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Controlling Crystal Size of Organic Semiconductors
A KAIST research team led by Professor Steve Park from the Department of Materials Science and Engineering
Recently, solution-processable organic semiconductors are being highlighted for their potential application in printed electronics, becoming a feasible technique to fabricate large-area flexible thin film at a low cost. The field-effect mobility of small-molecule organic semiconductors is dependent on the crystallinity, crystal orientation, and crystal size. A variety of solution-based coating techniques, such as ink-jet printing, dip-coating, and solution shearing have been developed to control the crystallinity and crystal orientation, but a method for developing techniques to increase the crystal size of organic semiconductors is still needed.
To overcome this issue, the research team developed an inorganic polymer micropillar-based solution shearing system to increase the crystal size of an organic semiconductor with pillar size. Using this technique, the crystallization process of organic semiconductors can be controlled precisely, and therefore large-area organic semiconductor thin film with controlled crystallinity can be fabricated.
A variety of solution-based coating techniques cannot control the fluid-flow of solutions appropriately, so the solvent evaporates randomly onto the substrate, which has difficulty in the fabrication of organic semiconductor thin film with a large crystal size.
The research team integrated inorganic polymer microstructures into the solution shearing blade to solve this issue. The inorganic polymer can easily be microstructured via conventional molding techniques, has high mechanical durability, and organic solvent resistance. Using the inorganic polymer-based microstructure blade, the research team controlled the size of small molecule organic semiconductors by tuning the shape and dimensions of the microstructure. The microstructures in the blade induce the sharp curvature regions in the meniscus line that formed between the shearing blade and the substrate, and therefore nucleation and crystal growth can be regulated. Hence, the research team fabricated organic semiconductor thin-film with large crystals, which increases the field-effect mobility.
The research team also demonstrated a solution shearing process on a curved surface by using a flexible inorganic polymer-based shearing blade, which expands the applicability of solution shearing.
Professor Park said, “Our new solution shearing system can control the crystallization process precisely during solvent evaporation.” He added, “This technique adds another key parameter that can be utilized to tune the property of thin films and opens up a wide variety of new applications.
The results of this work entitled “Inorganic Polymer Micropillar-Based Solution Shearing of Large-Area Organic Semiconductor Thin Films with Pillar-Size-Dependent Crystal Size” was published in the July 2018 issue of Advanced Materials as a cover article.
2018.10.30 View 5325 -
Professor Baik Awarded Sangsan Young Mathematician Prize
(Professor Hyungryul Baik)
Professor Hyungryul Baik from the Department of Mathematical Sciences was honored as the recipient of the 2018 Sangsan Prize for Young Mathematicians by the Korean Mathematical Society (KMS).
The Sangsan Prize recognizes young mathematicians who finished their degree within the previous five years and have begun an outstanding research career. Professor Baik was recognized for his studies in the fields of low-dimensional topology, geophysical mathematics, and geometric theory. In particular, his Ph.D. dissertation presented a new criterion that completely identifies the hyperbolic surface group, making an inference about the nature of the hyperbolic manifold group.
Recently, Professor Baik co-published a paper entitled Spaces of Invariant Circular Orders of Groups with Professor Eric Samperton at the University of California Santa Barbara in the renowned academic journal Groups, Geometry, and Dynamics in 2018.
Professor Baik earned his BS at KAIST and finished his MS and Ph.D. in mathematics in 2014 at Cornell University. He joined KAIST as a faculty member last year.
2018.10.30 View 5321 -
KAIST Thanks Supporters for Building KAIST of Today
KAIST hosted its first Fundraising Gala on October 26, 2018. It was organized to demonstrate deep gratitude to those who have made contributions to KAIST, making it possible to progress every year.
The KAIST Development Foundation (KDF) endeavored to make a meaningful and inclusive event by collecting archives that show the history of donations while sending invitatio ns to all the members of KAIST, including donors and potential donors as well as professors and student representatives.
Approximately 200 distinguished guests attended the gala, including major donors, Chairperson of KDF Soo Young Lee and Chairman Beang Ho Kim, Former Minister of Science Dr. Geun Mo Jung, Former Minister of Science and Technology Woo Sik Kim, and KAIST alumni including the first Korean astronaut So-Yeon Yi.
