Chem
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Levitating 2D Semiconductor for Better Performance
(from top: Professor Yeon Sik Jung and PhD candidate Soomin Yim)
Atomically thin 2D semiconductors have been drawing attention for their superior physical properties over silicon semiconductors; nevertheless, they are not the most appealing materials due to their structural instability and costly manufacturing process. To shed some light on these limitations, a KAIST research team suspended a 2D semiconductor on a dome-shaped nanostructure to produce a highly efficient semiconductor at a low cost.
2D semiconducting materials have emerged as alternatives for silicon-based semiconductors because of their inherent flexibility, high transparency, and excellent carrier transport properties, which are the important characteristics for flexible electronics.
Despite their outstanding physical and chemical properties, they are oversensitive to their environment due to their extremely thin nature. Hence, any irregularities in the supporting surface can affect the properties of 2D semiconductors and make it more difficult to produce reliable and well performing devices. In particular, it can result in serious degradation of charge-carrier mobility or light-emission yield.
To solve this problem, there have been continued efforts to fundamentally block the substrate effects. One way is to suspend a 2D semiconductor; however, this method will degrade mechanical durability due to the absence of a supporter underneath the 2D semiconducting materials.
Professor Yeon Sik Jung from the Department of Materials Science and Engineering and his team came up with a new strategy based on the insertion of high-density topographic patterns as a nanogap-containing supporter between 2D materials and the substrate in order to mitigate their contact and to block the substrate-induced unwanted effects.
More than 90% of the dome-shaped supporter is simply an empty space because of its nanometer scale size. Placing a 2D semiconductor on this structure creates a similar effect to levitating the layer. Hence, this method secures the mechanical durability of the device while minimizing the undesired effects from the substrate. By applying this method to the 2D semiconductor, the charge-carrier mobility was more than doubled, showing a significant improvement of the performance of the 2D semiconductor.
Additionally, the team reduced the price of manufacturing the semiconductor. In general, constructing an ultra-fine dome structure on a surface generally involves costly equipment to create individual patterns on the surface. However, the team employed a method of self-assembling nanopatterns in which molecules assemble themselves to form a nanostructure. This method led to reducing production costs and showed good compatibility with conventional semiconductor manufacturing processes.
Professor Jung said, “This research can be applied to improve devices using various 2D semiconducting materials as well as devices using graphene, a metallic 2D material. It will be useful in a broad range of applications, such as the material for the high speed transistor channels for next-generation flexible displays or for the active layer in light detectors.”
This research, led by PhD candidate Soomin Yim, was published in Nano Letters in April.
Figure 1. Image of a 2D semiconductor using dome structures
2018.08.28 View 6027 -
Visualizing Chemical Reaction on Bimetal Surfaces
Catalysts are the result of many chemists searching to unravel the beauty of molecules and the mystery of chemical reactions. Professor Jeong Young Park from the Department of Chemistry, whose research focuses on catalytic chemical reactions, is no exception. His research team recently made breakthroughs in addressing long-standing questions for understanding reaction mechanisms on bimetal catalysts.
During the studies reported in Science Advances, following a publication in Nature Communications this month, Professor Park’s research team identified that the formation of metal–oxide interfaces is the key factor responsible for the synergistic catalytic effect in bimetal catalysts. The team confirmed this fundamental reaction mechanism through in situ imaging of reaction conditions. This is the first visualization of bimetal surfaces under reaction conditions, signifying the role of metal–oxide interfaces in heterogeneous catalysis.
Bimetallic materials have outstanding catalytic performance, which opens a new pathway for controlling electronic structures and binding energy in catalysts. Despite considerable research on various catalytic reaction efficiencies, there are yet unanswered questions on the underlying principles behind the improved performance. Even more, it was very hard to figure out what led to the efficiency because the structure, chemical composition, and oxidation state of bimetallic materials change according to reaction conditions.
Recently, some research groups suggested that oxide–metal interfacial sites formed by the surface segregation of bimetallic nanoparticles might be responsible for the increased catalytic performance. However, they failed to present any definitive evidence illustrating the physical nature or the fundamental role of the oxide–metal interfaces leading to the improved performance.
