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‘OSK Rising Stars 30’ Recognizes Four KAISTians
Four KAISTians were selected as star researchers to brighten the future of optics in commemoration of the 30th anniversary of the Optical Society of Korea (OSK). As ‘OSK Rising Stars 30’, the OSK named 27 domestic researchers under the age of 40 who have made significant contributions and will continue contributing to the development of Korea’s optics academia and industry.
Professor YongKeun Park from the Department of Physics was selected in recognition of his contributions to the field of biomedical optics. Professor Park focuses on developing novel optical methods for understanding, diagnosing, and treating human diseases, based on light scattering, light manipulation, and interferometry. As a member of numerous international optics societies including the OSA and the SPIE and a co-founder of two start-up companies, Professor Park continues to broaden his boundaries as a leading opticist and entrepreneur.
Professor Jonghwa Shin from the Department of Materials Science and Engineering was recognized for blazing a trail in the field of broadband metamaterials. Professor Shin’s research on the broadband enhancement of the electric permittivity and refractive index of metamaterials has great potential in both academia and industry.
Professor Hongki Yoo from the Department of Mechanical Engineering is expected to create a significant ripple effect in the diagnosis of cardiovascular disorders through the development of new optical imaging techniques and applications.
Finally, Dr. Sejeong Kim, a KAIST graduate and a Chancellor’s postdoctoral research fellow at the University of Technology Sydney (UTS), was acknowledged for her optical device research utilizing two-dimensional materials. Dr. Kim’s research at UTS now focuses on the introduction of micro/nano cavities for new materials.
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2020.03.16 View 11399 -
COVID-19 Update: All Undergrad Housing Closed
KAIST stepped up preventive measures against the outbreak of COVID-19 by closing all housing complexes for undergraduate students.
Provost Kwang-Hyung Lee, in an email to KAIST community members on March 12, advised all undergraduate students who had already moved in to the dormitories to move out by March 23. The university opened the spring semester on March 16, two weeks later than originally scheduled, due to the outbreak. All in-person classes have been shifted to online classes and this will continue until further notice.
“The dormitory would likely become the source of a COVID-19 cluster on the campus. Given the gravity of the current situation, we can’t help but make this unprecedented measure. It is fully for the best interests for our students’ health and safety. It saddens me to say that students are required to go back to their homes,” said Provost Lee. Dormitory fees will be refunded, and transportation and storage services will be provided for students who return back home. It has not yet been decided when they can return to the campus.
There are four exceptional cases for this special measure: 1. when a student does not have legal residency in Korea, 2. if a student’s legal residence is located in a severely affected region such as Daegu, Chongdo, and Kyongsan, 3. if students in their final semester before the graduation need to take a research class that is not available online, 4. if students have a very special reason that does not allow them to stay at home. Such students are required to meet the Associate Vice President of Student Life for approval of the exceptional stay.
Meanwhile, the first day of the online semester on March 16 saw an overwhelming amount of traffic on the remote educational platform, the KAIST learning management system (KLMS), and the real-time platform, Zoom. The two systems were both overloaded. The Dean of the KAIST Academy sent an email to the community, explaining the technical glitch causing the overload. He said his office had fixed the problem, allowing resumed access to the system from inside and outside the campus. Considered the nature of classes that are difficult or impossible to provide online, the university decided to cancel the some of physical training classes such as golf, dance sports, badminton, swimming, and tennis this semester.
Social distancing is another issue the university is enhancing throughout the campus. The university announced new lunch break shifts to disperse the dining hall crowds; the first shift is from 11:30 to 12:30 and the second shift is from 12:30 to 13:30, effective from March 17. The COVID-19 response bulletin also instructed KAIST community members to sit in a row, not face to face, when eating together with colleagues, and asked them to refrain from talking while eating. In addition, a total of 29 virus and fine duster filtering machines have been installed across the campus dining facilities.
The bulletin posted on March 13 restressed the importance of wearing a face mask in compact areas such as elevators and refrain the non-essential business or personal travel. Parents who need to take care of their children due to the closure of schools and day care centers are advised to work from home.
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2020.03.16 View 8332 -
3D Hierarchically Porous Nanostructured Catalyst Helps Efficiently Reduce CO2
- This new catalyst will bring CO2 one step closer to serving as a sustainable energy source. -
KAIST researchers developed a three-dimensional (3D) hierarchically porous nanostructured catalyst with carbon dioxide (CO2) to carbon monoxide (CO) conversion rate up to 3.96 times higher than that of conventional nanoporous gold catalysts. This new catalyst helps overcome the existing limitations of the mass transport that has been a major cause of decreases in the CO2 conversion rate, holding a strong promise for the large-scale and cost-effective electrochemical conversion of CO2 into useful chemicals.