(Student cheer leading club, ELKA)
At the gala, KAIST shared its 47 years of funding and an expenditure summary with major performances achieved from the year it was founded. According to the summary, KAIST has received more than 323.1 billion won since 1971. The total number of donors was 12,906 while the number of contribution reached 77,710.
Among the total funding (323.1 billion won), corporate gifts made up 43.1% of the total and individual gifts stood at 39.1%, showing that KAIST has received and is receiving support evenly from companies and individuals.
Taking a close look at the major donors, there is an interesting fact about KAIST’s fundraising culture. There has been continuous support from individuals who did not have any personal or academic ties with KAIST before donating. However, they have made large gifts to KAIST so that the best students in the fields of science and technology can be fostered for the sake of national development. The major donors included Young Han Kim (1999), Moon Soul Chung (2001), Byiung Joon Park (2007), Keun Chul Ryu (2008), Beong Ho Kim (2009), Chun Shik Cho and E won Oh (2010), Soo Young Lee (2012), Tae-won Chey (2014), Jeong Ja Cho (2015), and Chang Kun Sohn (2017).
Especially, M. S. Chung, B. H. Kim, C. S. Cho and S. Y. Lee made additional mega-gifts to KAIST, showing continuous support for KAIST’s development.
Nevertheless, the KAIST fundraising culture could not be created with major donors only. Among the total number of donors (12,906), alumni showed the strong engagement standing at 40.4% while parents and students were at 26.1% and 12.7% respectively. The contribution numbers follow the order of alumni (34.8%), parents (20.3%), staff (20%), professors (13.3%), and students (5.7%). These statistics imply that individual’s constant donations play a significant part in the fundraising culture of KAIST.
Additionally, engagement continues to rise every year, and it reached 12,039 gifts in 2017, which increased 5.7 times over ten years.
(from left: Executive Director of KDF Young-gul Kim KAIST President Sung-Chul Shin)
These valuable gifts are the vital fuel for KAIST’s progress. As of 2018, KAIST has spent 205.8 billion won: 81.9 billion won for construction and facilities operation, 79.7 billion won for academics and research, 39 billion won for academic management, and 5.2 billion won for scholarships.
The construction and facilities operation fund aided the evolution of physical infrastructure. KAIST endowed the ChungMoonSoul Building for promoting convergence between information and biotechnology, the Yang Bun Soon Building for bio and brain engineering studies, and the Chunghi & Byiung Jun Park KI Building for multi and interdisciplinary research. Their generous gifts built the foundation for KAIST taking off towards becoming a global leading university.
Meanwhile, the academic and research funds provided opportunities to professors and students to carry out creative research and academic missions. The academic management fund helped open new departments (i.e. The Cho Chun Shik Graduate School of Green Transportation and the Moon Soul Graduate School of Future Strategy) and their programs, for which their names came from the major donors.
(The first Korean astronaut So-Yeon Yi)
At the gala, special events were held for two exclusive moments that contributed to promoting and making a better image for KAIST to the public. One was the 10th anniversary of the space exploration of the first Korean astronaut Dr. Yi. The other was the 20th anniversary of the TV drama series, called ‘KAIST’ which was aired from 1999 to 2000. The writer and main casting crew members joined the event. They said that it was their first time to gather in one place after the show last aired and this event would be memorable for them as well.
President Sung-Chul Shin said, “These gifts play the role of seed money that helps KAIST obtain competence in a global scenario. I hope people have more interest in supporting KAIST through this event.”
1 Total Amount of Gift
2 Total Donors
3 Expenditure Number of Contribution
4 Expenditure
2018.10.29 View 6759 -
KAIST Launches Woorisae II
Professor Sejin Kwon from the Department of Aerospace Engineering and his team succeeded in launching a science rocket, named ‘Woorisae II’ at Saemanguem reclamation. This rocket was developed in collaboration with the Satellite Technology Research Lab (SaRTec).
The test-firing was conducted at 10:43 am on Sunday October 28, 2018 (35°N 42’ 06” 126°E 33’ 36”, Radius of 0.6NM). This launch was the follow-up to the previous launch that was cancelled due to not gaining approval for using the airspace.
