Department+of+Physics
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Observing Individual Atoms in 3D Nanomaterials and Their Surfaces
Atoms are the basic building blocks for all materials. To tailor functional properties, it is essential to accurately determine their atomic structures. KAIST researchers observed the 3D atomic structure of a nanoparticle at the atom level via neural network-assisted atomic electron tomography.
Using a platinum nanoparticle as a model system, a research team led by Professor Yongsoo Yang demonstrated that an atomicity-based deep learning approach can reliably identify the 3D surface atomic structure with a precision of 15 picometers (only about 1/3 of a hydrogen atom’s radius). The atomic displacement, strain, and facet analysis revealed that the surface atomic structure and strain are related to both the shape of the nanoparticle and the particle-substrate interface.
Combined with quantum mechanical calculations such as density functional theory, the ability to precisely identify surface atomic structure will serve as a powerful key for understanding catalytic performance and oxidation effect.
“We solved the problem of determining the 3D surface atomic structure of nanomaterials in a reliable manner. It has been difficult to accurately measure the surface atomic structures due to the ‘missing wedge problem’ in electron tomography, which arises from geometrical limitations, allowing only part of a full tomographic angular range to be measured. We resolved the problem using a deep learning-based approach,” explained Professor Yang.
The missing wedge problem results in elongation and ringing artifacts, negatively affecting the accuracy of the atomic structure determined from the tomogram, especially for identifying the surface structures. The missing wedge problem has been the main roadblock for the precise determination of the 3D surface atomic structures of nanomaterials.
The team used atomic electron tomography (AET), which is basically a very high-resolution CT scan for nanomaterials using transmission electron microscopes. AET allows individual atom level 3D atomic structural determination.
“The main idea behind this deep learning-based approach is atomicity—the fact that all matter is composed of atoms. This means that true atomic resolution electron tomogram should only contain sharp 3D atomic potentials convolved with the electron beam profile,” said Professor Yang.
“A deep neural network can be trained using simulated tomograms that suffer from missing wedges as inputs, and the ground truth 3D atomic volumes as targets. The trained deep learning network effectively augments the imperfect tomograms and removes the artifacts resulting from the missing wedge problem.”
The precision of 3D atomic structure can be enhanced by nearly 70% by applying the deep learning-based augmentation. The accuracy of surface atom identification was also significantly improved.
Structure-property relationships of functional nanomaterials, especially the ones that strongly depend on the surface structures, such as catalytic properties for fuel-cell applications, can now be revealed at one of the most fundamental scales: the atomic scale.
Professor Yang concluded, “We would like to fully map out the 3D atomic structure with higher precision and better elemental specificity. And not being limited to atomic structures, we aim to measure the physical, chemical, and functional properties of nanomaterials at the 3D atomic scale by further advancing electron tomography techniques.”
This research, reported at Nature Communications, was funded by the National Research Foundation of Korea and the KAIST Global Singularity Research M3I3 Project.
-Publication
Juhyeok Lee, Chaehwa Jeong & Yongsoo Yang
“Single-atom level determination of 3-dimensional surface atomic structure via neural network-assisted atomic electron tomography”
Nature Communications
-Profile
Professor Yongsoo Yang
Department of Physics
Multi-Dimensional Atomic Imaging Lab (MDAIL)
http://mdail.kaist.ac.kr
KAIST
2021.05.12 View 12664 -
Plasma Jets Stabilize Water to Splash Less
< High-speed shadowgraph movie of water surface deformations induced by plasma impingement. >
A study by KAIST researchers revealed that an ionized gas jet blowing onto water, also known as a ‘plasma jet’, produces a more stable interaction with the water’s surface compared to a neutral gas jet. This finding reported in the April 1 issue of Nature will help improve the scientific understanding of plasma-liquid interactions and their practical applications in a wide range of industrial fields in which fluid control technology is used, including biomedical engineering, chemical production, and agriculture and food engineering.
Gas jets can create dimple-like depressions in liquid surfaces, and this phenomenon is familiar to anyone who has seen the cavity produced by blowing air through a straw directly above a cup of juice. As the speed of the gas jet increases, the cavity becomes unstable and starts bubbling and splashing.
“Understanding the physical properties of interactions between gases and liquids is crucial for many natural and industrial processes, such as the wind blowing over the surface of the ocean, or steelmaking methods that involve blowing oxygen over the top of molten iron,” explained Professor Wonho Choe, a physicist from KAIST and the corresponding author of the study.
However, despite its scientific and practical importance, little is known about how gas-blown liquid cavities become deformed and destabilized.
In this study, a group of KAIST physicists led by Professor Choe and the team’s collaborators from Chonbuk National University in Korea and the Jožef Stefan Institute in Slovenia investigated what happens when an ionized gas jet, also known as a ‘plasma jet’, is blown over water. A plasma jet is created by applying high voltage to a nozzle as gas flows through it, which causes the gas to be weakly ionized and acquire freely-moving charged particles.