To specifically address this challenge, the research team carried out in situ observations of structural modulation on platinum–nickel bimetal catalysts under carbon monoxide oxidation conditions with ambient pressure scanning tunneling microscopy and ambient pressure X-ray photoelectron spectroscopy.
The team observed that platinum–nickel bimetal catalysts exhibited a variety of different structures depending on the gas conditions. Under ultrahigh vacuum conditions, the surface exhibited a platinum skin layer on the platinum–nickel alloyed surface, selective nickel segregation followed by the formation of nickel oxide clusters using oxygen gas, and finally the coexistence of nickel oxide clusters on the platinum skin during carbon monoxide oxidation. The research team found that the formation of interfacial platinum–nickel oxide nanostructures is responsible for a highly efficient step in the carbon monoxide oxidation reaction.
These findings illustrate that the enhancement of the catalytic activity on the bimetallic catalyst surface originates from the thermodynamically efficient reaction pathways at the metal–metal oxide interface, which demonstrates a straightforward process for the strong metal–support interaction effect. The formation of these interfacial metal–metal oxide nanostructures increases catalytic activity while providing a thermodynamically efficient reaction pathway by lowering the heat of the reactions on the surface. [J. Kim et al. Adsorbate-driven reactive interfacial Pt-NiO1-x nanostructure formation on the Pt3Ni(111) alloy surface, Science Advances (DOI: 10.1126/sciadv.aat3151 ]
Professor Park said that one way to monitor catalysts is to detect hot electrons associated with energy dissipation and conversion processes during surface reactions. His team led the real-time detection of hot electrons generated on bimetallic PtCo nanoparticles during exothermic hydrogen oxidation. The team successfully clarified the origin of the synergistic catalytic activity of PtCo nanoparticles with corresponding chemicurrent values.
By estimating the chemicurrent yield, the research team conclude that the catalytic properties of the bimetallic nanoparticles are strongly governed by the oxide–metal interface, which facilitates hot electron transfer. [H. Lee et al. Boosting hot electron flux and catalytic activity at metal–oxide interfaces of PtCo bimetallic nanoparticles, Nature Comm, 9, 2235 (2018)].
Professor Park explained, “We feel that the precise measurement of hot electrons on catalysts gives insight into the mechanism for heterogeneous catalysis, which can help with the smart design of highly reactive materials. The control of catalytic activity via electronic engineering of catalysts is a promising prospect that may open the door to the new field of combining catalysis with electronics, called “catalytronics.” He added that the study also establishes a strategy for improving catalytic activity for catalytic reactions in industrial chemical reactors.
Professors Park and Yousung Jung from the Department of Chemical and Biomolecular Engineering and the Graduate School of EEWS conducted this research in collaboration with Professor Bongjin Mun from the Department of Physics at GIST.
Figure 1. Evolution of surface structures of PtNi bimetal surfaces under various ambient conditions.
Figure 2. Formation of Pt-CoO interface leads to the catalytic enhancement of PtCo bimetal catalysts.
2018.07.25 View 8941 -
Students' Continued Gratitude Extends to Their Spouses
Here is a story of a group of KAIST graduates who still cherish the memory of their professor who passed away in 2003.
They are former students from the Department of Materials Science and Engineering and SDV Lab and their spouses. They created a group, called ‘Chun-sa-heoi’ meaning members who love Dr. Soung-Soon Chun. They reunite every February 26, the date that Dr. Chun passed away.
Chun-sa-heoi is comprised of twelve former students who are now professors, board members of major companies, and an attorney. From his first graduate, Professor Jae Gon Kim at Hanyang University to the most recent graduate, Attorney Jaehwan Kim, Chun-sa-heoi is marking 40 years of their bond.
Dr. Chun was teaching at the University of Utah when he received a call from the Korean government asking him to join KAIST in 1972 as a visiting professor.
He first introduced and established the Department of Materials Engineering, which was considered to be an advanced field at that time. During 30 years of dedication in this field, he fostered 48 Masters and 26 PhD graduates.