Professor Kwon’s team put a great deal of effort into securing the land for the rocket launch. As a result, they got approval from the Saemangeum Development and Investment Agency for the land and the Ministry of Land, Infrastructure and Transport for the use of the airspace. The Republic of Korea Air Force and United States Air Force also approved the use of the airspace for the launch of the science rocket for research purposes.
Woorisae II is 2.2 meters long with a diameter of 20cm, and weighs 13kg without a payload. The rocket is powered by a hybrid rocket with hydrogen peroxide oxidizer producing 100 kg of force. The Woorisae II sounding rocket was designed to burn for five seconds and then continue inertial flight for 20 seconds. The target altitude of Woorisae II was set at 3,300 feet to comply with the airspace approval.
The team developed the core components, including a hybrid rocket propulsion system, flight computer and parachute recovery system, as well as a ground control station. The flight data was transmitted to the ground station and recorded to onboard computer memory.
When a malfunction occurs during the flight, Woorisae II was designed to terminate the power flight for safety by shutting the propellant valve and deploying the recovery parachute. All the rocket subsystems and components were developed and supplied by domestic startup companies such as INOCOM and NARA SPACE TEHCNOLOGY.
Generally, sounding rockets reach an altitude beyond 30km and are widely used for testing rocket engines and reentry materials as well as for conducting microgravity experiments. Instruments for atmospheric science can also be installed to measure fine dust and high altitude atmosphere. Besides these science and technology purposes, most advanced spacefaring countries have sounding rocket programs to train and educate young people in the field of space science.
Professor Kwon said, “We will plan to launch upgraded rockets on November 4 and December 6 because we already received approval from the related agencies for using this land and airspace. Based on the experiment, we are planning to develop a cost-efficient small launch vehicle that is capable of delivering a cube satellite into Earth’s orbit.”
(Photos of preparing the rocket launch)
2018.10.29 View 8262 -
Lens-free OLEDs with Efficiency comparable to that of Inorganic LEDs
(from left: Professor Seunghyup Yoo and PhD candidate Jinouk Song)
The use of organic light-emitting diodes (OLEDs) has extended to various applications, but their efficiency is still lagging behind inorganic light-emitting diodes. In this research, a KAIST team provided a systematic way to yield OLEDs with an external quantum efficiency (EQE) greater than 50% with an external scattering medium.
Having properties suitable for thin and flexible devices, OLEDs are popular light sources for displays, such as mobile devices and high quality TVs. In recent years, numerous efforts have been made to apply OLEDs in lighting as well as light sources for vehicles.
For such applications, high efficiency is of the upmost importance for the successful deployment of light sources. Thanks to continuous research and the development of OLEDs, their efficiency is steadily on the rise, and a level equivalent to inorganic LEDs has been demonstrated in some reports.
However, these highly efficient OLEDs were often achieved with a macroscopic lens or complex internal nanostructures, which undermines the key advantages of OLEDs as an affordable planar light sources and tends to hinder their stable operation, thus putting a limitation to their commercialization.
Among various methods proven effective for OLED light extraction, a team led by Professor Seunghyup Yoo at the School of Electrical Engineering focused on the external scattering-based approach, as it can maintain planar geometry and compatibility with flexibility. It is also able to be fabricated on a large scale at a low cost and causes no interference with electrical properties of OLEDs.
Conventionally, research on enhancing OLED light extraction using light scattering has been conducted empirically in many cases. This time, the team developed comprehensive and analytical methodology to theoretically predict structures that maximize efficiency.
Considering OLEDs with the external scattering layers as a whole rather than two separate entities, the researchers combined the mathematical description of the scattering phenomena with the optical model for light emission within an OLED to rapidly predict the characteristics of many devices with various structures. Based on this approach, the team theoretically predicted the optimal combination of scattering layers and OLED architectures that can lead to the maximum efficiency.
Following this theoretical prediction, the team experimentally produced the optimal light scattering film and incorporated it to OLEDs with orange emitters having a high degree of horizontal dipole orientation. As a result, the team successfully realized OLEDs exhibiting EQE of 56% and power efficiency of 221 lm/W. This is one of the highest efficiencies ever realized for an OLED unit device without the help of a macroscopic lens or internal light extraction structures.
