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Improving your memory

Revolutionary plastic memory devices developed Recent increases in demand for mobile devices have stimulated the development of nonvolatile memory devices with high performance. These nonvolatile memory devices are unpowered computer memory devices such as USB flash drives. However, with recent developments will soon see foldable electronic newspapers, books, magazines, and even wearable computers. Professor Moonhor Ree (Department of Chemistry) and Professor Ohyun Kim (Department of Electronic and Electrical Engineering) research team, in their paper entitled, “Novel Digital Nonvolatile Memory Devices Based on Semiconducting Polymer Thin Films” published in Advanced Functional Materials, described the development of low-cost, high-performance, digital nonvolatile memory devices based on semiconducting polymers. They also reported their memory devices are switchable in a very low voltage range with a very high ON/OFF current ratio. The low critical voltages have the advantage for nonvolatile memory device applications of low operation voltages and hence low power consumption. Until now, all nonvolatile memories are fabricated with inorganic materials that are used in complementary metal-oxide semiconductor processes, and are based on charge storage. Their disadvantages of slow programming, limited endurance, and high voltage requirements have prompted the research team into investigation of organic and polymer materials which exhibit easier processability, flexibility, high mechanical strength, and scalability at low cost. However due to high ON/OFF voltages, development of polymer based nonvolatile memory devices have remained work in progress, until now. “The high ON/OFF switching ratio and stability of these devices, as well as their repeatable writing, reading and erasing capability with low power consumption, opens up a possibility of mass production of high performance digital nonvolatile polymer memory devices with low cost,” Professor Ree said, adding it would revolutionize microelectronics by providing extremely inexpensive, lightweight, and versatile components that can be printed onto plastics, glasses or metal foils. The research was supported by the Korea Science & Engineering Foundation, Samsung Electronics, and the Korean Ministry of Education. Professor Moonhor Ree Department of Chemistry Email: ree@postech.ac.kr Phone: +82-54-279-2120 Professor Ohyun Kim Department of Electronic and Electrical Engineering Email: ohkim@postech.ac.kr Phone: +82-54-279-2215

New Sepsis Medication Development to Rev Up

POSTECH, joining hands with Dong-A University and Seoul Pharmaceutical Co., Ltd., hastens development of a novel sepsis medication materialized with domestic technology. POSTECH team of Professor Sung Ho Ryu and Professor Yoon-Keun Kim (Department of Life Science), in a joint research with Professor Yoe-Sik Bae of Dong-A University, supported by POSCO and Ministry for Health, Welfare and Family Affairs, has developed peptides that effectively prevent progression of sepsis. In animal experiments, the peptide ligands newly developed for formyl peptide receptor like-1 (FPRL1) in septic mice resulted in a survival rate of 80% whereas those that didn’t get the injection died within 24 hours. Sepsis, the cause of over 200,000 deaths yearly in the United States alone, is a serious medical condition occurring when host immune defenses fail to combat invading microbes: a pathogen enters the blood vessels and causes a whole-body inflammatory state and blood coagulation, eventually leading to organ dysfunction and death. The only choice for severe sepsis medication has been the multinational corporation Eli Lilly’s ‘Xigris’ which has a low curing rate and a high price. The new sepsis treating substance, whose development technology is to be transferred to Seoul Pharmaceutical Co., Ltd. based on the agreement signed on January 22, 2009, is low molecular peptides which accelerate the host’s defense mechanism. The therapeutic receptor enhances the bactericidal activity, and inhibits both the production of pro-inflammatory mediators induced by lipopolysaccharide and cecal ligation and puncture induced immune cell apoptosis. The peptides, being low molecular ones, do not harm the immune system nor have as many side effects. In addition, the composition process is simple, allowing for low cost production. These advantages, added to the therapeutic and bactericidal properties of the peptides, are presumed to contribute to the development of new and more effective sepsis medications, expectantly to overcome the limits of the existing one.

