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  • A research group of Prof. In Su KIM decorated the cover paper of JACS

    Pharmacy Prof. KIM, IN SU

    A research group of Prof. In Su KIM decorated the cover paper of JACS

    A research group of Prof. In Su KIM decorated the cover paper of JACS A research group led by Prof. In Su KIM, School of Pharmacy at Sungkyunkwan University, decorated the cover paper of ‘JACS (Journal of the American Chemical Society, IF: 13.858)’, which is the world's preeminent journal in chemistry, on the June. A research on artificial molecular computers that could mimic advanced functions in the cell signaling system is a global interest. The artificial computing systems perform various math functions based on electrical signals, but in vivo, their specific and advanced functions are realized through information processing of appropriate chemical signals. In particular, the cell signaling processes can communicate and synchronize each other in a precisely organized manner to implement their specific functions. As such, much effort has been devoted to developing artificial computing systems analogous to biological signaling processes. This research team first reports an artificial three-state molecular computer capable of performing advanced functions similar to those found in biological computing process. This was achieved by control of molecular recognition and three electronic states via ionic chemical stimuli. Especially, it was also demonstrated that the developed system conducted a cascade reaction for a high-valued organic chemical and functional polymer synthesis. It is also envisioned that artificial molecular computers mimicking the intravascular signaling system hold a great promise in developing smart drug delivery systems that would be used for early diagnosis and treatment of many important diseases. This research was supported by a Basic Research Laboratory (BRL) grant of the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP).

  • Perovskite Solar Cells with Inorganic Electron & Hole Transport Layers Exhibit Long-Term Stability

    Energy Science Prof. SHIN, HYUN JUNG

    Perovskite Solar Cells with Inorganic Electron & Hole Transport Layers Exhibit Long-Term Stability

    Research groups from Sungkyunkwan University have recently reported that they developed highly stable perovskite solar cells under extreme environments by improving passivation techniques of perovskite solar cells. Perovskite is the name of a crystal structure, and for the perovskite solar cells, the materials refer to special compositional groups that have organic and inorganic halide ions. Perovskite solar cells have shown extremely rapid improvement of power conversion efficiency with low processing costs. However, the short-term lifetime of the device and the poor stability of the material under moisture, heat, light, and electrical biases remain to be overcome for commercialization. The architecture of the solar cells has inverted planar devices (so-called p-i-n devices; light illumination through hole transport layers) with FTO/NiO/Perovskite/PCBM/AZO/Ag. AZO has been deposited via atmoic layer deposition method, which produces pinhole-free, uniform, and dense films. The AZO-deposited perovskite solar cells exhibited similar performances to the control solar cells due to negligible charge transporting retardation by the 3 orders of magnitude higher conductivity of AZO compared to that of PCBM. The ALD-grown AZO (ALD-AZO) layers also acted as dense, uniform, and impermeable passivation layers that prevented ingress of water into the perovskite films, egress of the volatile components of perovskite when heated, and interfacial degradation between the perovskite-PCBM heterojunction and the Ag electrode caused by unfavorable chemical reactions. The authors found that the stability of perovskite solar cells with an AZO layer is superior to the control devices. While the control solar cells degraded rapidly under light illumination at room temperature in spite of an additional passivation layer, AZO-perovskite solar cells maintained 99.5% of their initial efficiency for 500 hours. The unique role of AZO, distinguished from additional passivating layers, is to prevent moisture penetration as well as interdiffusion at the perovskite/Ag interface when illuminated. These perovskite solar cells showed their stability in a more severe environment, exhibiting a power conversion efficiency of 18.45% and retaining 86.7% of their initial efficiency for 500 hours under continuous 1-sun illumination at 85°C in ambient air with electrical biases (at the maximum power point). This research on highly stable perovskite solar cells with inorganic charge transport layers has been published in Advanced Materials (IF 19.791) as an inside cover story by Prof. SHIN and Mr. SEO (Department of Energy Science) and Prof. PARK (School of Chemical Engineering) at Sungkyunkwan University. Published article: Seo, S., Jeong, S., Bae, C., Park, N.-G., and Shin, H., "Perovskite Solar Cells with Inorganic Electron- and Hole-Transport Layers Exhibiting Long-Term (≈500 h) Stability at 85°C under Continuous 1 Sun Illumination in Ambient Air.", Advanced Materials, 1801010 (2018).

