Press releases on Research & Outcome
▣ Prof. Jang-Sik Lee: Organic-Transistor Memory Four Times More Efficient for Information Storage


 Prof, Jank-Sik Lee’s research team of POSTECH Materials Science and Engineering Department developed a technology to increase the information storage capacity of organic-transistor by four times, which could be used as flexible memory of next generation wearable computers.

Prof. Lee’s team announced that it succeeded in increasing the reliability of stored information by four times by putting a nano silica shell on gold nanoparticles, which consist of the layer for information storage in organic-transistor memory. According to the experiment, the organic-transistor memory with silica shell-covered gold nanoparticles maintained 60% of stored memory after one year, four times as efficient as the memory using only gold nanoparticles that recorded 15%.

Prof. Lee said, “Even though this new technology is not sufficient for immediate commercialization of organic-transistor memory, it provides a fundamental solution to improve the information storage capability which was the biggest obstacle, and drastically reduce the manufacturing processes.”


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Design of an Efficient Charge-Trapping Layer with a Built-In Tunnel Barrier for Reliable Organic-Transistor Memory.

Advanced Materials 26, 47, 8010-8016, December 17 (2014)

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▣ Prof. Tae-Woo Lee: Development of superfast metal Nanofiber Electrode Printing Technology


 Electrodes used for a variety of portable, wearable devices are required to be small and efficient at the same time. The new technology to print such micro-sized, high-density electrodes has been developed by a Korean research team.

 

The POSTECH team of Prof. Tae-woo Lee and Ph.D. candidate Yeongjun Lee in the Materials Science and Engineering department published the high-speed metal nanofiber printing technology in Advanced Materials, the prestigious academic journal in materials science.

The paper on the technology was selected as an inside cover and listed on the top which reveals its abstract to the public proving the great attention from the academia.

 

There have been conventional methods to produce nano-sized electrodes such as photolithography and electron beamlithography, but the processing was too complicated and expensive. Also, the latest metal electrode and wire printing technology had limitation in producing a metal wire having a diameter of 1㎛ or less.

 

Prof. Tae-Woo Lee’s research team succeeded in printing a large-scale-aligned array of copper nanofibers which has a diameter of hundreds nanometer and electrical properties similar to those of metal, using the team’s unique E-nanowire printing technology that aligns nanowires directly on substrate through an electric field.

Also, the POSTECH team successfully made the electrode for organic transistors, proving the potential of the new technology.

 

The new technology has been praised for not only fast fabrication of large-scale-aligned metal nanowires but also large cost reduction.

 

The technology could be applied to a variety of transparent electrodes including displays, memories, solar cells and touch screen panels and to high-integrated circuits. Particularly, if combined with other advanced domestic technologies on the global level, it is expected to contribute to the development of Korea’s soft electronics industry.

Further, the defects in the metal interconnections that are created in the course of producing large-scale electrodes such as display panels are expected to be repaired with the technology, drastically raising previous transference numbers in the electronics industry.

 

The team leader Prof. Tae-Woo Lee said, “The cost and time is remarkably reduced with simplified method, compared to conventional nanoelectrode manufacturing, and it will advance the commercialization of high-integrated electronic devices using metal nanoelectrodes.” He also added that the new technology will be used as basis for realizing wearable computer, fiber electronic devices, and flexible displays, whose markets will grow into the size of KRW 50 trillion by 2020.

 

The research is funded by the government’s Global Frontier Project ‘Center for Advanced Soft Electronics,’ conducted by Ministry of Science, ICT and Future Planning.


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Individually Position-Addressable Metal-Nanofiber Electrodes for Large-Area Electronics.

Advanced Materials 26, 47, 8010-8016, December 17 (2014)

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▣ Prof. Jong-Lam Lee: Development of Technology for Enhancing Transmittance and Conductivity


  As smart and wearable devices such as wearing computer and wrist watches have come into the spotlight, various devices and solar cells to be applied to wearable gear have competitively been developed. Especially, light and flexible organic solar cells are expected to be applied to new devices which can be charged easily.

 

POSTECH Materials Science and Engineering department’s research team including Prof. Jong-Lam Lee and Ph.D. candidate Juyoung Ham developed a transparent electrode technology, which can be applied to flexible solar cells. The technology, which is using a simple process that looks similar to putting on a stamp, was published on the cover of the renowned Advanced Energy Materials’s October issue, receiving attention from the academia.