World's fastest nano-transistor developed

30-nano class Gallium Arsenide (GaAs) nano-transistor: comparative advantages in its performance Easy manufacturing process: less than half the cost of commercialization It is possible to receive and enjoy various multimedia contents such as music, movies, and other data, at speeds of several tens of Mbps using high-speed internet widely available in households. Studies on the improvement of communication speeds have been continuously conducted over the recent years. Professor Yoon-Ha Jeong and research team have successfully succeeded in developing 35-nano GaAs nano-transistors (metamorphic HEMT) that are more than 10 times faster than existing transistors. It will be now possible to develop the world's fastest 30-nano GaAs transistors and is expected to lead to the development of next generation ultra high-speed semiconductor elements. The transistor developed by the research team is a type of ultra-high frequency nano-electronic element becomes a core element in such ultra high-speed communication system. Because the various composites-based elements including HEMTs (High Electron Mobility Transistors) can be operated in an ultra-high frequency band differed from the silicon-based element that can be operated within a frequency band of several GHz, it is considered as important factor in the development of ultra high-speed wire and wireless communication system in an ultra-high frequency band. Studies on the HEMT have been conducted all over the world, as part of the endeavor to develop ultra-high frequency nano-electronic elements. mHEMT adequate to the production of ultra-high frequency nano-electronic elements HEMT is an electronic element that is produced by a heterojunction method based on characteristics of 2DEG (two-dimensional electron gas) which makes possible ultra high-speed operation using fast movements in electrons. Presently, InP (Indium Phosphide)-based HEMT represents the highest performance. However, it is difficult to use InP boards with a large area due to difficulties in handling (easy breakable), even though the InP-based HEMT shows very high performance. In addition, it represents a low rate in price versus performance due to its high prices. The mHEMT (metamorphic HEMT) solves these disadvantages. Technical difficulties in the production of ultrahigh frequency nano-electronic elements It is possible to obtain faster operation speeds by reducing the length of its gate based on the characteristics of such elements. Thus, the production of microscopic gates plays an important role in improving the ultra-high frequency nanoelectronic elements. The gate used in the HEMT is called a “T-gate” because of its similar shape to the letter T. The T-gate has been widely used because it is able to reduce the gate resistance and minimize the gate length at the same time. The T-gate is easily fallen due to the weight of its head section during the production of elements while the gate length is reduced to increase operation speed. Therefore, it represents difficulties in overcoming of technical limitations in production of nano-class electronic elements. The scales of such a gate reported has been usually approached to the circuit production technology with a level of 100-nano class represented by MIT, including the 50-nano class gate technology published by the Nano Research Center at the University of Glasgow, Scotland. In addition, the 25-nano class gate production technology represented by the Fujitsu Research Center, Japan, using oxides (SiO2) was reported as a gate support as the case stands. Increasing the element performance and re-productivity with a zigzag T-gate The research team solved the problem in the production of microscopic T-gates by creating a new zigzag T-gate method. It is possible to support the heavy head section of a T-gate while the gate length is maintained if the leg of a T-gate is fabricated as a zigzag shape. It is the same idea as the fact that a sheet of folded paper with a zigzag shaped edge shows more easy standing on a floor than a sheet of thin and sharp edged paper. The new technology using a zigzag T-gate method increases the performance and re-productivity of elements and that is highly evaluated as a new technology that achieves the stable gate forming technology without oxides, which have been used as a gate support. The recently developed 35-nano mHEMT has a zigzag shaped T-gate structure which represents more than 520 GHz of the maximum oscillation frequency (fmax) determining the operation speed of the ultra-high frequency of nano-electronic elements. This speed is similar to that of InP-based transistors and is the fastest among GaAs-based nano-electronic elements. In addition, it represents a balance due to its excellent current gain cutoff frequency and maximum oscillation frequency, and shows a 520 GHz of maximum oscillation frequency through improving the maximum oscillation frequency of the conventional mHEMT more than 120 GHz. This will improve the operation speed more than 10 times faster than the existing silicon elements. Furthermore, it makes possible to perform mass production due to less than half the cost of conventional products and easy production process. These factors will boost the development of next generation ultra high-speed semiconductor elements. Professor Y. S. Park of Rensselaer Polytechnic Institute (RPI), one of the world's experts in this field, commented that the nano-electronic element developed by Professor Jeong will play an epochal role in the development of ultra-high frequency elements and circuits. The basic technology developed by the team was published in IEEE Electron Device Letters in its August 2007 issue and have domestic and international patents pending. Professor Yoon-Ha Jeong Department of Electronic and Electrical Engineering Director, National Center for Nanomaterials Technology Tel: +82-54-279-2220/0201 Fax: +82-54-279-5109/0210 Email: yhjeong@postech.ac.kr

