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Phys.org: Researchers develop non-iridescent, structural, full-spectrum pigments for reflective displays
The latest research work by Professor Shin-Hyun Kim of Chemical and Biomolecular Engineering at KAIST on the “microcapsulation og photonic crystals using osmotic pressure” has been published by Phys.org, a leading web-based science, research and technology news. For the articles, please click the link below:February 20, 2014Researchers develop non-iridescent, structural, full-spectrum pigments for reflective displayshttp://phys.org/news/2014-02-non-iridescent-full-spectrum-pigments.html
Photonic crystals allow the fabrication of miniaturized spectrometers
By Courtesy of Nanowerk Photonic crystals allow the fabrication of miniaturized spectrometers (Nanowerk Spotlight) Spectrometers are used in materials analysis by measuring the absorption of light by a surface or chemical substance. These instruments measure properties of light over a specific portion of the electromagnetic spectrum. In conventional spectrometers, a diffraction grating splits the light source into several beams with different propagation directions according to the wavelength of the light. Thus, to achieve sufficient spatial separation for intensity measurements at a small slit, a long light path – i.e., a large instrument – is required. However, for lab-on-a-chip or microTAS (total analysis system) applications, the spectrometer must be integrated into a sub-centimeter scale device to produce a stand-alone platform. To achieve this, researchers at the Korea Advanced Institute of Science and Technology (KAIST) propose a new paradigm in which the spectrometer is based on an array of photonic crystals with different bandgaps. "Because photonic crystals refelct light of different wavelengths selectively depending on their bandgaps, we can generate reflected light spanning the entire wavelength range for analysis at different spatial positions using patterned photonic crystals," Seung-Man Yang, Director of the National Creative Research Initiative Center for Intergrated Optofluidic Systems and Professor of the Department of Chemical & Biomolecular Engineering at KAIST, tells Nanowerk. "Therefore, when the light source impinges on the patterned photonic crytals, we can construct the spectrum using the reflection intensity profile from the constituent photonic crystals." Photonic crystals – also known as photonic band gap material – are similar to semiconductors, only that the electrons are replaced by photons (i.e. light). By creating periodic structures out of materials with contrast in their dielectric constants, it becomes possible to guide the flow of light through the photonic crystals in a way similar to how electrons are directed through doped regions of semiconductors. The photonic band gap (that forbids propagation of a certain frequency range of light) gives rise to distinct optical phenomena and enables one to control light with amazing facility and produce effects that are impossible with conventional optics. To demonstrate this new concept based on patterned photonic crystals, Yang and his group used non-close-packed colloidal crystals of silica particles dispersed in photocurable resin. Due to the repulsive interparticle potential, monodisperse silica particles spontaneously crystallize into non-close-packed face-centered cubic (fcc) structures at volume fractions above 0.1. Therefore, the particle volume fraction determines both the lattice constant and the bandgap position. a) Optical image of an ETPTA film containing porous photonic crystal stripe patterns with 20 different bandgaps. b) Reflectance spectra from the 20 strips. c) Optical microscope image of the middle region with the parallel stripe pattern (denoted as white-dotted box in a). d) Cross-sectional SEM images of first, sixth, eleventh and seventeenth strips. The scale bars in a, c and d are 1 cm, 2mm and 2 µm, respectively. (reprinted with permission from Wiley-VCH Verlag) Reporting their findings in a recent issue of Advanced Materials ("Integration of Colloidal Photonic Crystals toward Miniaturized Spectrometers"), the KAIST team has demonstrated the integration of colloidal photonic crystals with 20 different bandgaps into freestanding films (prepared by soft lithography), and their application as a spectrometer. Yang explains that the team was able to precisely control the photonic bandgap by varying the particle size and volume fration. "The prepared colloidal composite structures showed high physical rigidity and chemical resistivity" he says. "The composite structure is suitable for spectroscopic use due to the small full widths at half maximum (FWHMs) of the reflectance spectra, which mean that there is little overlap of the reflectance spectra of neighboring photonic crystal strips." "On the other hand" says Yang, "porous photonic crystals showed large FWHMs and high reflectivities, which should prove useful in many practical photonic applications that require high optical performance and physical rigidity as well as simple and inexpensive preparation." In addition to fabricating miniaturized spectrometers, which can for instance be integrated into small lab-on-a-chip devices, these integrated photonic crystals can be potentially used for tunable band reflection mirrors, optical switches, and tunable lasing cavities. Moreover, patterned photonic crystals with RGB colors are well-suited for use in reflection-mode microdisplay devices. Yang points out that, although the spectrometric resolution can be reduced by employing the smaller bandgap interval and photonic bandwidth, there is a limitation. "Now, we are studying photonic crystals with continuous modulation of bandgap position. We expect that the photonic crystals can reduce the resolution to 0.01 nm." By Michael Berger. Copyright 2010 Nanowerk
Three Professors Selected as IEEE Fellows
Three Korea Advanced Institute of Science and Technology (KAIST)’s professors, Ju-Jang Lee, Yong-Hee Lee, and Hoi-Jun Yoo, were selected as a part of the 2008 Institute of Electrical and Electronics Engineers, Inc (IEEE)’s “Fellows.” A Fellow is the highest level of membership given only to those “with an extraordinary record of accomplishments” in their field of study. Although some IEEE memberships can be gained freely by all, the Fellow status is bestowed only by the IEEE Board of Directors. Professor Ju-Jang Lee was awarded the Fellow status “for contributions to intelligent robust control and robotics.” Robust control is a system’s stable maintenance under many inputs in a dynamic environment. A part of KAIST’s Electrical Engineering Department, Professor Ju-Jang Lee has conducted successful research in these fields, and has published 538 papers. He also holds many patents in and outside of the country, and is the General Chair for two upcoming IEEE conferences in 2008 and 2009. Professor Yong-Hee Lee of KAIST’s Physics Department was recognized for his “contributions to photonic devices based upon vertical cavity surface emitting lasers and photonic crystals.” Photonic devices are those that allow the practical use of photons, and photon crystals are structures that affect the motion of photons. Professor Yong-Hee Lee is an expert in the field of Photonics and his works have been cited over 2500 times. He is also an outstanding speaker, giving over 30 lectures in front of international audiences in the past 5 years, and receiving The Distinguished Lecturer’s Award from IEEE. Professor Hoi-Jun Yoo was granted the prestigious Fellow status for his “contributions to low-power and high-speed VLSI design.” VLSI stands for ‘very large scale integration’ and refers to the skill for packing a huge number of semiconductors on an integrated circuit. Professor Lee’s Fellow status is noteworthy in that he studied, worked, and researched solely in Korea. He is also the youngest of the three KAIST professors to be granted membership in the class of 2008 Fellowship. IEEE also recognized Professor Yoo as the most frequent publisher during the past 8 years. IEEE, originally concentrating on Electric Engineering, has now branched into many related fields. It is a nonprofit organization, and its aim is to be the world"s leading professional association for the advancement of technology. For its Fellow Class of 2008, 295 members were chosen; which is less that 0.1% of their total members.By KAIST Herald on December, 2007
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