 

The transparent electrodes for organic solar cells have been currently made from indium tin oxide (ITO). ITO is better than other materials in resistance and transmittance, but it requires a high temperature of 300℃ or over for production and is unavailable for flexible cells due to its inflexibility.

 

In order to devise new transparent electrode technology, the research team applied the flexibility of polymers, and the method to maximize light scattering by forming nanometer patterns on polymers through nanoimprint.

 

In addition, Prof. Lee’s team found out through the Pohang Light Source that light absorption occurring in the process of forming thin metal films on polymer is caused by plasmon effect at the boundary surface between polymer and metal, and the production of plasmon could be suppressed by increasing the surface energy of polymer layer.

As a result, higher electric conductivity was obtained in a thin metal film with 8nm thickness than in conventional ITO electrodes of 170nm thickness.

 

The organic solar cell that used the developed electrode recorded a 17% increase of photocurrent density, which is the best result among organic solar cells using ITO replacements.

 

The leader Prof. Jong-Lam Lee said, “Our technology could be applied to flexible or folding devices as well as organic solar cells, and take an important role in advancing commercialization of wearable electronics.”


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Three-Dimensional Nanostructured Indium-Tin-Oxide Electrodes for Enhanced Performance of

Bulk Heterojunction Organic Solar Cells.

Advanced Energy Materials 4, 7, may 13 (2014)

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▣ Prof. Jong Kyu Kim: Technology for producing hydrogen energy from water


 A domestic research team developed a new nanomaterial that enables to split water using sunlight (solar radiation energy).* When water is split, oxygen and hydrogen are produced. Hydrogen is expected to be the cleanest energy among the next generation energy sources, and its production is to be the essential and fundamental technology to solve the global energy issue of the future.

 

* Solar Radiation Energy: A light energy of 125,000 terawatt from the sun is daily received on the earth. The tremendous amount is about 10,000 times as large as that is consumed by the whole mankind every day.

 

** Hydrogen: It can be used as similar energy source as gasoline and diesel, and when used in fuel cells, it produces electric power without pollution. Since current hydrogen production is made from fossil fuels, hydrogen can’t be deemed a clean energy.

 

The joint research team, which consists of Prof. Jong Hyeok Park’s Sungkyunkwan University Chemical Engineering team with M.S. candidate Xinjian Shi and Prof. Jong Kyu Kim’s POSTECH Material Science and Engineering team including Ph.D. candidate Il Yong Choi, conducted this research funded by Mid-Career Researcher Support Program of Ministry of Science, ICT and Future Planning. The research outcome was published in Nature Communications online on September 2nd.

 

(The title of the paper: Efficient photoelectrochemical hydrogen production from bismuth vanadate-decorated tungsten trioxide helix nanostructures)

 

The hydrogen production by solar water splitting has been attempted from the ‘70s and called the holy grail,* but its efficiency was so low that commercialization seemed unlikely.

 

* Holy grail: It is the chalice that appears in the legends of medieval times and is said to be used by Jesus Christ in the Last Supper. The nickname was created in the sense that the ubiquitous water is magically turned into Valuable hydrogen energy.

 

The research team discovered that they could increase the solar-to-hydrogen conversion efficiency to 6% or more by using their core technology that makes helical nanostructures in tungsten oxide and bismuth vanadate.

 

*Solar-to-hydrogen conversion efficiency: The percentage of the hydrogen energy that can be generated from solar radiation energy. The 6% efficiency means that 6% of solar radiation energy can be converted into hydrogen energy.

 

Bismuth vanadate easily absorbs the sunlight but showed a low efficiency for hydrogen production, but ​in this research, tungsten trioxide helical nanostructures coated with bismuth vanadate in a nanometer-level thickness allowed efficient formation of electrons* and electric holes** and, consequently the solar-to-hydrogen conversion efficiency was drastically raised.

 

*, ** When a semiconductor material absorbs the sunlight, electrons (-) and electric holes (+) of difference energy levels are produced depending on the type of the materials.

 

Particularly, the helical nanostructure of tungsten oxide increased the efficiency of sunlight absorption to about 100%, and the team has made this new discovery known for the first time in the world boosting the hope for high-efficiency hydrogen production.