  • Identification of epigenetic gene regulation in the genome of marine seaweed by Prof. Hwan Su YOON

    Biological Sciences Prof. YOON, HWAN SU

    Identification of epigenetic gene regulation in the genome of marine seaweed by Prof. Hwan Su YOON

    After completing the first human draft genome by the Human Genome Project (HGP) in 2003, many genome projects were initiated in the field of medicine and natural science. A genome is the total set of genetic information including all the genes of a living organism; therefore, if it is completely decoded, it will provide a lot of information about the function of the genes as well as the evolutionary relationship of living organisms. Recently, "Collaborative Genome Projects" have been launched by multiple ministries, and the Ministry of Oceans and Fisheries aims to decode genomes from 100 marine organisms. Professor Hwan Su YOON and his research group in the Department of Biological Sciences are leading the analysis of 30 marine algal genomes, including diverse seaweeds. As the first product, they completed the whole genome of Gracilariopsis chorda and published in "Molecular Biology and Evolution" (5 years IF 14.558). It is the second complete nuclear genome among approximately 7,000 red algal seaweed species. G. chorda is a popular edible seaweed for diet foods and salads, and it is also used in the agar production industry. From this paper, they generated a high-quality 92.1 Mb draft genome assembly from the red seaweed G. chorda, including methylation and small (s)RNA data. They analyzed these as well as other Archaeplastida genomes to address three questions: 1) What is the role of repeats and transposable elements (TEs) in the genome size variation of red algae, 2) what is the history of genome duplication and gene family expansion/reduction in these taxa, and 3) is there any evidence for TE suppression in the genome of red algae? See the details at the MBE journal website (https://doi.org/10.1093/molbev/msy081). Furthermore, Prof. YOON’s group has utilized the genome information to the application field. For example, the carbonic anhydrase of G. chorda shows much higher activities than that of humans. The carbonic anhydrase catalyzes the rapid interconversion of carbon dioxide and water to bicarbonate and protons (or vice versa); therefore, it could be used to remove carbon dioxide from polluted gases (collaborative research with Prof. Inhwan HWANG at POSTECH). In addition, with Prof. Jong Hwan KWAK in the department of Pharmacology, they found highly effective metabolic compounds for alleviating diabetes and arteriosclerosis from G. chorda. In this manner, the genomic information from marine algae is a valuable resource not only for academic but also industrial purposes. See Prof. YOON’s other research activities (http://bio.skku.edu/glter/wiki/Hwan%20Su%20Yoon)

  • Research on Fabrication of Biomimetic Microfibril Structures using 3D Printing

    Bio-Mechatronic Engineering Prof. KIM, GEUNHYUNG

    Research on Fabrication of Biomimetic Microfibril Structures using 3D Printing

    In the human body, microfibril structures can be found in several types of tissue, such as muscles, nerves, and even tendons. In particular, muscle tissues have uniaxially-aligned microfibrous structures. The team (first author: Won Jin KIM) led by Geun Hyung KIM (Department of Biomechatronics Engineering at Sungkyunkwan University) fabricated a structure composed of bundled poly (e-caprolactone) (PCL) microfibers coated with collagen. To obtain the bundle of uniaxially-aligned (PCL) microfibers, 4D printing methods using a poly (vinyl alcohol) (PVA) fibrillation/leaching process were used. PVA was dissolved in distilled water to fibrillate the PVA. Then, PCL was added to the PVA solution and mixed. After mixing, the PVA/PCL mixture was printed using a 3D printer. The fabricated 3D structure was immersed in water to leach the fibrillated PVA. By using this simple fabricating method, a uniaxially micropatterned/fibrous PCL bundle was achieved. The fabricated structure was supplemented with collagen to increase the biocompatibility of the PCL bundle. The hybrid microfibrillated structure promoted myoblast proliferation and myogenic differentiation. “Due to the 4D printing process, it was able to have high efficiency in the fabrication of 3D scaffolds with highly aligned microfibrous bundles. In addition, a variety of designs and complex microscale-patterned 3D structures were constructed because of a highly versatile 3D printing method,” Prof. KIM said. Published article: W. Kim, M. Kim, G. H. Kim, Adv. Funct. Mater. 2018, 1800405. Article link: https://onlinelibrary.wiley.com/doi/epdf/10.1002/adfm.201800405

  • Fabrication of a Stable New Polymorph Gold Nanowire with Sixfold Rotational Symmetry

