research
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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 14085 -
Systems biology demystifies the resistance mechanism of targeted cancer medication
Korean researchers have found the fundamental resistance mechanism of the MEK inhibitor, a recently highlighted chemotherapy method, laying the foundation for future research on overcoming cancer drug resistance and improving cancer survival rates. This research is meaningful because it was conducted through systems biology, a fusion of IT and biotechnology.
The research was conducted by Professor Gwang hyun Cho’s team from the Department of Biology at KAIST and was supported by the Ministry of Education, Science and Technology and the National Research Foundation of Korea.
The research was published as the cover paper for the June edition of the Journal of Molecular Cell Biology (Title: The cross regulation between ERK and PI3K signaling pathways determines the tumoricidal efficacy of MEK inhibitor).
Targeted anticancer medication targets certain molecules in the signaling pathway of the tumor cell and not only has fewer side effects than pre-existing anticancer medication, but also has high clinical efficacy. The technology also allows the creation of personalized medication and has been widely praised by scientists worldwide.
However, resistances to the targeted medication have often been found before or during the clinical stage, eventually causing the medications to fail to reach the drug development stage. Moreover, even if the drug is effective, the survival rate is low and the redevelopment rate is high.
An active pathway in most tumor cells is the ERK (Extracellular signal-regulated kinases) signaling pathway. This pathway is especially important in the development of skin cancer or thyroid cancer, which are developed by the mutation of the BRAF gene inside the path. In these cases, the MEK (Extracellular signal-regulated kinases) inhibitor is an effective treatment because it targets the pathway itself. However, the built-up resistance to the inhibitor commonly leads to the redevelopment of cancer.
Professor Cho’s research team used large scale computer simulations to analyze the fundamental resistance mechanism of the MEK inhibitor and used molecular cell biological experiments as well as bio-imaging* techniques to verify the results.
* Bio-imaging: Checking biological phenomena at the cellular and molecular levels using imagery
The research team used different mutational variables, which revealed that the use of the MEK inhibitor reduced the transmission of the ERK signal but led to the activation of another signaling pathway (the PI3K signaling pathway), reducing the effectiveness of the medication. Professor Cho’s team also found that this response originated from the complex interaction between the signaling matter as well as the feedback network structure, suggesting that the mix of the MEK inhibitor with other drugs could improve the effects of the targeted anticancer medication.
Professor Cho stated that this research was the first of its kind to examine the drug resistivity against the MEK inhibitor at the systematic dimension and showed how the effects of drugs on the signaling pathways of cells could be predicted using computer simulation. It also showed how basic research on signaling networks can be applied to clinical drug use, successfully suggesting a new research platform on overcoming resistance to targeting medication using its fundamental mechanism.
2012.07.06 View 10420 -
New wireless charging device developed
The On-line Electric Vehicle (OLEV) developed by KAIST has made a step towards commercialization with the development of a more economic wireless charging device.
Professor Chun-Taek Rim from the Department of Nuclear and Quantum Engineering at KAIST has developed a new I-shaped wireless charging device that differs from the pre-existing rail-type electricity feeder. This device can be modularly produced and requires relatively less construction, significantly reducing the cost of implementation.
The KAIST OLEV is a new concept electric car that has a special electricity collecting device underneath it. The car’s battery is charged by magnetic fields produced from electric lines buried 15cm underneath the road. The vehicle was first tested in 2009, making it the first wireless electric car in the world. OLEV can be charged during stoppage time between traffic lights and receives real-time power when running. OLEV is currently in operation at the KAIST Munji Campus in Daejeon and is also being exhibited at the Yeosu Expo and Seoul Grand Park.
The device itself has a charging capacity of 15kW, and the electricity is supplied through an electricity feeder with a width of 80cm with a space interval of 20cm. Despite being hailed as a technological breakthrough and revolutionary concept, KAIST OLEV has been criticized for problems in commercialization, due to the difficulties in installing wires beneath existing roads, which costs a considerable amount of money.
