Research

Digital Non-Volatile Polymer Memory Device Developed:An Efficient, Low-Cost Means of Permanent Data Storage (2008.4.15)

Improvements in performance and reductions in cost of silicon-based nonvolatile memories, such as flash random access memory (flash-RAM), have rendered floppy discs and many other forms of portable storage obsolete. But for many uses that require data to be written only once, such as archiving and security applications, their cost effectiveness is limited. So-called write-onceread- many (WORM) memories made from low-cost polymer materials could provide a solution. The devices, developed by Professors Moonhor Ree, Ohyun Kim, Su-Moon Park and their research teams, are based on hyperbranched copper phthalocyanine (HCuPc) polymer. The starting material of the HCuPC polymer is copper phthalocyanine (CuPc) which is a common organic semiconductor. The CuPc material, which is usually grown by vacuum deposition techniques, does not usually exhibit switching behaviour that could be used for data storage. But when fabricated from solution to form thin polymer films, the HCuPC reveals electrical switching characteristics. The HCuPc polymer films initially exhibited a high-conductivity state (ON-state). The conduction processes within the device were found to be dominated by hole injection rather than electron injection. The active layer in the devices is short-circuited during the ON-state. Specifically, when a voltage of just over 2.5 V is applied across such an HCuPC film sandwiched between indium-tin-oxide and gold contacts, it switches from the ON-state to low conductivity state (OFF-state). This switching-OFF process of the devices is influenced by the magnitude of the injection current. This switching-OFF process is thought to be governed by the rupture of filaments which takes place when a voltage greater than the turn-off voltage is applied. The conductivity of the OFF-state was found to be more than millions of times smaller than the ON-state, making it easy to read the state of a device. And once switched to the OFF-state the devices remained permanently in that state, even when tested again a full year later. The simplicity of the devices and the fact that the films of which they are based can be fabricated from solution, not only makes them potentially much cheaper than silicon-based memories, it could enable them to store much larger amounts of data more efficiently. The density of the data that can be stored in silicon-based memories can only be improved by making the size of individual memory cells smaller. This is because they can only be fabricated in two-dimensions on the surface of a silicon chip. In contrast, because the HCuPC films are fabricated from solution, it should be possible to build 3-dimensional (3D) arrays of devices by spincoating or dip-coating multiple layers, to achieve very high storage densities. Overall, the HCuPc devices exhibited excellent WORM memory characteristics. These properties open up the possibility of a low-cost mass production of highly dense, and very stable digital non-volatile WORM memory devices. These research results were published in the journal Advanced Materials (volume 20, 1766-1771, 2008), and further highlighted by Nature Asia Materials (June 4, 2008). Professor Moonhor Ree Department of Chemistry Tel: +82-54-279-2120 Fax: +82-54-279-3399 E-mail: ree@postech.edu Professor Su-Moon Park Department of Chemistry Tel: +82-54-279-2102 Fax: +82-54-279-3399 E-mail: smpark@postech.edu Professor Ohyun Kim Department of Electronic and Electrical Engineering Tel: +82-54-279-2215 Fax: +82-54-279-2903 E-mail: ohkim@postech.edu

Microcantilevers with Nanochannels (2008.4.15)

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

Graphene Nanoribbon Spin-Valve Device (2008.6.15)

Spin-valve devices are a key component of a magnetoresistive random access memory. Mr. Woo Youn Kim and Professor Kwang Soo Kim of Department of Chemistry of POSTECH predicted supermagnetoresistance in a graphene nanoribbon device, the article of which has appeared in Nature Nanotech (3, 408-412, 2008). The reported graphene nanoribbon spin-valve device shows extremely large magnetoresistance (ten thousand times larger than that of conventional devices), which promises high speed access, and good sensitivity. The striking enhancement originates from the peculiar symmetry of band structures of graphene nanoribbon in addition to the spin symmetry. The characteristic symmetry of the graphene band structure plays the role of a spin filter in perfectly transmitting the spin current in the case of symmetric band alignments between both ends of the nanoribbon and in completely forbidding the spin current in the case of orthogonal symmetric alignments. This phenomenon is highly contrasted to conventional spin-valves of giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR) which utilizes only the spin symmetry and antisymmetry. The discovery of the GMR phenomenon was awarded the Nobel Prize in Physics last year. The present supermagnetoresistance ideally approaches to the infinite. Thus, the predicted new physics would open a new pathway much beyond the current limit of spin-valve devices. Professor Kwang Soo Kim Department of Chemistry Tel: +82-54-279-2110 Fax: +82-54-279-8137 E-mail: kim@postech.ac.kr

