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2018-10 29

[Academics][Researcher of the Month] New Technology of Patterning the Perovskite

Have you ever seen the integrated circuit in your device? A part of it, which resembles a tiny wafer, is called wafer. Before coming to be a part of our smartphones, laptops, and televisions, the wafer goes under a complex set of procedures, one step of which is lithography, also known as patterning. As the name suggests, lithography is imprinting patterns on a clean film or substrate. The traditional way of doing this is called photolithography, which, simply put, involves placing a photoresist mask with the pattern on top of the wafer and shooting a UV light so that the pattern is etched onto the wafer. However, there exists a problem with this method. In the field of solar cell and Light Emitting Diode (LED), a material that has been under spotlight for many years for its overpowering efficiency is named perovskite. However, this material is extremely unstable when met with water. Thus, in order to use it, it needs to be surrounded by polymer to make a composite. The problem lies in that the composite is almost impossible to stabilize and pattern using the traditional photolithography. Nevertheless, Professor Kang Young-jong (Department of Chemistry) made this possible, inventing a new patterning technique called, Size-exclusion lithography. A diagram of Perovskite and Size-exclusion lithography (Photo courtesy of Kang) What is Size-exclusion lithography? What Kang did was coat the wafer with a mixture of two materials, polymer and perovskite. When the wafer is shot with UV light, polymer as well as perovskite nanoparticles are created. The polymer starts to entangle in a chain shape, called a polymer mesh. It first increases in size but soon starts shrinking – on the other hand, perovskite nanoparticles become larger. Consequently, the nanoparticle escapes the polymer mesh and re-arranges itself, arriving at a phenomena called Size-expansion. Using this phenomena, Kang was able to make the pattern arrange by itself on the wafer, without the need of photolithography. This new technology is significant in many ways. First of all, what was deemed impossible (patterning of perovskite composite) was made possible. Also, since the process of etching is no longer necessary, the wafer-making process will be simpler. Moreover, when it comes to stability, the perovskite composite can edure a full day dipped in boiling water, as it had previously lost its function after only a couple of hours, mid-air. Kang Young-jong (Department of Chemistry) invented a new technology with better stability and a simpler process through this research. The remaining task Although a significant discovery, Kang says there are many more hurdles to jump over for an actual device to be complete. For that reason, there was recently a joining of a professor specializing in such a field, and the team is working together on developing LED using perovskite, ultimately leading to a completion of an actual device. Kang evaluates this finding as “ultimately, a contribution to the development of LED.” Kang gains the energy to keep on researching from his various hobbies. He enjoys the final outcome of a continuation of a hard process, and the future for his research seems bright. Lim Ji-woo il04131@hanyang.ac.kr Photos by Park Geun-hyung

2018-10 11

[Performance]Hanyang Ranked 5th in '2019 QS Graduate Employability Rankings'

Hanyang University ranked 121-130th worldwide in the '2019 QS Graduate Employability Rankings' announced on September 11, by QS(Quacquarelli Symonds), a British agency that conducts university evaluations. It has significant rised from 201st in 2017, to 201~250th in 2018 to 121~130th for the year of 2019. ▲2019 QS Graduate Employability Rankings Domestic University Ranking (Source: QS) This year's QS Graduate Employability Rankings was ranked by evaluating five indicators of the 666 universities in the world. The five indicators are: ▲ Employer reputation (30%) ▲ Partnership with employers (25%) ▲ Alumni outcomes (25%) ▲ Partnership with employers (10%) ▲ Graduate employment rate, were found that Hanyang University was highly evaluated evenly on the five indicators. The highest ranking among domestic universities was found by Seoul National University (23rd). In addition, 12 domestic universities including KAIST (76th), Sungkyunkwan University (79th), Yonsei University (93rd), Hanyang University (121-130th) and POSTECH (251-300th) are reported to be in the rankings. ▲2019 QS Graduate Employability Rankings Domestic University Ranking (Source: QS) The first place in the world is the Massachusetts Institute of Technology (MIT), followed by the Stanford University (2nd), UCLA (3rd), Harvard University (4th) and the University of Sydney (5th) were ranked as TOP5. ▶ Source: QS official website https://www.topuniversities.com/university-rankings/employability-rankings/2019

