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KAIST Develops Fiber-Like Light-Emitting Diodes for Wearable Displays
Professor Kyung-Cheol Choi and his research team from the School of Electrical Engineering at KAIST have developed fiber-like light-emitting diodes (LEDs), which can be applied in wearable displays. The research findings were published online in the July 14th issue of Advanced Electronic Materials. Traditional wearable displays were manufactured on a hard substrate, which was later attached to the surface of clothes. This technique had limited applications for wearable displays because they were inflexible and ignored the characteristics of fabric. To solve this problem, the research team discarded the notion of creating light-emitting diode displays on a plane. Instead, they focused on fibers, a component of fabrics, and developed a fiber-like LED that shared the characteristics of both fabrics and displays. The essence of this technology, the dip-coating process, is to immerse and extract a three dimensional (3-D) rod (a polyethylene terephthalate fiber) from a solution, which functions like thread. Then, the regular levels of organic materials are formed as layers on the thread. The dip-coating process allows the layers of organic materials to be easily created on the fibers with a 3-D cylindrical structure, which had been difficult in existing processes such as heat-coating process. By controlling of the withdrawal rate of the fiber, the coating's thickness can also be adjusted to the hundreds of thousandths of a nanometer. The researchers said that this technology would accelerate the commercialization of fiber-based wearable displays because it offers low-cost mass production using roll-to-roll processing, a technology applied to create electronic devices on a roll of flexible plastics or metal foils. Professor Choi said, “Our research will become a core technology in developing light emitting diodes on fibers, which are fundamental elements of fabrics. We hope we can lower the barrier of wearable displays entering the market.” The lead author of the published paper, Seon-Il Kwon, added, “This technology will eventually allow the production of wearable displays to be as easy as making clothes.” Picture 1: The Next Generation Wearable Display Using Fiber-Based Light-Emitting Diodes Picture 2: Dip-Coating Process to Create Fiber-Based Light-Emitting Diodes Picture 3: Fiber-Based Light-Emitting Diodes
KAIST Researchers Develops Hyper-Stretchable Elastic-Composite Energy Harvester
A research team led by Professor Keon Jae Lee (http://fand.kaist.ac.kr) of the Department of Materials Science and Engineering at KAIST has developed a hyper-stretchable elastic-composite energy harvesting device called a nanogenerator. Flexible electronics have come into the market and are enabling new technologies like flexible displays in mobile phone, wearable electronics, and the Internet of Things (IoTs). However, is the degree of flexibility enough for most applications? For many flexible devices, elasticity is a very important issue. For example, wearable/biomedical devices and electronic skins (e-skins) should stretch to conform to arbitrarily curved surfaces and moving body parts such as joints, diaphragms, and tendons. They must be able to withstand the repeated and prolonged mechanical stresses of stretching. In particular, the development of elastic energy devices is regarded as critical to establish power supplies in stretchable applications. Although several researchers have explored diverse stretchable electronics, due to the absence of the appropriate device structures and correspondingly electrodes, researchers have not developed ultra-stretchable and fully-reversible energy conversion devices properly. Recently, researchers from KAIST and Seoul National University (SNU) have collaborated and demonstrated a facile methodology to obtain a high-performance and hyper-stretchable elastic-composite generator (SEG) using very long silver nanowire-based stretchable electrodes. Their stretchable piezoelectric generator can harvest mechanical energy to produce high power output (~4 V) with large elasticity (~250%) and excellent durability (over 104 cycles). These noteworthy results were achieved by the non-destructive stress- relaxation ability of the unique electrodes as well as the good piezoelectricity of the device components. The new SEG can be applied to a wide-variety of wearable energy-harvesters to transduce biomechanical-stretching energy from the body (or machines) to electrical energy. Professor Lee said, “This exciting approach introduces an ultra-stretchable piezoelectric generator. It can open avenues for power supplies in universal wearable and biomedical applications as well as self-powered ultra-stretchable electronics.” This result was published online in the March issue of Advanced Materials, which is entitled “A Hyper-Stretchable Elastic-Composite Energy Harvester.” YouTube Link: “A hyper-stretchable energy harvester” https://www.youtube.com/watch?v=EBByFvPVRiU&feature=youtu.be Figure: Top row: Schematics of hyper-stretchable elastic-composite generator enabled by very long silver nanowire-based stretchable electrodes. Bottom row: The SEG energy harvester stretched by human hands over 200% strain.