X-Ray Decreases Surface Tension of Water (2008.5.29)

X-ray imaging shows in real-time and in in-vivo that intensive irradiation of x-rays significantly decreases the surface tension of water in droplets and capillary tubes. X-rays are used in a variety of experimental studies of liquids, in particular, of water. The present synchrotron sources allow intense irradiation, possibly enabling to alter the basic property of surface tension. In spite of its potential impact, this issue has been still unexplored. In 1896 Wilson roughly showed that x-rays ionized the air molecules, and the electrons and ions created cloud nuclei in a cloud chamber. His cloud chamber was used to visualize ionizing radiation and opened up modern quantum physics. The x-ray-induced ionization of matter was studied in quantum physics through photoelectric effect and Compton scattering. In soft-matter physics, it was also known that electrostatic potential changes surface tension, as found by Lippmann in 1873. However, no one has ever observed the radiation effects on the surface tension of water. Professor Jung Ho Je and his research team from Korea, Switzerland, and Taiwan for the first time observed that xray- induced charge build-up leads to a large decrease of the effects of natural surface tension of water in droplets and capillary tubes. The team discovered the x-ray-induced surface tension reduction from direct experimental observations with phase contrast microradiology. The evidence was obtained with three different types of experiments at the 7B2 beamline of the Pohang Light Source (2.5 GeV, 150 mA storage ring in Pohang, Korea). Spatially-coherent synchrotron x-rays in the photon energy range 10-60 keV were used to irradiate water molecules and simultaneously to image the induced effects. They also developed a general physical model to link surface tension and surface ionization by unifying the related equations suggested by Lippmann and Rayleigh. This model successfully described the experimental observations that x-ray photons, by ionizing water molecules and creating charges, change the surface tension of water. The overall results showed a fundamental connection between ionizing radiation and surface tension. The team addressed that “the so far undetected phenomenon is explained by ionization and surface charge creation and can potentially affect many x-ray experimental techniques as well as different natural events.” In particular, this striking phenomenon might be an important issue due to current development of x-ray free-electronlasers with unprecedented brilliance. The research was published in May issue of Physical Review Letters, entitled, “Decreased surface tension of water by hard-x-ray irradiation”. Professor Jung Ho Je Department of Materials Science and Engineering Tel: +82-54-279-2143 Fax: +82-54-279-2992 E-mail:jhje@postech.ac.kr

Consciousness versus Unconsciousness: Standard for Partition (2008.12.2)

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 Activin/Nodal Signaling by Rap2-Directed Receptor Trafficking (2008.7.7)

