Semiconductors are the basis of all modern electronics—from the smallest switches in the widely prevalent personal computers and smartphones to large-area displays in various information media. The conducting properties (e.g. currents passing more easily in one direction than the other, variable resistance, etc.) of these materials are made truly useful because they may be purposely altered through doping, which is the deliberate and controlled introduction of impurity atoms into the crystal structure.

Through recent advancements in the field, two-dimensional semiconductors (natural semiconductors with thicknesses on the atomic scale) and complex electronics based on them have tantalized potentials for myriad applications such as nano-circuitry and flexible electronics, but the efficient assembly of complex 2D devices on integrated circuits requires novel scalable procedures not yet realized. Now, collaborative research led by POSTECH has successfully developed a process to directly write integrated circuits on a 2D semiconductor using visible laser.

Professor Moon-Ho Jo, from the Department of Materials Science and Engineering, fabricated integrated circuits (ICs) on a 2D semiconductor (2H-MoTe2) using a self-aligned doping approach with a scanning visible light probe. The research team demonstrated that this elegant approach of programmable doping is not only accurate and reliable but also efficient. This achievement was published in Nature Electronics as an editorial selection for the celebration of the 60 years of the ICs.

The team used chemical vapor deposition and mechanical exfoliation methods to deposit metal patterns onto 2H-MoTe2 semiconductor layers and created otherwise pristine (nominally undoped) n-type semiconductors. At this point, laser was selectively scanned over the metal patterns. The team discovered that the MoTe2 channels between the illuminated contacts displayed p-type semiconductor characteristics. In other words, the team developed a reliable, controllable and efficient method of p-type doping for 2D semiconductors.

Professor Jo expressed his anticipation in applying this new approach to the development of massively parallel circuitry based on 2D semiconductors as this method allows for accurate and quick writing of 2D circuits with both n-type and p-type characteristics on the same atomic plane.

This work was supported in part by the Institute for Basic Science (IBS) and the National Research Foundation of Korea.

The Korean Mathematical Society awarded Professor Youngju Choie with the prestigious KMS Prize at the 2018 Joint Meeting of the Korean Mathematical Society and the German Mathematical Society.

Since 1982, the prize has been annually given to the top mathematician in Korea. This year’s prize is made even more notable due to the fact that Professor Choie became the first ever female recipient of the prize. Hyang-Sook Lee, the President of the Korean Mathematical Society, expressed her excitement and said, “The KMS Prize represents a lifelong dedication to excellence in mathematics. As such, I am delighted to present the prize to its first female recipient.”

After receiving her Ph.D. from Temple University, Professor Choie has been with the Department of Mathematics at POSTECH since 1990. An expert of number theory and modular forms, Professor Choie’s contributions into research of L-functions was credited for the decision to bestow the highest honor given by the Korean Mathematical Society.

Professor Choie is also a Member of the Board of Trustees of the National Research Foundation of Korea, the President of the Korean Women in Mathematical Sciences, and a Fellow of the American Mathematical Society.

Global Night @POSTECH

Friday, November 9, 2018

(Video to be uploaded)

Pyrotechnics—from the Greek words pyro (fire) and tekhnikos (made by art)—is the science of materials capable of self-contained and self-sustained exothermic chemical reactions that produce heat, light, gas, smoke, and/or sound. Aside from spectacular fireworks displays, pyrotechnics permeate our daily lives through safety matches, automotive airbags, and military applications, among others. The mechanical applications of pyrotechnics through pyrotechnic mechanical devices (PMD) are prevalent in critical industries such as aerospace and national defense.

As the old saying ‘keep your powder dry’ goes, the proper management and maintenance of PMDs are essential not only to maximize their reliability and efficiency but also for the safety of its users. Accordingly, the aging of propellants of the PMDs is considered one of the primary factors of the performance and maintenance, but extensive research into the subject has been sparse. Now, collaborative research conducted by POSTECH and Pukyong National University has uncovered the chemistry behind the aging mechanism of Boron Potassium Nitrate (BKNO₃)—one of the most commonly used commercial propellants.

PMDs, and by extension, its propellants, must have long-term stability for reliable usage whenever the situation arises. However, the aging phenomena of PMDs mean that they must be disposed periodically to minimize safety concerns in critical applications. The research team recognized the importance of shedding light on the underpinnings of the aging mechanism to increase the disposal period that would in turn lead to economic efficiency and greater safety in industries like aerospace and national defense.

Professor Taiho Park from the Department of Chemical Engineering at POSTECH and Professor Yong Sun Won from Pukyong National University used X-ray photoelectron spectroscopy and transmission electron microscopy to verify the formation of oxide shells on the surface of the boron particles from exposure to humidity, which in turn decreased its efficacy. This achievement was published in the world-renowned Scientific Reports.

During their investigation into the aging mechanism of BKNO₃, the team was able to rule out extraneous internal factors and discovered that humidity levels affected the heat of reaction and reaction rate. Through TEM-EDS studies, they found that the thickness of the resulting oxide shells gradually increased through prolonged exposure to humidity and were reciprocally related to its efficacy.