Light Driven Drug-Enzyme Reaction Catalytic Platform Developed
Low Cost Dye Used, Hope for Future Development of High Value Medicinal Products to Treat Cardiovascular Disease and Gastric Ulcers A KAIST research team from the Departments of Materials Science and Engineering and of Chemical and Biomolecular Engineering, led respectively by Professors Chan Beum Park and Ki Jun Jeong, has developed a new reaction platform to induce drug-enzyme reaction using light. The research results were published in the journal Angewandte Chemie, International Edition, as the back cover on 12 January 2015. Applications of this technology may enable production of high value products such as medicine for cardiovascular disease and gastric ulcers, for example Omeprazole, using an inexpensive dye. Cytochrome P450 is an enzyme involved in oxidative response which has an important role in drug and hormone metabolism in organisms. It is known to be responsible for metabolism of 75% of drugs in humans and is considered a fundamental factor in new drug development. To activate cytochrome P450, the enzyme must receive an electron by reducing the enzyme. In addition, NADPH (a coenzyme) needs to be present. However, since NADPH is expensive, the use of cytochrome P450 was limited to the laboratory and has not yet been commercialized. The research team used photosensitizer eosin Y instead of NADPH to develop “Whole Cell Photo-Biocatalysis” in bacteria E. coli. By exposing inexpensive eosin Y to light, cytochrome P450 reaction was catalyzed to produce the expensive metabolic material. Professor Park said, “This research enabled industrial application of cytochrome P450 enzyme, which was previous limited.” He continued, “This technology will help greatly in producing high value medical products using cytochrome P450 enzyme.” The research was funded by the National Research Foundation of Korea and KAIST's High Risk High Return Project (HRHRP). Figure 1: Mimetic Diagram of Electron Transfer from Light to Cytochrome P450 Enzyme via Eosin Y, EY Figure 2: The back cover of Angewandte Chemie published on 12 January 2015, showing the research results
KAIST Develops a Method to Transfer Graphene by Stamping
Professor Sung-Yool Choi’s research team from KAIST's Department of Electrical Engineering has developed a technique that can produce a single-layer graphene from a metal etching. Through this, transferring a graphene layer onto a circuit board can be done as easily as stamping a seal on paper. The research findings were published in the January 14th issue of Small as the lead article. This technology will allow different types of wafer transfer methods such as transfer onto a surface of a device or a curved surface, and large surface transfer onto a 4 inch wafer. It will be applied in the field of wearable smart gadgets through commercialization of graphene electronic devices. The traditional method used to transfer graphene onto a circuit board is a wet transfer. However, it has some drawbacks as the graphene layer can be damaged or contaminated during the transfer process from residue from the metal etching. This may affect the electrical properties of the transferred graphene. After a graphene growth substrate formed on a catalytic metal substrate is pretreated in an aqueous poly vinyl alcohol (PVA) solution, a PVA film forms on the pretreated substrate. The substrate and the graphene layers bond strongly. The graphene is lifted from the growth substrate by means of an elastomeric stamp. The delaminated graphene layer is isolated state from the elastomeric stamp and thus can be freely transferred onto a circuit board. As the catalytic metal substrate can be reused and does not contain harmful chemical substances, such transfer method is very eco-friendly. Professor Choi said, “As the new graphene transfer method has a wide range of applications and allows a large surface transfer, it will contribute to the commercialization of graphene electronic devices.” He added that “because this technique has a high degree of freedom in transfer process, it has a variety of usages for graphene and 2 dimensional nano-devices.” This research was sponsored by the Ministry of Science, ICT and Future Planning, the Republic of Korea. Figure 1. Cover photo of the journal Small which illustrates the research findings Figure 2. Above view of Graphene layer transferred through the new method Figure 3. Large surface transfer of Graphene
Breakthrough in Flexible Electronics Enabled by Inorganic-based Laser Lift-off
Flexible electronics have been touted as the next generation in electronics in various areas, ranging from consumer electronics to bio-integrated medical devices. In spite of their merits, insufficient performance of organic materials arising from inherent material properties and processing limitations in scalability have posed big challenges to developing all-in-one flexible electronics systems in which display, processor, memory, and energy devices are integrated. The high temperature processes, essential for high performance electronic devices, have severely restricted the development of flexible electronics because of the fundamental thermal instabilities of polymer materials. A research team headed by Professor Keon Jae Lee of the Department of Materials Science and Engineering at KAIST provides an easier methodology to realize high performance flexible electronics by using the Inorganic-based Laser Lift-off (ILLO). The ILLO process involves depositing a laser-reactive exfoliation layer on rigid substrates, and then fabricating ultrathin inorganic electronic devices, e.g., high density crossbar memristive memory on top of the exfoliation layer. By laser irradiation through the back of the substrate, only the ultrathin inorganic device layers are exfoliated from the substrate as a result of the reaction between laser and exfoliation layer, and then subsequently transferred onto any kind of receiver substrate such as plastic, paper, and even fabric. This ILLO process can enable not only nanoscale processes for high density flexible devices but also the high temperature process that was previously difficult to achieve on plastic substrates. The transferred device successfully demonstrates fully-functional random access memory operation on flexible substrates even under severe bending. Professor Lee said, “By selecting an optimized set of inorganic exfoliation layer and substrate, a nanoscale process at a high temperature of over 1000 °C can be utilized for high performance flexible electronics. The ILLO process can be applied to diverse flexible electronics, such as driving circuits for displays and inorganic-based energy devices such as battery, solar cell, and self-powered devices that require high temperature processes.” The team’s results were published in the November issue of Wiley’s journal, ‘ Advanced Materials, ’ as a cover article entitled “ Flexible Crossbar-Structured Resistive Memory Arrays on Plastic Substrates via Inorganic-Based Laser Lift-Off.” ( http://onlinelibrary.wiley.com/doi/10.1002/adma.201402472/abstract ) This schematic picture shows the flexible crossbar memory developed via the ILLO process. This photo shows the flexible RRAM device on a plastic substrate.
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