research
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Robot Drone Man: A
Research Professor Ilhan Bae of the Moon Soul Graduate School of Future Strategy at KAIST created a life-size humanoid robot on a drone platform, which gives users the experience of virtual flight and an opportunity to interact with people at remote locations. Professor Bae calls his new creation a "telepresence robot."
This avatar drone is a new application of drone and robotics technology, which extends the reach of human presence and mobility, Professor Bae explained his research.
“As a futurist, I forecast that drone technology will soon evolve to become another body for humans, and I wanted to demonstrate this potential application of drones. Avatar drones are especially useful for people who need to meet or manage other people face to face in remote locations,” he said.
For example, if elderly people with physical disabilities want to engage in social gatherings, this avatar drone is designed to help them do just that.
For more details, please see the link below:
Behind the Music: How Robot Drone Man Built His Flying Avatar
IEEE Spectrum, November 7, 2016
2016.11.08 View 6326 -
Technology to Allow Non-Magnetic Materials to Have Magnetic Properties by Professor Chan-Ho Yang
Professor Chan-Ho Yang and his research team from the Department of Physics at KAIST have developed a technology that allows non-magnetic materials to have magnetic properties or, in reverse, to remove magnetic properties from a magnet using an electric field.
Based on this research, it is expected that if magnetic-material-based data storage is developed, applications for high-speed massive data transfer will be possible.
The results of this research, with Ph.D. candidate Byung-Kwon Jang as the first author, were published online in Nature Physics on October 3.
Very small magnets exist inside of any materials. If the direction of the minuscule magnets is dis-aligned, pointing multiple directions, it is non-magnetic. If the direction is aligned in a certain direction, the material holds magnetic property just like any magnet we normally see.
Data storage capacity technology has rapidly advanced to the point where we can easily get a portable hard disk drive (HDD) with terabyte-level storage; however, the increase in storage is inevitably followed by slower data access speed for a storage device. Although HDDs are currently the most widely used data storage devices, their technical applications are limited due to their slow data access speed.
Other methods such as solid-state drives (SSDs), floating gates, and resistive switching have been developed as alternatives. Yet, they leave tracks every time data is written, and this can cause fatigue cumulative damage.
There have been many attempts to compose cells—the smallest data storage space on a storage device—with magnetic materials as that would enable faster data access speeds and remove fatigue cumulative damage. Generally, the techniques tried by researchers were to use induced magnetic fields through current flow. However, magnetic fields are very difficult to shield and can affect a large area. As a result, they alternate the magnetic property of adjacent cells. Because each cell cannot be adjusted one by one, it cannot also be arranged in a certain direction, and therefore, it is hard to change the magnetic state.
Professor Yang and his team adjusted the magnetic state by using magnetoelectric interaction to deal with this issue. Instead of using magnetic fields, magnetoelectric interaction is a method that uses an electric field to adjust the magnetic state. It has the advantage of smaller energy consumption as well.
Professor Yang's team demonstrated that cells facing random directions can be arranged in a certain direction by only inducing an electric field. In addition, the reverse was also proved to be feasible.
Until this research, most cases of previous findings were only feasible at extremely low temperatures or high temperatures, but the technology developed by the research team is practicable at room temperature by manipulating chemical pressure. It allows for a reversible magnetic state, and moreover, is non-volatile. Therefore, the results of this research are expected to provide the basis for developing next-generation information storage device.
Professor Yang said, “The changes in the electric magnetic state will be accompanied by entropy changes” and added, “Our research is expected to open new potential for future applications not only for magnetoelectric devices, but also for thermoelectric effect.”
This research has been worked on jointly with Dr. Si-Yong Choi from the Korea Institute of Materials Science, Prof. Yoon-Hee Jeong from the Pohang University of Science and Technology, Dr. Tae-Yeong Koo from the Pohang Accelerator Laboratory, Dr. Kyung-Tae Ko from the Max Planck Institute for Chemical Physics of Solids, Dr. Jun-Sik Lee and Dr. Hendrik Ohldag from the SLAC National Accelerator Laboratory of the United States, and Prof. Jan Seidel from the University of New South Wales of Australia.
The research was supported by the Mid-Career Researcher Program of the National Research Foundation of Korea, Global Research Network Support Project, Leading Research Center Support Project (Condensed Quantum Coherence Research Center), Global Frontier Project (Hybrid Interface Materials Research Group), and others.
Picture: The concept graphic for the electric-field-induced magnetic phase switching the magnetic direction
2016.11.04 View 7838 -
Extremely Thin and Highly Flexible Graphene-Based Thermoacoustic Speakers
A joint research team led by Professors Jung-Woo Choi and Byung Jin Cho of the School of Electrical Engineering and Professor Sang Ouk Kim of the Material Science and Engineering Department, all on the faculty of the Korea Advanced Institute of Science and Technology (KAIST), has developed a simpler way to mass-produce ultra-thin graphene thermosacoustic speakers.
Their research results were published online on August 17, 2016 in a journal called Applied Materials & Interfaces. The IEEE Spectrum, a monthly magazine published by the Institute of Electrical and Electronics Engineers, reported on the research on September 9, 2016, in an article titled, “Graphene Enables Flat Speakers for Mobile Audio Systems.” The American Chemical Society also drew attention to the team’s work in its article dated September 7, 2016, “Bringing Graphene Speakers to the Mobile Market.”
