graphene
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KAIST Researchers Fabricate Defect-free Graphene for Lithium-ion Batteries
Although graphene has been hailed as promising materials for lithium-ion batteries, making it for large-scale production has remained a challenging task for researchers. So far, high-quality graphene has been produced at the expense of large volume. It is possible to fabricate bulk quantities of graphene, but they will likely contain many defects.
Recently, a KAIST research team, headed by Professors Jung-Ki Park and Hee-Tak Kim from the Department of Chemical and Biomolecular Engineering, developed a fabrication method to produce a large amount of defect-free graphene (df-G) while preserving the structural integrity of the graphene.
This research result was published online in the July 11, 2014 issue of Nano Letters, entitled "Defect-free, Size-tunable Graphene for High-performance Lithium Ion Battery."
Phys.org, a science, research and technology news website, published an article on this research. To read article, please visit the link below:
Phys.org, August 22, 2014
“Scientists fabricate defect-free graphene, set record reversible capacity for Co3O4 node in Li-ion batteries”
http://phys.org/news/2014-08-scientists-fabricate-defect-free-graphene-reversible.html
2014.09.07 View 9400 -
News Article on the Development of Synthesis Process for Graphene Quantum Dots
Before It's News, an international online news agency, highlighted the recent research conducted by KAIST professors (Seokwoo Jeon of the Department of Materials Science and Engineering, Yong-Hoon Cho of the Department of Physics, and Seunghyup Yoo of the Department of Electrical Engineering) on the development of synthesis process for graphene quantum dots, nanometer-sized round semiconductor nanoparticles that are very efficient at emitting photons. If commercialized, this synthetic technology will lead the way to the development of paper-thin displays in the future.
For the article, please go to the link below:
Before It’s News, September 3, 2014“Graphene quantum dots prove highly efficient in emitting light”
http://beforeitsnews.com/science-and-technology/2014/09/graphene-quantum-dots-prove-highly-efficient-in-emitting-light-2718190.html
2014.09.07 View 11688 -
Extracting Light from Graphite: Core Technology of Graphene Quantum Dots Display Developed
Professor Seokwoo Jeon of the Department of Materials Science and Engineering, Professor Yong-Hoon Cho of the Department of Physics, and Professor Seunghyup Yoo of the Department of Electrical Engineering announced that they were able to develop topnotch graphene quantum dots from graphite.
Using the method of synthesizing graphite intercalation compound from graphite with salt and water, the research team developed graphene quantum dots in an ecofriendly way.
The quantum dots have a diameter of 5 nanometers with their sizes equal and yield high quantum efficiency. Unlike conventional quantum dots, they are not comprised of toxic materials such as lead or cadmium. As the quantum dots can be developed from materials which can be easily found in the nature, researchers look forward to putting these into mass production at low cost.
The research team also discovered a luminescence mechanism of graphene quantum dots and confirmed the possibility of commercial use by developing quantum dot light-emitting diodes with brightness of 1,000 cd/m2, which is greater than that of cellphone displays.
Professor Seokwoo Jeon said, “Although quantum dot LEDs have a lower luminous efficiency than existing ones, their luminescent property can be further improved” and emphasized that “using quantum dot displays will allow us to develop not only paper-thin displays but also flexible ones.”
Sponsored by Graphene Research Center in KAIST Institute for NanoCentury, the research finding was published online in the April 20th issue of Advanced Optical Materials.
Picture 1: Graphene quantum dots and their synthesis
Picture 2: Luminescence mechanism of graphene quantum dots
Picture 3: Structure of graphene quantum dots LED and its emission
2014.09.06 View 15928 -
Professor Sang-Ouk Kim Publishes Review Article in the Journal of "Nature Materials"
Nature Materials, a
peer-reviewed scientific journal published by Nature Publishing Group, covers a
range of topics within materials science from materials engineering and
structural materials. The
journal invited Professor Sang-Ouk Kim of Materials Science and Engineering at
KAIST to contribute to the April issue of 2014. Professor Kim,
together with his doctoral student, Ju-Young Kim, wrote a review article in the
“News and Views” section of the journal, which was entitled “Liquid Crystals:
Electric Fields Line Up Graphene Oxide.” The
News and Views is a peer-reviewed section where an academic authority in a particular
field reviews and evaluates papers published in the journal. In
the article, Professor Kim reviewed a paper written by Jang-Kun Song et al. and
highlighted important research outcomes such as the efficient electric field switching
of graphene oxide (GO) liquid-crystals in low-concentration dispersions and the
demonstration of a prototype of a GO liquid-crystal display. This technology
could lead the development of a flexible display. Professor
Kim is an eminent scholar who has reported for the first time in the world on
the solvent-based graphene oxide liquid crystals formation in 2011. For the article, please go to: http://www.kaist.ac.kr/_prog/download.php?filename=Nature_Materials_Professor_Sang-Ouk_Kim_Apr_2014.pdf
2014.03.26 View 8938 -
Core Technology for Lithium Air Secondary Battery Developed
KAIST-Kyonggi University joint research team developed composite catalyst out of nano fiber and graphene
Five times improvement in capacity compared to lithium-ion secondary battery, driving 800 km at maximum
The core technology for lithium air secondary battery, the next generation high capacity battery, has been developed.