As CO2 emissions increase and fossil fuels deplete globally, reducing and converting CO2 to clean energy electrochemically has attracted a great deal of attention as a promising technology. Especially due to the fact that the CO2 reduction reaction occurs competitively with hydrogen evolution reactions (HER) at similar redox potentials, the development of an efficient electrocatalyst for selective and robust CO2 reduction reactions has remained a key technological issue.
Gold (Au) is one of the most commonly used catalysts in CO2 reduction reactions, but the high cost and scarcity of Au pose obstacles for mass commercial applications. The development of nanostructures has been extensively studied as a potential approach to improving the selectivity for target products and maximizing the number of active stable sites, thus enhancing the energy efficiency.
However, the nanopores of the previously reported complex nanostructures were easily blocked by gaseous CO bubbles during aqueous reactions. The CO bubbles hindered mass transport of the reactants through the electrolyte, resulting in low CO2 conversion rates.
In the study published in the Proceedings of the National Academy of Sciences of the USA (PNAS) on March 4, a research group at KAIST led by Professor Seokwoo Jeon and Professor Jihun Oh from the Department of Materials Science and Engineering designed a 3D hierarchically porous Au nanostructure with two different sizes of macropores and nanopores. The team used proximity-field nanopatterning (PnP) and electroplating techniques that are effective for fabricating the 3D well-ordered nanostructures.
The proposed nanostructure, comprised of interconnected macroporous channels 200 to 300 nanometers (nm) wide and 10 nm nanopores, induces efficient mass transport through the interconnected macroporous channels as well as high selectivity by producing highly active stable sites from numerous nanopores.
As a result, its electrodes show a high CO selectivity of 85.8% at a low overpotential of 0.264 V and efficient mass activity that is up to 3.96 times higher than that of de-alloyed nanoporous Au electrodes.
“These results are expected to solve the problem of mass transfer in the field of similar electrochemical reactions and can be applied to a wide range of green energy applications for the efficient utilization of electrocatalysts,” said the researchers.
This work was supported by the National Research Foundation (NRF) of Korea.
Image credit: Professor Seokwoo Jeon and Professor Jihun Oh, KAIST
Image usage restrictions: News organizations may use or redistribute this image, with proper attribution, as part of news coverage of this paper only.
Publication:
Hyun et al. (2020) Hierarchically porous Au nanostructures with interconnected channels for efficient mass transport in electrocatalytic CO2 reduction. Proceedings of the National Academy of Sciences of the USA (PNAS). Available online at https://doi.org/10.1073/pnas.1918837117
Profile:
Seokwoo Jeon, PhD
Professor
jeon39@kaist.ac.kr
http://fdml.kaist.ac.kr
Department of Materials Science and Engineering (MSE)
https://www.kaist.ac.kr
Korea Advanced Institute of Science and Technology (KAIST)Daejeon, Republic of Korea
Profile:
Jihun Oh, PhD
Associate Professor
jihun.oh@kaist.ac.kr
http://les.kaist.ac.kr
Department of Materials Science and Engineering (MSE)
Department of Energy, Environment, Water and Sustainability (EEWS)
KAIST
Profile:
Gayea Hyun
PhD Candidate
cldywkd93@kaist.ac.kr
http://fdml.kaist.ac.kr
Flexible Devices and Metamaterials Laboratory (FDML)
Department of Materials Science and Engineering (MSE)
KAIST
Profile:
Jun Tae Song, PhD
Assistant Professor
song.juntae@cstf.kyushu-u.ac.jp
http://www.cstf.kyushu-u.ac.jp/~ishihara-lab/
Department of Applied Chemistry
https://www.kyushu-u.ac.jp
Kyushu UniversityFukuoka, Japan
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2020.03.13 View 17424 -
Scientists Observe the Elusive Kondo Screening Cloud
Scientists ended a 50-year quest by directly observing a quantum phenomenon
An international research group of Professor Heung-Sun Sim has ended a 50-year quest by directly observing a quantum phenomenon known as a Kondo screening cloud. This research, published in Nature on March 11, opens a novel way to engineer spin screening and entanglement. According to the research, the cloud can mediate interactions between distant spins confined in quantum dots, which is a necessary protocol for semiconductor spin-based quantum information processing. This spin-spin interaction mediated by the Kondo cloud is unique since both its strength and sign (two spins favor either parallel or anti-parallel configuration) are electrically tunable, while conventional schemes cannot reverse the sign.
This phenomenon, which is important for many physical phenomena such as dilute magnetic impurities and spin glasses, is essentially a cloud that masks magnetic impurities in a material. It was known to exist but its spatial extension had never been observed, creating controversy over whether such an extension actually existed.
Magnetism arises from a property of electrons known as spin, meaning that they have angular momentum aligned in one of either two directions, conventionally known as up and down. However, due to a phenomenon known as the Kondo effect, the spins of conduction electrons—the electrons that flow freely in a material—become entangled with a localized magnetic impurity, and effectively screen it. The strength of this spin coupling, calibrated as a temperature, is known as the Kondo temperature.