Thermoacoustic speakers generate sound waves from temperature fluctuations by rapidly heating and cooling conducting materials. Unlike conventional voice-coil speakers, thermoacoustic speakers do not rely on vibrations to produce sound, and thus do not need bulky acoustic boxes to keep complicated mechanical parts for sound production. They also generate good quality sound in all directions, enabling them to be placed on any surface including curved ones without canceling out sounds generated from opposite sides.
Based on a two-step, template-free fabrication method that involved freeze-drying a solution of graphene oxide flakes and the reduction/doping of oxidized graphene to improve electrical properties, the research team produced a N-doped, three-dimensional (3D), reduced graphene oxide aerogel (N-rGOA) with a porous macroscopic structure that permitted easy modulation for many potential applications.
Using 3D graphene aerogels, the team succeeded in fabricating an array of loudspeakers that were able to withstand over 40 W input power and that showed excellent sound pressure level (SPL), comparable to those of previously reported 2D and 3D graphene loudspeakers.
Choong Sun Kim, the lead author of the research paper and a doctoral student in the School of Electrical Engineering at KAIST, said:
“Thermoacoustic speakers have a higher efficiency when conducting materials have a smaller heat capacity. Nanomaterials such as graphene are an ideal candidate for conductors, but they require a substrate to support their extremely thinness. The substrate’s tendency to lose heat lowers the speakers’ efficiency. Here, we developed 3D graphene aerogels without a substrate by using a simple two-step process. With graphene aerogels, we have fabricated an array of loudspeakers that demonstrated stable performance. This is a practical technology that will enable mass-production of thermosacoustic speakers including on mobile platforms.”
The research paper is entitled “Application of N-Doped Three-Dimensional Reduced Graphene Oxide Aerogel to Thin Film Loudspeaker.” (DOI: 10.1021/acsami.6b03618)
Figure 1: A Thermoacoustic Loudspeaker Consisted of an Array of 16 3D Graphene Aerogels
Figure 2: Two-step Fabrication Process of 3D Reduced Graphene Oxide Aerogel Using Freeze-Drying and Reduction/Doping
Figure 3: X-ray Photoelectron Spectroscopy Graph of the 3D Reduced Graphene Oxide Aerogel and Its Scanning Electron Microscope Image
2016.10.05 View 13501 -
Direct Utilization of Elemental Sulfur for Microporous Polymer Synthesis
Using elemental sulfur as an alternative chemical feedstock, KAIST researchers have produced novel microporous polymers to sift CO2 from methane in natural-gas processing.
Methane, a primary component of natural gas, has emerged recently as an important energy source, largely owing to its abundance and relatively clean nature compared with other fossil fuels. In order to use natural gas as a fuel, however, it must undergo a procedure called “hydrodesulfurization” or “natural gas sweetening” to reduce sulfur-dioxide emissions from combustion of fossil fuels. This process leads to excessive and involuntary production of elemental sulfur. Although sulfur is one of the world’s most versatile and common elements, it has relatively few large-scale applications, mostly for gunpowder and sulfuric acid production.
Thus, the development of synthetic and processing methods to convert sulfur into useful chemicals remains a challenge. A research team led by Professor Ali Coskun from the Graduate School of EEWS (Energy, Environment, Water and Sustainability) at Korea Advanced Institute of Science and Technology (KAIST) has recently introduced a new approach to resolving this problem by employing elemental sulfur directly in the synthesis of microporous polymers for the process of natural-gas sweetening.
Natural gas, containing varying amounts of carbon dioxide (CO2) and hydrogen sulfide (H2S), is generally treated with amine solutions, followed by the regeneration of these solutions at increased temperatures to release captured CO2 and H2S. A two-step separation is involved in removing these gases. The amine solutions first remove H2S, and then CO2 is separated from methane (CH4) with either amine solutions or porous sorbents such as microporous polymers.
Using elemental sulfur and organic linkers, the research team developed a solvent and catalyst-free strategy for the synthesis of ultramicroporous benzothiazole polymers (BTAPs) in quantitative yields. BTAPs were found to be highly porous and showed exceptional physiochemical stability. In-situ chemical impregnation of sulfur within the micropores increased CO2 affinity of the sorbent, while limiting diffusion of CH4. BTAPs, as low-cost, scalable solid-sorbents, showed outstanding CO2 separation ability for flue gas, as well as for natural and landfill gas conditions.
The team noted that: “Each year, millions of tons of elemental sulfur are generated as a by-product of petroleum refining and natural-gas processing, but industries and businesses lacked good ideas for using it. Our research provides a solution: the direct utilization of elemental sulfur into the synthesis of ultramicroporous polymers that can be recycled back into an efficient and sustainable process for CO2 separation. Our novel polymeric materials offer new possibilities for the application of a little-used natural resource, sulfur, to provide a sustainable solution to challenging environmental issues.”
This work was published online in Chem on September 8, 2016 and also highlighted in C&EN (Chemical & Engineering News) by the American Chemical Society (ACS) on September 19, 2016. The research paper was entitled “Direct Utilization of Elemental Sulfur in the Synthesis of Microporous Polymers for Natural Gas Sweetening.” (DOI: 10.1016/j.chempr.2016.08.003)
Figure 1. A Schematic Image of Direct Utilization of Elemental Sulfur
This image shows direct utilization of elemental sulfur in the synthesis of microporous polymers and its gas separation performance.