A research team formed by KAIST Department of Materials Science’s Professors Il-Doo Kim and Seokwoo Jeon, and Kyonggi University Department of Materials Science’s Professor Yong-Joon Park has created a lithium air secondary battery, with five times greater storage than the lithium-ion secondary battery, by developing a nano fiber-graphene composite catalyst. The research results are published in the August 8th online edition of Nano Letters.
A cathode of a lithium-ion battery consists of graphite and an anode of the battery consists of a lithium transition metal oxide. Lithium-ion batteries are widely used in mobile phones and laptops. However, lithium-ion batteries cannot support electric vehicles, providing energy for only 160 kilometers on one full charge. The lithium air secondary battery just developed by the research team uses lithium on the cathode and oxygen on the anode. It is earning a popular acknowledgement among the next generation secondary battery research community for having lightweight mass and high energy density.
However, lithium-ion batteries remain difficult to commercialize because of their short lifespan. Lithium and oxygen meet up to form lithium oxide (Li2O2) at discharge, and decompose again at charge. In a traditional lithium air battery, this cycle does not occur smoothly and results in high resistance, thereby reducing the lifespan of the battery. It is thus essential to develop high efficiency catalyst that facilitates the formation and decomposition of lithium oxides.
The research team used electric radiation to develop a nano composite catalyst by mixing cobalt oxide nano fiber and graphene. The performance of the battery has been maximized by settling nonoxidative graphene, which has high specific surface area and electrical conductivity, on catalyst active cobalt oxide nano fiber. Applying the nano composite catalyst on both poles of the lithium air battery resulted in an improved lifespan of over 80 recharge cycles with capacity greater than 100mAh/g, five times greater than a lithium ion battery. The newly discovered charge-discharge property is the highest among the reported performances of the lithium air battery so far.
The lithium air battery is cheap to make, as the main materials are metal oxide and graphene. “There are yet more issues to resolve such as stability, but we will collaborate with other organizations to open up the era of electronic vehicles,” said Professor Il-Doo Kim. “We hope to contribute to vitalizing the fields of next generation lithium air battery by leading nanocatalyst synthesis technology, one of the core materials in the fields of secondary battery,” Professor Kim spoke of his aspiration.
The graduate students participated in the research are Won-Hee Ryu, a postdoctorate at KAIST Department of Materials Science, Sungho Song, a PhD candidate at KAIST Department of Materials Science, and Taek-Han Yoon, a graduate student at Kyonggi University.
Picture I: Schematic Diagram of Lithium Air Battery Made of Nano Composite Catalysts
Picture II: Images of Cobalt Oxide Nano Fibers and Graphene Nano Composite Catalysts
Picture III: Images of Manufacturing Process of Cobalt Oxide Nano Fibers and Graphene Nano Composite Catalysts for Lithium Air Battery
2013.10.18 View 11022 -
Secondary, High Capacity Battery developed from Rice Husks
Rice husks, a waste product from rice polishing, has been successfully utilized as the silicon anode for use in high capacity lithium ion secondary batteries. The new silicon anode derived from rice husks exhibit superior output and lifespan.
Professor Choi Jang Wook (The Graduate School of Energy, Environment, Water and Sustainability (EEWS)) and Professor Park Seung Min (Department of Biochemistry) and their respective research teams separated naturally occurring, highly porous silica material within the rice husks and developed a 3-dimensional, highly porous silicon anode material.
The result of the research effort was published in the online edition of the Proceedings of the National Academy of Sciences (PNAS) journal, a world renowned journal in the field of natural sciences.
Silicon has attracted much attention as anode material for next generation lithium ion secondary batteries because it exhibits 3~5 times higher capacity than conventional graphene. The high capacity will pave the way to lithium secondary batteries with higher energy densities than conventional batteries. It is anticipated that the application of silicon batteries will yield electronic devices with a longer duration for use in addition to electronic vehicles boasting longer mileage.