The research team used an optical technique combined with high-speed imaging to observe the profiles of the water surface cavities created by both neutral helium gas jets and weakly ionized helium gas jets. They also developed a computational model to mathematically explain the mechanisms behind their experimental discovery.
The researchers demonstrated for the first time that an ionized gas jet has a stabilizing effect on the water’s surface. They found that certain forces exerted by the plasma jet make the water surface cavity more stable, meaning there is less bubbling and splashing compared to the cavity created by a neutral gas jet.
Specifically, the study showed that the plasma jet consists of pulsed waves of gas ionization propagating along the water’s surface so-called ‘plasma bullets’ that exert more force than a neutral gas jet, making the cavity deeper without becoming destabilized.
“This is the first time that this phenomenon has been reported, and our group considers this as a critical step forward in our understanding of how plasma jets interact with liquid surfaces. We next plan to expand this finding through more case studies that involve diverse plasma and liquid characteristics,” said Professor Choe.
This work was supported by KAIST as part of the High-Risk and High-Return Project, the National Research Foundation of Korea (NRF), and the Slovenian Research Agency (ARRS).
Image Credit: Professor Wonho Choe, KAIST
Usage Restrictions: News organizations may use or redistribute these materials, with proper attribution, as part of news coverage of this paper only.
Publication: Park, S., et al. (2021) Stabilization of liquid instabilities with ionized gas jets. Nature, Vol. No. 592, Issue No. 7852, pp. 49-53. Available online at https://doi.org/10.1038/s41586-021-03359-9
Profile:
Wonho Choe, Ph.D.
Professor
wchoe@kaist.ac.kr
https://gdpl.kaist.ac.kr/
Gas Discharge Physics Laboratory (GDPL)
Department of Nuclear and Quantum Engineering
Department of Physics
Impurity and Edge Plasma Research Center (IERC)
http://kaist.ac.kr/en/
Korea Advanced Institute of Science and Technology (KAIST)
Daejeon, Republic of Korea
(END)
2021.04.01 View 11445 -
Deep-Learning and 3D Holographic Microscopy Beats Scientists at Analyzing Cancer Immunotherapy
Live tracking and analyzing of the dynamics of chimeric antigen receptor (CAR) T-cells targeting cancer cells can open new avenues for the development of cancer immunotherapy. However, imaging via conventional microscopy approaches can result in cellular damage, and assessments of cell-to-cell interactions are extremely difficult and labor-intensive. When researchers applied deep learning and 3D holographic microscopy to the task, however, they not only avoided these difficultues but found that AI was better at it than humans were.
Artificial intelligence (AI) is helping researchers decipher images from a new holographic microscopy technique needed to investigate a key process in cancer immunotherapy “live” as it takes place. The AI transformed work that, if performed manually by scientists, would otherwise be incredibly labor-intensive and time-consuming into one that is not only effortless but done better than they could have done it themselves. The research, conducted by the team of Professor YongKeun Park from the Department of Physics, appeared in the journal eLife last December.
A critical stage in the development of the human immune system’s ability to respond not just generally to any invader (such as pathogens or cancer cells) but specifically to that particular type of invader and remember it should it attempt to invade again is the formation of a junction between an immune cell called a T-cell and a cell that presents the antigen, or part of the invader that is causing the problem, to it. This process is like when a picture of a suspect is sent to a police car so that the officers can recognize the criminal they are trying to track down. The junction between the two cells, called the immunological synapse, or IS, is the key process in teaching the immune system how to recognize a specific type of invader.
Since the formation of the IS junction is such a critical step for the initiation of an antigen-specific immune response, various techniques allowing researchers to observe the process as it happens have been used to study its dynamics. Most of these live imaging techniques rely on fluorescence microscopy, where genetic tweaking causes part of a protein from a cell to fluoresce, in turn allowing the subject to be tracked via fluorescence rather than via the reflected light used in many conventional microscopy techniques.
However, fluorescence-based imaging can suffer from effects such as photo-bleaching and photo-toxicity, preventing the assessment of dynamic changes in the IS junction process over the long term. Fluorescence-based imaging still involves illumination, whereupon the fluorophores (chemical compounds that cause the fluorescence) emit light of a different color. Photo-bleaching or photo-toxicity occur when the subject is exposed to too much illumination, resulting in chemical alteration or cellular damage.
One recent option that does away with fluorescent labelling and thereby avoids such problems is 3D holographic microscopy or holotomography (HT). In this technique, the refractive index (the way that light changes direction when encountering a substance with a different density—why a straw looks like it bends in a glass of water) is recorded in 3D as a hologram.
Until now, HT has been used to study single cells, but never cell-cell interactions involved in immune responses. One of the main reasons is the difficulty of “segmentation,” or distinguishing the different parts of a cell and thus distinguishing between the interacting cells; in other words, deciphering which part belongs to which cell.