Professor Chul Soon Park from the School of Electrical Engineering is one of the former students of Dr. Chun. He explained, “Dr. Chun always cared about his students and guided them in better directions even after they graduated. My gratitude towards him still stays deep in my heart, so I keep maintaining the relationship with him.”
Mrs. Bok Yeon Choi, the spouse of KOREATECH Professor Sang-Ho Kim, first met Dr. Chun and his wife, Myung-Ja Chun in 1987 when she married her husband, who was enrolled in the graduate program at that time. “The Chuns showed affection to not only Dr. Chun’s students but also their families. They took care of us like a family,” she recalled.
Although Dr. Chun passed away in 2003, they continue to pay visits to Mrs. Chun, and they naturally organized this group, expressing gratitude to the Chuns. And their reunions keep on going even after Mrs. Chun moved to Los Angeles where her children are residing. Whenever the former students have a business trip to the U.S, they do not forget to visit Mrs. Chun.
But this year was somewhat more special for Mrs Chun and Chun-sa-heoi. In April, twelve spouses from Chun-sa-heoi invited Mrs. Chun to Hawaii to celebrate her 80th birthday. Mrs. Chun means a lot to the spouses because she has played the role of supporter to them. When they needed advice, she always answered sincerely and encouraged them.
There are numerous relationships among students and professors over the history of KAIST; however, the story of the Chuns and Chun-sa-heoi is very special because their relationship extends to their spouses, beyond the student-professor relationship.
This photo was taken in last April when Chun-sa-heoi celebrated the 80th birthday of Mrs. Chun in Hawaii.
? Who is Dr. Chun?
(Dr. Soung-Soon Chun)
Dr. Chun returned to Korea from the United States in 1972 following a call from the Korean government. At that time, the government policy was to bring back prominent scientists from abroad to develop national science and technology. From the time of KAIST’s foundation, he dedicated himself as a professor. He established the Department of Materials Engineering, where he fostered students and made significant academic contributions in his field.
While holding a position as a professor at the University of Utah, he developed a chemical vapor deposition method with tungsten and applied this method to cutting tools, making a contribution to the economic development of Korea.
When government-funded institutes, including KAIST, faced difficulties due to early retirements and tax credits being cut off, he was appointed as the vice president of KAIST and ardently proposed ways to promote the institute. During his term as vice president and president, he contributed to making KAIST a global research-centered educational institute. Before he passed away at the age of 69 in 2003, he held the position of president of the Daejeon National University of Technology and the Presidential Advisory Council on Science and Technology.
2018.07.13 View 6062 -
Platinum Catalyst Has Price Lowed and Durability Doubled
(Professor Cho in the Department of Materials Science and Engineering)
Professor EunAe Cho in the Department of Materials Science and Engineering reported a fuel cell catalyst that shows 12 times higher performance and twice the durability than previously used platinum catalyst.
Fuel cells, eco-friendly power generators, are said to be running air purifiers. A hydrogen vehicle powered by fuel cells can allegedly purify more than 98 percent of the particulate matter and ultrafine particles from the amount of air that 70 adults breathe.
Despite this peculiarity, the high price of platinum, which is used as an electrode catalyst, remains a big challenge to accelerating commercialization. In addition, recently developed ‘nano-structured platinum catalysts’ have not yet commercialized due to its meager oxygen reduction reaction and durability in fuel cell.
Addressing all those challenges, Professor Cho’s team reported a platinum catalyst costing 30 percent less but boasting 12 times higher performance.
The research team, to this end, combined the platinum with nickel, then applied various metallic elements for making the most efficient performance. Among others, they found that the addition of gallium can modulate the oxygen intermediate binding energy, leading to enhanced catalytic activity of the oxygen reduction reaction.
They made octahedron nanoparticle platinum-nickel alloy and could efficiently achieve 12-times high performance with the platinum catalyst by adding gallium to the surface of octahedron.
Existing fuel cell catalysts have issues in practical fuel cell applications. However, Professor Cho’s team experimentally proved the high performance of the catalyst even in the fuel cell, and is expected to be practically applied to the existing procedure.