    Energy Science Prof. SHIN, HYUN JUNG

    Fabrication of a Stable New Polymorph Gold Nanowire with Sixfold Rotational Symmetry

    Gold is the first metal used by humans, and it is deeply involved in human life. This was possible because gold was found to be almost pure in nature and easy to process without heating or melting. As one of the most chemically stable metals, gold adopts only one crystal structure. The crystal structure is closely related to the intrinsic properties of materials. When the crystal structure is changed, physical and chemical properties, including electrical and optical properties, are changed. Therefore, it is important to control the polymorphism to achieve reliable material or device properties. The crystal structure of gold is face-centered cubic (fcc) with 3-fold rotational symmetry by nature. For the first time, Prof. SHIN, Ms. LEE, and Dr. BAE (Department of Energy Science at Sungkyunkwan University) have published a stable hexagonal non-close packed structure (ncp-2H) of gold in Advanced Materials (IF 19.791) as a cover story. They report not only excelent stability of ncp-2H gold, but also different physical properties different from those of fcc. Schematic illustration of the experimental procedures for the confined growth of gold nanowires They fabricated the gold nanowires in a confined system of TiO2 nanotubes via the photoelectrochemical reduction of gold ions. During ultraviolet illumination, excited photoelectrons in the conduction band of TiO2 reduced the Au ions to metallic Au. At the early stage of the nucleation process, various polymorphs are able to be formed; however, they are eventually transformed to fcc, the most thermodynamically stable form in nature. They suggest that isolated ncp-2H gold seeds at the nucleation stage survive and grow by a diffusion-limited process under the nanoscale confinement provided by TiO2 nanotubes. They supported the possibility that nanoscale confinement influenced polymorph formation through control experiments. This study is particularly noteworthy that it suggests that different theories from that of classical thermodynamics are required for nanoscale confined systems. Published article: S. Lee, C. Bae, J. Lee, S. Lee, S. H. Oh, J. Kim, G.-S. Park, H. S. Jung and H. Shin, "Fabrication of a Stable New Polymorph Gold Nanowire with Sixfold Rotational Symmetry," Advanced Materials, 30, 1706261 (2018). (Cover Illustration)

  • Direct Imaging of Two Dimensional Electron Gas by Electron Holography

    Energy Science Prof. OH, SANG HO

    Direct Imaging of Two Dimensional Electron Gas by Electron Holography

    Atomically controlled interfaces of complex oxides provide new opportunities for materials design and synthesis. They have been the origin of a wide variety of new physical phenomena and properties, arising primarily from the natural quantum confinement of electrons at these interfaces, involving a strong correlation between the electronic and atomic structure. One notable example is the electronic reconstruction of the interface between insulating perovskite oxides that leads to the formation of an interfacial two-dimensional electron gas (2DEG). The 2DEG is known to be formed from the occupied 3d-orbitals of cations within a few nanometers of the interface and often involve an interplay of electronic states with distinct orbital character and symmetry. Different 2DEGs and the related properties are expected by the orbital-selective quantum confinement which is strongly correlated with the crystallographic orientation. Prof. Sang Ho OH of Department of Energy Science demonstrated that 2DEGs at oxide interfaces can be spatially mapped at subnanometer resolution using in-line electron holography and illustrated the power of this method by looking at the 2DEGs formed at (001) and (111) oriented LaAlO3/SrTiO3 interfaces and showing distinctly different spatial extent and charge density profiles across them. Prof. Sang Ho Oh and his Ph.D. student, Dr. Kyung Song now at KIMS, have successfully calibrated all variables affecting the 2DEG distribution, for example, the sample thickness, the mean inner potential and permittivity (ε), and thereby extracted intrinsic properties of 2DEG. Especially, taking account of the nonlinearity of the permittivity of oxide with electric field is essential, as the presence of the 2DEG leads to strong electric fields near the interface where the 2DEG is confined. The field-dependent permittivity has been calculated via analytical approach based on Landau theory and also directly through DFT calculation. These results provide the first direct evidence of the control of 2DEG properties through the interface orbital configuration and reveal the unprecedented capability of in-line holography to probe oxide heterostructures. According to Prof. OH, the electron holography technique developed in the present work will play an important role in development of future oxide-based electronic devices as it is a unique tool bridging various emergent properties arising from quantized electrons at interfaces, such as ferromagnetism, superconductivity and metal-insulator transition, with the function and performance of devices. The work has been conducted through international collaboration with Prof. Chang-Beom EOM, Prof. Christoph KOCH, Prof. Mark RZCHOWSKI and Prof. Evgeny TSYMBAL, Prof. Young-Min KIM and Prof. Si-Young CHOI and published recently in the March issue of Nature Nanotechnology. A companion paper has been published back to back in Nature Materials, demonstrating the formation of two-dimensional hole gas (2DHG) at the p-type LaAlO3/SrTiO3 interface. The work has been supported by National Research Foundation (NRF) of Korea and AFOSR Asian Office of Aerospace Research and Development (AOARD).