Manual segmentation, or marking out the different parts manually, is one option, but it is difficult and time-consuming, especially in three dimensions. To overcome this problem, automatic segmentation has been developed in which simple computer algorithms perform the identification.
“But these basic algorithms often make mistakes,” explained Professor YongKeun Park, “particularly with respect to adjoining segmentation, which of course is exactly what is occurring here in the immune response we’re most interested in.”
So, the researchers applied a deep learning framework to the HT segmentation problem. Deep learning is a type of machine learning in which artificial neural networks based on the human brain recognize patterns in a way that is similar to how humans do this. Regular machine learning requires data as an input that has already been labelled. The AI “learns” by understanding the labeled data and then recognizes the concept that has been labelled when it is fed novel data. For example, AI trained on a thousand images of cats labelled “cat” should be able to recognize a cat the next time it encounters an image with a cat in it. Deep learning involves multiple layers of artificial neural networks attacking much larger, but unlabeled datasets, in which the AI develops its own ‘labels’ for concepts it encounters.
In essence, the deep learning framework that KAIST researchers developed, called DeepIS, came up with its own concepts by which it distinguishes the different parts of the IS junction process. To validate this method, the research team applied it to the dynamics of a particular IS junction formed between chimeric antigen receptor (CAR) T-cells and target cancer cells. They then compared the results to what they would normally have done: the laborious process of performing the segmentation manually. They found not only that DeepIS was able to define areas within the IS with high accuracy, but that the technique was even able to capture information about the total distribution of proteins within the IS that may not have been easily measured using conventional techniques.
“In addition to allowing us to avoid the drudgery of manual segmentation and the problems of photo-bleaching and photo-toxicity, we found that the AI actually did a better job,” Professor Park added.
The next step will be to combine the technique with methods of measuring how much physical force is applied by different parts of the IS junction, such as holographic optical tweezers or traction force microscopy.
-Profile
Professor YongKeun Park
Department of Physics
Biomedical Optics Laboratory
http://bmol.kaist.ac.kr
KAIST
2021.02.24 View 13014 -
KAIST Celebrates 50-Year Anniversary with 2,712 New Graduates via 2021 Commencement Ceremony
KAIST is proud to announce the graduation of 2,712 students, including 668 PhDs and 1,331 master’s degree recipients. The pandemic could not stop the university from recognizing each graduate's remarkable and original achievements. A pandemic-proof blended commencement ceremony was held on Friday, February 19, and livestreamed to the graduates and their loved ones.
KAIST decided to take extra precautions to protect graduates and other attendees’ health and well-being.
For the virtual ceremony, only 83 out of the 2,712 graduates were invited to attend the ceremony in person. Graduates were divided into four groups to attend at four different places in Daejeon and Seoul campuses and watch the ceremony via Zoom. No family members or friends of the graduates were allowed to participate at the campus, but happily cheered the graduates via YouTube.
This year’s valedictorian, Hyun-Young Park from the School of Electrical Engineering, received the Award of the Minister of Science and ICT. Salutorian Yeh-Lin Cho from the Department of Materials Science and Engineering received the Award of the KAIST Board of Trustees, while the recipient of the KAIST Presidential Award was Min-Jae Kim from the Department of Bio and Brain Engineering. The Award of the KAIST Development Foundation Chairman and the KAIST Alumni Association Presidential Award were conferred to Kyung-Tae Kim from the Department of Physics and Min-Woo Jung from the Department of Civil and Environmental Engineering, respectively.
President Sung-Chul Shin, Chairman of the Board of Trustees Woo Sik Kim, and a very limited number of faculty members and administrative staff officiated the commencement ceremony from the KAIST Auditorium.
President Shin applauded the graduates’ hard work and dedication in his commencement speech. He also delivered a very special congratulatory message to the bachelor’s degree awardees.
“This year’s commencement is especially meaningful for me. I was appointed as the 16th president of KAIST on February 23, 2017, and met you for the first time on February 28 at the matriculation ceremony. We promised each other—as freshmen and as the first alumnus president—to do our best for the next four years,” President Shin recalled.
He added, “I have done my best to keep my promise, and now my term will end on February 22. Of course, the past four years were even more precious because you were all a part of it.”
In conclusion, President Shin said, “I am proud of you for keeping your end of the promise. Thank you for becoming who you are today. I have high hopes for the bright future that you will be shaping for KAIST and our society.”
The livestream ceremony is archived for viewing on KAIST's Official YouTube Channel.
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2021.02.19 View 9456 -
KAIST International Symposium Highlights the Value of Science through Global Collaboration
The presidents of three premier science and technology universities shared their belief that universities should move forward to embrace social changes while maintaining the importance of academics for future generations during the KAIST International Symposium on February 16.