Figure 2. BTAP’s Breakthrough Experiment under Pre-mixed Gas Conditions
This data presents the breakthrough measurements for CO2-containing binary gas-mixture streams with different feed-gas compositions to investigate the CO2 capture capacity of ultramicroporous benzothiazole polymers (BTAPs) for large-scale applications under simulated conditions of natural and landfill gases.
2016.10.05 View 8967 -
Continuous Roll-Process Technology for Transferring and Packaging Flexible Large-Scale Integrated Circuits
A research team led by Professor Keon Jae Lee from KAIST and by Dr. Jae-Hyun Kim from the Korea Institute of Machinery and Materials (KIMM) has jointly developed a continuous roll-processing technology that transfers and packages flexible large-scale integrated circuits (LSI), the key element in constructing the computer’s brain such as CPU, on plastics to realize flexible electronics.
Professor Lee previously demonstrated the silicon-based flexible LSIs using 0.18 CMOS (complementary metal-oxide semiconductor) process in 2013 (ACS Nano, “In Vivo Silicon-based Flexible Radio Frequency Integrated Circuits Monolithically Encapsulated with Biocompatible Liquid Crystal Polymers”) and presented the work in an invited talk of 2015 International Electron Device Meeting (IEDM), the world’s premier semiconductor forum.
Highly productive roll-processing is considered a core technology for accelerating the commercialization of wearable computers using flexible LSI. However, realizing it has been a difficult challenge not only from the roll-based manufacturing perspective but also for creating roll-based packaging for the interconnection of flexible LSI with flexible displays, batteries, and other peripheral devices.
To overcome these challenges, the research team started fabricating NAND flash memories on a silicon wafer using conventional semiconductor processes, and then removed a sacrificial wafer leaving a top hundreds-nanometer-thick circuit layer. Next, they simultaneously transferred and interconnected the ultrathin device on a flexible substrate through the continuous roll-packaging technology using anisotropic conductive film (ACF). The final silicon-based flexible NAND memory successfully demonstrated stable memory operations and interconnections even under severe bending conditions. This roll-based flexible LSI technology can be potentially utilized to produce flexible application processors (AP), high-density memories, and high-speed communication devices for mass manufacture.
Professor Lee said, “Highly productive roll-process was successfully applied to flexible LSIs to continuously transfer and interconnect them onto plastics. For example, we have confirmed the reliable operation of our flexible NAND memory at the circuit level by programming and reading letters in ASCII codes. Out results may open up new opportunities to integrate silicon-based flexible LSIs on plastics with the ACF packing for roll-based manufacturing.”
Dr. Kim added, “We employed the roll-to-plate ACF packaging, which showed outstanding bonding capability for continuous roll-based transfer and excellent flexibility of interconnecting core and peripheral devices. This can be a key process to the new era of flexible computers combining the already developed flexible displays and batteries.”
The team’s results will be published on the front cover of Advanced Materials (August 31, 2016) in an article entitled “Simultaneous Roll Transfer and Interconnection of Silicon NAND Flash Memory.” (DOI: 10.1002/adma.201602339)
YouTube Link: https://www.youtube.com/watch?v=8OJjAEm27sw
Picture 1: This schematic image shows the flexible silicon NAND flash memory produced by the simultaneous roll-transfer and interconnection process.
Picture 2: The flexible silicon NAND flash memory is attached to a 7 mm diameter glass rod.
2016.09.01 View 11300 -
KAIST Team Develops Semi-Transparent Solar Cells with Thermal Mirror Capability
A research team led by KAIST and Sungkyunkwan University professors has created semi-transparent perovskite solar cells that demonstrate high-power conversion efficiency and transmit visible light while blocking infrared light, making them great candidates for solar windows.
Modern architects prefer to build exteriors designed with glass mainly from artistic or cost perspectives. Scientists, however, go one step further and see opportunities from its potential ability to harness solar energy. Researchers have thus explored ways to make solar cells transparent or semi-transparent as a substitute material for glass, but this has proven to be a challenging task because solar cells need to absorb sunlight to generate electricity, and when they are transparent, it reduces their energy efficiency.
Typical solar cells today are made of crystalline silicon, but it is difficult to make them translucent. Semi-transparent solar cells under development use, for example, organic or dye-sensitized materials, but compared to crystalline silicon-based cells, their power-conversion efficiencies are relatively low. Perovskites are hybrid organic-inorganic halide-based photovoltaic materials, which are cheap to produce and easy to manufacture. They have recently received much attention as the efficiency of perovskite solar cells has rapidly increased to the level of silicon technologies in the past few years.
Using perovskites, a Korean research team led by Professor Seunghyup Yoo of the Electrical Engineering School at KAIST and Professor Nam-Gyu Park of the Chemical Engineering School at Sungkyunkwan University developed a semi-transparent solar cell that is highly efficient and, additionally, functions very effectively as a thermal-mirror.
The team has developed a top transparent electrode (TTE) that works well with perovskite solar cells. In most cases, a key to success in realizing semi-transparent solar cells is to find a TTE that is compatible with a given photoactive material system, which is also the case for perovskite solar cells. The proposed TTE is based on a multilayer stack consisting of a metal film sandwiched between a high refractive-index (high-index) layer and an interfacial buffer layer. This TTE, placed as a top-most layer, can be prepared without damaging ingredients used in perovskite solar cells. Unlike conventional transparent electrodes focusing only on transmitting visible light, the proposed TTE plays the dual role of passing through visible light while reflecting infrared rays. The semi-transparent solar cells made with the proposed TTEs exhibited average power conversion efficiency as high as 13.3% with 85.5% infrared rejection.