The new I-shaped wireless charging device reduces the width of the electricity feeder by 10cm, a mere one-eighth of the size of the previous version, and greatly increases the charging power to 25kW. Furthermore, the left and right permissible space of automobiles has increased to 24cm and the magnetic field complies with the international design guidelines, making the OLEV safe for the human body.
The reduction of the width has made the mass production of modules possible, making the installation of KAIST OLEV more economical and marketable. Professor Rim emphasized that compared with the existing rail-type electricity feeder, the new technology will need only one-tenth of the construction time and 80% of the cost, significantly improving OLEV’s constructability and workability.
The research was published in the IEEE Transactions on Power Electronics last December, and Professor Rim was invited to talk at the Conference on Electric Roads & Vehicles, which was held in February in the United States, about the new technology.
2012.07.06 View 10719
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The hereditary factor of autism revealed
Korean researchers have successfully investigated the causes and hereditary factors for autistic behavior and proposed a new treatment method with fewer side effects.
This research was jointly supported by the Ministry of Education, Science and Technology and the National Research Foundation as part of the Leading Researcher and Science Research Center Program
The research findings were publishing in the June edition of Nature magazine and will also be introduced in the July edition of Nature Reviews Drug Discovery, under the title ‘Autistic-like social behavior in Shank2-mutant mice improved by restoring NMDA receptor function’.
The research team found that lack of Shank2 genes in mice, which are responsible for the production of synapse proteins, caused autistic-like behavior. The results strongly suggested that the Shank2 gene was linked to autistic behavior and that Shank2 deficiency induced autistic behaviors.
Autism is a neural development disorder characterized by impaired social interaction, repetitive behavior, mental retardation, anxiety and hyperactivity. Around 100 million people worldwide display symptoms of autistic behavior. Recent studies conducted by the University of Washington revealed that 1 out of 3 young adults who display autistic behavior do not fit into the workplace or get accepted to college, a much higher rate than any other disorder. However, an effective cure has not yet been developed and current treatments are limited to reducing repetitive behavior.
The research team confirmed autistic-like social behavior in mice without the Shank2 genes and that the mice had decreased levels of neurotransmission in the NMDA receptor. The mice also showed damaged synaptic plasticity* in the hippocampus**.
* Plasticity: ability of the connectionbetween two neurons to change in strength in response to transmission of information
**Hippocampus: part of the brain responsible for short-term and long-term memory as well as spatial navigation.
The research team also found out that, to restore the function of the NMDA receptor, the passive stimulation of certain receptors, such as the mGLuR5, yielded better treatment results than the direct stimulation of the NMDA. This greatly reduces the side effects associated with the direct stimulation of receptors, resulting in a more effective treatment method.
This research successfully investigated the function of the Shank2 gene in the nerve tissue and showed how the reduced function of the NMDA receptor, due to the lack of the gene, resulted in autistic behavior. It also provided new possibilities for the treatment of autistic behavior and impaired social interaction
2012.06.24 View 10731
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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 12378
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High Capacity Molecular Storage Technology Developed by KAIST Professor Omar M. Yaghi
KAIST research team has succeeded in developing the technology that allows high capacity protein storage.
Professor Omar M. Yaghi (Graduate School of EEWS) and his research team succeeded in developing the core technology that enables the storage of various types of proteins by developing a metal organic structure. The result of their research was published in the May edition of Science magazine.
The newly developed technology can store various types and sizes of proteins. This property is expected to pave way to: 1) development of high capacity, high integration drugs 2) development of virus separation compounds 3) selective removal of protein causing negative reactions in the body 4) permanent preservation of rare polymeric proteins, among other expectations.
In addition it becomes possible to selectively remove and preserve all the body’s cells including stem cells which will aid the development of cures for incurable diseases and increase life expectancy and medical technology in general.
Conventional metal-organic structure used 7 Angstrom large small single molecules and therefore could not be used in the storage of large molecules or proteins. Its usability was proven only as potential high capacity gas storage structure. In addition the internal structure of the metal organic structure is cross linked which made it even more difficult to store large proteins within the structure.