2018-10 08

[Academics][Excellent R&D] The Korean Imitation Game

Until just several decades ago, warfare was in the form of military, unlike today's contemporary world where the international society puts heavy emphasis on global peace. This, in other words, means the use of military force has become limited and instead, the role of information warfare has now become a crucial factor in defedning a country's existence. Professor Yoon Dong-weon (Department of Electronic Engineering) and the Signal Intelligence Research Center (SIRC) are now in charge of the frontline of signal intelligence alongside the Defense Acquisition Program Administration (DAPA). The Signal Intelligence Research Center (SIRC) A specialized research center refers to those who have been appointed in grafting the high leveled technology of the private sector into technology that is developed and used for the purpose of national defense. It is DAPA, which designates the specialized research centers, appointing the SIRC as the one responsible for signal intelligence until 2020. Being a six-year project, and being funded with 12.5 billion won in total, the SIRC is the first specialized research center to have a recurring demand troop. (From left) Professor Yoon Dong-weon (Department of Electronic Engineering) and Ahn Seong-jin (Department of Electronic Engineering, Master's Degree) are analyzing the signal codes. The center mainly consists of four laboratories, with each serving its own purpose: signal collection technology, signal processing technology, voice information technology, and code reconstruction technology. With Hanyang University taking the lead in the overall research, 17 schools and 34 professors in total are currently participating. Being a six-year project divided into mainly two stages, the center has successfully completed the first part of research and has moved on to the second stage in 2018. The Importance of Signal Intelligence (SIGINT) According to Yoon, who is the current director of the SIRC, one the most fundamental concepts of information warfare is signal intelligence, which is intelligence-gathering by the interception of signals. National intelligence is mainly divided in to two categories, which are tactical intelligence and strategic intelligence. Tactical intelligence refers to short-term information, whereas strategic intelligence focuses more upon long-term information. From this perspective, strategic intelligence is a comprehensive national intelligence that has to be studied and researched persistently. Consisting of imagery intelligence (IMINT), human intelligence (HUMINT), open-source intelligence (OSINT), and signal intelligence (SIGINT), it is SIGINT that is being mainly focused upon in the contemporary society and has to be studied in order to preserve the existence of a nation from a strategic level. Yoon is explaining the importance of signal intelligence in the contemporary society and how it should be persistently studied in order to defend the nation's existence. “Signal intelligence is once again divided into communication intelligence (COMINT), electronic intelligence (ELINT), and foreign instrumental signal intelligence (FISINT). Out of the three, it is communication intelligence that the research center is mainly focusing upon. It is easier if one thinks of the movie ‘The Imitation Game (Morten Tyldum, 2014)’ and how signal intelligence is used in defending the existence of the country,” explained Yoon. Yoon also mentioned that although we currently live in an era of peace, it is important to keep track of potential threats and consistently prepare ourselves, given that we are surrounded by countries that have strong abilities of signal intelligence. “SIRC will always lead an edge in defending national security and signal intelligence,” ended Yoon determinedly. Choi Seo-yong tjdyd1@hanyang.ac.kr Photos by Lee Jin-myung

2018-10 08

[Academics][Researcher of the Month] Increasing Charging Efficiency in Lithium-ion Battery