The symposium, one of the events to celebrate KAIST’s 50th anniversary, highlighted the future role of universities over the next 50 years by hosting a panel featuring ETH Zurich President Joël Mesot, Caltech President Thomas Rosenbaum, and KAIST President Sung-Chul Shin. Members of the foreign diplomatic corps representing seven countries also explored the new model of global collaboration in the second session.
President Rosenbaum of Caltech said that even though society is changing, the role of universities will not be different since the value of knowledge will always be important. He said that universities must embrace change.
He said that universities should move forward fearlessly if they believe it would impact wider society positively. He added that universities should also be courageous enough to take a new path based on longer-term perspectives and lessons learned from successes. One of the roles of universities is to establish various hypotheses and possible prospects, raise doubts, and go forward with a strong will for the future generations to come.
He cited LIGO (the Laser Inerferometer Gravitational-wave Observatory), as a good example of a successful university-research collaboration. LIGO is funded by the National Science Foundation in the US and operated by Caltech and MIT. Approximately 1300 scientists from around the world, including the Max Planck Society in Germany and the Science and Technology Facilities Council in the UK, participate in the LIGO Scientific Collaboration. In 2019, the international team of scientists detected the collision of two black holes with masses about 142 times the mass of the sun in the most massive collision ever detected. MIT Physicist Rainer Weiss shared the Nobel Prize in Physics with Professor Barry Barish and Professor Kip Thorn from the Department of Physics at Caltech in recognition of their contribution to the LIGO detector and the observation of gravitational waves.
President Mesot of ETH Zurich stressed that universities should foster young talents well versed with creative thinking and entrepreneurship in this new era. He also said that COVID-19 has reaffirmed the importance of science and global collaborations beyond borders to address global challenges such as pandemics. President Mesot said COVID-19 has taught us the value of science and R&D, adding that the roll-out of a vaccine in only one year would have been impossible without the decades-long R&D foundation that universities and industries have established.
He also gave the example of the MRI as a reason universities should provide strong basic science research foundation. In 1944 in the US, Dr. Isidor Isaac Rabi won the Nobel Prize in Physics for his discovery of nuclear magnetic resonance. The MRI research inspired many ETH professors for further studies and led them to win the Nobel Prize in Physics in 1952 for their MRI basic theory and in 1991 the Nobel Prize in Chemistry with the development of high-resolution spectroscopy. “The MRI first started 80 years ago and still applies in today’s medicine. We should focus on research which will keep such value,” President Mesot said.
Meanwhile President Shin also said that the age of the Fourth Industrial Revolution has been deemed the "winner takes all" era. At this highly competitive time, R&D activities are more meaningful if they produce the world’s best, first, and only outcomes.
“We aim to achieve excellence in research with long-term innovative research support systems. We will conduct R&D activities that will lead the megatrends of the Fourth Industrial Revolution: hyper-connectivity, super-intelligence, and meta-convergence. In addition, we will double down to conduct forward-looking flagship research that will enhance the happiness and prosperity of all humanity in the areas of global warming, infectious diseases, bio-medicine, energy and environment, smart technology, and post-AI.”
Responding to one of the student’s question about what mindsets are expected of students enrolled in government-funded national universities, President Mesot made three suggestions. First, they should remember that they are privileged, so they should give back their talents to society. They should also be patient with what they are doing even when they don’t achieve the desired results. Lastly, they should remain open to new ideas and be flexible when encountering disruptions.
Seven diplomats stationing in Korea including Rob Rapson, US Charge d’Affairs ad Interim Rob Rapson, UAE Ambassador Abdulla Saif Al Nuaimi, Kenyan Ambassador Mwende Mwinzi, Danish Ambassador Einar Jensen, Pakistani Ambassador Mumtaz Zahar Baloch, Egyptian Ambassador Haem Fahmy, and UK Ambassador Simon Smith joined the second session themed KAIST for the Global Community.
They all agreed that KAIST is one of the shining examples of successful international collaboration stemming from the international aid loan from USAID. Five decades later, KAIST now is working to help the Kenyan government to establish Kenya KAIST with a 95-million US funding from the Korea Exim Bank.
While stressing the importance of global collaboration for inclusive growth in the global community, the seven diplomats gave their insights on the newly transforming global environment intertwined with COVID-19 and the Fourth Industrial Revolution.
In the face of global changes caused by emerging technologies and carbon neutrality, the ambassadors expressed a strong desire to make collaborations between KAIST and their countries to propel new innovations in industry and education in their countries.
2021.02.17 View 9275 -
Drawing the Line to Answer Art’s Big Questions
- KAIST scientists show how statistical physics can reveal art trends across time and culture. -
Algorithms have shown that the compositional structure of Western landscape paintings changed “suspiciously” smoothly between 1500 and 2000 AD, potentially indicating a selection bias by art curators or in art historical literature, physicists from the Korea Advanced Institute of Science and Technology (KAIST) and colleagues report in the Proceedings of the National Academy of Sciences (PNAS).