  • Prof. Yong Taik LIM Develops Implantation of Synthetic Immune Niche that Prevents Tumor Recurrance

    SKKU Advanced Institute of Nano Technology Prof. LIM, YONGTAIK

    Prof. Yong Taik LIM Develops Implantation of Synthetic Immune Niche that Prevents Tumor Recurrance

    Cancer vaccines are an attractive option for improving disease-free survival following surgical resection of solid tumors. However, several clinical studies have shown that while cancer vaccines can routinely induce protection in a prophylactic model, the same vaccines often show only limited therapeutic efficacy. The tumor immunosuppressive network, formed by interactions between cancer cells and host immune cells, is a major obstacle to achieving complete tumor eradication. Myeloid-derived suppressor cells (MDSCs) can be considered critical players in tumor-induced immunosuppression in both animal models and cancer patients, which they have a remarkable ability to suppress the activation and proliferation of T cells. Therefore, the depletion of MDSCs would strengthen immunity of tumor-bearing mice. Recently, Prof. Yong Taik LIM’s group of Sungkyunkwan University reported a novel implantable, engineered 3-dimensional porous scaffolds which were designed to generate synergistic action between MDSC-depleting agents and cancer vaccines consisting of whole tumor lysates and nanogel-based adjuvants. The local peritumoral implantation of the synthetic immune niche (termed immuneCare-DISC, iCD) as a post-surgical treatment in an advanced-stage primary 4T1 breast tumor model generated systemic anti-tumor immunity and prevented tumor recurrence at the surgical site as well as the migration of residual tumor cells into the lungs, resulting in 100% survival. These therapeutic outcomes were achieved through the inhibition of immunosuppressive MDSCs in tumors and spleens by releasing gemcitabine and recruitment/activation of dendritic cells, enhanced population of CD4+ and CD8+ T cells, and increased IFN-γ production by cancer vaccines from the iCD. This combined spatiotemporal modulation of tumor-derived immunosuppression and vaccine-induced immune stimulation through the iCD is expected to provide an immune niche for preventing of postoperative tumor recurrence and metastasis.

  • Prof. Won Sub YOON develops high-performance battery that can travel up to 400km with one charge

    Biomedical Engineering Prof. PARK, CHUN GWON

    Prof. Won Sub YOON develops high-performance battery that can travel up to 400km with one charge