When a new phone launches, one can visibly notice that one of the main improvements are longer battery life with a faster charging speed. Needless to say, batteries are a crucial part of an electronic device and there are continuous developments made in order to increase their efficiency. Likewise, Professor Park Won-il (Division of Materials Science and Engineering) carried out experiments and research on the negative electrodes of lithium-ion batteries to improve the efficiency of battery charging. Along with various others, Park wrote a thesis with the title “Controlling electric potential to inhibit solid-electrolyte interphase formation on nanowire anodes for ultra fast lithium-ion batteries.” Professor Park Won-il (Division of Materials Science and Engineering) talks about how the experiments were carried out on the lithium-ion batteries. The lithium-ion battery is well-known as it is included in most wireless devices such as electric cars. The lithium-ion battery contains both a cathode, which is the positively charged electrode for batteries and an anode electrolyte, a negatively charged electrode. Park’s research was focused on the materials of the anode electrolyte. When a battery is running, a potential drop occurs between the cathode and electrolyte anode. Due to this drop, a solid-electrolyte interphase layer forms on the active material surface. Park focused on researching the active material that goes in the anode electrolyte in order to increase battery charging efficiency. Originally, the basic material utilized was graphite, which has the capacity of 360 mAh/g (milliampere hours per gram). However, to follow the demand of a higher capacity material, Park decided to implement Nickel Silicide, the capacity of which is 1300 mAh/g, four times that of graphite. Figure C shows how Nickel Silicide (NiSi) was utilized in order to inhibit solid-electrolyte interphase. (Photo Courtesy of Park) In the thesis, a three-dimensional macro graphite nano tube model to control the electric potential and prevent solid-electrolyte interphase utilizing Nickel Silicide was introduced. Solid-electrolyte interphase occurs when the potential drop, established between cathode and anode, drives to decompose the electrolyte and form a solid-electrolyte interphase layer. This enabled the potential drop to take place on the potential sheath instead of the active material surface. After countless experiments, up to two thousand, utilizing Nickel Silicide showed outstanding performance under 20C, taking less than a minute to fully charge. The capacity of a battery is generally rated at 1C, which means that it takes one hour to fully charge. (From left) Chang Won-jun (Division of Materials Science and Engineering, '16) and Professor Park Won-il (Division of Materials Science and Engineering) mentioned that the experiment was carried out more than two thousand times. When asked how long it took to complete the experiments, Chang Won-jun (Division of Materials Science and Engineering, ’16), who led the majority of experiments, said that they began in June of 2017, and their thesis submission and revision started at the end of December that year. Although the repetitive experiment proved that the performance of lithium-ion batteries utilizing Nickel Silicide was outstanding, deriving the precise evidence proving that solid-electrolyte interphase took place outside the surface was the task that took seven to eight months. Park concluded more research is still needed. In the current state, it will take more time for the newly developed structure to work. However, he hopes for the concept to be utilized on the betterment of lithium-ion batteries and become a breakthrough for battery charging in the future. Seok Ga-ram carpethediem@hanyang.ac.kr Photos by Park Kuen-hyung

2018-09 17

[Special][Card News] Setting a Good Example of Cooperation

▲ Click to read the English article - Setting a Good Example of Cooperation ▲ 카드뉴스의 원본 기사는 아래에서 읽을 수 있습니다 - 글로벌 한양, 중국유학생들을 위한 '맞춤형 지원' 노력

2018-09 07

[Academics]Professor Kim Tae-won (Division of Mechanical Engineering), developed survivability signal information technology

The death rate of firefighters was 38 per 100,000 people in 2017, which was 4.8 times that of the U.S. In the last five years, 438 police officers have died while on duty. As such, a group of job security workers have been exposed to numerous dangers. Those who need to be protected, such as emergency patients or the elderly living alone, are also vulnerable. Kim Tae-won, a professor in the Division of Mechanical Engineering, is studying ways to increase their survivability rate. It was selected by the Convergence Research Center (CRC) of the Ministry of Science and ICT's leading research center, developing 'Survivability Signal Information Technology'. Survivability Signal Information Survivability analysis techniques are based on changes in the state of the body and things caused by an accident. This technique can help save a person from an emergency. Bio-signals tell if a person lying on the road is asleep or physically dangerous. In the case of emergency patients, survivability indicators and information, such as viability, are derived through biological signals. The selected information is sent to the appropriate medical staff during transport to the emergency center. This information allows medical staff to prepare for emergency measures, including surgery. As the bio-signals enable quick judgment and response, the survivability rate of patients can be increased. Kim’s source technology based on survivability signal information is at the world’s highest level, which is expected to produce new concepts of invention. In recognition of the creativity and spirit of the research subjects, the research is being conducted through the support of the Korea Research Foundation, selected as a CRC (fusion field). It formed a business group with a joint research institute, including 10 core researchers, and students with master's and doctorate degrees. The total study period is seven years and consists of two stages. ▲ Professor Kim Tae-won (Division of Mechanical Engineering) explained that the study of survivability signal information involves experts from various fields such as social studies and psychology as well as mechanical engineering. For the past nine years, Kim studied basic technologies such as analysis and model development related to survivability skills at the Defense Specialized University Research Center. Now, beyond the survival of soldiers, his research has extended its coverage to civilian safety. In addition to the already proven track record, they have teamed up with experts in engineering, medicine, medical engineering, and social psychology to add further technologies. It integrates physical signals, body signals, and psychological analysis to enable more accurate index settings. "Reinterpreting physical signals and vital signs into psychological data to obtain the substantial information necessary for survivability." As the scope of application has expanded, it is to prepare for a number of risk factors. First, experts from various fields classified the 'work environment information', 'risk factors' and 'risk levels' to apply survivability information technology. In addition, it will conduct verification and empirical research development technologies through collaborating with relevant institutions, such as hospitals, fire and police departments. It is going to analyze physical and psychological risk factors and protection factors of each occupational group responsible for social safety, which will be linked to biometric recognition systems. The technology also identifies the relationship between vital signs, body and psychological data. This will help develop risk prevention programs and post-treatment programs for each occupational group. ▲ Along with the advancement of survivability signal information platform technology based on biometric measurements and analysis, psychosocial link survivability enhancement programs are also being developed. For more, more precious lives The empirical goal of the research is to build signal information measurement sensors, antennas, and communication systems into wearable forms and attach them to the human body. Through an invention with wearable sensors, it is planning to use it widely, from social safety to life safety. Based on IoT, it can be utilized in all fields such as Smart Home, Smart Car, Distribution Industry, Wearable Mobile, Health Care, and others. In order to effectively apply the survivability signal information technology, legal and institutional issues such as privacy and personal information laws should be solved together. "The technology to be developed through this research will contribute, not only to social safety workers, but also the physical and mental safety and health of the general public, including emergency patients,” said Kim. ▲ Professor Kim Tae-won (Division of Mechanical Engineering) poses with students who have conducted the research together.

