar Thermal Energy Harvesting: an Experimental Evaluation on the Trade-off Effects of the Spectral Optical Properties

Microscale radiation in thermophotovoltaic devices- : A review

Design of tungsten complex gratings for thermophotovoltaic radiators

Development of a polarization-insensitive thermophotovoltaic emitter with a binary grating

Development of mid-infrared surface plasmon resonance-based sensors with highly-doped silicon for biomedical and chemical applications