 

As for solar cells that converse solar radiation energy into electricity, the produced power disappears if it is not immediately used, but the hydrogen energy, which is a chemical energy produced from solar energy, can be stored and transported like gasoline or LPG, and hence related research is expected to expand.

 

 

Prof. Jong Hyeok Park said, “This research laid the important foundation for commercialization of hydrogen energy production using solar radiation and water.”



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Efficient photoelectrochemical ​hydrogen production from ​bismuth vanadate-decorated ​tungsten trioxide helix nanostructures.

Small 10, 18 (2014)

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▣ Prof. Hyun Myung Jang: Suggestion of new analysis method on quantum dot lattice distortion


 A quantum dot, which is a millionth as thick as a strand of hair, has been applied to a variety of devices including semiconductors, displays, optical sensors and medical appliances, and recently its application has broadened to light fixtures proving the great potential. However, a band gap, which determines the electric conductivity of a material, has been pointed out as the obstacle for the application, and how to tune a band gap is a critical issue debated by researchers.

 

While most researchers use chemical methods, a domestic research team developed the first-ever mechanical way to tune a band gap.

 

Dr. Eui-Hyun Kong’s research team with the guidance of Prof. Hyun Myung Jang at the POSTECH Materials Science and Engineering, in collaboration with Ph.D. candidate Soo-Hyun Joo (academic adviser: Prof. Hyoung Seop Kim) and Senior Researcher Hyun-Jin Park at National Institute for Nanomaterial Technology, developed a new method to tune a band gap by inducing thermal residual stress*1 in a quantum dot and distorting the lattice. This job will be issued as the September issue cover in the prominent academic journal Small.

 

The research has profound significance as it suggested a new understanding, while it applied the finite element method*2 to a quantum dot for the first time and predicted lattice distortion.

 

A band gap, also called an energy gap, means the difference in energy between when an electron exists and when it does’t. This difference in energy determines the electrical conductivity of a material, and a quantum dot is used in displays and semiconductors due to its electrical conductivity. Therefore, turing a band gap is closely related to improving optical and electrical properties of quantum dots.

 

This mechanical band gap tuning does not require expensive equipment or a lengthy process, and could reduce the production cost remarkably.

 

Also, Dr. Kong’s team applied the new method to quantum dot-sensitized solar cells, and approved the feasibility of the technology with an increase of efficiency to over 60%.

 

In the April issue of the same journal Small, the lead author Dr. Kong published another paper as the cover of the journal.

 

 

1. Residual Stress

 

Residual stress is the stress that remains in the material when external force is removed. Stress increases as the the outer force increases, but the increase reaches a limit and the material is destroyed when it reaches the material's own yield stress. In metal, stress can be caused by hardening or welding.

 

2. Finite Element Method

 

It is a numerical analysis method in which a problem domain is divided by a finite number of elements and analyzed through modeling.


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Quantum Dots: Bandgap Tuning with Thermal Residual Stresses Induced in a Quantum Dot (Small 18/2014)

Small 10, 18 (2014)

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▣ Prof. Sei Kwang Hahn: Development of hydrogel for delivery of cell therapeutic agent


  Prof. Sei Kwang Hahn’s team of POSTECH Materials Science and Engineering published its research outcome on hydrogel for regenerative medicine that drastically improves in vivo delivery of cell therapy drugs and the cure for incurable diseases.

 

This paper, which is titled ‘Light-guiding hydrogels for cell-based sensing and optogenetic synthesis in vivo,appeared in the latest online issue of Progress in Polymer Science (IF = 26.854), the esteemed academic journal in materials science. The article introduces a variety of advanced technologies for polymer hydrogels that could increase the persistence of cell therapy drugs for incurable diseases with enhanced stability in the body.

 

Also, the paper expands on the diagnosis and treatment technology using in vivo light-guiding hydrogels, which was jointly developed by Harvard Medical School and published on Nature Photonics. This research reported for the first time in the world that newly developed light-guiding hydrogel of superior optical properties could be effectively used for curing diabetes by putting optogenetic hydrogel into the body and inducing the production of insulin with light. Tother with the technology, Prof. Hahn’s team developed a method to visualize the toxic heavy metal levels in the body and attracted attention for the academia.