    A research team led by Prof. Won-Sub YOON, Department of Energy Science (DOES) at Sungkyunkwan University, has lifted the fundamental restriction on the breaking point of the lattice and unraveled the enigma of nickel effect on layered cathode materials that has existed for decades in the battery field. Consequently, they discovered the possibility of developing a high-performance battery which can travel up to 400km by one charge. While the technology of lithium ion batteries has been greatly successful since its advent in powering portable electronic devices, further advancements are insatiably demanding for wider applications such as in electric vehicles and grid-power storages. One of the key areas in these efforts is development of new positive electrode ‘cathode’ materials with higher energy densities to replace the lithium cobalt oxide that is currently prevailing as the cathode material. The research is very focused on increasing the amount of Li-ions ‘inserted’ in the electrode material, which affects the charge storage capacity, the speed of Li-ion movement within the crystal lattice of the electrode material, which affects the battery power, and the structural stability of the material upon in-and-out transport of Li-ion, which affects the battery life. Compared to other material families, the ‘layered’ materials are the most attractive in the sense of the three attributes listed above, and layered lithium transition metal oxides containing nickel (Ni), cobalt (Co) and manganese (Mn) have recently emerged as a promising family of cathode materials. Aside from lithium ions, other elements play a role as building blocks forming a host structure for Li-ions (guests) to be inserted or extracted. Depending on the properties of the host structure, its electrochemical performance as a battery material is determined. For these multi-component layered systems, the current trend moves toward increasing the content of Ni in layered systems (known as Ni-rich layered materials) since Ni is capable of uptaking and delivering twice the charge, i.e., Li-ions of the other two. As Ni atoms occupy a large part of the transition metal layer in the host structure, it becomes a major factor in determining the overall properties of the host structure. Therefore, understanding the effect of increasing Ni content on the layered structure is important to designing high-energy electrode materials. This series of materials containing Ni and other elements appear to inevitably have so-called ‘cation disorder,’ a phenomenon in which some of the Li-ions and Ni atoms switch positions from their own layers. This happens due to the fact that some of the Ni atoms exist in the valence state 2+ lower than Co or Mn as synthesized. The presence of Ni atoms in the Li-ion layer adversely affects the Li-ion movement in the Li-ion layer. In contrast to such a general perception, the study finds that the degree of cation disorders is mitigated upon increasing the Ni content in the lattice up to a certain concentration, and also reports that the oxidation state of Ni in the pristine compounds contributes significantly to cation disorder. Moreover, it is demonstrated that the extent of cation disorder critically affects the phase transition behavior during charging or discharging, and as a result, the phase transition becomes smoother with increasing Ni content. This smooth phase transition reduces the strain on structural behavior during cycling; consequently, it enhances the cycle performance of the electrode material. In addition to the relationship between the Ni content and the phase transition, it was discovered that the actual environment in which Li-ions are situated is not directly linked to the total height, a sum of the Li-ion layer and the transition metal layer (c-axis). The height of the lithium layer becomes larger with increasing Ni content, even though the c-axis decreases. More importantly, it is shown that the lithium ion channel retains the environment where lithium ions can visit or leave, even if the c-axis shrinks from the initial dimension. The results for the Ni-rich layered materials that are counter-intuitive account for the superior electrochemical performance, and address the misconception of Ni element in Ni-rich layered systems. Furthermore, this article provides a new perspective on the role of Ni in layered systems and disputes the conventional view concerning the c-axis parameter that has been considered a key factor in interpreting the behavior of Li-ion movement and the corresponding electrochemical performance. Hence, these results may suggest some aspects to consider in the design of high-energy electrode materials for next-generation batteries.

  • Prof. Won Sub YOON develops high-performance battery that can travel up to 400km with one charge

    Energy Science Prof. YOON, WON SUB

    Prof. Won Sub YOON develops high-performance battery that can travel up to 400km with one charge

    A research team led by Prof. Won-Sub YOON, Department of Energy Science (DOES) at Sungkyunkwan University, has lifted the fundamental restriction on the breaking point of the lattice and unraveled the enigma of nickel effect on layered cathode materials that has existed for decades in the battery field. Consequently, they discovered the possibility of developing a high-performance battery which can travel up to 400km by one charge. While the technology of lithium ion batteries has been greatly successful since its advent in powering portable electronic devices, further advancements are insatiably demanding for wider applications such as in electric vehicles and grid-power storages. One of the key areas in these efforts is development of new positive electrode ‘cathode’ materials with higher energy densities to replace the lithium cobalt oxide that is currently prevailing as the cathode material. The research is very focused on increasing the amount of Li-ions ‘inserted’ in the electrode material, which affects the charge storage capacity, the speed of Li-ion movement within the crystal lattice of the electrode material, which affects the battery power, and the structural stability of the material upon in-and-out transport of Li-ion, which affects the battery life. Compared to other material families, the ‘layered’ materials are the most attractive in the sense of the three attributes listed above, and layered lithium transition metal oxides containing nickel (Ni), cobalt (Co) and manganese (Mn) have recently emerged as a promising family of cathode materials. Aside from lithium ions, other elements play a role as building blocks forming a host structure for Li-ions (guests) to be inserted or extracted. Depending on the properties of the host structure, its electrochemical performance as a battery material is determined. For these multi-component layered systems, the current trend moves toward increasing the content of Ni in layered systems (known as Ni-rich layered materials) since Ni is capable of uptaking and delivering twice the charge, i.e., Li-ions of the other two. As Ni atoms occupy a large part of the transition metal layer in the host structure, it becomes a major factor in determining the overall properties of the host structure. Therefore, understanding the effect of increasing Ni content on the layered structure is important to designing high-energy electrode materials. This series of materials containing Ni and other elements appear to inevitably have so-called ‘cation disorder,’ a phenomenon in which some of the Li-ions and Ni atoms switch positions from their own layers. This happens due to the fact that some of the Ni atoms exist in the valence state 2+ lower than Co or Mn as synthesized. The presence of Ni atoms in the Li-ion layer adversely affects the Li-ion movement in the Li-ion layer. In contrast to such a general perception, the study finds that the degree of cation disorders is mitigated upon increasing the Ni content in the lattice up to a certain concentration, and also reports that the oxidation state of Ni in the pristine compounds contributes significantly to cation disorder. Moreover, it is demonstrated that the extent of cation disorder critically affects the phase transition behavior during charging or discharging, and as a result, the phase transition becomes smoother with increasing Ni content. This smooth phase transition reduces the strain on structural behavior during cycling; consequently, it enhances the cycle performance of the electrode material. In addition to the relationship between the Ni content and the phase transition, it was discovered that the actual environment in which Li-ions are situated is not directly linked to the total height, a sum of the Li-ion layer and the transition metal layer (c-axis). The height of the lithium layer becomes larger with increasing Ni content, even though the c-axis decreases. More importantly, it is shown that the lithium ion channel retains the environment where lithium ions can visit or leave, even if the c-axis shrinks from the initial dimension. The results for the Ni-rich layered materials that are counter-intuitive account for the superior electrochemical performance, and address the misconception of Ni element in Ni-rich layered systems. Furthermore, this article provides a new perspective on the role of Ni in layered systems and disputes the conventional view concerning the c-axis parameter that has been considered a key factor in interpreting the behavior of Li-ion movement and the corresponding electrochemical performance. Hence, these results may suggest some aspects to consider in the design of high-energy electrode materials for next-generation batteries.