2018-09 04

[Academics][Researcher of the Month] Internal Level Interaction Between the Cell and Sensory Organs

The minute you leave out a banana on your desk, fruit flies start to appear out of nowhere. Even when you think you have taken good care of the peel, the little creatures never fail to sniff out its location. While one may think they are simply annoying pests, professor Shim Ji-won (Department of Life Science) uses them as her main test subject for her studies. Shim Ji-won (Department of Life Science) explains that her experiment will surely help future clinical and applied research, August 31st, 2018. Shim recently published her study under the title of “Systemic Control of Immune Cell Development by Integrated Carbon Dioxide and Hypoxia Chemosensation in Drosophila.” Although the title itself may sound complicated, it is based on quite an interesting theory that the hypoxia-sensing neurons (hypoxia: oxygen deficiency in a biotic environment) that detect the level of CO2 and oxygen have a direct influence on the number of expanding blood cells. Shim’s findings indicate the link between environmental gas sensation and myeloid (relating to bone marrow / spinal cord) cell development in Drosophila, which in other words are--fruit flies. According to Shim, a similar relationship exists in humans, but the underlying mechanisms have yet to be established as the human anatomy is way too complex to see the direct interaction between the nerve and the immune system. Before divng into the details of the research, a bit of human anatomy is in order. Blood cells are created in the spinal cord and bone marrow, which also decide each cell’s function after receiving various signals from the brain through the nerve system. Functional cells are created according to the body’s state, fulfilling whatever is needed. This includes immune cells, which are created in response to something in the body that is not balanced or is under stress due to internal or external factors. Within the sensory organs, there also exists various receptors (organs or cells which are able to respond to light, heat, or other external stimuli and transmit a signal to a sensory nerve) that can each sense different things. Each of them would send signals to our nerve system which would then send signals to our spinal cord that creates the functional cells. The bottle where the fruit flies are kept. The bottom paste is the fruit flies' food consisting of sugar, corn, and flour. Regarding this matter, numerous studies on cell interaction with the external environment have already been conducted. The brain to blood cell interaction was an area that many researchers have researched, but there were not many done on the internal interactions such as from cell to cell interaction and its influence on the brain. In this sense, Shim’s study was revolutionary. Shim conducted her experiments by first creating mutated flies that did not have certain receptors. As a result, the ones without receptors that could sense CO2 showed drastic results. Because CO2 and oxygen are the two main conditions to human existence, the balance between the two is crucial. When the balance between the two levels breaks, as can be seen in the test results, it causes an internal change such as the increase in the number of cell expansion and immune reaction. This was quite revolutionary, as it meant that even without the brain’s direct order, the human body starts to create more functional blood cells as a response when the nerve system detects an imbalance in the CO2 and oxygen levels. Shim (in the center) and her students in the lab. “For humans, the nerve system is inside our body and is linked with so many different receptors, so it is too complex to research right away. However, for fruit flies, their nerve system also exists on the exterior, so that they are very much sensitive to external conditions. Also, it is easier to control it as I can simply get rid of a few receptors, and that could shut down one of their sensory organs. Now the interesting thing is, when we release high levels of CO2 near the fruit flies, they fly as far away as they can. Here I suspected that there must be a correlation between the sensory organs and the immune system which keeps the body in check, so I used fruit flies to test out this theory,” said Shim. Currently, various experiments are being carried out by Shim and her students relating to this study. The studies include a blood brain barrier interaction, a brain to blood interaction, a bi-directional interaction, and so on. Shim hopes that the studies conducted on the fruit flies will pave the road. “Our sensory organs and the nerve system greatly affect and are affected by the brain. For example, those with Alzheimer's cannot really smell things. This is because there is a neuro degeneration and incongruity in the immune system. We do not know how directly related the functions of the olfactory nerve and the brain are associated, but that is another research study to be done in the future after the fruit flies experiment,” said Shim. Park Joo-hyun julia1114@hanyang.ac.kr Photos by Kang Cho-hyun