 

In addition, the drug delivery system for cell therapy using self-assembling hydrogels is detailed in the paper as well. The animal testing showed that when genetically modified stem cells to cure incurable diseases such as cancer, stroke and myocardial infarction were put into the body through injectable hydrogel, anticancer protein was biosynthesized to halt the growth of cancer cells. The technology transfer contract has been made with Genexine, Inc (CEO Young Chul Sung, professor at POSTECH Department of Life Science) and the commercialization of the drug delivery system for cell therapy has been accelerated.

 

This research was funded as part of Cell Regeneration Technology Development Project of Biomedical Technology Team under the auspices of Ministry of Science, ICT and Future Planning. Prof. Hahn said, “This new injectable hydrogel technology for regenerative medicine is expected to remarkably increase the effectiveness of existing drugs for a range of incurable diseases.”


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In situ-forming injectable hydrogels for regenerative medicine.

Progress in Polymer Science 39, 1973-1986 (2014)

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▣ Prof. Tae-Woo Lee: Development of technology for improving efficiency of flexible perovskite solar cells


 Solar cells have been attracting great attention from the academia as well as governments in the hope that they could replace fossil fuels. As for silicon solar cells, while the efficiency is 20%, the production process is so arduous and expensive. However, cheaper solar cells have low efficient to be commercialized.

 

Against the circumstances, hybrid solar cells using organometallic halide perovskites, which have conducting and semiconducting nature and even superconductivity with the unique, crystal structures, have come into the limelight, because they enables cost reduction and mass production at once. Such solar cells are expected to have a drastically enhanced photoelectric conversion efficiency, and the technology to develop them was selected as one of the ten most innovative technologies for 2013 by the prestigious scientific journal, Science.

 

The research team including Prof. Tae-Woo Lee and Ph.D. candidate Kyung-Geun Lim of POSTECH Materials Science and Prof. Jin Young Kim of UNIST developed a new solar cell with high efficiency using flexible organometallic halide perovskites, and published the achievement in Advanced Materials, the renowned academic journal in materials science.

 

The team developed a polymer auxiliary layer customized for perovskites, which don’t need high temperature process as flexible polymer materials, and consequently raised the efficiency of perovskite solar cells and opened up possibilities for commercializing flexible or folding solar cells sooner.

 

The conventional methods used metallic oxides as auxiliary layers requiring high temperature process, and flexible device could not be made due to fragility. And using a polymer auxiliary layer was suggested but photoelectric conversion efficiency was too low.

 

The research team applied self-organized hole extraction layer (SOHEL)*2 to the active layer of perovskite solar cells, using self-organized conductive polymer compounds. Especially, because the hole extraction layer can self-control the composition of a polymer on the surface of thin film, and make the work function suitable for perovskites, the electric potential losses are prevented after solar cells absorb the light maximizing efficiency.

 

The self-organized hole extraction layer can be applied to any type of perovskite, and it has great potential to be widely used in other materials.

 

The research showed that the new technology raised the previous efficiency of 8% to 11.7%, and can be applied to flexible plastic substrate as well.

 

The team expressed their view that the new technology has offered the possibility to use solar cells in portable electronics including cell phones and tablet PCs, and for Korea to lead the world in the solar sell technologies.



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Boosting the Power Conversion Effi ciency of Perovskite Solar Cells Using Self-Organized

Polymeric Hole Extraction Layers with High Work Function.

Nature Comm 5, 5369, (2014)

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▣ Prof. Hyoung Seop Kim and Prof. Tae-Woo Lee: POSTECH Researchers Recognized for Excellent Research


 By Ministry of Science, ICT and Future Planning, and Korea Institute of S&T Evaluation and Planning

 

POSTECH research teams have not only won a number of research awards but also received a good evaluation by government agencies.

 

The Ministry of Science, ICT and Future Planning has recently announced the 100 Best R&D Outcomes for 2014, and the list included the names of POSTECH Prof. Tae-Woo Lee of Materials Science and Engineering, Prof. Hwang Cheol-Sang of Life Science, Prof. Dong Pyo Kim of Chemical Engineering and Prof. Hee Cheul Choi of Chemistry.