The team believes that if the semi-transparent perovskite solar cells are scaled up for practical applications, they can be used in solar windows for buildings and automobiles, which not only generate electrical energy but also enable the smart heat management for indoor environments, thereby utilizing solar energy more efficiently and effectively.
This result was published as a cover article in the July 20, 2016 issue of Advanced Energy Materials. The research paper is entitled “Empowering Semi-transparent Solar Cells with Thermal-mirror Functionality.” (DOI: 10.1002/aenm.201502466)
The team designed the transparent electrode (TE) stack in three layers: A thin-film of silver (Ag) is placed in between the bottom interfacial layer of molybdenum trioxide (MoO3) and the top high-index dielectric layer of zinc sulfide (ZnS). Such a tri-layer approach has been known as a means to increase the overall visible-light transmittance of metallic thin films via index matching technique, which is essentially the same technique used for anti-reflection coating of glasses except that the present case involves a metallic layer.
Traditionally, when a TE is based on a metal film, such as Ag, the film should be extremely thin, e.g., 7-12 nanometers (nm), to obtain transparency and, accordingly, to transmit visible light. However, the team took a different approach in this research. They made the Ag TE two or three times thicker (12-24 nm) than conventional metal films and, as a result, it reflected more infrared light. The high refractive index of the ZnS layer plays an essential role in keeping the visible light transmittance of the proposed TTE high even with the relatively thick Ag film when its thickness is carefully optimized for maximal destructive interference, leading to low reflectance (and thus high transmittance) within its visible light range.
The team confirmed the semi-transparent perovskite solar cell’s thermal-mirror function through an experiment in which a halogen lamp illuminated an object for five minutes through three mediums: a window of bare glass, automotive tinting film, and the proposed semi-transparent perovskite solar cell. An infrared (IR) camera took thermal images of the object as well as that of each window’s surface. The object’s temperature, when exposed through the glass window, rose to 36.8 Celsius degrees whereas both the tinting film and the cell allowed the object to remain below 27 Celsius degrees. The tinting film absorbs light to block solar energy, so the film’s surface became hot as it was continuously exposed to the lamp light, but the proposed semi-transparent solar cell stayed cool since it rejects solar heat energy by reflection, rather than by absorption. The total solar energy rejection (TSER) of the proposed cell was as high as 89.6%.
Professor Yoo of KAIST said, “The major contributions of this work are to find transparent electrode technology suitable for translucent perovskite cells and to provide a design approach to fully harness the potential it can further deliver as a heat mirror in addition to its main role as an electrode. The present work can be further fine-tuned to include colored solar cells and to incorporate flexible or rollable form factors, as they will allow for greater design freedom and thus offer more opportunities for them to be integrated into real-world objects and structures such as cars, buildings, and houses.”
The lead authors are Hoyeon Kim and Jaewon Ha, both Ph.D. candidates in the School of Electrical Engineering at KAIST, and Hui-Seon Kim, a student in the School of Chemical Engineering at Sungkyunkwan University. This research was supported mainly by the Climate Change Research Hub Program of KAIST.
Picture 1: Semi-transparent Perovskite Solar Cell
This picture shows a prototype of a semi-transparent perovskite solar cell with thermal-mirror functionality.
Picture 2: A Heat Rejection Performance Comparison Experiment
This picture presents thermal images taken by an infrared camera for comparing the heat rejection performance of bare glass, automotive tinting film, and a semi-transparent perovskite solar cell after being illuminated by a halogen lamp for five minutes.
2016.08.02 View 12389 -
KAIST Develops Transparent Oxide Thin-Film Transistors
With the advent of the Internet of Things (IoT) era, strong demand has grown for wearable and transparent displays that can be applied to various fields such as augmented reality (AR) and skin-like thin flexible devices. However, previous flexible transparent displays have posed real challenges to overcome, which are, among others, poor transparency and low electrical performance. To improve the transparency and performance, past research efforts have tried to use inorganic-based electronics, but the fundamental thermal instabilities of plastic substrates have hampered the high temperature process, an essential step necessary for the fabrication of high performance electronic devices.
As a solution to this problem, a research team led by Professors Keon Jae Lee and Sang-Hee Ko Park of the Department of Materials Science and Engineering at the KAIST has developed ultrathin and transparent oxide thin-film transistors (TFT) for an active-matrix backplane of a flexible display by using the inorganic-based laser lift-off (ILLO) method. Professor Lee’s team previously demonstrated the ILLO technology for energy-harvesting (Advanced Materials, February 12, 2014) and flexible memory (Advanced Materials, September 8, 2014) devices.
The research team fabricated a high-performance oxide TFT array on top of a sacrificial laser-reactive substrate. After laser irradiation from the backside of the substrate, only the oxide TFT arrays were separated from the sacrificial substrate as a result of reaction between laser and laser-reactive layer, and then subsequently transferred onto ultrathin plastics ( thickness). Finally, the transferred ultrathin-oxide driving circuit for the flexible display was attached conformally to the surface of human skin to demonstrate the possibility of the wearable application. The attached oxide TFTs showed high optical transparency of 83% and mobility of even under several cycles of severe bending tests.