First author JeongHoon Lim said their work demonstrates the gallium-added octahedral nanoparticles can be utilized as a highly active and durable oxygen reduction reaction catalyst in practical fuel cell applications. It will make it feasible for the mass production of the catalysts.
Professor Cho also said, “Our study realized the two main goals: an affordable price and increased performance of fuel cells. We hope this will make a contribution to the market competitiveness of fuel cell electric vehicles.”
This research was described in Nano Letters in April and was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP), the National Research Foundation (NRF), and the Agency for Defense Development (ADD).
(Figure: HAADF STEM images with EDX analyses and line scanning profiles of (a) Ga-PtNi/C and (b) PtNi/C during the voltage-cycling tests. The composition changes of Ni, Pt, and Ga atoms in the nanoparticles were determined by EDX (inset in the EDX mapping results)).
2018.05.15 View 6968 -
Capillary Forces at Work for Lithium-Sulfur Batteries
Professor Do Kyung Kim from the KAIST Department of Materials Science and Engineering and his team succeeded in developing high-areal-capacity lithium sulfur batteries (Li-S batteries) by capturing polysulfide with carbon nanofibers. This research will provide new batteries to replace existing lithium rechargeable batteries, shifting the commercialization of related technologies ahead.
Electrical vehicles and large-scale energy storage systems necessitate the development of batteries with high energy density and cost effectiveness, and Li-S batteries are known to be one of the promising alternatives to the predominant lithium ion batteries.
With six times as much energy density, Li-S batteries theoretically thrust electric vehicle to twice the distance of lithium ion batteries. Therefore, they have been spotlighted as next-generation lithium rechargeable batteries because they can go up to 400km once charged.
However, several issues make it challenging to readily commercialize Li-S batteries. The low electrical conductivity of sulfur, volumetric expansion and contraction of the battery during charge and discharge, and permanent damage of the electrode caused by the dissolution of the lithium polysulfide into the electrolyte – known as the “shuttle effect” – are three of the biggest obstacles to commercial-grade Li-S batteries.
While there have been numerous attempts to curb, avoid, or alleviate these issues — such as the physical encapsulation of sulfur using various metal oxides or carbonaceous matrices — most of them entail utilizing zero-dimensional (0D) carbon materials. This encapsulation method has been somewhat effective in enhancing the electrical conductivity of sulfur while simultaneously tolerating some volumetric alterations and suppressing the shuttle effect. The downside of 0D carbon material-based encapsulation methods is their complicated synthetic processing and the limited mass loading of sulfur.
With this in mind, the team set out to employ one-dimensional (1D) carbon materials instead. Unlike the 0D case, 1D carbon materials render a large surface area and a long-range conduction path for electrons and lithium ions. Being 1D also solves the undesirable high-contact resistance problem frequently encountered by 0D carbon material-based encapsulation.
The key to developing the proposed material was to exploit the capillary force to decrease the energy associated with the dissolution of polysulfides. As such, carbon nanofibers (CNFs) were found to be suitable for high-areal-capacity lithium-sulfur batteries since capillary force acting between CNFs can take advantage of the high electrical conductivity with the suppressed dissolution of sulfides.
The research findings show that sulfur was successfully contained in between the CNFs by wetting due to the capillary force without the need for complicated synthetic processing, as in the 0D case. The research results indicate that the sulfur contained per unit area (mg/cm2) is five times greater for the newly implemented method, which then enabled the lithium-sulfur battery to achieve an areal capacity of 7 mAh/cm2, which amounts to as much as at most seven times that of conventional lithium ion batteries.
First author Jong Hyuk Yun stated that the unprecedented methods utilized in this study will help further and widen the progress of lithium batteries in general. Meanwhile, Professor Kim said, “This study brought us closer to commercial-grade high-capacity Li-S batteries, which are applicable for a wide variety of products, including electric vehicles, unmanned aerial vehicles (UAVs), and drones.”
This research, led by PhD candidate Yun, was published in the 18th issue of this year’s Nano Letters.