KAIST statistical physicist Hawoong Jeong worked with statisticians, digital analysts and art historians in Korea, Estonia and the US to clarify whether computer algorithms could help resolve long-standing questions about design principles used in landscape paintings, such as the placement of the horizon and other primary features.
“A foundational question among art historians is whether artwork contains organizing principles that transcend culture and time and, if yes, how these principles evolved over time,” explains Jeong. “We developed an information-theoretic approach that can capture compositional proportion in landscape paintings and found that the preferred compositional proportion systematically evolved over time.”
Digital versions of almost 15,000 canonical landscape paintings from the Western renaissance in the 1500s to the more recent contemporary art period were run through a computer algorithm. The algorithm progressively divides artwork into horizontal and vertical lines depending on the amount of information in each subsequent partition. It allows scientists to evaluate how artists and various art styles compose landscape artwork, in terms of placement of a piece’s most important components, in addition to how high or low the landscape’s horizon is placed.
The scientists started by analysing the first two partitioning lines identified by the algorithm in the paintings and found they could be categorized into four groups: an initial horizontal line followed by a second horizontal line (H-H); an initial horizontal line followed by a second vertical line (H-V); a vertical followed by horizontal line (V-H); or a vertical followed by a vertical line (V-V) (see image 1 and 2). They then looked at the categorizations over time.
They found that before the mid-nineteenth century, H-V was the dominant composition type, followed by H-H, V-H, and V-V. The mid-nineteenth century then brought change, with the H-V composition style decreasing in popularity with a rise in the H-H composition style. The other two styles remained relatively stable.
The scientists also looked at how the horizon line, which separates sky from land, changed over time. In the 16th century, the dominant horizon line of the painting was above the middle of the canvas, but it gradually descended to the lower middle of the canvas by the 17th century, where it remained until the mid-nineteenth century. After that, the horizon line began gradually rising again.
Interestingly, the algorithm showed that these findings were similar across cultures and artistic periods, even through periods dominated by a diversity in art styles. This similarity may well be a function, then, of a bias in the dataset.
“In recent decades, art historians have prioritized the argument that there is great diversity in the evolution of artistic expression rather than offering a relatively smoother consensus story in Western art,” Jeong says. “This study serves as a reminder that the available large-scale datasets might be perpetuating severe biases.”
The scientists next aim to broaden their analyses to include more diverse artwork, as this particular dataset was ultimately Western and male biased. Future analyses should also consider diagonal compositions in paintings, they say.
This work was supported by the National Research Foundation (NRF) of Korea.
Publication:
Lee, B, et al. (2020) Dissecting landscape art history with information theory. Proceedings of the National Academy of Sciences (PNAS), Vol. 117, No. 43, 26580-26590. Available online at https://doi.org/10.1073/pnas.2011927117
Profile:
Hawoong Jeong, Ph.D.
Professor
hjeong@kaist.ac.kr
https://www.kaist.ac.kr
Department of Physics
Korea Advanced Institute of Science and Technology (KAIST)
Daejeon, Republic of Korea
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2020.11.13 View 11957 -
Highly Efficient Charge-to-Spin Interconversion in Graphene Heterostructures
Researchers present a new route for designing a graphene-based active spintronic component
KAIST physicists described a route to design the energy-efficient generation, manipulation and detection of spin currents using nonmagnetic two-dimensional materials. The research team, led by Professor Sungjae Cho, observed highly efficient charge-to-spin interconversion via the gate-tunable Rashba-Edelstien effect (REE) in graphene heterostructures.
This research paves the way for the application of graphene as an active spintronic component for generating, controlling, and detecting spin current without ferromagnetic electrodes or magnetic fields.
Graphene is a promising spintronic component owing to its long spin diffusion length. However, its small spin-orbit coupling limits the potential of graphene in spintronic applications since graphene cannot be used to generate, control, or detect spin current.
“We successfully increased the spin-orbit coupling of graphene by stacking graphene on top of 2H-TaS2, which is one of the transition metal dichalcogenide materials with the largest spin-orbit coupling. Graphene now can be used to generate, control, and detect spin current,” Professor Cho said.
The Rashba-Edelstein effect is a physical mechanism that enables charge current-to-spin current interconversion by spin-dependent band structure induced by the Rashba effect, a momentum-dependent splitting of spin bands in low-dimensional condensed matter systems.
Professor Cho’s group demonstrated the gate-tunable Rashba-Edelstein effect in a multilayer graphene for the first time. The Rahsba-Edelstein effect allows the two-dimensional conduction electrons of graphene to be magnetized by an applied charge current and form a spin current. Furthermore, as the Fermi level of graphene, tuned by gate voltage, moves from the valence to conduction band, the spin current generated by graphene reversed its spin direction.
This spin reversal is useful in the design of low-power-consumption transistors utilizing spins in that it provides the carrier “On” state with spin up holes (or spin down electrons) and the "Off" state with zero net spin polarization at so called “charge neutrality point” where numbers of electrons and holes are equal.