Professor Yaghi’s team used molecular structure over 5nm in length in the development of the metal-organic structure to solve the problem associated with size of structure. The ordered structure of the structure’s pore was observed for the first time using Transmission Electron Microscope.
The new structure enables the ordered storage of large proteins and was able to store vitamin and proteins like myoglobin at high capacity for the first time in the world.
2012.05.30 View 8258
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Successful Development of Excavation System of Biomarkers containing Protein Decomposition Control Enzyme Information
A Korean team of researchers successfully developed a biomarker excavation system named E3Net that excavates biomarkers containing information of the enzymes that control the decomposition of proteins. The development of the system paved the possibility of development of new high quality biomarkers.
*Biomarker: Molecular information of unique patterns derived from genes and proteins that allow the monitoring of physical changes from genetic or environmental causes.
Professor Lee Kwan Soo’s team (Department of Biological Sciences) composed of Doctorate candidate Han Young Woong, Lee Ho Dong Ph.D. and Professor Park Jong Chul published a dissertation in the April edition of Molecular and Cellular Proteomics. (Dissertation Title: A system for exploring E3-mediated regulatory networks of cellular functions).
Professor Lee’s team compiled all available information of the enzyme that controls protein decomposition (E3 enzyme) and successfully compiled the inter-substrate network by extracting information from 20,000 biology related data base dissertations. The result was the development of the E3Net system that analyzes the related cell function and disease.
Cells have a system that produces, destroys, and recycles proteins in response to the ever changing environmental conditions. Error in these processes leads to disease.
Therefore finding the relationship between E3 enzymes that control the decomposition of proteins and the substrates will allow disease curing and prevention to become much easier. E3 enzyme is responsible for 80% of the protein decomposition and is therefore predicted to be related to various diseases.
However the information on E3 enzyme and inter-substrate behavior are spread out among numerous dissertations and data bases which prevented methodological analysis of the role of the related cells and characteristics of the disease itself.
Professor Lee’s team was successful in creating the E3Net that compiled 2,201 pieces of E3 substrate information, 4,896 pieces of substrate information, and 1,671 pieces of inter-substrate relationship information. This compilation allows for the systematic analysis of cells and diseases.
The newly created network is 10 times larger than the existing network and is the first case where it is possible to accurately find the cell function and related diseases.
It is anticipated that the use of the E3Net will allow the excavation of new biomarkers for the development of personalized drug systems.
The research team applied the E3Net to find tens of new candidate biomarkers related to the major modern diseases like diabetes and cancer.
2012.05.30 View 11679
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Production of chemicals without petroleum
Systems metabolic engineering of microorganisms allows efficient production of natural and non-natural chemicals from renewable non-food biomass
In our everyday life, we use gasoline, diesel, plastics, rubbers, and numerous chemicals that are derived from fossil oil through petrochemical refinery processes. However, this is not sustainable due to the limited nature of fossil resources. Furthermore, our world is facing problems associated with climate change and other environmental problems due to the increasing use of fossil resources. One solution to address above problems is the use of renewable non-food biomass for the production of chemicals, fuels and materials through biorefineries. Microorganisms are used as biocatalysts for converting biomass to the products of interest. However, when microorganisms are isolated from nature, their efficiencies of producing our desired chemicals and materials are rather low. Metabolic engineering is thus performed to improve cellular characteristics to desired levels. Over the last decade, much advances have been made in systems biology that allows system-wide characterization of cellular networks, both qualitatively and quantitatively, followed by whole-cell level engineering based on these findings. Furthermore, rapid advances in synthetic biology allow design and synthesis of fine controlled metabolic and gene regulatory circuits. The strategies and methods of systems biology and synthetic biology are rapidly integrated with metabolic engineering, thus resulting in "systems metabolic engineering".