Microcantilevers with Nanochannels

The invention of the scanning tunnel microscope (STM) opened the door to nanoworld, enabling humankind to actually touch and feel the individual atoms at the surface of a material. It has inspired a series of inventions such as the atomic force microscope (AFM), the lateral force microscope (LFM), the magnetic force microscope (MFM), etc. Recently, the scanning probe microscope (SPM), which encompasses all these inventions, has evolved into the millipede technology which has a potential to make competing data storage technologies obsolete. A common denominator of these exciting developments is a microscopic structure fabricated by MEMS techniques: the microcantilever. Microcantilevers are not confined to imaging microscopy. They can also be found in the nanopatterning efforts using near-field scanning optical microscopy (NSOM), scanning electrochemical microscopy (SECM), dip-pen nanolithography (DPN), as well as in microsensors. Microcalorimeters offering ultra-high sensitivity have been demonstrated, and ultra-low (ppb) concentrations of toxic gases in air detected. Moreover, surface stresses were measured for the self-assembly of alkanethiols on gold, DNA hybridization or receptor-ligand binding. By using a nanoscale resonator, a mass sensitivity of a few femtograms was reported. Microcantilevers certainly have fundamental advantages as microsensors. Thousands of microcantilevers can be prepared in a single wafer, so they are well-suited for miniaturization. The detection mechanisms are very simple - just measuring the bending deformation or the shift of the resonance frequency of a beam. Chemical or biological stimuli are directly converted to mechanical responses, resulting in a high degree of selectivity and efficiency. We have devised novel microcantilevers with a radically different material and structure, as well as fabrication method. Figures 1(a) through (c) show SEM photographs of the proposed microcantilever array at different magnifications. The overall shape of the microcantilever array can be seen in Figure 1(a). All cantilevers have the same thickness (2μm) and length (50μm), but different widths ranging from 10μm to 50 μm. Figure 1(b) is the magnified image of the edge of one microcantilever in Figure 1(a). Straight nanochannels are clearly visible at this magnification. Further magnification in Figure 1(c) unveils the hexagonal arrangement of nanochannels on the surface of the microcantilever. This photograph was taken from the bottom surface to prove the presence of nanochannels all the way through the thickness of the microcantilever. These nanochannels with extremely high aspect ratio are impossible to obtain by conventional lithographic techniques. The centerpiece of this novel development is the wellknown nanomaterial, anodic aluminum oxide (AAO). It typically has parallel channels of tens of nanometers in diameter up to hundreds of microns in length. It has been commonly used as molds for nanomaterials such as nanotubes and nanowires, taking advantage of these high-aspect-ratio nanochannels. Moreover, replicas of these nanochannels can also be applied in many important fields such as nanoimprint lithography, superhydrophobic surface, and photonic crystals. Recently, AAO technology has experienced a major technological leap by adopting photolithography. This combination will result in various MEMS/NEMS structures with nanochannels in the years to come. To our knowledge, microcantilevers have been made exclusively of isotropic materials until now. Since the operation of a microcantilever relies on the bending of the beam, Young’s modulus is an important material property. A microcantilever made of an isotropic material has a fixed Young’s modulus, so cantilever design is rather limited. In contrast, our microcantilevers possess tunable nanochannels. Since the nanochannels are arranged in one direction, the AAO is not isotropic, and the Young’s modulus is by no means a unique material property. In fact, our microcantilever has multiple Young’s moduli depending upon the direction, and, best of all, the Young’s moduli can be controlled by varying the dimensions of the nanochannels. This is an extremely important advantage in the design of microcantilevers, which has the potential to greatly expand their applicability. The mere presence of nanochannels is beneficial to some applications. Microcantilevers are frequently operated in a vibration mode which has a high sensitivity. The resistance from the surrounding fluid consumes much energy, and eventually causes damping of the vibration of a microcantilever. It becomes a serious problem when microcantilevers are used as remote sensors with microbattery power sources. With the microcantilevers developed here, gas molecules freely move through the nanochannels, so that the resistance is reduced greatly. The deflection of a cantilever stems from the change in surface energy. Therefore, a large surface area is generally advantageous in most sensor applications. Cantilevers based on AAO can provide surface areas several orders of magnitude larger than conventional silicon cantilevers with flat surfaces. The fabrication method for the microcantilevers proposed here is quite different from that of conventional silicon counterparts. The proposed method consists of (1) AAO fabrication by anodization, (2) patterning on the AAO layer by photolithography, (3) fabrication of the beam structures by anisotropic etching of the AAO layer, and (4) removal of the substrate below the AAO layer by electrochemical etching. The fabrication process of AAO microcantilevers is outlined with the corresponding SEM images in Figure 2. The first step is to form an AAO layer on top of an aluminum layer. The particular sample shown in Figure 2(a) has hexagonally ordered nanochannels 30nm in diameter. The channel diameter, the channel-tochannel distance, and the thickness of the AAO layer can be controlled by changing the anodization conditions such as reaction time, applied voltage, temperature, etc. Patterns of microcantilevers are made in the second step by conventional photolithography. A thin layer of aluminum was deposited on the surface of the AAO as a transfer layer, followed by the spin coating of a photoresist layer. The transfer layer is necessary to provide a smooth surface, which generates sharper boundaries. Patterns for the microcantilevers were formed on the photoresist layer using a photomask, and transferred to the transfer layer