The size of the cloud is another important parameter for a material containing multiple magnetic impurities because the spins in the cloud couple with one another and mediate the coupling between magnetic impurities when the clouds overlap. This happens in various materials such as Kondo lattices, spin glasses, and high temperature superconductors.
Although the Kondo effect for a single magnetic impurity is now a text-book subject in many-body physics, detection of its key object, the Kondo cloud and its length, has remained elusive despite many attempts during the past five decades. Experiments using nuclear magnetic resonance or scanning tunneling microscopy, two common methods for understanding the structure of matter, have either shown no signature of the cloud, or demonstrated a signature only at a very short distance, less than 1 nanometer, so much shorter than the predicted cloud size, which was in the micron range.
In the present study, the authors observed a Kondo screening cloud formed by an impurity defined as a localized electron spin in a quantum dot—a type of “artificial atom”—coupled to quasi-one-dimensional conduction electrons, and then used an interferometer to measure changes in the Kondo temperature, allowing them to investigate the presence of a cloud at the interferometer end.
Essentially, they slightly perturbed the conduction electrons at a location away from the quantum dot using an electrostatic gate. The wave of conducting electrons scattered by this perturbation returned back to the quantum dot and interfered with itself. This is similar to how a wave on a water surface being scattered by a wall forms a stripe pattern. The Kondo cloud is a quantum mechanical object which acts to preserve the wave nature of electrons inside the cloud.
Even though there is no direct electrostatic influence of the perturbation on the quantum dot, this interference modifies the Kondo signature measured by electron conductance through the quantum dot if the perturbation is present inside the cloud. In the study, the researchers found that the length as well as the shape of the cloud is universally scaled by the inverse of the Kondo temperature, and that the cloud’s size and shape were in good agreement with theoretical calculations.
Professor Sim at the Department of Physics proposed the method for detecting the Kondo cloud in the co-research with the RIKEN Center for Emergent Matter Science, the City University of Hong Kong, the University of Tokyo, and Ruhr University Bochum in Germany.
Professor Sim said, “The observed spin cloud is a micrometer-size object that has quantum mechanical wave nature and entanglement. This is why the spin cloud has not been observed despite a long search. It is remarkable in a fundamental and technical point of view that such a large quantum object can now be created, controlled, and detected.
Dr. Michihisa Yamamoto of the RIKEN Center for Emergent Matter Science also said, “It is very satisfying to have been able to obtain real space image of the Kondo cloud, as it is a real breakthrough for understanding various systems containing multiple magnetic impurities. The size of the Kondo cloud in semiconductors was found to be much larger than the typical size of semiconductor devices.”
Publication:
Borzenets et al. (2020) Observation of the Kondo screening cloud. Nature, 579. pp.210-213. Available online at https://doi.org/10.1038/s41586-020-2058-6
Profile:
Heung-Sun Sim, PhD
Professor
hssim@kaist.ac.kr
https://qet.kaist.ac.kr/
Quantum Electron Correlation & Transport Theory Group (QECT Lab)
https://qc.kaist.ac.kr/index.php/group1/
Center for Quantum Coherence In COndensed Matter
Department of Physics
https://www.kaist.ac.kr
Korea Advanced Institute of Science and Technology (KAIST)
Daejeon, Republic of Korea
2020.03.13 View 15723 -
COVID-19 Update: All Classes to Go Online after Semester Opens
All classes of undergraduate and graduate courses will go online from March 16 in a protective measure for the KAIST community to slow the spread of COVID-19. No decision has yet been made for how long the online classes will last. The spring semester will start two weeks later than scheduled due to the outbreak of the COVID-19.
For online classes, professors are uploading their taped class video clips onto the KAIST Learning Management System (KLMS). These classes will be conducted in both real time and on demand. The video conferencing solution Zoom will be employed for real-time online classes, and professors and students will interact using the bulletin board function for on-demand classes.
The university is scaling up its institutional response to protect the KAIST community against the outbreak of the disease following the cancellation and postponing of major academic events including the commencement and matriculation ceremonies scheduled in February and March.
The new protective measures include all sports complexes and facilities temporarily closing from February 24. All building entrance gates are only accessible with those carrying a KAIST ID card. A total of nine fever monitors have been installed in the university headquarter building, main library, dining halls, the day care center at Daejeon campus, and at the Seoul campus.
The Emergency Response Team is posting a daily bulletin and response manual on the KAIST portal system with updates on the number of confirmed cases in Daejeon and other regions including Seoul as well as reminder notices to help contain the spread.
Provost Kwang-Hyung Lee advised KAIST community members to refrain from traveling to the gravely affected region and foreign countries in an email sent on March 11. Anyone who has a travel history in those regions should report it to the Emergency Response Team and self-quarantine for two weeks at home or in a designated dorm complex.