Figure 1. Electrochemical reaction leading to the containment of the sulfur within the carbon nanofiber and the corresponding specific capacity of the battery over a number of charge-discharge cycles
Figure 2. SEM images of the first discharged electrode containing lithium sulfide at the junction between the nanofibers, and the first charged electrode
Figure 3. carbon nanofiber effectively absorbing liquid based lithium polysulfide
2018.05.14 View 7330 -
Undergrad's Paper Chosen as the Cover Article in Soft Matter
(from left: Research Professor KyuHan Kim and Undergrad Student Subeen Kim)
A KAIST undergraduate student, Subeen Kim, had his paper chosen as the cover article in an international journal during his senior year.
There have been an increasing number of undergraduate students who were published as the first author because the KAIST Undergraduate Research Participation program allows more active research participation by undergraduate students.
Through URP, Kim successfully published his paper in the internationally-renowned journal, Soft Matter, which is published by the Royal Society of Chemistry, and it was chosen as the cover article of that journal in February 2018.
This publication means a lot to him because he designed the cover image himself, based on his imagination and observations.
His research is about controllable one-step double emulsion formation. Double emulsion is a system in which dispersed droplets contain additional immiscible liquid droplets.
Having great retention ability, double emulsion has been used in various applications in the food industry, in cosmetics, and for drug delivery. Nevertheless, two-step emulsification is a conventional approach to produce double emulsions that typically leads to partial destabilization of the emulsion formed during the initial stage. Hence, it does not ensure the stability of a double emulsion. On the other hand, a microfluidic approach with various flow-focusing techniques has been developed, but it has low production efficiency and thus limited industrial applications.
Kim’s results came from the process of phase inversion to solve this problem. He identified the instant formation of double emulsions during the process of phase inversion. Based on this finding, he proposed criteria to achieve high stability of double emulsion.
Through constant research, he developed a quite general method using a combination of an oil soluble poly methyl methacrylate (PMMA) and hydrophobic silica nanoparticle (HDK H18). This new method enables one-step and stable production of double emersions in a stable manner. It also allows control of the number and the volume of inner oil droplets inside the outer water droplets by adjusting PMMA and HDK H18.
Kim enrolled at KAIST as a KAIST Presidential Fellowship and Presidential Science Scholarship in 2014. While studying both chemical and biomolecular engineering and chemistry he has been developing his hypothesis and conducting research.
He was able to begin conducting research because he has taken part in URP projects twice. In his sophomore year, he studied the formation of high internal phase double emulsions. After one year, he conducted research to produce superabsorbent resins, which are the base material for diapers, by using colloid particles. Using partial research outcomes, he published his paper in Nature Communications as a second author.
Kim said, “Double majoring the chemical and biomolecular engineering and chemistry has helped me producing this outcome. I hope that this research contributes to commercializing double emulsions. I will continue to identify accurate principles to produce chemicals that can be controlled exquisitely.”
Figure 1. The cover article of Soft Matter
2018.05.03 View 9431 -
Printed Thermo-Plasmonic Heat Patterns for Neurological Disorder Treatment
(Professor Nam and Dr. Kang, right)
A KAIST team presented a highly customizable neural stimulation method. The research team developed a technology that can print the heat pattern on a micron scale to enable the control of biological activities remotely.
The researchers integrated a precision inkjet printing technology with bio-functional thermo-plasmonic nanoparticles to achieve a ‘selective nano-photothermal neural stimulation method.’
The research team of Professor Yoonkey Nam at the Department of Bio and Brain Engineering expects this will serve as an enabling technology for personalized precision neuromodulation therapy for patients with neurological disorders.
The nano-photothermal neural stimulation method uses the thermo-plasmonic effect of metal nanoparticles to modulate the activities of neuronal networks. With the thermo-plasmonic effect, metal nanoparticles can absorb specific wavelength of illuminated light to efficiently generate localized heat. The research team discovered the inhibitory behavior of spontaneous activities of neurons upon photothermal stimulation four years ago. Since then, they have developed this technology to control hyperactive behaviors of neurons and neural circuits, which is often found in neurological disorders such as epilepsy.