by removing the exposed area using aluminum etchant. Since the aluminum etchant also dissolves alumina, the channels in the underlying AAO layer were slightly widened during this step. The SEM image in Figure 2(b) shows the microcantilever patterns formed on the AAO. The brighter area is the area with the exposed AAO, though the channels are not visible at this magnification. Note that the microcantilevers were intentionally fabricated with different widths for later measurements. After the pattern transfer, the sample was immersed in a phosphoric acid solution to remove the AAO in the exposed area. The acid solution penetrated into the nanochannels of the exposed area, while the area blocked by the photoresist was protected from the acid solution. As a result, the AAO in the exposed area was selectively etched away. The SEM image in Figure 2(c) shows the structures after AAO etching. Although the AAO layer is rather thick, 10μm, the microcantilever patterns of the AAO were successfully formed with vertical sidewalls which are hard to obtain with the wet etching of silicon. The presence of nanochannels in the AAO made the anisotropic etching of the complex patterns possible. Note that the photoresist layer and the transfer layer still exist on top of the AAO structures. Suspended cantilevers are fabricated by removing the aluminum under the patterns without damaging the AAO. Electrochemical etching was chosen for this. Suspended microcantilvers are clearly observed in the SEM image of Figure 2(d). The conventional fabrication method for suspended microcantilevers requires a much more complex procedure including deposition, patterning, and etching. Low pressure chemical vapor deposition (LPCVD), plasma enhanced CVD (PECVD) as well as reactive ion etching (RIE) are frequently used in the fabrication of silicon microcantilevers. Our method greatly simplifies the fabrication process through electrochemical etching. The huge surface area of an AAO microcantilever offers an enormous number of binding sites. The adsorption of chemical or biological molecules on the binding sites of a cantilever shifts the resonance frequency. The relation between the mass of adsorbed materials and the shift of resonance frequency is given as , where f1 and f0 are the resonance frequencies after and before mass loading. The more molecules adsorbed on the surface of a cantilever, the larger the shift of the resonance frequency, as obvious from this equation. Figure 3 shows the shifts of the observed resonance frequencies after injecting saturated dodecanthiol on two different microcantilevers. Both cantilevers have the same thickness(2μm), length(250μm) and width(35μm), but the AAO microcantilever has vertically parallel pores with 50nm diameter while the silicon cantilever has a flat surface. The red line in this figure is the observed frequency shift of the AAO microcantilever as a function of time, and the black one is those of the Si cantilever. The shift of resonance frequency of the AAO microcantilever (68Hz) is about 6 times as large as that of the Si cantilever (11Hz) at the saturated condition. This large frequency shift is partly due to the large surface area of the AAO cantilever, and partly due to the different physical properties such as smaller Young’s modulus. Therefore, the AAO microcantilever is much more sensitive than the Si cantilever of identical overall dimensions. Moreover, the presence of nanochannels provides not only a large surface area, but also selectivity among different analytes based on a sieving mechanism. Thus, the AAO microcantilever seems to be a promising candidate for biosensors. The fabrication method proposed here offers more freedom than conventional methods. For example, AAO microcantilevers can be fabricated with thicknesses up to hundreds of micrometers. Figure 4(a) shows ultra-thick AAO microcantilevers of 100μm in thickness. The spring constant of a microcantilever increases in proportion to the cube of the thickness of the beam. Therefore, such thick microcantilevers are favorable for applications which require very stiff beams, i.e., they can operate at much higher frequencies. Note that these structures have vertical sidewalls which are hard to obtain with conventional microcantilever fabrication methods. The fabrication process of AAO microcantilevers also guarantees structural versatility at a larger scale. Such versatility is demonstrated in Figures 4(b) and 4(c) with rectangular and triangular loop microcantilevers. The former is routinely adopted in the microcalorimetric detection, while the latter is found in most AFMs. The nanochannels of an AAO cantilever can be made with only one end open. A sensing material with a special affinity to a specific analyte can be deposited inside the bottom of the nanochannels. A strand of DNA may attach to the sensing material without the interference of other DNAs, which is hard to achieve with microcantilevers with flat surfaces. The enormous difference in the surface area between the upper and the lower surfaces may create other interesting applications. In summary, we have reported microcantilevers which have a radically different material and structure, as well as fabrication method. They are made of alumina, and have hexagonally-arranged parallel channels tens of nanometers in diameter. They can provide a surface area several orders of magnitude larger than those of conventional microcantilevers. Precise control of the dimensions of the nanochannels is made possible through the versatile fabrication method, resulting in fine tuning of the physical properties. This fact gives us an additional handle for the design of microsensors. These revolutionary microcantilevers are made possible by combining photolithography with nanotemplates. This technique should greatly expand our ability to fabricate other 2-D structures with nanochannels, and has great potential to be the general fabrication method of various NEMS devices in the years to come. Professor Kun-Hong Lee Department of Chemical Engineering Tel: +82-54-279-2271 Fax: +82-54-279-8298 E-mail: ce20047@postech.ac.kr Professor Sangmin Jeon Department of Chemical Engineering Tel: +82-54-279-2329 Fax: +82-54-279-5528 E-mail:jeons@postech.ac.kr Professor Hyun Chul Park Department of Mechanical Engineering Tel: +82-54-279-2167 Fax: +82-54-279-5899 E-mail: hcpark@postech.ac.kr Professor Woonbong Hwang Department of Mechanical Engineering Tel: +82-54-279-2174 Fax: +82-54-279-5899 E-mail: whwang@postech.ac.kr