KAIST surveyed all community members’ travel histories last month and instructed those who had traveled to Daegu and foreign countries or had contact with a confirmed patient to go into self-isolation or work from home while conducting intensive self-monitoring. They have been asked to report their temperature to the Emergency Response Team twice a day. The response manual recommends canceling or postponing meetings and events at the campus. “If necessary, we ask that you make a conference call instead,” said the Emergency Response Team.
Meanwhile, the Academic Affairs Office decided to employ a flexible academic schedule in consideration of students’ circumstances during this extraordinary outbreak situation. “We still need to run 16 weeks of classes for the semester but we are being flexible in how the classes can be run. It will wholly depend on the professor and students’ discussions based on their situation. We won’t apply a unilateral mid-term and final exam week during this special time,” said the bulletin from the Academic Affairs Office.
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2020.03.11 View 8054 -
“A drop of water shall be returned with a rushing river.”
- Chinese KAISTians Donate Supplies to Fight COVID-19 in Daegu -
The Chinese community at KAIST donated 2.49 million won worth of personal protective equipment on March 4 to support on-site medical personnel in the city of Daegu. South Korea has been witnessing a significant surge in novel COVID-19 transmissions, and Daegu and nearby North Gyeongsang Province are the most affected regions.
As the COVID-19 situation grows more serious globally day by day, a Chinese master’s student from the KAIST Department of Civil and Environmental Engineering, Yuewen Jia, suggested a fundraising campaign on the KAIST Chinese Community’s WeChat messenger chat room, and her idea was enthusiastically supported by many peer-members. The KAIST Chinese Community is comprised of 105 undergraduates, graduates, post-doctoral fellows, researchers, and professors.
With Jia’s post-doc colleague Pei Li volunteering to manage the fundraising process, a total of 2.49 million won was collected in 12 days between January 27 and February 7.
The donors, including Qin Xu, a PhD candidate in the School of Electrical Engineering, reportedly asked for their donations to be used to support on-site medical personnel affected by the outbreak. They believed that medical supplies are the most essential in times like these. The group purchased personal protective equipment online and waited for more than 20 days until the items were finally delivered to them. The goods include 1,280 protective caps, 57 protective suits, 15 protective glasses, and two protective face shields.
Given the surging spread of the COVID-19 disease in Korea, where the confirmed cases have increased multi-fold since mid-February, the KAIST Chinese Community decided that their items should be used immediately in Korea, instead of being sent back to their home country as they had planned.
Guoyuan An, a student representative of the community studying for his master’s degree in the School of Computing, said, “Earlier, some members of the KAIST Chinese Community who had visited China were self-quarantined for two weeks in a special facility designated by KAIST as a precautionary measure. Thanks to the outstanding care we received from offices at KAIST including the COVID-19 Task Force Team, the International Office, the Student Offices, and the Clinic, those who were quarantined could return to campus safe and healthy.”
He continued, “KAIST and the Koreans as a whole spared no effort in helping China and Chinese people living in Korea fight the COVID-19 outbreak in its early days, and all of the members of the KAIST Chinese Community felt deeply grateful for all the attention and aid. This has been a definitive reason for us to change the donate recipient from China to Korea.”
“As an old Chinese saying goes, ‘A drop of water shall be returned with a rushing river.’ This proverb means that even if you receive a little help from others, you should return the favor with all you can when others are in need. We decided to make a donation ourselves in hopes that our small contribution could help on-site medical personnel work for the health and wellbeing of Koreans who are affected in that area.” he explained.
The donated items were delivered to the Division of Disaster Preparedness and Emergency Management at the Daegu Metropolitan Government Office, with help from the on-campus medical center KAIST Clinic Pappalardo Center and the KAIST International Scholar and Student Services (ISSS) Team.
Dr. Yun-Jung Lee, the executive director of the KAIST Clinic Pappalardo Center, expressed “a huge thank you to the KAIST Chinese Community for pitching in to help battle this national and global crisis.”
She added, “Their donations have been passed to those in desperate need, and their warm-hearted act of kindness will go a long way.”
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2020.03.05 View 9599 -
Coordination Chemistry and Alzheimer’s Disease
It has become evident recently that the interactions between copper and amyloid-b neurotoxically impact the brain of patients with Alzheimer’s disease. KAIST researchers have reported a new strategy to alter the neurotoxicity in Alzheimer’s disease by using a rationally designed chemical reagent.
This strategy, developed by Professor Mi Hee Lim from the Department of Chemistry, can modify the coordination sphere of copper bound to amyloid-b, effectively inhibiting copper’s binding to amyloid-b and altering its aggregation and toxicity. Their study was featured in PNAS last month.
The researchers developed a small molecule that is able to directly interact with the coordination sphere of copper–amyloid-b complexes followed by modifications via either covalent conjugation, oxidation, or both under aerobic conditions. The research team simply utilized copper–dioxygen chemistry to design a chemical reagent.