Professor Yoo said, “There are various technologies developed for improving OLED light extraction efficiency; nevertheless, most of them have not reached a level of practical use. This research mainly provides a systematic way to attain an EQE of 50% or higher in OLEDs while keeping in mind the constraints for commercialization. The approach shown here can readily be applied to lighting devices or sensors of wearable devices.”.
This research, co-led by Professor Jang-Joo Kim from Seoul National University and Professor Yun-Hi Kim from Gyeongsang National University, was published in Nature Communications on August 10, 2018. (J. Song et al. Nature Communications, 9, 3207. DOI: 10.1038/s41467-018-05671-x)
Figure 1.Photographs of OLEDs with SiO₂ -embedded scattering layers according to scatterance
2018.10.26 View 7573 -
A Molecular Sensor for In-Situ Analysis of Complex Biological Fluids
A KAIST research group presented a molecular sensor with a microbead format for the rapid in-situ detection of harmful molecules in biological fluids or foods in a collaboration with a Korea Institute of Materials Science (KIMS) research group. As the sensor is designed to selectively concentrate charged small molecules and amplify the Raman signal, no time-consuming pretreatment of samples is required.
Raman spectra are commonly known as molecular fingerprints. However, their low intensity has restricted their use in molecular detection, especially for low concentrations. Raman signals can be dramatically amplified by locating the molecules on the surface of metal nanostructures where the electromagnetic field is strongly localized. However, it is still challenging to use Raman signals for the detection of small molecules dissolved in complex biological fluids. Adhesive proteins irreversibly adsorb on the metal surface, which prevents the access of small target molecules onto the metal surface. Therefore, it was a prerequisite to purify the samples before analysis. However, it takes a long time and is expensive.
A joint team from Professor Shin-Hyun Kim’s group in KAIST and Dr. Dong-Ho Kim’s group in KIMS has addressed the issue by encapsulating agglomerates of gold nanoparticles using a hydrogel. The hydrogel has three-dimensional network structures so that molecules smaller than the mesh are selectively permeable. Therefore, the hydrogel can exclude relatively large proteins, while allowing the infusion of small molecules. Therefore, the surface of gold nanoparticles remains intact against proteins, which accommodates small molecules. In particular, the charged hydrogel enables the concentration of oppositely-charged small molecules. That is, the purification is autonomously done by the materials, removing the need for time-consuming pretreatment. As a result, the Raman signal of small molecules can be selectively amplified in the absence of adhesive proteins.
Using the molecular sensors, the research team demonstrated the direct detection of fipronil sulfone dissolved in an egg without sample pretreatment. Recently, insecticide-contaminated eggs have spread in Europe, South Korea, and other countries, threatening health and causing social chaos. Fipronil is one of the most commonly used insecticides for veterinary medicine to combat fleas. The fipronil is absorbed through the chicken skin, from which a metabolite, fipronil sulfone, accumulates in the eggs. As the fipronil sulfone carries partial negative charges, it can be concentrated using positively-charged microgels while excluding adhesive proteins in eggs, such as ovalbumin, ovoglobulin, and ovomucoid. Therefore, the Raman spectrum of fipronil sulfone can be directly measured. The limit of direct detection of fipronil sulfone dissolved in an egg was measured at 0.05 ppm.
Professor Kim said, “The molecular sensors can be used not only for the direct detection of harmful molecules in foods but also for residual drugs or biomarkers in blood or urine.” Dr. Dong-Ho Kim said, “It will be possible to save time and cost as no sample treatment is required.”
This research was led by graduate student Dong Jae Kim and an article entitled “SERS-Active Charged Microgels for Size- and Charge-Selective Molecular Analysis of Complex Biological Samples” was published on October 4, 2018 in Small and featured on the inside cover of the journal.
Figure 1. Schematic illustrating the concentration of charged small molecules and the exclusion of large adhesive proteins using a charged hydrogel microbead containing an agglomerate of gold nanoparticles. The Raman signal of the small molecules is selectively amplified by the agglomerate.
Figure 2. Confocal laser scanning microscope images showing the concentration of oppositely charged molecules, where negatively-charged microgels are denoted by red circles and positively-charged microgels are denoted by blue circles. Green fluorescence originates from negatively-charged dye molecules and red fluorescence originates from positively-charged dye molecules.