In order to overcome the limitation on the spatial selectivity and resolution of the previously developed nano-photothermal method, the team adopted an inkjet printing technology to micro pattern the plasmonic nanoparticles (a few tens of microns), and successfully demonstrated that the nano-photothermal stimulation can be selectively applied according to the printed patterns.
The researchers applied a polyelectrolyte layer-by-layer coating method to printing substrates in a way to improve the pattern fidelity and achieve the uniform assembly of nanoparticles. The electrostatic attraction between the printed nanoparticles and the coated printing substrate also helped the stability of the attached nanoparticles. Because the polyelectrolyte coating is biocompatible, biological experiments including cell culture are possible with the technology developed in this work.
Using printed gold nanorod particles in a few tens of microns resolution over a several centimeters area, the researchers showed that highly complex heat patterns can be precisely formed upon light illumination according to the printing image.
Lastly, the team confirmed that the printed heat patterns can selectively and instantaneously inhibit the activities of cultured hippocampal neurons upon near-infrared light illumination. Because the printing process is applicable to thin and flexible substrates, the technology can be easily applied to implantable neurological disorder treatment devices and wearable devices. By selectively applying the heat patterns to only the desired cellular areas, customized and personalized photothermal neuromodulation therapy can be applied to patients.
“The fact that any desired heat patterns can be simply ‘printed’ anywhere broadens the applicability of this technology in many engineering fields. In bioengineering, it can be applied to neural interfaces using light and heat to modulate physiological functions. As another engineering application, for example, printed heat patterns can be used as a new concept of anti-counterfeit applications,” said the principal investigator, Yoonkey Nam at KAIST. This work, led mainly by Dr. Hongki Kang, was published in ACS Nano on February 5th 2018.
2018.04.06 View 6522 -
Developing Flexible Vertical Micro LED
A KAIST research team led by Professor Keon Jae Lee from the Department of Materials Science and Engineering and Professor Daesoo Kim from the Department of Biological Sciences has developed flexible vertical micro LEDs (f-VLEDs) using anisotropic conductive film (ACF)-based transfer and interconnection technology. The team also succeeded in controlling animal behavior via optogenetic stimulation of the f-VLEDs.
Flexible micro LEDs have become a strong candidate for the next-generation display due to their ultra-low power consumption, fast response speed, and excellent flexibility. However, the previous micro LED technology had critical issues such as poor device efficiency, low thermal reliability, and the lack of interconnection technology for high-resolution micro LED displays.
The research team has designed new transfer equipment and fabricated a f-VLED array (50ⅹ50) using simultaneous transfer and interconnection through the precise alignment of ACF bonding process. These f-VLEDs (thickness: 5 ㎛, size: below 80 ㎛) achieved optical power density (30 mW/mm2) three times higher than that of lateral micro LEDs, improving thermal reliability and lifetime by reducing heat generation within the thin film LEDs.
These f-VLEDs can be applied to optogenetics for controlling the behavior of neuron cells and brains. In contrast to the electrical stimulation that activates all of the neurons in brain, optogenetics can stimulate specific excitatory or inhibitory neurons within the localized cortical areas of the brain, which facilitates precise analysis, high-resolution mapping, and neuron modulation of animal brains. (Refer to the author’s previous ACS Nano paper of “Optogenetic Mapping of Functional Connectivity in Freely Moving Mice via Insertable Wrapping Electrode Array Beneath the Skull.” )
In this work, they inserted the innovative f-VLEDs into the narrow space between the skull and the brain surface and succeeded in controlling mouse behavior by illuminating motor neurons on two-dimensional cortical areas located deep below the brain surface.
Professor Lee said, “The flexible vertical micro LED can be used in low-power smart watches, mobile displays, and wearable lighting. In addition, these flexible optoelectronic devices are suitable for biomedical applications such as brain science, phototherapeutic treatment, and contact lens biosensors.”