Answering how peptide modifications by a small molecule occur remains very challenging. The system includes transition metals and amyloidogenic proteins and is quite heterogeneous, since they are continuously being changed. It is critical to carefully check the multiple variables such as the presence of dioxygen and the type of transition metal ions and amyloidogenic proteins in order to identify the underlying mechanisms and target specificity of the chemical reagent.
The research team employed various biophysical and biochemical methods to determine the mechanisms for modifications on the coordination sphere of copper–Aꞵ complexes. Among them, peptide modifications were mainly analyzed using electrospray ionization-mass spectrometry.
Mass spectrometry (MS) has been applied to verify such peptide modifications by calculating the shift in exact mass. The research team also performed collision-induced dissociation (CID) of the target ion detected by MS to pinpoint which amino acid residue is specifically modified. The CID fragmentizes the amide bond located between the amino acid residues. This fragmental analysis allows us to identify the specific sites of peptide modifications.
The copper and amyloid-b complexes represent a pathological connection between metal ions and amyloid-b in Alzheimer’s disease. Recent findings indicate that copper and amyloid-b can directly contribute toward neurodegeneration by producing toxic amyloid-b oligomers and reactive oxygen species.
Professor Lim said, “This study illustrates the first experimental evidence that the 14th histidine residue in copper–amyloid-b complexes can be specifically modified through either covalent conjugation, oxidation, or both. Considering the neurotoxic implications of the interactions between copper and amyloid-b, such modifications at the coordination sphere of copper in amyloid-b could effectively alter its properties and toxicity.”
“This multidisciplinary study with an emphasis on approaches, reactivities, and mechanisms looks forward to opening a new way to develop candidates of anti-neurodegenerative diseases,” she added. The National Research Foundation of Korea funded this research.
2020.03.03 View 7716 -
Black Phosphorous Tunnel Field-Effect Transistor as an Alternative Ultra-low Power Switch
Researchers have reported a black phosphorus transistor that can be used as an alternative ultra-low power switch. A research team led by Professor Sungjae Cho in the KAIST Department of Physics developed a thickness-controlled black phosphorous tunnel field-effect transistor (TFET) that shows 10-times lower switching power consumption as well as 10,000-times lower standby power consumption than conventional complementary metal-oxide-semiconductor (CMOS) transistors.
The research team said they developed fast and low-power transistors that can replace conventional CMOS transistors. In particular, they solved problems that have degraded TFET operation speed and performance, paving the way to extend Moore’s Law.
In the study featured in Nature Nanotechnology last month, Professor Cho’s team reported a natural heterojunction TFET with spatially varying layer thickness in black phosphorous without interface problems. They achieved record-low average subthreshold swing values over 4-5 dec of current and record-high, on-state current, which allows the TFETs to operate as fast as conventional CMOS transistors with as much lower power consumption.
"We successfully developed the first transistor that achieved the essential criteria for fast, low-power switching. Our newly developed TFETs can replace CMOS transistors by solving a major issue regarding the performance degradation of TFETs,"Professor Cho said.
The continuous down-scaling of transistors has been the key to the successful development of current information technology. However, with Moore’s Law reaching its limits due to the increased power consumption, the development of new alternative transistor designs has emerged as an urgent need.
Reducing both switching and standby power consumption while further scaling transistors requires overcoming the thermionic limit of subthreshold swing, which is defined as the required voltage per ten-fold current increase in the subthreshold region. In order to reduce both the switching and standby power of CMOS circuits, it is critical to reduce the subthreshold swing of the transistors.
However, there is fundamental subthreshold swing limit of 60 mV/dec in CMOS transistors, which originates from thermal carrier injection. The International Roadmap for Devices and Systems has already predicted that new device geometries with new materials beyond CMOS will be required to address transistor scaling challenges in the near future. In particular, TFETs have been suggested as a major alternative to CMOS transistors, since the subthreshold swing in TFETs can be substantially reduced below the thermionic limit of 60 mV/dec. TFETs operate via quantum tunneling, which does not limit subthreshold swing as in thermal injection of CMOS transistors.
In particular, heterojunction TFETs hold significant promise for delivering both low subthreshold swing and high on-state current. High on-current is essential for the fast operation of transistors since charging a device to on state takes a longer time with lower currents. Unlike theoretical expectations, previously developed heterojunction TFETs show 100-100,000x lower on-state current (100-100,000x slower operation speeds) than CMOS transistors due to interface problems in the heterojunction. This low operation speed impedes the replacement of CMOS transistors with low-power TFETs.
Professor Cho said, “We have demonstrated for the first time, to the best of our knowledge, TFET optimization for both fast and ultra-low-power operations, which is essential to replace CMOS transistors for low-power applications.” He said he is very delighted to extend Moore’s Law, which may eventually affect almost every aspect of life and society. This study (https://doi.org/10.1038/s41565-019-0623-7) was supported by the National Research Foundation of Korea.