p-aminobenzoate N-oxygenase:Novel Enzyme Chemistry for Antibiotics Biosynthesis

Many clinically important drugs are natural products produced by bacteria and fungi. In particular, polyketide antibiotics have been found to be an extremely rich source of biologically active compounds with a broad range of pharmaceutical activities. Aromatic nitro groups are relatively rare functional groups in natural products including polyketide antibiotics but are found in diverse types of important antibiotics, such as chloramphenicol, pyrrolnitrin, aureothin, azomycin, and rufomycin. Surprisingly, the biosynthesis of aromatic nitro groups is poorly understood. To date, only two enzymes have been shown to catalyze the formation of aromatic nitro groups, and the catalytic mechanism is virtually uncharacterized. p-nitrobenzoate N-oxygenase (AurF) is involved in the biosynthesis of polyketide antibiotic aureothin and catalyzes the formation of p-nitrobenzoic acid (pNBA) from p-aminobenzoic acid. However, AurF shares no sequence similarity with any other functionally characterized oxygenases. The native enzymatic activity has not been demonstrated in vitro, and its catalytic mechanism is unclear. The nature of the cofactor remains a controversy, although AurF is a metalloenzyme. In these aspects, understanding the molecular mechanism of AurF provides the opportunity to diversify the core structures of polyketides containing aromatic nitro groups and to develop tools for new drug discovery. Research professor Yoo Seong Choi, together with a research team at University of Illinois at Urbana- Champagne (Professor Huimin Zhao’s group), successfully characterized the molecular mechanism of AurF by their combined biochemical and structural analysis. First of all, they restored the native enzymatic activity in vitro using chemical and biological reductants, respectively. The crystal structure of AurF in the oxidized state and the cocrystal structure with its product pNBA were also determined. Then, they resolved the controversy on the nature of the cofactor in AurF. From these results, they concluded that AurF is a new class of non-heme di-iron monooxygenase that catalyzes unusual sequential oxidation of aminoarenes to nitroarenes via hydroxylamine and nitroso intermediates. They expect that the study will not only advance basic understanding of the formation of nitro groups in natural product biosynthesis, but also provide insights into the origin of nitro groups in many medically important natural products. This work can possibly suggest tools to generate polyketide antibiotics with improved biological and pharmacological properties and to synthesize important aromatic nitro compounds. In addition, the architecture of the di-iron center, unique chemistry of AurF and easy enzyme preparation make AurF an excellent model for further investigation of the molecular mechanism of di-oxygen activation of metalloenzymes and for the application of combinatorial biosynthesis and industrial biocatalysis. The research was published in May issue of Proceedings of the National Academy of Sciences, entitled, “In vitro reconstitution and crystal structure of p-aminobenzoate N-oxygenase (AurF) involved in aureothin biosynthesis”. Professor Yoo Seong Choi Department of Chemical Engineering Tel: +82-54-279-8640 Fax: +82-54-279-5528 E-mail: yschoi@postech.ac.kr