 

Prof. Tae-Woo Lee was selected with his ultrafast nanowire printing technology for wearable electronic devices; Prof. Hwang Cheol-Sang’s research was on N-terminal methionine and predicting protein decomposition; Prof. Dong Pyo Kim was recognized for his new chemical process for dealing with toxic materials with safety; and Prof. Hee Cheul Choi developed nano-porous materials customized for the size of water pollutants.

 

Prof. Hyoung Seop Kim of POSTECH Materials Science and Engineering received the Shinhan Diamond Best Paper Award from Korean Powder Metallurgy Institute, and his student Jung-gi Kim in MS-PhD integrated course won the Best Poster Award at the 6th International Conference on Nanomaterials by Severe Plastic Deformation held in Metz, France with his presentation on numerical analysis of plastic deformation made by CST process.

 

Another POSTECH Materials Science and Engineering member, Dr. Ji San Lee (academic adviser: Prof. Jung Ho Je) attended the International Conference on Micro & Nanofluidics held in the Netherlands, and received the Best Video Prize from the famous high-speed camera producer Photron with his research on ultrafast dynamics of a water drop falling on the surface of liquid through x-ray imaging.

▣ Prof. Jung Ho Je: The Shape and Principle of Wetting Ridge due to Water Drop



 Prof. Jung Ho Je’s research team of POSTECH Materials Science and Engineering explained how a wetting ridge is formed with a water drop on a solid surface.

 

Prof. Jung Ho Je (POSTECH Materials Science and Engineering) and Su Ji Park (Ph.D. candidate) published a journal paper/article of how the elastic surface of a material is pulled up and forms a minute wetting ridge due to a water drop.

They found out through microscopy that the cusp of a wetting ridge on a water drop is in the shape of a hooked asymmetric triangle.

The research revealed that a wetting ridge is formed on a higher level on a softer material, and proportionate to the vertical force. The the shape of a wetting ridge, the team found out, was determined by three types of interfacial tension working on its cusp.

Such wetting ridges appear when a dewdrop forms on a leaf, a drop of skin care product is fallen on the skin, or an eye medicine is dropped in the eye.

This research is expected to help the understanding of the wetting in the cells that could influence their proliferation, differentiation and growth and to be applied to a wide range of fields including bio and nano research.

 

Prof. Jung Ho Je said, “The newly found principle of a wetting ridge will help understand the force balance in wetting, and the unique wetting phenomenon on a soft solid surface.” And he added that it could be used for the micro nano technologies including cell manipulation.

 

This research was funded by Leading Researcher Support Program sponsored by Ministry of Science, ICT and Future Planning and National Research Foundation of Korea.

The research outcome was published online in Nature Communications.


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Visualization of asymmetric wetting ridges on soft solids with X-ray microscopy.

Nature Comm 5, 5369, (2014)

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▣ Prof. Sei Kwang Hahn: Nanomedicine for Arthritis


  Prof. Sei Kwang Hahn’s team of POSTECH Materials Science and Engineering developed a new method to treat arthritis using nanotechnology.

 

The POSTECH research team including Prof. Sei Kwang Hahn and Ph.D. candidate Hwiwon Lee, in collaboration with Prof. Ji Hyeon Ju at College of Medicine, the Catholic University of Korea and Prof. Byung-Soo Kim at School of Chemical and Biological Engineering, Seoul National University, developed a complex for the treatment of rheumatoid arthritis by chemically bonded gold nanoparticles and hyaluronic acid known to have cartilage-protective lubricant effects and then physically combining antibody therapeutics.

 

Rheumatoid arthritis is an inflammatory immune disease with excessive production of microvessels. The anti-angiogenic nanomedicine has a drastically increased effectiveness compared to conventional arthritis medicine due to the synergistic effect produced by an immunosuppressive drug Tocilizumab. The paper on this research was published in the May 27 issue of ACS Nano, the world-renowned nanotechnology-specialized academic journal.

 

The research leader Prof. Sei Kwang Hahn said, “The newly developed complex using gold particles and the antibody therapeutic has showed an excellent effect for treating arthritis in the animal test. A follow-up research will develop it into a theranostic system for rheumatoid arthritis using the bio imaging property of gold nanoparticles.

In the recent five years, Prof. Sei Kwang Hahn’s team has published about 50 papers regarding development of biomaterials for nanomedicine in the prestigious academic journals including Nature, Photonics and Advanced Materials, and finished the application and registration of 40 or so patents.