The silicon anode is based on the 3-dimensional, highly porous structure of rice husks which remedies the problematic extreme volume expansion of conventional silicon anodes.
Utilization of inexpensive rice husks to create high value silicon anodes will cause a ripple effect on the industry and academia.
2013.08.23 View 9710 -
KAIST researchers verify and control the mechanical properties of graphene
KAIST researchers have successfully verified and controlled the mechanical properties of graphene, a next-generation material. Professor Park Jung Yong from the EEWS Graduate School and Professor Kim Yong Hyun from the Graduate School of Nanoscience and Technology have succeeded in fluorinating a single atomic-layered graphene sample and controlling its frictional and adhesive properties. This is the first time the frictional properties of graphene have been examined at the atomic level, and the technology is expected to be applied to nano-sized robots and microscopic joints.
Graphene is often dubbed “the dream material” because of its ability to conduct high amounts of electricity even when bent, making it the next-generation substitute for silicon semiconductors, paving the way for flexible display and wearable computer technologies. Graphene also has high potential applications in mechanical engineering because of its great material strength, but its mechanical properties remained elusive until now.
Professor Park’s research team successfully produced individual graphene samples with fluorine-deficiency at the atomic level by placing the samples in Fluoro-xenon (XeF2) gas and applying heat. The surface of the graphene was scanned using a micro probe and a high vacuum atomic microscope to measure its dynamic properties.
The research team found that the fluorinated graphene sample had 6 times more friction and 0.7 times more adhesiveness than the original graphene. Electrical measurements confirmed the fluorination process, and the analysis of the findings helped setup the theory of frictional changes in graphene.
Professor Park stated that “graphene can be used for the lubrication of joints in nano-sized devices” and that this research has numerous applications such as the coating of graphene-based microdynamic devices.
This research was published in the online June edition of Nano Letters and was supported by the Ministry of Science, Technology, and Education and the National Research Foundation as part of the World Class University (WCU) program.
2012.07.24 View 14191 -
Flexible Nanogenerator Technology
KAIST research team successfully developed the foundation technology that will enable to fabrication of low cost, large area nanogenerator.
Professor Lee Gun Jae’s team (Department of Materials Science and Engineering) published a dissertation on a nanogenerator using nanocomplexes as the cover dissertation of the June edition of Advanced Materials.
The developed technology is receiving rave reviews for having overcome the complex and size limitations of the nanogenerator fabrication process.
A nanogenerator is an electricity generator that uses materials in the nanoscale and uses piezoelectricity that creates electricity with the application of physical force.
The generation technology using piezoelectricity was appointed as one of top 10 promising technologies by MIT in 2009 and was included in the 45 innovative technologies that will shake the world by Popular Science Magazine in 2010.
The only nanogenerator thus far was the ZnO model suggested by Georgia Tech’s Professor Zhong Lin Wang in 2005.
Professor Lee’s team used ceramic thin film material BaTiO3 which has 15~20 times greater piezoelectric capacity than ZnO and thus improved the overall performance of the device. The use of a nanocomplex allows large scale production and the simplification of the fabrication process itself.
The team created a mixture of PDMS (polydimethylsiloxane) with BaTiO3 and either of CNT (Carbon Nanotube) or RGO (Reduced Graphene Oxide) which has high electrical conductivity and applied this mixture to create a large scale nanogenerator.
2012.06.18 View 12460
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High-resolution Atomic Imaging of Specimens in Liquid Observed by Transmission Electron Microscopes Using Graphene Liquid Cells
Looking into specimens in liquid at the atomic level to understand nanoscale processes so far regarded as impossible to witnessThe Korea Advanced Institute of Science and Technology (KAIST) announced that a research team from the Department of Materials Science and Engineering has developed a technology that enables scientists and engineers to observe processes occurring in liquid media on the smallest possible scale which is less than a nanometer.
Professor Jeong Yong Lee and Researcher Jong Min Yuk, in collaboration with Professors Paul Alivisatos’s and Alex Zettl’s groups at the University of California, Berkeley, succeeded in making a graphene liquid cell or capsule, confining an ultra-thin liquid film between layers of graphene, for real-time and in situ imagining of nanoscale processes in fluids with atomic-level resolution by a transmission electron microscope (TEM). Their research was published in the April 6, 2012 issue of Science. (http://www.sciencemag.org/content/336/6077/61.abstract)
The graphene liquid cell (GLC) is composed of two sheets of graphene sandwiched to create a sealed chamber where a platinum growth solution is encapsulated in the form of a thin slice. Each graphene layer has a thickness of one carbon atom, the thinnest membrane that has ever been used to fabricate a liquid cell required for TEM.