Professor Park expressed his excitement in applying this new understanding of the aging mechanism of BKNO₃ to not only broaden the understanding of PMDs, but also to increase its safety and contribute to the minimization of economic loss by prolonging their disposal period.

This work was supported in part by the Agency for Defense Development under the Precise Energy Release for the Pyrotechnic Mechanical Device program.

On behalf of K-STAR (Korean Universities for Science & Technology and Advanced Research), President Doh-Yeon Kim signed into effect the first multilateral MOU of the cooperative initiative with the INSA Group (Institut National des Sciences Appliquées) of France.

President Kim, representing K-STAR, attended the signing ceremony held on the 15^th in Paris alongside M’Hamed Drissi, Directeur de l’INSA Rennes. As part of South Korean President Moon Jae-in’s visit to France, the respective Ministers from both countries (Korea’s Ministry of Science and ICT and France’s Ministry of Higher Education, Research and Innovation) also attended the ceremony.

As the alliance of leading STEM universities in Korea, K-STAR is comprised of KAIST, DGIST, GIST, UNIST, and POSTECH. The INSA Group is the leading French group of grande écoles and is comprised of 6 INSA institutes: Centre Val de Loire, Lyon, Rennes, Rouen, Strasbourg, and Toulouse. The collaborative activities between the two national networks will include academic and student exchanges to foster international cooperation between and Korea and France.

The multilateral agreement between K-STAR and INSA Group is expected to usher in a new vibrant era of robust partnership in science and technology for both nations.

From the cargo ships and airplanes traversing the globe to the automobiles and buildings sprawled throughout the landscape, much of the modern world is built with and upon alloys such as steel. Metallurgists throughout history have passionately struggled to develop novel alloys that are both strong and ductile—properties often diametrically opposed but collectively desired. According to collaborative research conducted by POSTECH and KTH – Royal Institute of Technology, the development of an alloy that surpasses the existing limitation of strength and ductility may soon be possible.

Traditional alloys are usually composed of a main metal, such as iron, and small percentages of different elements, such as carbon. A small percentage of carbon (under 2%) combined with iron produces steel, which is a thousand-fold stronger than pure iron. In contrast to the base element paradigm, high-entropy alloys (HEAs) are new substances that are fabricated with equal or nearly equal quantities of multiple metals, and as such, may have highly desirable properties not found in nature. For example, a popular HEA among researchers is the CoCrFeMnNi, which has been found to have extremely high fracture toughness where both ductility and yield strength increase as the temperature decreases. However, many HEAs with such alluring properties are not thermodynamically stable under normal conditions, and consequently, further in-depth research has been limited.

Professor Se Kyun Kwon from the Graduate Institute of Ferrous Technology at POSTECH and Professor Levente Vitos from KTH used first-principle quantum mechanical tools to demonstrate that a deformation mechanism known as twinning could be precisely controlled to design HEAs with qualities that shatter current limitations. This achievement was published in the world-renowned journal Nature Communications.

Twinning is one of the fundamental modes by which metals and alloys can deform plastically. At the atomic level, alloys are made up of a grid-like structure. Under the appropriate amount of stress, the alloy will deform according to one of the deformation mechanisms. The research team’s theory demonstrated that the control of the specific mechanism is feasible, by which researchers will be able to “facilitate the optical harvesting of their properties.”

Professor Kwon expressed his excitement in applying this new understanding of the plasticity of HEAs to further research on not only designing but developing novel alloys with superb properties for usage in extreme and harsh conditions.

This work was supported in part by the Swedish Research Council, the Swedish Foundation for Strategic Research, and the National Research Foundation of Korea.

Professor Kimoon Kim (Director, Center for Self-assembly and Complexity, IBS) has published the first textbook on cucurbiturils entitled Cucurbiturils: Chemistry, Supramolecular Chemistry and Applications through the world-renowned World Scientific.

Once considered a peculiarity, cucurbiturils—molecules shaped like a hollow pumpkin—has since been propelled to the forefront of supramolecular chemistry due to their suitability as hosts for an array of neutral and cationic species. For years, Professor Kim, a prominent leader and internationally recognized authority in the field of supramolecular chemistry, has been working on a wide variety of functional materials based on cucurbiturils. In his career, he has published over 260 papers that have amassed over 22,600 citations. Most notably, his paper published in Nature in 2000 was selected as one of the 35 most notable papers among chemical related papers published in Nature from 1950 to 2000.

The textbook chronicles the history and development of cucurbiturils and provides a general introduction and a field-wide overview of the synthesis, properties and applications of the fascinating macrocyclic molecules. Comprised of nine chapters that detail among other topics, preparation, properties and host-guest chemistry, the textbook showcases the uses of cucurbiturils in chemistry, materials science and biology.

Professor Kim expressed his enthusiasm on the publication and commented that the textbook is “an essential resource for both new and experienced researchers, as it provides an overview of the diverse applications, new methodologies and research, as well as challenges in the field.”

The publication is made even more noteworthy because Professor Kim will donate his entire royalty to POSTECH to nurture the next generation of scientists.