Professor Lee said, “By using our ILLO process, the technological barriers for high performance transparent flexible displays have been overcome at a relatively low cost by removing expensive polyimide substrates. Moreover, the high-quality oxide semiconductor can be easily transferred onto skin-like or any flexible substrate for wearable application.”
These research results, entitled “Skin-Like Oxide Thin-Film Transistors for Transparent Displays,”
(http://onlinelibrary.wiley.com/doi/10.1002/adfm.201601296/abstract) were the lead article published in the July 2016 online issue of Wiley’s Advanced Functional Materials.
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References
[1] Advanced Materials, February 12, 2014, Highly-efficient, Flexible Piezoelectric PZT Thin Film Nanogenerator on Plastic Substrates
(http://onlinelibrary.wiley.com/doi/10.1002/adma.201305659/abstract)
[2] Advanced Materials, September 8, 2014, Flexible Crossbar-structured Resistive Memory Arrays on Plastic Substartes via Inorganic-based Laser Lift-off
(http://onlinelibrary.wiley.com/doi/10.1002/adma.201402472/abstract)
Picture 1: A Schamatic Image of Ultrathin, Flexible, and Transparent Oxide Thin-film Transistors
This image shows ultrathin, flexible, and transparent oxide thin-film transistors produced via the ILLO process.
Picture 2: Application of Uultrathin, Flexible, and Transparent Oxide Thin-film Transistors
This picture shows ultrathin, flexible, and transparent oxide thin-film transistors attached to a jumper sleeve and human skin.
2016.08.01 View 12409 -
Professor Seyun Kim Identifies a Neuron Signal Controlling Molecule
A research team led by Professor Seyun Kim of the Department of Biological Sciences at KAIST has identified inositol pyrophosphates as the molecule that strongly controls neuron signaling via synaptotagmin.
Professors Tae-Young Yoon of Yonsei University’s Y-IBS and Sung-Hyun Kim of Kyung Hee University’s Department of Biomedical Science also joined the team.
The results were published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) on June 30, 2016.
This interdisciplinary research project was conducted by six research teams from four different countries and covered a wide scope of academic fields, from neurobiology to super resolution optic imaging.
Inositol pyrophosphates such as 5-diphosphoinositol pentakisphos-phate (5-IP7), which naturally occur in corns and beans, are essential metabolites in the body. In particular, inositol hexakisphosphate (IP6) has anti-cancer properties and is thought to have an important role in cell signaling.
Inositol pentakisphosphate (IP7) differs from IP6 by having an additional phosphate group, which was first discovered 20 years ago. IP7 has recently been identified as playing a key role in diabetes and obesity.
Psychopathy and neurodegenerative diseases are known to result from the disrupted balance of inositol pyrophosphates. However, the role and the mechanism of action of IP7 in brain neurons and nerve transmission remained unknown.
Professor Kim’s team has worked on inositol pyrophosphates for several years and discovered that very small quantities of IP7 control cell-signaling transduction. Professor Yoon of Yonsei University identified IP7 as a much stronger inhibitor of neuron signaling compared to IP6. In particular, IP7 directly suppresses synaptotagmin, one of the key proteins in neuron signaling. Moreover, Professor Kim of Kyung Hee University observed IP7 inhibition in sea horse neurons.
Together, the joint research team identified inositol pyrophosphates as the key switch metabolite of brain-signaling transduction.
The researchers hope that future research on synaptotagmin and IP7 will reveal the mechanism of neuron-signal transduction and thus enable the treatment of neurological disorders.
These research findings were the result of cooperation of various science and technology institutes: KAIST, Yonsei-IBS (Institute for Basic Science), Kyung Hee University, Sungkyunkwan University, KIST, University of Zurich in Switzerland, and Albert-Ludwigs-University Freiburg in Germany.
Schematic Image of Controlling the Synaptic Exocytotic Pathway by 5-IP7 , Helping the Understanding of the Signaling Mechanisms of Inositol Pyrophosphates
2016.07.21 View 11624 -
Synthesized Microporous 3D Graphene-like Carbons
Distinguished Professor Ryong Ryoo of the Chemistry Department at KAIST, who is also the Director of the Center for Nanomaterials and Carbon Materials at the Institute for Basic Science (IBS), and his research team have recently published their research results entitled "Lanthanum-catalysed Synthesis of Microporous 3D Graphene-like Carbons in a Zeolite Template" on June 29, 2016 in Nature on a new method to synthesize carbons having graphene structures with 3D periodic micropores, a trait resulted from using a zeolite as a template for the synthesis. The research team expects this technology to find a range of useful applications such as in batteries and catalysts.
Graphene, an allotrope of carbon, which was discovered more than a decade ago, has led to myriad research that seeks to unlock its vast potential. Zeolites, commonly used microporous solid catalysts in the petrochemical industry, have recently attracted attention in the field of material science as a template for carbon synthesis. Zeolites’ individual crystal is distinguished by its unique 1 nanometer (nm)-size pore structures. These structures facilitate the accommodation of carbon nanotubes inside zeolites. In their paper, the research team showed that these nanoporous systems are an ideal template for the carbon synthesis of three-dimensional (3D) graphene architecture, but zeolite pores are too small to accommodate bulky molecular compounds like polyaromatic and furfuryl alcohol that are often used in carbon synthesis. Small molecules like ethylene and acetylene can be used as a carbon source to achieve successful carbonization within zeolite pores, but it comes at a great cost. The high temperatures required for the synthesis cause reactions of carbons being deposited randomly on the external surfaces of zeolites as well as their internal pore walls, resulting in coke deposition and consequently, causing serious diffusion limitations in the zeolite pores.