In the paper published online in Nature Chemical Biology on May 17, Professor Sang Yup Lee and his colleagues at the Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea present new general strategies of systems metabolic engineering for developing microorganisms for the production of natural and non-natural chemicals from renewable biomass. They first classified the chemicals to be produced into four categories based on whether they have thus far been identified to exist in nature (natural vs. nonnatural) and whether they can be produced by inherent pathways of microorganisms (inherent, noninherent, or created): natural-inherent, natural-noninherent, non-natural-noninherent, and non-natural-created ones. General strategies for systems metabolic engineering of microorganisms for the production of these chemicals using various tools and methods based on omics, genome-scale metabolic modeling and simulation, evolutionary engineering, synthetic biology are suggested with relevant examples. For the production of non-natural chemicals, strategies for the construction of synthetic metabolic pathways are also suggested. Having collected diverse tools and methods for systems metabolic engineering, authors also suggest how to use them and their possible limitations.
Professor Sang Yup Lee said "It is expected that increasing number of chemicals and materials will be produced through biorefineries. We are now equipped with new strategies for developing microbial strains that can produce our desired products at very high efficiencies, thus allowing cost competitiveness to those produced by petrochemical refineries."
Editor of Nature Chemical Biology, Dr. Catherine Goodman, said "It is exciting to see how quickly science is progressing in this field – ideas that used to be science fiction are taking shape in research labs and biorefineries. The article by Professor Lee and his colleagues not only highlights the most advanced techniques and strategies available, but offers critical advice to progress the field as a whole."
The works of Professor Lee have been supported by the Advanced Biomass Center and Intelligent Synthetic Biology Center of Global Frontier Program from the Korean Ministry of Education, Science and Technology through National Research Foundation.
Contact: Dr. Sang Yup Lee, Distinguished Professor and Dean, KAIST, Daejeon, Korea (leesy@kaist.ac.kr, +82-42-350-3930)
2012.05.23 View 11618
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New concept 'mole game' robot developed
A new game robot concept developed by KAIST researchers came in first place at a world-renowned virtual reality exhibition, despite being the first ever entry by a Korean team.
Professor Lee Woohun’s team from the Department of Industrial Design at KAIST won the first-place award of ‘Gran Prix du Jury’ at the famous virtual reality exhibition, Laval Virtual 2012, which was held between March 28th and April 1st, with the mole game robot, ‘MoleBot’.
MoleBot can be enjoyed in a completely physical environment unlike other virtual reality games and allows interaction between the virtual world and reality. Such imaginative interaction attracted numerous spectators during the exhibition.
The MoleBot table consists of approximately 15,000 small cubes, and as the object inside the table moves, the cubes slide as if a mole is inside. By using a joystick, users can enjoy physical interaction with the table and a wide range of games.
The MoleBot can also be operated with hand gestures using ‘Kinect’, a motion sensing input device developed by Microsoft, making it possible to enjoy games as if playing with a pet.
Professor Lee’s team came up with the project from a simple idea: ‘What if moles lived inside the table?’
The team first created a table that would hold and allow the movement of the cubes, and then placed a plastic mold underneath it with a layer of spandex in between to lessen the friction, allowing smooth and lifelike movement.
The mold contains magnets that allow the accurate delivery of mechanical movement. After two years of continued additional research, MoleBot was released to the world.
In the acceptance speech, Professor Lee said, ‘It is rare for a design team to win first place in an engineering exhibition’ and that ‘to achieve such a feat, the MoleBot’s technological creativity and artistic completeness became one’.
Professor Lee also said that ‘this concept of creating an interactive world on a table could potentially become a new game interface’ and that he would research on applying this MoleBot technology to different fields such as human-computer interaction, architecture, interior, and clothing.
Laval Virtual is a world-renowned exhibition that displays cutting edge technologies in the field of virtual reality. This year was the 14th exhibit, and over 10,000 people participated in it. The exhibition gives out 12 awards, one per field, and Professor Lee’s team won the highest award.
2012.05.07 View 10690 -
Biomimetic reflective display technology developed
Professor Shin Jung Hoon
The bright colors of a rainbow or a peacock are produced by the reflection and interference of light in transparent periodic structures, producing what is called a structural color. These colors are very bright and change according to the viewing angle. On the other hand, the wings of a morpho-butterfly also have structural colors but are predominantly blue over a wide range of angles. This is because the unique structure of the morpho-butterfly’s wings contains both order and chaos.