Publication:
Kim et al. (2020) Thickness-controlled black phosphorus tunnel field-effect transistor for low-power switches. Nature Nanotechnology. Available online at https://doi.org/10.1038/s41565-019-0623-7
Profile:
Professor Sungjae Cho
sungjae.cho@kaist.ac.kr
Department of Physics
http://qtak.kaist.ac.kr/
KAIST
Profile:
Seungho Kim, PhD Candidate
krksh21@kaist.ac.kr
Department of Physics
http://qtak.kaist.ac.kr/
KAIST
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2020.02.21 View 12227 -
New Graphene-Based Metasurface Capable of Independent Amplitude and Phase Control of Light
Researchers described a new strategy of designing metamolecules that incorporates two independently controllable subwavelength meta-atoms. This two-parametric control of the metamolecule secures the complete control of both amplitude and the phase of light.
A KAIST research team in collaboration with the University of Wisconsin-Madison theoretically suggested a graphene-based active metasurface capable of independent amplitude and phase control of mid-infrared light. This research gives a new insight into modulating the mid-infrared wavefront with high resolution by solving the problem of the independent control of light amplitude and phase, which has remained a long-standing challenge.
Light modulation technology is essential for developing future optical devices such as holography, high-resolution imaging, and optical communication systems. Liquid crystals and a microelectromechanical system (MEMS) have previously been utilized to modulate light. However, both methods suffer from significantly limited driving speeds and unit pixel sizes larger than the diffraction limit, which consequently prevent their integration into photonic systems.
The metasurface platform is considered a strong candidate for the next generation of light modulation technology. Metasurfaces have optical properties that natural materials cannot have, and can overcome the limitations of conventional optical systems, such as forming a high-resolution image beyond the diffraction limit. In particular, the active metasurface is regarded as a technology with a wide range of applications due to its tunable optical characteristics with an electrical signal.
However, the previous active metasurfaces suffered from the inevitable correlation between light amplitude control and phase control. This problem is caused by the modulation mechanism of conventional metasurfaces. Conventional metasurfaces have been designed such that a metaatom only has one resonance condition, but a single resonant design inherently lacks the degrees of freedom to independently control the amplitude and phase of light.
The research team made a metaunit by combining two independently controllable metaatoms, dramatically improving the modulation range of active metasurfaces. The proposed metasurface can control the amplitude and phase of the mid-infrared light independently with a resolution beyond the diffraction limit, thus allowing complete control of the optical wavefront.
The research team theoretically confirmed the performance of the proposed active metasurface and the possibility of wavefront shaping using this design method. Furthermore, they developed an analytical method that can approximate the optical properties of metasurfaces without complex electromagnetic simulations. This analytical platform proposes a more intuitive and comprehensively applicable metasurface design guideline.
The proposed technology is expected to enable accurate wavefront shaping with a much higher spatial resolution than existing wavefront shaping technologies, which will be applied to active optical systems such as mid-infrared holography, high-speed beam steering devices that can be applied for LiDAR, and variable focus infrared lenses.
Professor Min Seok Jang commented, "This study showed the independent control amplitude and phase of light, which has been a long-standing quest in light modulator technology. The development of optical devices using complex wavefront control is expected to become more active in the future."
MS candidate Sangjun Han and Dr. Seyoon Kim of the University of Wisconsin-Madison are the co-first authors of the research, which was published and selected as the front cover of the January 28 edition of ACS Nano titled “Complete complex amplitude modulation with electronically tunable graphene plasmonic metamolecules.”
This research was funded by the Samsung Research Funding & Incubation Center for Future Technology.
Publication:
Han et al. (2020) Complete Complex Amplitude Modulation with Electronically Tunable Graphene Plasmonic Metamolecules. ACS Nano, Vol. 14, Issue 1, pp. 1166-1175. Available online at https://doi.org/10.1021/acsnano.9b09277
Profile: Prof. Min Seok Jang, MS, PhD
jang.minseok@kaist.ac.kr
http://jlab.kaist.ac.kr/
Associate Professor
Jang Research Group
School of Electrical Engineering
Korea Advanced Institute of Science and Technology (KAIST)
http://kaist.ac.kr
Daejeon, Republic of Korea
Profile: Sangjun Han
sangjun.han@kaist.ac.kr
MS Candidate
School of Electrical Engineering
Korea Advanced Institute of Science and Technology (KAIST)
http://kaist.ac.kr
Daejeon, Republic of Korea
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2020.02.20 View 9543 -
New Catalyst Recycles Greenhouse Gases into Fuel and Hydrogen Gas
< Professor Cafer T. Yavuz (left), PhD Candidate Youngdong Song (center), and Researcher Sreerangappa Ramesh (right) >
Scientists have taken a major step toward a circular carbon economy by developing a long-lasting, economical catalyst that recycles greenhouse gases into ingredients that can be used in fuel, hydrogen gas, and other chemicals. The results could be revolutionary in the effort to reverse global warming, according to the researchers. The study was published on February 14 in Science.