Figure 3. Raman spectra measured from fipronil sulfone-spiked eggs, where the concentrations of fipronil sulfone are denoted; 0 ppm indicates no fipronil sulfone in the egg. The characteristic peaks of fipronil sulfone are denoted by the dotted lines.
2018.10.23 View 5871 -
Mussel-Inspired Defect Engineering Enhances the Mechanical Strength of Graphene Fibers
Researchers demonstrated the mussel-inspired reinforcement of graphene fibers for the improvement of different material properties. A research group under Professor Sang Ouk Kim applied polydopamine as an effective infiltrate binder to achieve high mechanical and electrical properties for graphene-based liquid crystalline fibers.
This bio-inspired defect engineering is clearly distinguishable from previous attempts with insulating binders and proposes great potential for versatile applications of flexible and wearable devices as well as low-cost structural materials. The two-step defect engineering addresses the intrinsic limitation of graphene fibers arising from the folding and wrinkling of graphene layers during the fiber-spinning process.
Bio-inspired graphene-based fiber holds great promise for a wide range of applications, including flexible electronics, multifunctional textiles, and wearable sensors. In 2009, the research group discovered graphene oxide liquid crystals in aqueous media while introducing an effective purification process to remove ionic impurities. Graphene fibers, typically wet-spun from aqueous graphene oxide liquid crystal dispersion, are expected to demonstrate superior thermal and electrical conductivities as well as outstanding mechanical performance.
Nonetheless, owing to the inherent formation of defects and voids caused by bending and wrinkling the graphene oxide layer within graphene fibers, their mechanical strength and electrical/thermal conductivities are still far below the desired ideal values. Accordingly, finding an efficient method for constructing the densely packed graphene fibers with strong interlayer interaction is a principal challenge.
Professor Kim's team focused on the adhesion properties of dopamine, a polymer developed with the inspiration of the natural mussel, to solve the problem. This functional polymer, which is studied in various fields, can increase the adhesion between the graphene layers and prevent structural defects.
Professor Kim’s research group succeeded in fabricating high-strength graphene liquid crystalline fibers with controlled structural defects. They also fabricated fibers with improved electrical conductivity through the post-carbonization process of polydopamine.
Based on the theory that dopamine with subsequent high temperature annealing has a similar structure with that of graphene, the team optimized dopamine polymerization conditions and solved the inherent defect control problems of existing graphene fibers.
They also confirmed that the physical properties of dopamine are improved in terms of electrical conductivity due to the influence of nitrogen in dopamine molecules, without damaging the conductivity, which is the fundamental limit of conventional polymers.
Professor Kim, who led the research, said, "Despite its technological potential, carbon fiber using graphene liquid crystals still has limits in terms of its structural limitations." This technology will be applied to composite fiber fabrication and various wearable textile-based application devices." This work, in which Dr. In-Ho Kim participated as first author was selected as a front cover paper of Advanced Materials on October 4.
This research was supported by the National Creative Research Initiative (CRI) Center for Multi-Dimensional Directed Nanoscale Assembly and the Nanomaterial Technology Development Program through the National Research Foundation of Korea funded by the Ministry of Science and ICT.
Figure 1. Cross-section SEM image of pure graphene fiber (left) and that of graphene fiber after two-stage defect control using polydopamine (middle and right).
2018.10.23 View 5924 -
Washing and Enrichment of Micro-Particles Encapsulated in Droplets
Researchers developed microfluidic technology for the washing and enrichment of in-droplet micro-particles. They presented the technology using a microfluidic chip based on surface acoustic wave (SAW)-driven acoustic radiation force (ARF).
The team demonstrated the first instance of acoustic in-droplet micro-particle washing with a particle recovery rate of approximately 90 percent. They further extended the applicability of the proposed method to in-droplet particle enrichment with the unprecedented abilities to increase the in-droplet particle quantity and exchange the droplet dispersed phase.
This proposed method enabled on-chip, label-free, continuous, and selective in-droplet micro-particle manipulation. The team demonstrated the first instance of in-droplet micro-particle washing between two types of alternating droplets in a simple microchannel, proving that the method can increase the particle quantity, which has not been achieved by previously reported methods.