The team from the IBS Center for Nanomaterials and Carbon Materials solved this conundrum with a novel approach. First author Dr. KIM Kyoungsoo explains: “The zeolite-template carbon synthesis has existed for a long time, but the problem with temperatures has foiled many scientists from extracting their full potential. Here, our team sought to find the answer by embedding lanthanum ions (La3+), a silvery-white metal element, in zeolite pores. This lowers the temperature required for the carbonization of ethylene or acetylene. Graphene-like sp2 carbon structures can be selectively formed inside the zeolite template, without carbon deposition at the external surfaces. After the zeolite template is removed, the carbon framework exhibits the electrical conductivity two orders of magnitude higher than amorphous mesoporous carbon, which is a pretty astonishing result. This highly efficient synthesis strategy based on the lanthanum ions renders the carbon framework to be formed in pores with a less than 1 nm diameter, just like as easily reproducible as in mesoporous templates. This provides a general method to synthesize carbon nanostructures with various topologies corresponding to the template zeolite pore topologies, such as FAU, EMT, beta, LTL, MFI, and LTA. Also, all the synthesis can be readily scaled up, which is important for practical applications in areas of batteries, fuel storage, and other zeolite-like catalyst supports.”
The research team began their experiment by utilizing La3+ ions. Dr. KIM elucidates why this silvery-white element proved so beneficial to the team, “La3+ ions are unreducible under carbonization process condition, so they can stay inside the zeolite pores instead of moving to the outer zeolite surface in the form of reduced metal particles. Within the pores, they can stabilize ethylene and the pyrocondensation intermediately to form a carbon framework in zeolites.”
In order to test this hypothesis, the team compared the amount of carbon deposited in La3+-containing form of Y zeolite (LaY) sample against a host of other samples such as NaY and HY. The experimental results indicate that all the LaY, NaY, and HY zeolite samples show rapid carbon deposition at 800°C. However, as the temperature decreases, there appears to be a dramatic difference between the different ionic forms of zeolites. At 600°C, the LaY zeolite is still active as a carbon deposition template. In contrast, both NaY and HY lose their carbon deposition functions almost completely.
The results, according to their paper published in Nature, highlight a catalytic effect of lanthanum for carbonization. By making graphene with 3D periodic nanoporous architectures, it promises a wide range of useful applications such as in batteries and catalysts but due to the lack of efficient synthetic strategies, such applications have not yet been successful. By taking advantage of the pore-selective carbon filling at decreased temperatures, the synthesis can readily be scaled up for studies requiring bulk quantities of carbon, in particular high electrical conductivity, which is a highly sought aspect for the production of batteries.
YouTube Link: https://youtu.be/lkNiHiB8lBk
Image 1: (Top to Bottom) Zeolite Template: Microporous Aluminosilicate; Zeolite ion exchanged with La3+ ions in aqueous solution; and Zeolite Template with La3+ ions
Image 2: (Top to Bottom) Catalytic carbonization progressed at La3+ ions-exchanged sites using ethylene as a carbon precursor. Carbon is highlighted in grey; Zeolite template removed in an acid solution (HF/ HCl); Microporous 3D graphene-like carbon
2016.07.01 View 9292 -
Unveiling the Distinctive Features of Industrial Microorganism
KAIST researchers have sequenced the whole genome of Clostridium tyrobutyricum, which has a higher tolerance to toxic chemicals, such as 1-butanol, compared to other clostridial bacterial strains.
Clostridium tyrobutyricum, a Gram-positive, anaerobic spore-forming bacterium, is considered a promising industrial host strain for the production of various chemicals including butyric acid which has many applications in different industries such as a precursor to biofuels. Despite such potential, C. tyrobutyricum has received little attention, mainly due to a limited understanding of its genotypic and metabolic characteristics at the genome level.
A Korean research team headed by Distinguished Professor Sang Yup Lee of the Chemical and Biomolecular Engineering Department at the Korea Advanced Institute of Science and Technology (KAIST) deciphered the genome sequence of C. tyrobutyricum and its proteome profiles during the course of batch fermentation. As a result, the research team learned that the bacterium is not only capable of producing a large amount of butyric acid but also can tolerate toxic compounds such as 1-butanol. The research results were published in mBio on June 14, 2016.
The team adopted a genoproteomic approach, combining genomics and proteomics, to investigate the metabolic features of C. tyrobutyricum. Unlike Clostridium acetobutylicum, the most widely used organism for 1-butanol production, C. tyrobutyricum has a novel butyrate-producing pathway and various mechanisms for energy conservation under anaerobic conditions. The expression of various metabolic genes, including those involved in butyrate formation, was analyzed using the “shotgun” proteome approach.
To date, the bio-based production of 1-butanol, a next-generation biofuel, has relied on several clostridial hosts including C. acetobutylicum and C. beijerinckii. However, these organisms have a low tolerance against 1-butanol even though they are naturally capable of producing it. C. tyrobutyricum cannot produce 1-butanol itself, but has a higher 1-butanol-tolerance and rapid uptake of monosaccharides, compared to those two species.