“We set out to develop an effective catalyst that can convert large amounts of the greenhouse gases carbon dioxide and methane without failure,” said Cafer T. Yavuz, paper author and associate professor of chemical and biomolecular engineering and of chemistry at KAIST.
The catalyst, made from inexpensive and abundant nickel, magnesium, and molybdenum, initiates and speeds up the rate of reaction that converts carbon dioxide and methane into hydrogen gas. It can work efficiently for more than a month.
This conversion is called ‘dry reforming’, where harmful gases, such as carbon dioxide, are processed to produce more useful chemicals that could be refined for use in fuel, plastics, or even pharmaceuticals. It is an effective process, but it previously required rare and expensive metals such as platinum and rhodium to induce a brief and inefficient chemical reaction.
Other researchers had previously proposed nickel as a more economical solution, but carbon byproducts would build up and the surface nanoparticles would bind together on the cheaper metal, fundamentally changing the composition and geometry of the catalyst and rendering it useless.
“The difficulty arises from the lack of control on scores of active sites over the bulky catalysts surfaces because any refinement procedures attempted also change the nature of the catalyst itself,” Yavuz said.
The researchers produced nickel-molybdenum nanoparticles under a reductive environment in the presence of a single crystalline magnesium oxide. As the ingredients were heated under reactive gas, the nanoparticles moved on the pristine crystal surface seeking anchoring points. The resulting activated catalyst sealed its own high-energy active sites and permanently fixed the location of the nanoparticles — meaning that the nickel-based catalyst will not have a carbon build up, nor will the surface particles bind to one another.
“It took us almost a year to understand the underlying mechanism,” said first author Youngdong Song, a graduate student in the Department of Chemical and Biomolecular Engineering at KAIST. “Once we studied all the chemical events in detail, we were shocked.”
The researchers dubbed the catalyst Nanocatalysts on Single Crystal Edges (NOSCE). The magnesium-oxide nanopowder comes from a finely structured form of magnesium oxide, where the molecules bind continuously to the edge. There are no breaks or defects in the surface, allowing for uniform and predictable reactions.
“Our study solves a number of challenges the catalyst community faces,” Yavuz said. “We believe the NOSCE mechanism will improve other inefficient catalytic reactions and provide even further savings of greenhouse gas emissions.”
This work was supported, in part, by the Saudi-Aramco-KAIST CO2 Management Center and the National Research Foundation of Korea.
Other contributors include Ercan Ozdemir, Sreerangappa Ramesh, Aldiar Adishev, and Saravanan Subramanian, all of whom are affiliated with the Graduate School of Energy, Environment, Water and Sustainability at KAIST; Aadesh Harale, Mohammed Albuali, Bandar Abdullah Fadhel, and Aqil Jamal, all of whom are with the Research and Development Center in Saudi Arabia; and Dohyun Moon and Sun Hee Choi, both of whom are with the Pohang Accelerator Laboratory in Korea. Ozdemir is also affiliated with the Institute of Nanotechnology at the Gebze Technical University in Turkey; Fadhel and Jamal are also affiliated with the Saudi-Armco-KAIST CO2 Management Center in Korea.
<Newly developed catalyst that recycles greenhouse gases into ingredients that can be used in fuel, hydrogen gas and other chemicals.>
Publication:
Song et al. (2020) Dry reforming of methane by stable Ni–Mo nanocatalysts on single-crystalline MgO. Science, Vol. 367, Issue 6479, pp. 777-781. Available online at http://dx.doi.org/10.1126/science.aav2412
Profile: Prof. Cafer T. Yavuz, MA, PhD
yavuz@kaist.ac.kr
http://yavuz.kaist.ac.kr/
Associate Professor
Oxide and Organic Nanomaterials for the Environment (ONE) Laboratory
Graduate School of Energy, Environment, Water and Sustainability (EEWS)
Korea Advanced Institute of Science and Technology (KAIST)
http://kaist.ac.kr
Daejeon, Republic of Korea
Profile: Youngdong Song ydsong88@kaist.ac.kr
Ph.D. Candidate
Department of Chemical and Biomolecular Engineering
Korea Advanced Institute of Science and Technology (KAIST)
http://kaist.ac.kr
Daejeon, Republic of Korea
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2020.02.17 View 17399 -
COVID-19 Update: Precautionary Measures Reschedule Spring Semester to March 16
(Campus-wide preventive measures against the new coronavirus are being enforced.)
In response to the coronavirus outbreak, KAIST has decided to alter the academic calendar, postponing the opening of the spring semester until March 16, two weeks behind the original schedule. This is following the decision of the Deans’ Council to postpone or cancel the major academic ceremonies and events scheduled in February.