“Our work is the first demonstration of charge-to-spin interconversion in a metallic TMD (transition-metal dichalcogenides) and graphene heterostructure with a spin polarization state controlled by a gate. We expect that the all-electrical spin-switching effect and the reversal of non-equilibrium spin polarization by the application of gate voltage is applicable for the energy-efficient generation and manipulation of spin currents using nonmagnetic van der Waals materials,” explained Professor Cho.
This study (https://pubs.acs.org/doi/10.1021/acsnano.0c01037) was supported by the National Research Foundation of Korea.
Publication:
Lijun Li, Jin Zhang, Gyuho Myeong, Wongil Shin, Hongsik Lim, Boram Kim, Seungho Kim, Taehyeok Jin, Stuart Cavill, Beom Seo Kim, Changyoung Kim, Johannes Lischner, Aires Ferreira, and Sungjae Cho, Gate-Tunable Reversible Rashba−Edelstein Effect in a Few-Layer Graphene/2H-TaS2 Heterostructure at Room Temperature. ACS Nano 2020. Link to download the paper: https://pubs.acs.org/doi/10.1021/acsnano.0c01037
Profile:
Professor Sungjae Cho, PhD
sungjae.cho@kaist.ac.kr
http://qtak.kaist.ac.kr
Department of Physics
Korea Advanced Institute of Science and Technology (KAIST)
https://www.kaist.ac.kr
Daejeon 34141, Korea
2020.05.18 View 10497 -
14-Day Drawing Challenge Helps Maintain a Sense of Connection Amid Prolonged Social Distancing
- “You need space, but you also need connections.” -
Schools and workplaces have closed and people are staying at home around the globe. Governments across the world have urged their people to keep a distance from others as a measure to slow the spread of the pandemic.
With the Korean government’s decision to extend the intensive social distancing campaign until at least April 19, people in Korea are advised to avoid nonessential trips, public facilities, and social gatherings for another two weeks or so.
This unprecedented prolonged social distancing drive leads people to feel fatigue and frustration. Such emotional stress is worse for those who live alone in a foreign country.
The International Scholar and Student Services (ISSS) Team at KAIST has been working around the clock to build a dedicated COVID-19 Mental Health Support Service to support the university’s international community on campus and abroad and help get them connected online.
As the COVID-19 situation lingers, there has been a growing demand for mental health support from many KAIST international members including 299 students who have been staying in Korea on their own and away from their families, as well as from those who could not return to campus from their overseas homes.
In response to this, the KAIST ISSS Team has been offering some special online events and programs that can help the KAIST international community stay feeling connected whereever they are, while still keeping a safe distance from each other.
For instance, the team is running an art-therapy program called ‘The 14-day Drawing Challenge’ March 30 through April 12. This program is online and individual-based, so it does not require any physical contact between participants.
Each participant is asked to draw a picture at home using the daily topics previously set by the ISSS Team over 14 days. The topics include (Day 1) self-portrait, (Day 2) spring flowers, (Day 3) if you could become anything…, (Day 4) funniest memory you have, (Day 5) animals at KAIST, (Day 6) something you love, (Day 7) country or city you want to visit, (Day 8) what’s for dinner? (Day 9) person you miss, (Day 10) your favorite place at KAIST, (Day 11) your feeling today, (Day 12) things in your favorite color, (Day 13) song lyrics, and (Day 14) your future self in 10 years.
Once all 14 pieces have been completed, submissions can be made online by sending an e-mail to the ISSS Team after scanning or taking a photo of each drawing. Selected submissions will be awarded small prizes for participation and shared through the university’s official website and SNS channels.
“All the participants need is paper, coloring tools, and their creativity and imagination. They don’t have to be a great artist to join this challenge. There is no right or wrong or good or bad. They just need to have fun drawing every day for two weeks, ease their coronavirus anxiety, and remain emotionally stable just like they did back in the normal days,” said Su-yeon Ahn, the manager of the KAIST ISSS Team. She added, “In times like these, you need space, but you also need connections. Our team wants our international students, professors, and researchers to build strong connections with each other, even online.”
Katherine Michelle Pena Santana, an M.S. candidate from the Department of Industrial and Systems Engineering who is taking part in ‘The 14-day Drawing Challenge,’ looked back and said, “Lately with the new coronavirus spreading around Korea and the entire world, I was feeling very anxious. I didn't get out of my room and lived by just looking at the same walls and creating some kind of a psychological burden on myself.”
Santana added that these kinds of activities could give many foreign members of KAIST an opportunity to not only relieve fear and stress, but also share each other’s experiences dealing with this pandemic. She explained that this is why she decided to participate in this challenge.
An undergraduate student from the Department of Physics, Ada Carpenter, appreciated the KAIST ISSS Team’s efforts to provide a variety of special online mental health support services to help the university’s international community socialize, while strictly following the government’s guidelines for social distancing. She expressed excitement about participating and said, “I’m so looking forward to the challenge of things that I wouldn’t normally draw.”