The research team peered inside the GLC to observe the growth and dynamics of platinum nanocrystals in solution as they coalesced into a larger size, during which the graphene membrane with the encapsulated liquid remained intact. The researchers from KAIST and the UC Berkeley identified important features in the ongoing process of the nanocrystals’ coalescence and their expansion through coalescence to form certain shapes by imaging the phenomena with atomic-level resolution.
Professor Lee said,
“It has now become possible for scientists to observe what is happening in liquids on an atomic level under transmission electron microscopes.”
Researcher Yuk, one of the first authors of the paper, explained his research work.
“This research will promote other fields of study related to materials in a fluid stage including physical, chemical, and biological phenomena at the atomic level and promises numerous applications in the future. Pending further studies on liquid microscopy, the full application of a graphene-liquid-cell (GLC) TEM to biological samples is yet to be confirmed. Nonetheless, the GLC is the most effective technique developed today to sustain the natural state of fluid samples or species suspended in the liquid for a TEM imaging.”
The transmission electron microscope (TEM), first introduced in the 1930s, produces images at a significantly higher resolution than light microscopes, allowing users to examine the smallest level of physical, chemical, and biological phenomena. Observations by TEM with atomic resolution, however, have been limited to solid and/or frozen samples, and thus it has previously been impossible to study the real time fluid dynamics of liquid phases.
TEM imaging is performed in a high vacuum chamber in which a thin slice of the imaged sample is situated, and an electron beam passes through the slice to create an image. In this process, a liquid medium, unlike solid or frozen samples, evaporates, making it difficult to observe under TEM.
Attempts to produce a liquid capsule have thus far been made with electron-transparent membranes of such materials as silicon nitride or silicon oxide; such liquid capsules are relatively thick (tens to one hundred nanometers), however, resulting in poor electron transmittance with a reduced resolution of only a few nanometers. Silicon nitride is 25 nanometers thick, whereas graphene is only 0.34 nanometers.
Graphene, most commonly found in bulk graphite, is the thinnest material made out of carbon atoms. It has unique properties such as mechanical tensile strength, high flexibility, impermeability to small molecules, and high electrical conductivity. Graphene is an excellent material to hold micro- and nanoscopic objects for observation in a transmission electron microscope by minimizing scattering of the electron beam that irradiates a liquid sample while reducing charging and heating effects.
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Figure 1. Schematic illustration of graphene liquid cells. Sandwiched two sheets of graphene encapsulate a platinum growth solution.
Figure 2. In-situ TEM observation of nanocrystal growth and shape evolution. TEM images of platinum nanocrystal coalescence and their faceting in the growth solution.
2012.04.23 View 11392 -
Inexpensive Separation Method of Graphene Developed
The problem with commercializing graphene that is synthesized onto metals over a wide area is that it can not be separated from the metal. However, a groundbreaking separation technology which is both cheap and environment friendly has been developed.
Prof. Taek soo Kim and Prof. Byung Jin Cho"s research teams have conducted this research under the support of the Global Frontier program and Researcher Support Program initiated by The Ministry of Education and Science and Korea Research Foundation. The research results have been posted on the online news flash of Nano Letters on februrary 29th. (Thesis title: Direct Measurement of Adhesion Energy of Monolayer Graphene As-Grown on Copper and Its Application to Renewable Transfer Process)
The research has generated exact results on the interfacial adhesive energy of graphene and its surface material for the first time. Through this, the catalyst metal are no longer to be used just once, but will be used for an infinite number of times, thereby being ecofriendly and efficient.
Wide area graphine synthesized onto the catalyst meatal are used in various ways such as for display and for solar cells. There has been much research going on in this field. However, in order to use this wide area graphene, the graphene must be removed from the catalyst metal without damage.
Until now, the metal had been melted away through the use of chemical substances in order to separate the graphene. However, this method has been very problematic. The metal can not be reused, the costs are very high, much harmful wastes were created in the process of melting the metals, and the process was very complicated.
The research teams of Professors Taek Su Kim and Byung Jin Cho measured the interfacial adhesive energy of the synthesized graphene and learned that it could be easily removed.
Also, the mechanically removed graphene was successfully used in creating molecular electronic devices directly. This has thus innovatively shortened the graphene manufacturing process. Also, it has been confirmed that the metalic board can be reused multiple times after the graphene is removed. A new, ecofriendly and cost friendly method of graphene manufacturing has been paved.