Structure and Mechanism of MukBEF Condensin Deciphered

A research team of Department of Life Science’s Center for Biomolecular Recognition and Division of Molecular and Life Science, consisting of Professor Byung-Ha Oh, Doctor Jae-Sung Woo, and Doctor Jae-Hong Lim, has solved secrets of the ring-shaped molecular structure of the MukBEF condensin, the key mediator of chromosome condensation. In eukaryotic organisms, chromosomes are found in the nucleus of every cell. Before cell division, chromosomes are condensed, and the two replicated copies of the chromosomes are partitioned into the two daughter cells. In prokaryotic organisms, chromosome condensation also takes place to insure partitioning of the replicated chromosomal copies into two newly divided cells. Chromosomes are long DNA molecules, ~1,000-10,000 times longer than the size of normal cells. How such a huge molecule can fit into a small volume in a cell and how the cell can divide replicated chromosomes into two exact halves without tangling and tearing is still a baffling mystery. Chromosome condensation is a well-known phenomenon, even mentioned in middle and high school textbooks, but the underlying mechanisms have been elusive. Professor Oh’s team brought to light the protein complex’s molecular structure as well as the functional mechanism. The findings are also expected to be utilized in applied research for development of antibiotics or anticancer substances, since cells cannot grow normally when chromosome condensation is hindered. The research outcomes were presented in the January 9, 2009 online issue of Cell. “This is only the beginning of research in the chromosome condensation area,” evaluated Professor Oh, declaring the team’s plans to continue research in condensation mechanism in eukaryotic cells which have more than one chromosome. He added that compared to prokaryotic cells, “condensation in eukaryotic cells is estimated to be controlled by much more intricate mechanisms because each chromosome is condensed separately.”

Novel Programmable &#38quot;Write-Read-Erase&#38quot; Non-Volatile Polymer Memory Device Operative Even in Space: Based On Poly...