According to the decision, the commencement ceremony scheduled on February 21 will be postponed; meanwhile the freshmen orientation and matriculation ceremonies have been cancelled. Additionally, the ceremonies for the KAIST anniversary and faculty retirement ceremony scheduled on February 14 and the faculty workshop on February 27 have been postponed. There have been no confirmed coronavirus cases among the KAIST community as of February 6.
The university is also enhancing campus-wide precautionary safety measures to prevent the spread of the disease. The Facilities Management Office said that they will start disinfecting all dining facilities, cafeterias, libraries, lecture halls, and student halls for two days from Feb. 6. Plastic gloves are provided at cafeteria, which is using buffet spoons and tongs, and cafeteria patrons are being asked to wear the plastic gloves when they place food on their own plate in a preventive measure to avoid possible contact between individuals.
KAIST also launched a 24/7-hour Emergency Response Team and disseminated a response manual to KAIST community members. The Office of Student Life surveyed students, faculty, and staff to report if anyone has traveled to China or been in contact with visitors who made a trip to China within the last two weeks.
The university designated a building in one of the dorm complexes as a quarantine facility and a total of 11 people who visited China have been self-quarantined for two weeks from January 31.
Provost and Executive Vice President Kwang Hyung Lee explained in his letter to KAIST community members on February 4 that the university is exerting all possible measures and efforts against the spreading virus and asked for every member’s cooperation to prevent the further spread of the disease.
“Those who self-quarantined don’t have any symptoms. This is just a precautionary measure. The self-quarantine at our facility is only limited to those who declared that they do not have a legal residence in Korea,” said Provost Lee. The transportation to the facility is specially arranged and meal boxes are delivered to the quarantined room individually. A full-time guard in front of the isolated dorm building will be on duty 24 hours a day.
He explained the university chose the Hwaam Complex as the self-quarantine facility because each building in the complex is set apart from the others and each room has its own bathroom and shower facilities. Provost Lee said that the university will use another dorm complex if any current dorm residents where the quarantine facility has been set up wish to move to other dorm complexes.
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2020.02.06 View 4483 -
Rachmaninoff the most innovative of 18th and 19th century composers according to network science
Rachmaninoff, followed by Bach, Brahms and Mendelssohn, was the most innovative of the composers who worked during the Baroque, Classical and Romantic eras of music (1700 to 1900) according to a study published in the open access journal EPJ Data Science.
A team of researchers from KAIST (Korea Advanced Institute of Science and Technology), calculated novelty scores for 900 classical piano compositions written by 19 composers between approximately 1700 and 1900. The scores were based on how musical compositions differed from all prior pieces of piano music and how they differed from previous piano works by the same composer. The authors found that composers from the Romantic era (1820 to 1910) tended to have high novelty scores.
The authors from the Graduate School of Culture Technology at KAIST created a computer model which divided each composition into segments called ‘codewords’. Each ‘codeword’ consisted of all of the notes played together at a given time. Sequences of ‘codewords’ were then compared between compositions. The similarities between the sequences were used to create novelty scores for each composer and to determine the extent to which composers influenced each other.
Juyong Park, the corresponding author, said: “Our model allows us to calculate the degree of shared melodies and harmonies between past and future works and to observe the evolution of western musical styles by demonstrating how prominent composers may have influenced each other. The period of music we studied is widely credited for having produced many musical styles that are still influential today.”
The model distinguished each new musical period from the one before it by the rise of newly dominant and highly influential composers that indicated dramatic shifts in musical styles. The authors found that compositions from the Classical period (1750 to 1820) tended to have the lowest novelty scores. During this period Haydn and Mozart were highly influential but were later overtaken by Beethoven during the Classical-to-Romantic transitional period.
The most innovative composer, indicated by the highest combined novelty score, was Rachmaninoff. His work during the Romantic era was novel when compared to the compositions of the other 18 composers included in the study, and his later works were novel compared to his earlier works.
Lower novelty did not necessarily correlate with low influence. Beethoven was ranked in the lower half of novelty scores yet was the most influential composer during the Romantic period (1820 to 1910) and is widely considered one of the greatest composers of all time.
Dr. Park said: “While novelty is necessary in a creative work it cannot account for all the creative and artistic qualities that go into creating melodies and harmonies that spread to later generations of composers. That may be why being more novel did not necessarily result in composers being more influential.”
The authors suggest that their method could be applied to narrative or visual artworks by creating codewords from groups of words or colours and shapes. However, they caution that as only piano compositions were included in their analysis, it is unknown whether including all works by the 19 composers would have resulted in another composer being identified as the most original.
Profile: Prof. Juyong Park, PhD
juyongp@kaist.ac.kr
Graduate School of Culture Technology (CT)
Korea Advanced Institute of Science and Technology (KAIST)
https://www.kaist.ac.kr
Daejeon 34141, Korea
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2020.01.31 View 5178