Through this discovery, it is expected that graphene will become easier to manufacture and that the period til the commercialization date of graphene will therefore be greatly reduced
Prof. Cho stated " This reserach has much academical meaning significance in that it has successfully defined the surfacial adhesive energy between the graphene and its catalyst material and it should receive much attention in that it solved the largest technical problem involved in the production of graphene.
2012.04.04 View 12625
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Closer to the Dream: Graphene
A technique that allows easy and larger observation area of graphene’s crystal face was developed by Korean Research Team.
The research team, led by Professor Jeong Hui Tae (KAIST), consists of Doctorate candidate Kim Dae Woo, Dr. Kim Yoon Ho (primary author), Doctorate candidate Jeong Hyun Soo. The research is supported by WCU (World Class Research University) Development Plan, Mid-Aged Researcher Support Business and was published in the online edition of Nature Nanotechnology.
(Dissertation: Direct visualization of large0area graphene domains and boundaries by optical birefringency)
Professor Jeong’s team used the optical property of the liquid display used in LCD to visualize the size and shape of the single crystals along a flat surface. The visualization of the single crystal allowed the measurement of a near theoretical value of electrical conductivity of graphene.
Graphene has great electrical conductivity, transparent, mechanically stable, flexible, and is therefore regarded as the next generation electrical material. However the polycrystalinity of graphene meant that the actual electrical, mechanical properties were lower than the theoretical values. The reason was thought to be because of the size of the crystal faces and boundary structures.
Therefore, in order to create graphene that has good properties, observing the domain and boundary of graphene crystal faces is essential.
The new technique developed by the research team is another step towards commercializing transparent electrodes, flexible display, and electric materials like solar cells.
2012.01.31 View 9580
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Spintronics: A high wire act by Nanowerk News
An article by Nanowerk News on the integration of ferromagnetic nanowire arrays on grapheme substrates was published. Professor Bong-Soo Kim from the Department of Chemistry, KAIST, led the research in conjunction with Hanyang University and Samsung in Korea.
http://www.nanowerk.com/news/newsid=22204.php
Posted: Jul 25th, 2011
Spintronics: A high wire act
(Nanowerk News) Graphene is a promising material for a wide range of applications due to its remarkable mechanical and electronic properties. An application of particular interest is spin-based electronics, or spintronics, in which the spin orientation of an electron is used to perform circuit functions in addition to its charge. Bongsoo Kim and colleagues from KAIST, Hanyang University and Samsung in Korea now report the integration of ferromagnetic nanowire arrays on graphene substrates, opening up a route for the construction of graphene-based spintronic devices using nanowires as spin-injecting contacts ("Epitaxially Integrating Ferromagnetic Fe1.3Ge Nanowire Arrays on Few-Layer Graphene").
The spin of an electron is a property that, like charge, can be used to encode, process and transport information. However, spin information is easily lost in most media, which has made spintronics difficult to realize in practice. In graphene, on the other hand, spin can be preserved for longer due to its peculiar electron transport properties. "Low intrinsic spin–orbit coupling, long spin diffusion lengths and vanishing hyperfine interaction are features of graphene that make it a promising medium for spin transport," explains Kim.
Scanning electron microscopy image of vertical iron germanide nanowires grown on graphene. (© ACS 2011)
A prerequisite for the realization of spintronic devices based on graphene is its integration with ferromagnetic contacts to allow spin injection. Kim and his co-workers found that nanowires of iron germanide (Fe1.3Ge) serve as efficient contacts for this purpose. "Iron germanide nanowires show low resistivity and room-temperature ferromagnetism, and they are compatible with existing complementary metal–oxide–semiconductor technologies," says Kim.
To produce the atomically well-defined interfacial contact between the nanowires and the graphene surface needed for optimum device performance, the researchers deposited the contacts by an epitaxial method based on chemical vapor transport. Through careful adjustment of deposition parameters such as carrier gas flow rate and reaction temperature, the researchers produced vertically aligned nanowires that are closely lattice-matched to the graphene sheets (see image).
Initially preparing the graphene sheets on a substrate of silicon oxide allowed the researchers to isolate the final nanowire–graphene structure by etching and then transfer it to another substrate, greatly expanding the versatility of the approach. It is a delicate process, however. "It is necessary to transfer the graphene films onto the substrate very carefully in order to avoid folding and wrinkling of the graphene," says Kim.
Source: Tokyo Institute of Technology
2011.07.26 View 10283