Professor Shin Jung Hoon’s team from the Department of Physics and the Graduate School of Nanoscience and Technology at KAIST produced a display that mimics the structure of the morpho-butterfly’s wings using glass beads.
This research successfully produced a reflective display (one that reflects external light to project images), which could be used to make very bright displays with low energy consumption. This technology can also be used to make anti-counterfeit bills, as well as coating materials for mobile phones and wallets.
The structure of the morpho-butterfly’s wings seems to be in periodic order at the 1-micrometer level, but contains disorder at the 100-nanometer level. So far, no one had succeeded in reproducing a structure with both order and disorder at the nanometer level.
Professor Shin’s team randomly aligned differently sized glass beads of a few hundred nanometers to create chaos and placed a thin periodic film on top of it using the semiconductor deposition method, thereby creating the morpho-butterfly-like structure over a large area.
This new development produced better color and brightness than the morpho-butterfly wing and even exhibited less color change according to angle. The team sealed the film in thin plastic, which helped to maintain the superior properties whilst making it more firm and paper-like.
Professor Shin emphasized that the results were an exemplary success in the field of biomimetics and that structural colors could have other applications in sensors and fashion, for example.
The results were first introduced on May 3rd in Nature as one of the Research Highlights and will be published in the online version of the material science magazine, Advanced Materials.
This research was jointly conducted by Professor Shin Jung Hoon (Department of Physics / Graduate School of Nanoscience and Technology at KAIST), Professor Park NamKyoo (Department of Electrical and Computer Engineering at Seoul National University), and Samsung Advanced Institute of Technology. The funding was provided by the National Research Foundation of Korea and the Ministry of Education, Science and Technology as part of the World Class University (WCU) project.
Figure 2. The biomimetic film can express many different colors
Figure 3. The biomimetic diplay and a morpho-butterfly
2012.05.07 View 13315 -
The output of terahertz waves enhanced by KAIST team
KAIST researchers have greatly improved the output of terahertz waves, the blue ocean of the optics world. This technology is expected to be applied to portable X-ray cameras, small bio-diagnostic systems, and in many other devices.
Professor Ki-Hun Jeong"s research team from the Department of Bio and Brain Engineering used optical nano-antenna technology to increase the output of terahertz waves by three times.
Terahertz waves are electromagnetic waves with frequencies between 100GHz to 30THz. They are produced when a femtosecond (10^-15 s) pulse laser is shone on a semiconductor substrate with photoconduction antennas, causing a photocurrent pulse of one picosecond (10^-12 s). Their long wavelengths, in comparison to visible light and infrared rays, give terahertz waves a high penetration power with less energy than X-rays, making them less harmful to humans.
These qualities allow us to see through objects, just as X-rays do, but because terahertz waves absorb certain frequencies, we can detect hidden explosives or drugs, which was not possible with X-rays. We can even identify fake drugs. Furthermore, using the spectral information, we can analyze a material"s innate qualities without chemical processing, making it possible to identify skin diseases without harming the body. However, the output was not sufficient to be used in biosensors and other applications.
Prof. Jeong"s team added optical nano-antennas, made from gold nano-rods, in between the photoconduction antennas and optimized the structure. This resulted in nanoplasmonic resonance in the photoconduction substrate, increasing the degree of integration of the photocurrent pulse and resulting in a three times larger output.
Hence, it is not only possible to see through objects more clearly, but it is also possible to analyze components without a biopsy.
Professor Jeong explained, "This technology, coupled with the miniaturization of terahertz devices, can be applied to endoscopes to detect early epithelial cancer" and that he will focus on creating and commercializing these biosensor systems.
This research was published in the March issue of the international nanotechnology journal ACS Nano and was funded by the Korea Evaluation Institute of Industrial Technology and the National Research Foundation of Korea.
Figure: Mimetic diagram of a THz generator with nano-antennas
2012.04.29 View 11215 -
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 11356