2018-08 24

[Infographics]2 Hanyang graduates became prosecutor through the Korean bar examination

On August 1, among the 21 newly hired law school graduates who passed the fourth bar exam, two graduates are from Hanyang University (9.5 percent), ranked to be the sixth highest among major universities in Korea. According to the analysis of newly hired prosecutor's affiliated college (who passed the 4th bar exam), 5 of them(23.8%) graduated from Korea University, 3 from Seoul National ·Sungkyunkwan·Yonsei University and Postech respectively, and 2 graduated from Hanyang University(9.5%). When it comes to its status by age, 9 of them are 31 years old (42.9 %), 4 are 32 years old(19%), 4 are 28 years old(19%), 3 are 29 years old(14.3%) and one 1 is 33 years old(4.8%). ▶ Link for the article of the law journal (only in Korean)

2018-08 07

[Academics][Excellent R&D] Developing Revolutionary Energy Harvesters

As it is a global agenda to adopt a lifestyle that is more environmentally friendly, developing technology that allows eco-friendly processes and production outcomes has also shifted into focus. Professor Sung Tae-hyun's (Electrical Engineering) research on energy harvesting technology is a prime example that shines a ray of hope onto our path of sustainable development. According to research from Cambridge University, only 12 percent of electric power generated from a power plant is used, while the other 88 percent goes to waste. Consequently, "energy harvesing," the idea of saving and using the wasted energy, has become a crucial research topic for more effective and efficient use of energy generated. It would eiminate concerns about creating a completely different type of power plant or unintentionally harming the environment. "Energy harvesting technology will allow us to convert various types of wasted energy into usable energy,” said Sung. Sung Tae-hyun (Electrical Engineering) explains the different types of energy and how massive an amount of it is wasted. There are different types of convertible energies such as piezoelectric energy (electric energy created from vibration), heat energy (electric energy created from heat), and photovoltaic energy (electric energy created from lighting). Sung focused on piezoelectric and photovoltaic energy when researching energy harvesting technology. The purpose of his research was to successfully create an "energy harvestor" with a sensor that detects the different types of energy, then converts them accordingly to electric energy that is entirely usable and more environmentally friendly. “Sensor technology is actually the core of the Fourth Industrial Revolution since everything is connected through internet of things (IoT). It can detect anything anywhere without limitations, and that’s what would make the energy conversion process more efficient, especially in places where all types of energy are generated.” Energy harvestors demonstrated in a smart factory (Photo courtesy of Sung) Sung is in charge of Hanyang University's (HYU's) SEED laboratory that researches energy harvesting technology. In 2011, it even broke a record for retaining the world’s best piezoelectric energy harvesting data. According to Sung, he approached the energy waste problem by first communicating with the workers in the field, detecting and redefining the problem at hand, moving on to the ideation process, creating prototypes, and then testing it out to see if it was realistically applicable and effective. Sung is now in the process of testing out the developed energy harvestors in four big industries such as LED production, smart factories (industry where the whole production process is combined with digital automation solutions), and industries where both offices and production scenes are located in the same building and power plants. “Currently, we are working on the development and commercialization of applicable IoT sensors applied to energy harvestors, but we hope to create harvestors with massive energy conversion capacity in the future. Not letting any energy go to waste is the main goal,” said Sung. Sung explains the application process of energy havestors in various industries. Behind Sung’s passionate research, there was a strong drive that was truly inspirational. “Our lab is called the SEED lab, like the seed in an apple. You may know how many seeds are generally in an apple, but you never know how many of them will actually become an apple. It is the work of a miracle, and that is the kind of miracle that our lab members wish to achieve together. I ask myself, what kind of fruit am I expecting in 10 or 20 years when I’m planting this seed? In other words, what is my goal in life that takes the form of the fruit? There are so many people that eat the seed before it grows just to fulfill their self-interest. I’d say that those people are myopic, as they may be full and satisfied for the moment, but they will not be in the future. It sure takes a long time to grow and harvest the seed, but once it grows and starts to bear fruit, a never-ending cycle begins. One seed will bear hundreds of fruits ever year. So the next question is, how will you use these fruits? For me, that’s the question of what I want to achieve in my life, and my life goal is to give back the fruits I’ve harvested to the society, and spread the happiness.” Sung talks about his beliefs and philosophy, ending with some inspirational advice for Hanyang students. “I hope that I can share this belief with the Hanyang community. I hope that we can work together to grow the seeds of Hanyang into a strong tree that will bear many fruits, and spread the miracle to the world. That being said, I would like to tell the students not to be afraid of failure, to have a life-goal that can change the world, not to be devastated from failure, to always be positive but not conceited nor arrogant, and to love challenges. Our body is systematically goal-oriented, and once we have a goal, it becomes our drive to keep going even when we are tired. On top of that, if you think that our purpose in life is for the happiness of our community, then you will become a true global leader.” Park Joo-hyun julia1114@hanyang.ac.kr Photos by Choi Min-ju