  • Creation of Two-Terminal Tunneling Random Access Memory (TRAM) Inspired by Brain Neurons

    Electronic and Electrical Engineering Prof. YU, WOOJONG

    Creation of Two-Terminal Tunneling Random Access Memory (TRAM) Inspired by Brain Neurons

    A new memory device inspired by the neuron connections of the human brain has been designed. The research, published in Advanced Materials as a back cover paper, highlights the device's highly reliable performance, long retention time, and endurance. Moreover, its flexibility makes it a promising tool for the next-generation soft electronics attached to clothes or the body. The brain is able to learn and memorize thanks to a huge number of connections between neurons. The information humans memorize is transmitted through synapses from one neuron to the next as an electro-chemical signal. Inspired by these connections, scientists constructed a memory called two-terminal tunneling random access memory (TRAM), where two electrodes referred to as 'drain' and 'source' resemble the two communicating neurons of the synapse. TRAM is made up of a stack of one-atom-thick or a few-atoms-thick 2D crystal layers: the semiconductor molybdenum disulfide (drain and source), a tunneling insulator of aluminum oxide (Al2O3), and a floating gate of graphene layer. The researchers secured a large-area memory integration technology using a large-area grown graphene and a two-dimensional semiconductor through chemical vapor deposition (CVD). In simple terms, memory creates program (logical-0) and erase (logical-1) states by charging and discharging the graphene floating gate through the h-BN tunneling barrier. By effective charge tunneling through the crystalline h-BN layer and storing charges in the graphene layer, TRAM demonstrates an ultimately low off-state current of 10-14 A, leading to ultra high off/on ratio over 109 about 103 times higher than other two-terminal memories. Furthermore, the absence of thick, rigid blocking oxides enables high flexibility, which is useful for soft electronics. Our memory device can be useful for next-generation neuromorphic systems and wearable, body-attachable electronics in the near future.