The study aimed to develop an in-droplet micro-particle washing and enrichment method based on SAW-driven ARF. When a droplet containing particles is exposed to an acoustic field, both the droplet and suspended particles experience ARF arising from inhomogeneous wave scattering at the liquid-liquid and liquid-solid interfaces. Unlike previous in-droplet particle manipulation methods, this method allows simultaneous and precise control over the droplets and suspended particles. Moreover, the proposed acoustic method does not require labelled particles, such as magnetic particles, and employs a simple microchannel geometry.
Microfluidic sample washing has emerged as an alternative to centrifugation because the limitations of centrifugation-based washing methods can be addressed using continuous washing processes. It also has considerable potential and importance in a variety of applications such as single-cell/particle assays, high-throughput screening of rare samples, and cell culture medium exchange.
Compared to continuous flow-based microfluidic methods, droplet-based microfluidic sample washing has been rarely explored due to technological difficulties. On-chip, in-droplet sample washing requires sample transfer across the droplet interface composed of two immiscible fluids. This process involves simultaneous and precise control over the encapsulated sample and droplet interface during the medium exchange of the in-droplet sample.
Sample encapsulation within individual microscale droplets offers isolated microenvironments for the samples. Experimental uncertainties due to cross-contamination and Taylor dispersion between multiple reagents can be reduced in droplet-based microfluidics.
This is the first research achievement made by the Acousto-Microfluidics Research Center for Next-Generation Healthcare, the cross-generation collaborative lab KAIST opened in May. This novel approach pairs senior and junior faculty members for sustaining the research legacy even after the senior researcher retires. The research center, which paired Chair Professor Hyung Jin Sung and Professors Hyoungsoo Kim and Yeunwoo Cho, made a breakthrough in microfluidics along with PhD candidate Jinsoo Park. The study was featured as the cover of Lab on a Chip published by Royal Society of Chemistry.
Jinsoo Park, first author of the study, believes this technology will may serve as an in-droplet sample preparation platform with in-line integration of other droplet microfluidic components. Chair Professor Sung said, “The proposed acoustic method will offer new perspectives on sample washing and enrichment by performing the operation in microscale droplets.”
Figure 1. (a) A microfluidic device for in-droplet micro-particle washing and enrichment; (b) alternatingly produced droplets of two kinds at a double T-junction; (c) a droplet and encapsulated micro-particles exposed to surface acoustic wave-driven acoustic radiation force; (d-h) sequential processes of in-droplet micro-particle washing and enrichment operation.
2018.10.19 View 6702 -
Six Professors Recognized for the National R&D Excellence 100
Six KAIST professors were listed among the 2018 National R&D Excellence 100 announced by the Ministry of Science and ICT and Korea Institute of S&T Evaluation and Planning.
Professor Il-Doo Kim from the Department of Materials Science and Engineering was recognized for his research on developing source technology for manufacturing a highly sensitive gas sensor with low power consumption. His work was recognized as most excellent in the field of mechanics and materials.
Additionally, Professor Ho Min Kim from the Graduate School of Medical Science & Engineering was listed as most excellent in the field of life and marine science for providing structural insights into the mechanism of proteins that regulates synapse development.
Meanwhile, Professor Byong-Guk Park from the Department of Materials Science and Engineering was listed as excellent in the field of mechanics and materials for his work on thermal spin current.
In the field of energy and environment, Professor Jae Woo Lee from the Department of Chemical and Biomolecular Engineering was listed as excellent for his work on CO₂ conversion to carbon materials.
Last but not least, Professor Min H. Kim from the School of Computing and Professor Kyung Cheol Choi from the School of Electrical Engineering were recognized as being excellent in the field of information and electronics. Professor Kim was recognized for image processing technology that reconstructs interlaced high-dynamic range video while Professor Choi was lauded for realizing flexible displays on fabrics.
A certificate from the Minister of Ministry of Science and ICT will be conferred to the scientists and their names will be listed on a special 2018 National R&D Excellence 100 plaque to celebrate their achievement.
These six professors will be nominated for merits including the Order of Merit, the President’s commendation, and the Prime Minister’s commendation and given privileges during the process of new R&D project selection.