TGFβ ligands belonging to the Activin/Nodal family, induces mesoderm and endoderm, specifies the embryonic axes, promotes gastrulation movements, maintains pluripotency of embryonic stem cells, and determines left-right asymmetry in vertebrates. Activin/Nodal ligands signal through type I and type II transmembrane serine/threonine kinase receptors. Ligand binding induces the formation of heteromeric receptor complexes in which type II receptors phosphorylate and activate type I receptors. The activated type I receptors transduce the signal inside the cell through the phosphorylation of the receptor-regulated Smads (R-Smads), Smads 2, and/or Smad3. Once activated, RSmads form complexes with common mediator-Smad (co-Smad), Smad4, and translocate into the nucleus, where they regulate gene expression with DNA-binding partners and transcriptional cofactors both positively and negatively. The strength of Activin/Nodal signaling is represented by the levels of active nuclear Smad2, which are regulated at several steps in signaling cascade. Differential occupancy of receptor leads to varying levels of activated Smad2, and induces different sets of target genes. A recent study demonstrated that the length of time, for which the Activin-Activin receptor signaling complex dwells in the endocytic pathway, determines the duration of the serine/threonine kinase activity of receptor, thereby controlling the intracellular concentration of active Smad2. In fact, endocytosis occurred through the clathrin-dependent endocytic route is required for promotion of Smad-dependent signaling activation. Alternatively, internalization via the lipid-raft/caveolar compartments leads to the accelerated receptor degradation which is mediated by Smad7/Smurf2 complex. Thus, proper partitioning of receptors into two distinct compartments may be essential for the fine control of receptor availability and signaling activity. However, the molecular mechanism underlying this segregation remains unknown. In this study, we showed that Rap2, a member of Ras GTPase family, regulates the trafficking of Activin/Nodal receptors to modulate signaling activity. Rap2 was required for sorting of internalized Activin/Nodal receptors into recycling pathway in the absence of ligand activation and thus maintaining their proper levels at the cell surface. Ligand-activated receptors were not recycled to the plasma membrane, but their turnover was delayed by Rap2. Interestingly, Rap2 counteracted Smad7 function in these processes. We also found that there is difference in the efficiency of Activin/Nodal receptor recycling between dorsal and ventral halves of early embryo, which is regulated by the temporally dynamic expression of Rap2. This led to the differential onset of Smad2 phosphorylation across the dorsoventral axis of Xenopus early embryo. Therefore, our data identify Rap2 as a key player in the regulation of receptor trafficking that might affect cell responsiveness to extracellular ligands and signaling duration. Professor Jin-Kwan Han Department of Life Science Tel: +82-54-279-2126 Fax: +82-54-279-2199 E-mail: jkh@postech.ac.kr

Metal Atom Chains on Graphene Nanoribbons (2008.12.31)

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.

Regulation of Stomatal Response to Elevated CO2 Concentration by AtABCB14 (2008.9.7)

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

Structure and Mechanism of MukBEF Condensin Deciphered (2009.1.9)

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.”

High Quality Ferroelectric Memory with Tb/In2 Density Realized by Nanotechnology (2008.6.15)

Ajoint research between POSTECH (Pohang University of Science and Technology) and Max Planck Institute of Microstructure Physics, Halle, has produced an advanced technology applicable to the development of the permanent memory, FeRAM, which can save 176 billion bits per square inch (published in Nature Nanotechnology, vol. 3, page 402). FeRAM has attracted many researchers’ interest because of its excellent characters such as nonvolatility, fast read and write, and high reliability. However, limitation in realizing large scale integration of ferroelectrics on a single chip has hindered the wide applications of FeRAM. In order to achieve the density of terabit per square inch, the size of ferroelectrics must be less than 25nm. It is well known that ferroelectric properties could be vanished if the size of ferroelectrics reduces down to nano scales: the size effect. Therefore, it is necessary to not only develop a novel method to fabricate nano-sized ferroelectrics, but also to investigate the intrinsic size effects of ferroelectrics in order for the widespread use of the computers containing memories with ultra high density, no booting, and no refresh process to be advanced. In this sense, the development of 65nm sized metal (Pt) - ferroelectric (PZT) - metal (Pt) nanocapacitors is a valuable work for the potential applications of FeRAM. Metal-ferroelectric-metal nanocapacitors were fabricated by stencil method using ultra-thin anodic alumina mask with honeycomb arrayed 65nm sized pores. Firstly, an aluminum plate was electrochemically oxidized. In this process, the 65nm sized pores were self-ordered. When the aluminum is shaped with a punch beforehand, the pores arrange themselves in a completely regular pattern. The anodic alumina mask was then transferred to platinum coated magnesium oxide substrate. By taking advantage of excellent thermal stability of anodic alumina, ferroelectric materials as well as electrode materials could be deposited into the extremely tiny pores at a high temperature. During the entire process, there was no thermal treatment nor use of chemicals or physical damages, resulting in high quality nanocapacitors. By removing the mask after deposition of platinum top electrode material, 176 billion bits per square inch of Pt-PZT-Pt nanocapacitors were obtained. In principle, other materials could be used as well for the ferroelectrics and electrodes as fatigue free capacitors. The success of this project is due to the fruitful Korea- Germany cooperation. The project was supported by the Korea Research Foundation, the ‘Brain Korea 21 Program’, the Volkswagen Foundation, and the German Research Foundation. Professor Sunggi Baik Department of Materials Science and Engineering Tel: +82-54-279-2001 Fax: +82-54-279-2709 E-mail:sgbaik@postech.ac.kr