As technology continues to get smaller, and as memory needs become more demanding, the microelectronics industry requires devices that are more cost-efficient and lightweight. And, while organic memory materials have shown some promise on improvement in performance and reductions in cost, they still lack some of the essential qualities, such as durable performance even in a harsh condition, needed for application in a wide variety of fields. So-called Non-Volatile Memories (NVM) from thermally and dimensionally stable polymer materials could provide a solution. The devices, developed by Professor Moonhor Ree, Professor Ohyun Kim, Dr. Suk Gyu Hahm, and their research teams, are based on a thermally and dimensionally stable polyimide containing carbazole moieties. The polyimide material, 6F-HAB-CBZ PI, is thermally stable from -200 up to 400oC, and the device performance is also robust even in a space temperature range from -120 to 150oC. For a common organic semiconductor, organic active materials are usually grown by delicate vacuum deposition techniques and do not usually exhibit switching behaviour used for data storage when they are exposed to an ambient condition because of its weak sustainability. But when fabricated from solution to form thin polymer films, the 6F-HAB-CBZ PI reveals perennial electrical switching characteristics. The new polyimide, 6F-HAB-CBZ PI, exhibits excellent unipolar ON and OFF switching behavior. The PI film is initially present in the OFF state. The PI film can be electrically switched on by applying a positive or negative bias with a current compliance set at a low level, and then switched off by applying a positive or negative bias with a current compliance set at a higher level than the turn-on current compliance. The ON-switching voltages are in the ranges of +1.7V to +2.7V during the positive voltage sweep and -1.7V to -2.7V during the negative voltage sweep, and the OFF-switching voltages are in the ranges of +0.3V to +0.7V during the positive voltage sweep and -0.3V to -0.7V during the negative voltage sweep. Overall, these ON- and OFF-switching voltages are very low. These low switching voltages have the advantage for memory device applications of low operation voltages and hence of low power consumption. With this very low power consumption, the device can be repeatedly written, read and erased in air. The ON/OFF current ratio of the devices is in the range 103-1011, depending on the level of the turn-on compliance current and the reading voltage. A higher turn-on compliance current and a lower reading voltage result in a higher ON/OFF current ratio. In particular, the ON/OFF current ratio of 1011 is the highest value reported so far. The ease of the devices and the fact that the films on which they are based can be fabricated through solution not only enable them to be fabricated with potentially much lower cost than silicon-based memories, but also make it possible to build 3-dimensional (3D) arrays of devices by spin-coating or dip-coating multiple layers to achieve very high storage densities, considering that silicon-based memories can only be improved by making the size of individual memory cells smaller because of its dimensional limitation where it can only be fabricated in two-dimensions on the surface of a silicon chip. Overall, the high ON/OFF switching ratio and stability of these devices, as well as their repeatable writing, reading and erasing capability with low power consumption, open up the possibility of mass production of high performance non-volatile memory devices at low cost. These research results were published in the journal Advanced Functional Materials (volume 20, 1766-1771, 2008). Professor Moonhor Ree Department of Chemistry Tel: +82-54-279-2120 Fax: +82-54-279-3399 Email: ree@postech.ac.kr Professor Ohyun Kim Department of Electronic and Electrical Engineering Tel: +82-54-279-2215 Fax: +82-54-279-2903 Email: ohkim@postech.ac.kr Dr. Suk Gyu Hahm Department of Chemistry Tel: +82-54-279- 2922 Fax: +82-54-279- 3399 Email: hamsg@postech.ac.kr

Consciousness versus Unconsciousness: Standard for Partition

The way to prevent intra-operative awareness has been paved by joint efforts of medical science and physics. Intra-operative awareness, familiarized through some thriller movies, is a unique physiological phenomenon which causes the patient under general anesthesia to recover consciousness during surgery. The patient experiencing intra-operative awareness may feel the pain or pressure of surgery, hear conversations, or feel as if he cannot breathe, but may be unable to communicate any distress because he has been given a paralytic or muscle relaxant. Professor Seunghwan Kim (Department of Physics), in a joint research with Doctor UnCheol Lee of University of Michigan, who is a POSTECH graduate, and Professor Gyu-Jeong Noh of Seoul Asan Medical Center, has demonstrated the mechanism behind loss and recovery of consciousness through anesthesia, and detected the exact moment when a subject loses consciousness after being administered an anesthetic. Utilizing the analytic method called nonlinear dynamics which is used mainly to identify complex physical phenomena, Professor Kim’s team investigated the functional organization of brain activities in the conscious and anesthetized states. Recordings were obtained from 14 subjects who underwent induction of general anesthesia with propofol, and in the analysis, the team demonstrated that loss of consciousness is reflected by the breakdown of the spatiotemporal organization of gamma waves, and that induction of general anesthesia with propofol reduces the capacity for information integration in the brain. Additionally captured was the moment the amount of information going from the frontal to the occipital lobes rapidly dropped, which coincided with loss of consciousness. The data congregated through the research directly supports the information integration theory of consciousness and the cognitive unbinding paradigm of general anesthesia. The results of the study were published in the November 20, 2008 online issue of Consciousness and Cognition.