< Short Self-interview Video Clip Filmed by Ada Carpenter >
The COVID-19 Mental Health Support Service by the KAIST ISSS Team will be continually updated with new information and enhanced with other tools and support over the coming weeks and months. Some of the upcoming events and programs include ‘The Online Guitar Lessons’, ‘The Growing Houseplants Challenge’, and ‘The Any Song Challenge*’.
* The song titled “Any Song” by Korean rapper Zico has been gaining attention on social media thanks to many celebrities taking on the ‘Any Song Challenge’, performing a short dance to the chorus of the song and sharing it on social media.
(END)
2020.04.08 View 11086 -
Highly Efficient and Stable Double Layer Solar Cell Developed
Solar cells convert light into energy, but they can be inefficient and vulnerable to the environment, degrading with, ironically, too much light or other factors, including moisture and low temperature. An international research team has developed a new type of solar cell that can both withstand environmental hazards and is 26.7% efficient in power conversion.
They published their results on March 26 in Science.
The researchers, led by Byungha Shin, a professor from the Department of Materials Science and Engineering at KAIST, focused on developing a new class of light-absorbing material, called a wide bandgap perovskite. The material has a highly effective crystal structure that can process the power needs, but it can become problematic when exposed to environmental hazards, such as moisture. Researchers have made some progress increasing the efficiency of solar cells based on perovskite, but the material has greater potential than what was previously achieved.
To achieve better performance, Shin and his team built a double layer solar cell, called tandem, in which two or more light absorbers are stacked together to better utilize solar energy. To use perovskite in these tandem devices, the scientists modified the material’s optical property, which allows it to absorb a wider range of solar energy. Without the adjustment, the material is not as useful in achieving high performing tandem solar cells. The modification of the optical property of perovskite, however, comes with a penalty — the material becomes hugely vulnerable to the environment, in particular, to light.
To counteract the wide bandgap perovskite’s delicate nature, the researchers engineered combinations of molecules composing a two-dimensional layer in the perovskite, stabilizing the solar cells.
“We developed a high-quality wide bandgap perovskite material and, in combination with silicon solar cells, achieved world-class perovskite-silicon tandem cells,” Shin said.
The development was only possible due to the engineering method, in which the mixing ratio of the molecules building the two-dimensional layer are carefully controlled. In this case, the perovskite material not only improved efficiency of the resulting solar cell but also gained durability, retaining 80% of its initial power conversion capability even after 1,000 hours of continuous illumination. This is the first time such a high efficiency has been achieved with a wide bandgap perovskite single layer alone, according to Shin.
“Such high-efficiency wide bandgap perovskite is an essential technology for achieving ultra-high efficiency of perovskite-silicon tandem (double layer) solar cells,” Shin said. “The results also show the importance of bandgap matching of upper and lower cells in these tandem solar cells.”
The researchers, having stabilized the wide bandgap perovskite material, are now focused on developing even more efficient tandem solar cells that are expected to have more than 30% of power conversion efficiency, something that no one has achieved yet,
“Our ultimate goal is to develop ultra-high-efficiency tandem solar cells that contribute to the increase of shared solar energy among all energy sources,” Shin said. “We want to contribute to making the planet healthier.”
This work was supported by the National Research Foundation of Korea, the Korea Institute of Energy Technology Evaluation and Planning, the Ministry of Trade Industry and Energy of Korea, and the U.S. Department of Energy.
Other contributors include Daehan Kim, Jekyung Kim, Passarut Boonmongkolras, Seong Ryul Pae and Minkyu Kim, all of whom affiliated with the Department of Materials Science and Engineering at KAIST. Other authors include Byron W. Larson, Sean P. Dunfield, Chuanxiao Xiao, Jinhui Tong, Fei Zhang, Joseph J. Berry, Kai Zhu and Dong Hoe Kim, all of who are affiliated with the National Renewable Energy Laboratory in Colorado. Dunfield is also affiliated with the Materials Science and Engineering Program at the University of Colorado; Berry is also affiliated with the Department of Physics and the Renewable and Sustainable Energy Institute at the University of Colorado Boulder; and Kim is also affiliated with the Department of Nanotechnology and Advanced Materials Engineering at Sejong University. Hee Joon Jung and Vinayak Dravid of the Department of Materials Science and Engineering at Northwestern University; Ik Jae Park, Su Geun Ji and Jin Young Kim of the Department of Materials Science and Engineering at Seoul National University; and Seok Beom Kang of the Department of Nanotechnology and Advanced Materials Engineering of Sejong University also contributed.