The team identified most of the genes involved in the central metabolism of C. tyrobutyricum from the whole-genome and shotgun proteome data, and this study will accelerate the bacterium’s engineering to produce useful chemicals including butyric acid and 1-butanol, replacing traditional bacterial hosts.
Professor Lee said,
“The unique metabolic features and energy conservation mechanisms of C. tyrobutyricum can be employed in the various microbial hosts we have previously developed to further improve their productivity and yield. Moreover, findings on C. tyrobutyricum revealed by this study will be the first step to directly engineer this bacterium.”
Director Jin-Woo Kim at the Platform Technology Division of the Ministry of Science, ICT and Future Planning of Korea, who oversees the Technology Development Program to Solve Climate Change, said,
“Over the years, Professor Lee’s team has researched the development of a bio-refinery system to produce natural and non-natural chemicals with the systems metabolic engineering of microorganisms. They were able to design strategies for the development of diverse industrial microbial strains to produce useful chemicals from inedible biomass-based carbon dioxide fixation. We believe the efficient production of butyric acid using a metabolic engineering approach will play an important role in the establishment of a bioprocess for chemical production.”
The title of the research paper is “Deciphering Clostridium tyrobutyricum Metabolism Based on the Who-Genome Sequence and Proteome Analyses.” (DOI: 10.1128/mBio.00743-16)
The lead authors are Joungmin Lee, a post-doctoral fellow in the BioProcess Research Center at KAIST, currently working in CJ CheilJedang Research Institute; Yu-Sin Jang, a research fellow in the BioProcess Research Center at KAIST, currently working at Gyeongsang National University as an assistant professor; and Mee-Jung Han, an assistant professor in the Environmental Engineering and Energy Department at Dongyang University. Jin Young Kim, a senior researcher at the Korea Basic Science Institute, also participated in the research.
This research was supported by the Technology Development Program to Solve Climate Change’s research project entitled “Systems Metabolic Engineering for Biorefineries” from the Ministry of Science, ICT and Future Planning through the National Research Foundation of Korea (NRF-2012M1A2A2026556).
Schematic Diagram of C. tyrobutyricum’s Genome Sequence and Its Proteome Profiles
The picture below shows the complete genome sequence, global protein expression profiles, and the genome-based metabolic characteristics during batch fermentation of C. tyrobutyricum.
2016.06.20 View 10521 -
Graphene-Based Transparent Electrodes for Highly Efficient Flexible OLEDs
A Korean research team developed an ideal electrode structure composed of graphene and layers of titanium dioxide and conducting polymers, resulting in highly flexible and efficient OLEDs.
The arrival of a thin and lightweight computer that even rolls up like a piece of paper will not be in the far distant future. Flexible organic light-emitting diodes (OLEDs), built upon a plastic substrate, have received greater attention lately for their use in next-generation displays that can be bent or rolled while still operating.
A Korean research team led by Professor Seunghyup Yoo from the School of Electrical Engineering, KAIST and Professor Tae-Woo Lee from the Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH) has developed highly flexible OLEDs with excellent efficiency by using graphene as a transparent electrode (TE) which is placed in between titanium dioxide (TiO2) and conducting polymer layers. The research results were published online on June 2, 2016 in Nature Communications.
OLEDs are stacked in several ultra-thin layers on glass, foil, or plastic substrates, in which multi-layers of organic compounds are sandwiched between two electrodes (cathode and anode). When voltage is applied across the electrodes, electrons from the cathode and holes (positive charges) from the anode draw toward each other and meet in the emissive layer. OLEDs emit light as an electron recombines with a positive hole, releasing energy in the form of a photon. One of the electrodes in OLEDs is usually transparent, and depending on which electrode is transparent, OLEDs can either emit from the top or bottom.
In conventional bottom-emission OLEDs, an anode is transparent in order for the emitted photons to exit the device through its substrate. Indium-tin-oxide (ITO) is commonly used as a transparent anode because of its high transparency, low sheet resistance, and well-established manufacturing process. However, ITO can potentially be expensive, and moreover, is brittle, being susceptible to bending-induced formation of cracks.
Graphene, a two-dimensional thin layer of carbon atoms tightly bonded together in a hexagonal honeycomb lattice, has recently emerged as an alternative to ITO. With outstanding electrical, physical, and chemical properties, its atomic thinness leading to a high degree of flexibility and transparency makes it an ideal candidate for TEs. Nonetheless, the efficiency of graphene-based OLEDs reported to date has been, at best, about the same level of ITO-based OLEDs.
As a solution, the Korean research team, which further includes Professors Sung-Yool Choi (Electrical Engineering) and Taek-Soo Kim (Mechanical Engineering) of KAIST and their students, proposed a new device architecture that can maximize the efficiency of graphene-based OLEDs. They fabricated a transparent anode in a composite structure in which a TiO2 layer with a high refractive index (high-n) and a hole-injection layer (HIL) of conducting polymers with a low refractive index (low-n) sandwich graphene electrodes. This is an optical design that induces a synergistic collaboration between the high-n and low-n layers to increase the effective reflectance of TEs. As a result, the enhancement of the optical cavity resonance is maximized. The optical cavity resonance is related to the improvement of efficiency and color gamut in OLEDs. At the same time, the loss from surface plasmon polariton (SPP), a major cause for weak photon emissions in OLEDs, is also reduced due to the presence of the low-n conducting polymers.