 

[The new rheumatoid arthritis treatment mechanism, which uses anti-angiogenic gold nanoparticles and an antibody therapeutic effectively combining with IL-6, has remarkably advanced effects with the anti-angiogenic gold nanoparticle-antibody therapeutic complex and disturbance in the combination of f IL-6 and IL-6 receptor.

 

[Terms]

※ Gold nanoparticle

Nano-sized gold has advantageous physical, chemical and biological properties, and can be used in a variety of fields including biotechnology, medicine, electronics and materials engineering.

※ Antibody therapeutics

They treat diseases using antibodies which can combine exclusively with necessary receptors regarding diseases. Since a number of patents for related innovator products have recently been expired, efforts to develop biosimilars are actively ongoing in the world.

※ Hyaluronic acid

As one of the biopolymers found in skin, musculoskeletal system, joints and eyeballs, hyaluronic acid is highly adhesive to skin and mucous membranes, viscoelastic and biocompatible and is used for arthritis treatment, ophthalmic surgery, cosmetic filler, drug delivery and tissue engineering.


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HyaluronateGold Nanoparticle/Tocilizumab Complex for the Treatment of Rheumatoid Arthritis

ACS NAno 8, 5, 4790-4798 (2014)
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▣ Prof. Jong Kyu Kim, Prof. Jong-Lam Lee: Increased Light Harvesting Efficiency for Solar Cells with ‘Helix’





  Development of Ways to Enhance Solar Cell Performance through Three-Dimensional Structured

 

Silicon solar cells are expected to replace fossil fuels which are already now under commercialization, but they are expensive. To significantly reduce the production cost, organic solar cells using organic dye have been developed by many researchers and their efficiency still need to be substantially raised for commercialization.

A domestic research team has published an interesting research outcome that, a three-dimensional helical structure could maximize light harvesting of organic solar cells.

 

POSTECH Materials Science and Engineering’s research team consisting of Prof. Jong Kyu Kim, Prof. Jong-Lam Lee, Ph.D. candidate Hyunah Kwon and Juyoung Ham published their research outcome as the cover of the prestigious Advanced Energy Materials, receiving attention from the academia. The published paper demonstrated that, three-dimensional helical-structured electrodes drastically enhanced light harvesting and efficiency of organic solar cells.

 

Organic solar cells usually show a low efficiency in light harvesting, since they are made of very thin films. However, the research demonstrated that if the electrodes are made in a three-dimensional helical structure, dissipation of sunlight can be prevented and absorption be maximized with dispersion of light.

 

The electrical properties were also enhanced and consequently the efficiency of these organic solar cells recorded 10% higher than conventional solar cells.

 

Also, the method called ‘glancing angle deposition’ to create the helical structure, which is simply to tilt or rotate the substrates during deposition of a nano material into a substrate, can be applied to various materials and substrates and diversify the shape of a nanostructure.

 

The wide application of the method is hoped to be useful for numerous fields including photoelectrochemical cells, which split hydrogen and oxygen from the water, and dye-sensitized solar cells that generate solar energy by simply coating window panes with dye.

This research was conducted with the support from Global Research Network Project and Key Research Center Support Project of National Research Foundation of Korea.


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Three-Dimensional Nanostructured Indium-Tin-Oxide Electrodes for Enhanced Performance of

Bulk Heterojunction Organic Solar Cells

Advanced Energy Materials 4, 7, 4126-4132 (2014) (IF: 15.409) Cover

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▣ Prof. Hyun Myung Jang: Solve the Puzzle about Ferroelectricity of Mutiferroics


  A domestic research team found out the reason behind the puzzling properties of multiferroics including ferroelectricity. Since the multiferroics have both electrical and magnetic properties, they can be used for next generation nonvolatile memory which has the both quality of a hard disk and DRAM and also capable of storing massive data. This research outcome is so important as to be selected as the cover of a prestigious academic journal in materials science.

 

POSTECH research team consisting of MS-PhD integrated course student Seungwoo Song in Division of Advanced Materials Science, and Prof. Hyun Myung Jang in both Division of Advanced Materials Science and Department of Materials Science and Engineering discovered the cause of ferroelectricity in multiferroic LuMnO3 through first-principles calculations. Plenty of research have been conducted to reveal the causes of multi ferroics having both ferroelectricity and ferromagnetism, but no one has suggested a satisfying answer.