He recently established a startup company ( FRONICS Inc. ) based on micro LED technology and is looking for global partnerships for commercialization. This result entitled “ Optogenetic Control of Body Movements via Flexible Vertical Light-Emitting Diodes on Brain Surface ” was published in the February 2018 issue of Nano Energy.
Figure 1. Comparison of μ-LEDs Technology
2018.01.29 View 12264 -
Plasma, an Excellent Sterilizer to Remove Harmful Bacteria
(PhD candidate Joo Young Park, Professor Wonho Choe and PhD researcher Sanghoo Park)
KAIST researchers are using plasma to remove bacteria that are stuck to surfaces of plastic bottles and food. This novel technology will contribute to disinfection in medical settings as well as food and agricultural industries.
Professor Wonho Choe and his team from the Department of Physics developed a technology that removes biofilm, which is comprised of microorganisms, by using plasma as a non-thermal sterilization method.
Plasma contains multiple bactericidal agents, including reactive species. In particular, the chemicals formed in aqueous solution during plasma exposure have the potential for high antibacterial activity against various bacterial infections.
The team treated water with plasma to see how effectively bactericidal agents in the plasma water can remove biofilm comprised of harmful microorganism such as Escherichia coli, Salmonella, and Listeria.
The team identified that reactive species, including hydroxyl radical, hydrogen peroxide, ozone, nitrite, and superoxide produced during plasma treatment, showed considerable ability to remove the biofilm. Hydrogen peroxide showed the strongest effect removing the biofilm; however, the hydroxyl radical also played a significant role in removing biofilm. Despite having a concentration 100 to 10,000 times lower than other reactive species, the hydroxyl radical showed a high biofilm removal efficacy owing to its strong oxidative power.
These findings reveal that plasma can be used as a no-residual and safe sterilization process alternative to conventional methods. With these outcomes, the team is planning to develop and commercialize a technology that can produce hydroxyl radicals with plasma.
Professor Choe has registered a patent for flexible packaging materials that facilitate plasma and completed the technology transfer to the startup company, named ‘Plasmapp’, which focuses on commercializing bactericidal technology.
“This research outcome will be the foundation for understanding plasma control technology and physicochemical interactions between plasma and microorganisms. It will also become an accelerator for utilizing plasma technology in the medical, food, and agricultural fields,” said Professor Choe.
This research, led by PhD candidate Joo Young Park and PhD researcher Sanghoo Park in collaboration with Professor Cheorun Jo’s team from Seoul National University, was published in ACS Applied Materials and Interfaces on December 20, 2017.
Figure 1. Flexible packaging materials that facilitate plasma
Figure 2. Schematic diagram of biofilm treatment with plasma
Figure 3. Concept of plasma application and evaluation result of reactive species' efficacy
Figure 4. STERPACK, the product launched by Plasmapp
2018.01.25 View 8927 -
Lifespan of Fuel Cells Maximized Using Small Amount of Metals
(Professor Jung (far right) and his team)
Fuel cells are key future energy technology that is emerging as eco-friendly and renewable energy sources. In particular, solid oxide fuel cells composed of ceramic materials gain increasing attention for their ability to directly convert various forms of fuel such as biomass, LNG, and LPG to electric energy.
KAIST researchers described a new technique to improve chemical stability of electrode materials which can extend the lifespan by employing a very little amount of metals.
The core factor that determines the performance of solid oxide fuel cells is the cathode at which the reduction reaction of oxygen occurs. Conventionally, oxides with perovskite structure (ABO3) are used in cathodes. However, despite the high performance of perovskite oxides at initial operation, the performance decreases with time, limiting their long-term use. In particular, the condition of high temperature oxidation state required for cathode operation leads to surface segregation phenomenon, in which second phases such as strontium oxide (SrOx) accumulate on the surface of oxides, resulting in decrease in electrode performance. The detailed mechanism of this phenomenon and a way to effectively inhibit it has not been suggested.
Using computational chemistry and experimental data, Professor WooChul Jung’s team at the Department of Materials Science and Engineering observed that local compressive states around the Sr atoms in a perovskite electrode lattice weakened the Sr-O bond strength, which in turn promote strontium segregation. The team identified local changes in strain distribution in perovskite oxide as the main cause of segregation on strontium surface. Based on these findings, the team doped different sizes of metals in oxides to control the extent of lattice strain in cathode material and effectively inhibited strontium segregation.