Under this approach, graphene-based OLEDs exhibit 40.8% of ultrahigh external quantum efficiency (EQE) and 160.3 lm/W of power efficiency, which is unprecedented in those using graphene as a TE. Furthermore, these devices remain intact and operate well even after 1,000 bending cycles at a radius of curvature as small as 2.3 mm. This is a remarkable result for OLEDs containing oxide layers such as TiO2 because oxides are typically brittle and prone to bending-induced fractures even at a relatively low strain. The research team discovered that TiO2 has a crack-deflection toughening mechanism that tends to prevent bending-induced cracks from being formed easily.
Professor Yoo said, “What’s unique and advanced about this technology, compared with previous graphene-based OLEDs, is the synergistic collaboration of high- and low-index layers that enables optical management of both resonance effect and SPP loss, leading to significant enhancement in efficiency, all with little compromise in flexibility.” He added, “Our work was the achievement of collaborative research, transcending the boundaries of different fields, through which we have often found meaningful breakthroughs.”
Professor Lee said, “We expect that our technology will pave the way to develop an OLED light source for highly flexible and wearable displays, or flexible sensors that can be attached to the human body for health monitoring, for instance.”
The research paper is entitled “Synergistic Electrode Architecture for Efficient Graphene-based Flexible Organic Light-emitting Diodes” (DOI. 10.1038/NCOMMS11791). The lead authors are Jae-Ho Lee, a Ph.D. candidate at KAIST; Tae-Hee Han, a Ph.D. researcher at POSTECH; and Min-Ho Park, a Ph.D. candidate at POSTECH.
This study was supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF) through the Center for Advanced Flexible Display (CAFDC) funded by the Ministry of Science, ICT and Future Planning (MSIP); by the Center for Advanced Soft-Electronics funded by the MSIP as a Global Frontier Project; by the Graphene Research Center Program of KAIST; and by grants from the IT R&D Program of the Ministry of Trade, Industry and Energy of Korea (MOTIE).
Figure 1: Application of Graphene-based OLEDs
This picture shows an OLED with the composite structure of TiO2/graphene/conducting polymer electrode in operation. The OLED exhibits 40.8% of ultrahigh external quantum efficiency (EQE) and 160.3 lm/W of power efficiency. The device prepared on a plastic substrate shown in the right remains intact and operates well even after 1,000 bending cycles at a radius of curvature as small as 2.3 mm.
Figure 2: Schematic Device Structure of Graphene-based OLEDs
This picture shows the new architecture to develop highly flexible OLEDs with excellent efficiency by using graphene as a transparent electrode (TE).
2016.06.07 View 13808 -
Next-Generation Holographic Microscope for 3D Live Cell Imaging
KAIST researchers have developed a revolutionary bio-medical imaging tool, the HT-1, to view and analyze cells, which is commercially available.
Professor YongKeun Park of the Physics Department at KAIST and his research team have developed a powerful method for 3D imaging of live cells without staining. The researchers announced the launch of their new microscopic tool, the holotomography (HT)-1, to the global marketplace through a Korean start-up that Professor Park co-founded, TomoCube (www.tomocube.com).
Professor Park is a leading researcher in the field of biophotonics and has dedicated much of his research career to working on digital holographic microscopy technology. He collaborated with TomoCube’s R&D team to develop a state-of-the-art, 2D/3D/4D holographic microscope that would allow a real-time label-free visualization of biological cells and tissues.
The HT is an optical analogy of X-ray computed tomography (CT). Both X-ray CT and HT share the same physical principle—the inverse of wave scattering. The difference is that HT uses laser illumination whereas X-ray CT uses X-ray beams. From the measurement of multiple 2D holograms of a cell, coupled with various angles of laser illuminations, the 3D refractive index (RI) distribution of the cell can be reconstructed. The reconstructed 3D RI map provides structural and chemical information of the cell including mass, morphology, protein concentration, and dynamics of the cellular membrane.
The HT enables users to quantitatively and non-invasively investigate the intrinsic properties of biological cells, for example, dry mass and protein concentration. Some of the research team’s breakthroughs that have leveraged HT’s unique and special capabilities can be found in several recent publications, including a lead article on the simultaneous 3D visualization and position tracking of optically trapped particles which was published in Optica on April 20, 2015.
Current fluorescence confocal microscopy techniques require the use of exogenous labeling agents to render high-contrast molecular information. Therefore, drawbacks include possible photo-bleaching, photo-toxicity, and interference with normal molecular activities. Immune or stem cells that need to be reinjected into the body are considered particularly difficult to employ with fluorescence microscopy.
“As one of the two currently available, high-resolution tomographic microscopes in the world, I believe that the HT-1 is the best in class regarding specifications and functionality. Users can see 3D/4D live images of cells, without fixing, coating or staining cells. Sample preparation times are reduced from a few days or hours to just a few minutes,” said Professor Park.
Two Korean hospitals, Seoul National University Hospital in Bundang and Boramae Hospital in Seoul, are using this microscope currently. The research team has also introduced the HT-1 at the Photonics West Exhibition 2016 that took place on February 16-18 in San Francisco, USA.
Professor Park added, “Our technology has set a new paradigm for cell observation under a microscope. I expect that this tomographic microscopy will be more widely used in future in various areas of pharmaceuticals, neuroscience, immunology, hematology, and cell biology.”
Figure 1: HT-1 and Its Specifications
Figure 2: 3D Images of Representative Biological Cells Taken with the HT-1
2016.03.29 View 12796