 

The research team had an idea from the fact that, there is a large gap between the temperature to produce structural polarity (~1560℃) and that for electrical polarity (~1020℃). And they analyzed the movement of atoms when electrical polarity is not present but structural polarity emerges and identified that, electrical polarity is caused by the coupling of symmetric and asymmetric movements of atoms.

 

The team concluded that while the structural polarization at 1560℃ is influenced by symmetric movement of atoms and so electrical polarization is not accompanied, at 1020℃ electrical polarization is induced because of the asymmetric and symmetric movements of atoms are coupled.

 

As the phenomenon revealed is common in hexagonal manganese oxides, this research is forecast to influence the development of room-temperature multiferroics and ferroelectric memory device (F-RAM).

 

The paper was not only presented at the 23rd Symposium on Dielectric Properties and 15th Workshop on Ferroelectric Devices/Materials and awarded the Best Presentation Prize, but also published as the cover of the latest issue of Journal of Materials Chemistry C, which is the prestigious academic journal in materials science published by Royal Society of Chemistry.

 

The research was funded by General Researcher Support Program of National Research Foundation of Korea, and High Performance Computing-Use Research Support Project of Korea Institute of Science and Technology Information.

 

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Mode coupling between nonpolar and polar phonons as the origin of improper

ferroelectricity in hexagonal LuMnO3

Materials Chemistry C 2, 4126-4132 (2014) (IF: 15.409) Cover

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▣ Prof. Tae-Woo Lee: Fabrication of inexpensive, large-scale and superfast graphene nanoribbon


 A domestic research team developed a technology for inexpensive and fast fabrication of graphene nanoribbons, using organic nanowire lithography that enables alignment and patterning. The new technology made it possible to easily produce graphene nanoribbons on a large area in desirable shapes. This technology is also expected to facilitate commercialization of wearable electronics and flexible displays based on excellent electrical properties of graphene nanoribbons and the transparency and flexibility unique to graphenes.

With the support from Center for Advanced Soft Electronics (Director Kilwon Cho) established by Global Frontier Program of Ministry of Science, ICT and Future Planning, Prof. Tae-Woo Lee led the research and Prof. Wentao Xu participated as the lead author. The paper was published on the April 10 online issue of Advanced Materials, the prominent academic journal in materials science. (The title of the paper: Rapid Fabrication of Designable Large-Scale Aligned Graphene Nanoribbons by Electro-hydrodynamic Nanowire Lithography)

 

Graphene has been attracting attention as one of the most promising materials for next generation high integrated electronic circuits, but since it had no band bap (an energy range that electrons can have) it could not be used for semiconducting electronic devices benefitting from band gaps. However, because nanoribbon graphene has a band gap and it increases as its width gets narrower, narrow graphene nanoribbons can acquire the semiconducting properties.

 

A range of methods for producing graphene nanoribbons have been introduced, but they were expensive and took a long time. They had also limitation limitation for commercialization since large-scale width and alignment modification were required to be applied to electronic devices such as transistors and memories.

The research team formed graphene on a silicone substrate through chemical vapor deposition, aligned organic nanowires on the substrate in the desirable position and produced graphene nanoribbons along the nanowires after going through the oxygen plasma etching (removing the unnecessary elements). The new method overcomes the weaknesses of the conventional way which is slow and expensive and does not allow large-scale patterning.

 

The produced graphene nanoribbons have a sub-10-nm width and band gap. Using them as channels of field-effect transistors, the team also succeeded in producing an electronic device that shows a on/off current ratio of ca.70 and hole mobility value of 300cm2V-1s-1 at room temparature, proving the potential for development of electronic devices.

 

The research team said, “Unlike the conventional method, the new technique enables production of large-scale graphene nanoribbons in desirable position and length as well as inexpensive simple process and eventually is expected to accelerate the development of electronic devices using graphene nanoribbons.” They also added that this research outcome could be the foundation for the realization of wearable computers and flexible electronics, whose market is projected to grow to a 50-trillion-won size by 2020.



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Rapid Fabrication of Designable Large-Scale Aligned Graphene Nanoribbons by

Electro-hydrodynamic Nanowire Lithography

Advanced Materials 26, 21, 3459-3464 (2014) (IF: 15.409)

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