Professor Jung said, “This technology can be implemented by adding a small amount of metal atoms during material synthesis, without any additional process.” He continued, “I hope this technology will be useful in developing high-durable perovskite oxide electrode in the future.”
The study co-led by Professor Jung and Professor Jeong Woo Han at Department of Chemical Engineering, University of Seoul was featured as the cover of Energy and Environmental Science in the first issue of 2018.
(Figure1.Correlation between the extent of lattice strain in electrode, strontium segregation, and electrode reaction.)
(Figure 2. Cathode surface of solid oxide fuel cell stabilized using the developed technology)
2018.01.18 View 7536 -
Easier Way to Produce High Performing, Flexible Micro-Supercapacitor
(Professor Minyang Yang and PhD Student Jae Hak Lee)
Professor Minyang Yang from the Department of Mechanical Engineering and his team developed a high-energy, flexible micro-supercapacitor in a simple and cost-effective way.
Compared to conventional micro-batteries, such as lithium-ion batteries, these new batteries, also called supercapacitors, are significantly faster to charge and semi-permanent.
Thin, flexible micro-supercapacitors can be a power source directly attached to wearable and flexible electronics.
However, fabrication of these micro-supercapacitors requires a complex patterning process, such as lithography techniques and vacuum evaporation. Hence, the process requires expensive instruments and toxic chemicals.
To simplify the fabrication of micro-supercapacitors in an eco-friendly manner, the team developed laser growth sintering technology. This technology manufactures superporous silver electrodes and applies them to the supercapacitors’ electrodes.
The team used a laser to form micro-patterns and generated nanoporous structures inside. This laser-induced growth sintering contributed to shortening the manufacturing process from ten steps to one.
Moreover, the team explored this unique laser growth sintering process –nucleation, growth, and sintering –by employing a particle-free, organometallic solution, which is not costly compared to typical laser-sintering methods for metallic nanoparticle solutions used in the printing of micro-electrodes.
Finally, unlike the typical supercapacitors comprised of a single substance, the team applied an asymmetric electrode configuration of nanoporous gold and manganese dioxide, which exhibits a highly-specific capacitance, to operate at a high voltage.
This method allows the team to develop energy storage with a high capacity. This developed micro-supercapacitor only requires four seconds to be charged and passed more than 5,000 durability tests.
Professor Yang said, “This research outcome can be used as energy storage installed in wearable and flexible electronic devices. Through this research, we are one step closer to realizing a complete version of flexible electronic devices by incorporating a power supply.”
This research, led by PhD candidate Jae Hak Lee, was selected as the cover of Journal of Materials Chemistry A on December 21, 2017.
Figure 1. Cover of the Journal Materials Chemistry A
Figure 2. Manufactured micro-supercapacitor and its performance
Figure 3. Laser growth sintering mechanism
Figure 4. Structural change of the silver conductor according to the irradiated laser energy
2018.01.18 View 7164 -
Professor Jung Awarded the Pople Medal by the APATCC
(Professor Yousung Jung)
Professor Yousung Jung of the Graduate School of EEWS won the Pople Medal from the Asia-Pacific Association of Theoretical & Computational Chemists (APATCC).
The Pople Medal has been awarded annually since 2007 to recognize young scholars in the fields of theoretical/computational chemistry in honor of Sir John Anthony Pople, who passed away in 2004. Dr. Pople was a British theoretical chemist and a Nobel laureate in 1998 for his development of computational methods in quantum chemistry.
The Pople Medal is awarded to scientists at or under the age of 45 in the Asia-Pacific region who have distinguished themselves through pioneering and important contributions.
Professor Jung was honored for his outstanding contributions to developing efficient electronic structure methods and their applications to energy materials discovery. He has published more than 120 papers in prestigious academic journals. He also has an h-index of 44, and has been cited more than 8,000 times.
2018.01.10 View 6371