Image credit: Professor Byungha Shin, 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: Kim et al. (2020) “Efficient, stable silicon tandem cells enabled by anion-engineered wide band gap perovskites”. Science. Available online at https://doi.org/10.1126/science.aba3433
Profile:
Byungha Shin
Professor
byungha@kaist.ac.kr
http://energymatlab.kaist.ac.kr/
Department of Materials Science and Engineering
KAIST
Profile:
Daehan Kim
Ph.D. Candidate
zxzx4592@kaist.ac.kr
http://energymatlab.kaist.ac.kr/
Department of Materials Science and Engineering
KAIST
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2020.03.27 View 21437 -
COVID-19 Update: Students and Professors Adjust to 1,200 Online Classes
- Approximately 1,200 online classes are being offered during the cyber semester. -
COVID-19 is transforming the way KAISTians live. Many restrictions imposed to contain the spread of the virus have us adjusting to a new environment swiftly. A cyber MOU signing ceremony with a foreign partner university took place on March 25, as did a cyber Board of Trustees Meeting on March 26. KAIST’s Main Campus is normally one of the most iconic picnic destinations for the citizens of Daejeon, but this is not the case this spring, as the campus has been temporarily closed to protect our own community as well as our neighboring communities.
KAIST has been offering approximately 1,200 courses remotely since this semester opened on March 16 and will do so until further notice. Students and faculty members are experiencing the newly emerging norms of remote education in this time of social distancing. This unexpected disruption might advance the new digital pedagogy at KAIST, which was already ahead of the curve with its online learning and teaching infrastructure.
Professor Youngsun Kwon, the Dean of KAIST Academy and the Director of the Center for Excellence in Learning and Teaching, said, “We had already initiated the KAIST Learning Management System (KLMS) in 2011 for introducing flipped learning, a student-centric creative-learning pedagogy. Since then, about nine percent of all our classes have been run using this methodology. Students pre-study the online streaming lecture materials that professors have uploaded in advance outside the classroom, and in-class activities are mainly group discussions and problem-solving activities.”
According to Dean Kwon, the university was planning to further introduce real-time online education from this spring semester and were in the process of setting up the system started from last year. “Our plan was to connect the real-time video conferencing service Zoom to our existing remote educational platform KLMS. However, things related to COVID-19 all happened so rapidly that we didn’t yet have a full-fledged connection,” said Dean Kwon.
Professors had to choose either to conduct their lectures remotely in the form of a pre-made one-way lesson or a real-time two-way lesson. They could also modify them using both platforms. Professor Youngchul Kim from the Department of Civil and Environmental Engineering said, “I had to also make some changes in my class activities and assignments. I removed a group design project and some tutorial workshops that were meant to provide students with hands-on experience using design tools such a 3D printer and a laser cutting system. Ironically, I found that students seem to focus on online lectures more intensely than I expected. I feel like students give me their thoughts and respond much quicker as well.”
Unfortunately, the online learning and teaching infrastructure and resources that had been put in place could not handle the overwhelming volume of classes being uploaded over very short period of time.
To handle the new demand, IT technicians are setting up the technical environment with stable servers to improve network traffic. For professors, teaching assistants, and students to teach and learn better in an online space, department offices have been lending spare equipment such as laptops, tablets, headsets, and webcams to those who do not have their own, based on availability. Academic support staff have also been pitching in by developing the best guidelines for online training.
“Even in these uncharted waters, all of the members of KAIST are doing their best to keep the ship steadily sailing in the right direction. I am very grateful for everyone’s efforts to make things work,” said Dean Kwon.
About 60% of the courses currently offered online are being uploaded using the non-real-time KLMS, and the remaining 40% are run in real time via Zoom. Each class runs for 50 minutes per academic credit, and comprises at least 25 minutes of lecture, a Q&A session, and a group discussion.
Students enrolled in the 481 courses that include experiments are asked to conduct their experiments individually after watching a 50-minute online lecture. Experimental, practical, and physical courses that are impossible to provide online have been cancelled or postponed until the next semester or summer/winter breaks.
“I find the online lessons quite convenient for the courses that I am taking this semester, especially the non-real-time ones, because I can watch the lecture videos over and over again even after the class has finished to understand the contents better,” said Jaymee Palma, an undergraduate student from the Department of Chemistry.
Ada Carpenter, an undergraduate student from the Department of Physics, added, “Students who normally feel uncomfortable speaking in class raise their questions on an online Q&A board more easily. Besides, I saw many other students asking questions and leading a discussion verbally as well. I think, when students join a synchronous Zoom classroom, they are more engaged than when just attending a regular lecture in a conventional classroom. It’s like everyone can sit in the front row of the class.”
Still, there are reportedly pedagogical, logistical, and technological challenges to these extraordinary educational measures. Some students express concerns about keeping up with professors and other students if they don’t have sufficient technological knowledge and skills. Some also cite the disadvantage of online classes having much less interaction and engagement among students and between professors and students than offline ones. “Fortunately, I think my professors are all excellent, so I can immerse myself well during all my cyber classes,” said Sang-Hyeon Lee, a graduate student from the School of Computing.
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2020.03.26 View 9800 -
‘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 11884 -
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 16529