  • Research on Short Career Horizons and Firm Innovation by Prof. Sang Kyun KIM

    Business Administration Prof. KIM, SANGKYUN

    Research on Short Career Horizons and Firm Innovation by Prof. Sang Kyun KIM

    As the business environment is rapidly changing, firms are required to formulate and implement strategies which help them to adapt to environmental and technological changes, to achieve innovation and long-term competitive advantages, and even to survive. Strategy scholars view a company's chief executive officer (CEO) as the most powerful actor in the decision-making process and call for further research to understand the role of CEOs in the innovation process beyond the simple relationship between CEOs' personal characteristics and financial performance. Building on labor market evaluations and legacy conservation motivation perspectives that explain risk aversion by CEOs facing a short career horizon, this study seeks to unpack the mechanisms linking a CEO's career horizon to a firm's breakthrough innovations. Using 10-year panel data from 681 U.S. firms, we find that a short career horizon induces a CEO to become risk-averse and thus forego investing in risky breakthrough innovations because they could harm the firm's short-term performance, endangering job prospects and CEO legacies in the short term. The results also show that the impact of a short career horizon on breakthrough innovations is partially mediated by a reduction in R&D spending. Furthermore, different performance implications associated with a firm’s exploitation and exploration activities affect a CEO's willingness to commit to such breakthrough innovations. That is, when a firm leverages internal knowledge within a familiar technological domain (i.e., a focus on exploitation), this mitigates the behavioral tendencies of a CEO with a short career horizon, such as not pursuing breakthrough innovations, while such behavioral tendencies are exacerbated when a firm applies external technologies with an unfamiliar trajectory (i.e., a focus on exploration). This study contributes to the literature on CEO decision-making and firm innovation. First, our study contributes to the literature on CEO decision-making by elucidating a mechanism that can explain the influence of a CEO’s career horizon on a firm’s ability to generate breakthrough innovations. Second, we emphasize the role of CEOs in the innovation process by suggesting that motivational factors can shape a CEO’s willingness to allocate firm resources to risky projects, which in turn can affect firms achieving breakthrough innovations. Practically, this research provides insights to those seeking to develop breakthrough innovations and manage organizational learning and innovation process for their firms. The alignment between a CEO’s willingness to take risks and a firm’s emphasis on organizational learning in both familiar and unfamiliar technological trajectories has an influence on firm innovations. It implies that CEOs play an important role in producing breakthrough innovations and that a strategic alignment between the willingness to take risks and the firm’s engagement in risky strategies can enable the firm to achieve greater innovations.

  • Highly Efficient Thin-Film Transistor via Cross-Linking 1T Edge Functional 2H Molybdenum Disulfides

    Chemistry Prof. LEE, HYOYOUNG

    Highly Efficient Thin-Film Transistor via Cross-Linking 1T Edge Functional 2H Molybdenum Disulfides

    Research on flexible thin film transistors (TFTs) has been steadily under way, with the next generation devices being noted. Molybdenum disulfide (MoS2), one of the two-dimensional materials, has excellent optical, electrical and chemical properties and is used in field effect transistors (FETs). However, most of the synthesis studies are concentrated on chemical vapor deposition, and it is necessary to make a method to manufacture MoS2 while maintaining crystallinity through an inexpensive solution process. In this study, MoS2 FET was implemented through a solution process by selectively modifying the edge of MoS2 only with organic compounds, without using metal ions at all. The paper was published in ACS Nano (2017, 11, 12832-12839) by the researchers led by Hyoyoung LEE (CINAP-IBS, Professor of Chemistry) with Mun Seok JEONG (Professor of Energy Science). To exfoliate the 2D MoS2 bulk materials into single-layer edge-1T basal-2H MoS2 sheets, they used 4-carboxy-benzenediazonium (+N2-benzene-COOH) tetrafluoroborate. Edge-exposed nucleophilic sulfides of the bulk MoS2 can act as substitutes for the electrophiles of +benzene-COOH diazonium salts. The chemically attached polar COOH functional group facilitates the exfoliation by creating an increased electrostatic repulsion force between the MoS2 nanosheets. As a result, the configuration of the resulting exfoliated HOOC-benzene-MoS2 sheets (e-MoS2) is changed to the conducting 1T or 1T′ phase through functionalization at the edge part, while remaining in the semiconducting 2H phase at the basal plane. Compared with n-BuLi exfoliated MoS2 (n-MoS2) and basal plane functionalized MoS2 (b-MoS2), which mainly have metallic 1T or 1T′ phase during the chemical treatment showing the on/off ratio of <100, e-MoS2 has a relatively high mobility (μ= 1.2 cm2/(V s) and on/off ratio (= 106) due to the low number of defect sites in the e-MoS2 nanosheets. PDDA (polydiallyldimethylammonium chloride) is used as a cationic layer, while e-MoS2 is used as an anionic layer for the channel film formation. Cross-linking via hydrogen bonding of the negatively charged COOH of the e-MoS2 sheets with the help of a cationic polymer provided good film formation for solution processing TFT channels. The e-MoS2 TFT exhibited great electrical performance (average mobility of 170.8 cm2/(V s) at 1 V and on/off ratio of 106) on SiO2/Si substrates and also a high mobility of 36.34 cm2/(V s) (on/off ratio of 103) on PDMS/PET substrates for flexible TFTs.

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