Regulation of Stomatal Response to Elevated CO2 Concentration by AtABCB14

Climate change caused by increasing atmospheric CO2 is a major environmental problem of the 21st century. There has been much discussion about how to reduce CO2 output and prevent global warming. In this respect, plants are an important part of the overall picture as they are primary CO2 consumers and are directly challenged by increasing CO2 levels. Moreover, plants vary in their responses to elevated CO2. Plants that adapt better to this change are expected to out-compete their neighbors, which would cause instability in present ecosystems and unpredictable changes in weather and climate. In plants, CO2 uptake and water release occur through stomata. Stomata are formed by a pair of highly specialized epidermal cells, termed guard cells, and their opening and closing must be tightly controlled for optimal plant performance. It has been known for a long time that guard cells respond to high CO2 by closing their stomata. However, only recently have the molecular and cellular mechanisms for sensing and responding to high CO2 concentrations begun to be understood. CO2 is now known to have a direct effect on guard cells and to elicit stomatal closing through complex molecular interactions between currently ill-defined positive and negative factors. Our research into the role of ABC transporters in guard cell regulation resulted in the identification of an ABCB-type ABC transporter that is strongly expressed in guard cells and localized at the plasma membrane. We observed in intact leaves that, under elevated CO2 conditions, deletion mutants of AtABCB14 closed their stomata more rapidly than their wild-type counterparts, whereas AtABCB14-overexpressing mutants closed their stomata only partially. Further detailed analyses using E. coli and HeLa cell revealed that AtABCB14 plays a role as a malate importer. Thus, we conclude that AtABCB14 negatively regulates stomatal movement by transporting malate into the guard cell under elevated CO2 condition. These results are entirely novel and have strong implications for our current knowledge about the regulation of pore size under high CO2 condition. A topic that has not alone major repercussions for basic plant science but also for agriculture, especially within the perspective of rising atmospheric CO2 concentrations and the need to assure adequate food production for future generations. In addition, these results are very exciting for the broad and diverse ABC transporter community which is composed of scientists studying ABC transporters in all kingdoms of life, from prokaryotes to human. According to the reports up to now, ABC proteins of the same sub-family have similar functions and their functions are conserved between organisms also. In fact, many functional studies of genes were performed using homology with already identified genes. Thus, our studies may be helpful for identifying unknown roles of ABC proteins, and provide clues to solve the functions of animal ABC proteins for which the mutants are difficult to obtain. Professor Youngsook Lee Department of Life Science Tel: +82-54-279-8185 Fax: +82-54-279-2199 Email: ylee@postech.ac.kr Dr. Miyoung Lee Department of Life Science Tel: +82-54-279-5980 Fax: +82-54-279-2199 E-mail: anny98@postech.ac.kr

Metal Atom Chains on Graphene Nanoribbons

Professor Seung-Hoon Jhi and Ph.D. Candidate Seon-Myeong Choi, both of the Department of Physics, in their study of metal doped graphene nanoribbons, discovered that the adsorbed metal atoms form atomic chains which can be used as reagents to identify the edge atomic structures of the graphene nanoribbons and also as gate-driven spin valves to control the spin current in graphene nanoribbons. Graphene, the basic structural element of all graphitic materials including graphite, carbon nanotubes and fullerenes, is a one-atom-thick planar sheet of carbon atoms that are densely packed in a honeycomb crystal lattice. Placed in layers on top of each other, it would take 200,000 membranes to reach high enough to match the thickness of a human hair. Graphene nanostructures have attracted great attention due to their unique and intriguing electronic and transport properties. Particularly, the graphene nanoribbons’ carrier mobility is very promising for high-speed electronic devices. Professor Jhi’s team studied electronic and magnetic properties of alkali and alkaline-earth metal doped graphene nanoribbons by the pseudopotential density functional method. The findings are that strong site dependence is observed in metal adsorption on graphene nanoribbons, and that the adsorbed metal atoms are found to spontaneously form atomic chains at the edges of zigzag-edged graphene nanoribbons. The self-assembled atomic chains can be used to analyze the atomic structures of the graphene nanoribbon edges, which had proved difficult due to the extreme thinness of graphene. Also, such doped graphene nanoribbons exhibited intriguing magnetic properties such as hysteresis and spin compensation as metal atoms switch from one edge to another at alternating gate voltages. Using this phenomenon, the research team suggested a schematic model for the spin-valve structure that drives alkali metal atoms from one edge of a zigzag-edged graphene nanoribbon to the other. The research outcomes were presented in the December 31, 2008 issue of Physical Review Letters.