2018-07 30

[Academics][Researcher of the Month] Observation of Unique Properties of Anti-PT-Symmetric Systems

Professor Song Seok-ho (Department of Physics) has recently announced his research on the observation of an Anti-Parity-Time (APT)-Symmetric exceptional point and energy-difference conserving dynamics in electric circuit resonators. When dividing an electric circuit in half, the two parts show a symmetric stream in both time and space. This is referred to as Parity-Time (PT) Symmetry, which enables electricity to flow in the same stream in both directions inside an electric circuit. By "breaking" the unidirectional converter, the symmetric stream of the forward and backward propagation differs, and the PT-Symmetric form is broken. This picture shows the breaking of the Parity-Time (PT) - symmetric form and how the flow of light changes. By breaking the symmetric middle part, the forms of foward and backward propagation differ, which allows for the creation of diodes. (Photo courtesy of Song) Breaking the PT-Symmetric form allows for the creation of diodes which are semiconductor devices that allow electricity to flow only in one direction and prevent any form of backward propagation. Being a key element of the flow of electricity within an electric circuit, the creation of photodiodes has been a long-term goal in the field of nanophotonics. Based upon the idea of substituting electricity with light, which would allow electric devices to be used with higher speed and energy efficiency, nanophotonics have long been troubled with a loss of energy due to the absence of diodes which allow the efficient flow of energy. Thus, Song’s current research of creating diodes through the "breaking" of PT Symmetries has significance, as it may provide a foothold for the creation of photodiodes. Song has verified his research by successfully breaking symmetries within electric circuits formed with resistance-electric condensers. The experimental process was made as simple as possible based upon the professor’s belief that easy verification leads to easy commercialization. “It is the process of thinking out ideas that should be given effort, whereas the experimental process should be done with ease,” explained Song. This can be seen in the fact that only simple devices with educational purposes were used in the verification of this research. Professor Song Seok-ho shared his research philosophy of the making process which should receive the bulk of time and effort. On the other hand, he mentioned that the experimental process should be conducted as simply as possible, as simple verification leads to simple commercialization. When asked of his future plans, Song explained how he has managed to break through one mere field of nanophotonics. He also maintained that “there are so many fields to overcome. By applying concepts to each field, breaking through the current limitations of physics is my next goal.” Succeeding with the observation of anti-PT-symmetries, it does not seem like it will be long before Song provides another foothold towards a novel breakthrough in the field of nanophotonics. Choi Seo-yong tjdyd1@hanyang.ac.kr Photos by Choi Min-ju