2018.10.18 View 4321 -
Dr. Sejeong Kim Recognized as Excellent Young Scientist
(Dr. Sejeong Kim)
Dr. Sejeong Kim, a postdoctoral research associate in the School of Mathematical and Physical Sciences at the University of Technology Sydney was honored to receive the Excellence Award for a Young Scientist by the Korea Federation of Women’s Science & Technology Association (KOFWST). The award ceremony will be held on October 31 in Seoul.
KOFWST recognizes ten promising young female scientists and engineers every year who show significant potential, passion, and remarkable achievement in their work. The awardees are selected among those who finished their degree within the previous five years. Dr. Kim earned her Ph.D. in physics at KAIST in 2014 and was selected as the winner in the field of physics in recognition of her outstanding research activities in photonics.
Dr. Kim conducted various research activities in the field of photonics and was published in high impact journals including Nano Letters and Advanced materials. In July, she developed the first photonic cavity from van der Waals materials and published the study in Nature Communications titled “Photonic Crystal Cavities from Hexagonal Boron Nitride.” At UTS, she carries out research activities supervised by Professor Igor Aharonovich and has engaged in many science outreach activities.
2018.10.18 View 4893 -
Skin Hardness to Estimate Better Human Thermal Status
(Professor Young-Ho Cho and Researcher Sunghyun Yoon)
Under the same temperature and humidity, human thermal status may vary due to individual body constitution and climatic environment. A KAIST research team previously developed a wearable sweat rate sensor for human thermal comfort monitoring. Furthering the development, this time they proposed skin hardness as an additional, independent physiological sign to estimate human thermal status more accurately. This novel approach can be applied to developing systems incorporating human-machine interaction, which requires accurate information about human thermal status.
Professor Young-Ho Cho and his team from the Department of Bio and Brain Engineering had previously studied skin temperature and sweat rate to determine human thermal comfort, and developed a watch-type sweat rate sensor that accurately and steadily detects thermal comfort last February (title: Wearable Sweat Rate Sensors for Human Thermal Comfort Monitoring ).
However, skin temperature and sweat rate are still not enough to estimate exact human thermal comfort. Hence, an additional indicator is required for enhancing the accuracy and reliability of the estimation and the team selected skin hardness. When people feel hot or cold, arrector pili muscles connected to hair follicles contract and expand, and skin hardness comes from this contraction and relaxation of the muscles. Based on the phenomenon of changing skin hardness, the team proposed skin hardness as a new indicator for measuring human thermal sensation.
With this new estimation model using three physiological signs for estimating human thermal status, the team conducted human experiments and verified that skin hardness is effective and independent from the two conventional physiological signs. Adding skin hardness to the conventional model can reduce errors by 23.5%, which makes its estimation more reliable.
The team will develop a sensor that detects skin hardness and applies it to cognitive air-conditioning and heating systems that better interact with humans than existing systems.
Professor Cho said, “Introducing this new indicator, skin hardness, elevates the reliability of measuring human thermal comfort regardless of individual body constitution and climatic environment. Based on this method, we can develop a personalized air conditioning and heating system that will allow affective interaction between humans and machines by sharing both physical and mental health conditions and emotions.”
This research, led by researchers Sunghyun Yoon and Jai Kyoung Sim, was published in Scientific Reports, Vol.8, Article No.12027 on August 13, 2018. (pp.1-6)
Figure 1. Measuring human thermal status through skin hardness
Figure 2. The instrument used for measuring human thermal status through skin hardness
2018.10.17 View 5525 -
High-Performance Flexible Transparent Force Touch Sensor for Wearable Devices
Researchers reported a high-performance and transparent nanoforce touch sensor by developing a thin, flexible, and transparent hierarchical nanocomposite (HNC) film. The research team says their sensor simultaneously features all the necessary characters for industrial-grade application: high sensitivity, transparency, bending insensitivity, and manufacturability.
Force touch sensors that recognize the location and pressure of external stimuli have received considerable attention for various applications, such as wearable devices, flexible displays, and humanoid robots. For decades, huge amounts of research and development have been devoted to improving pressure sensitivity to realize industrial-grade sensing devices. However, it remains a challenge to apply force touch sensors in flexible applications because sensing performance is subject to change and degraded by induced mechanical stress and deformation when the device is bent.
To overcome these issues, the research team focused on the development of non-air gap sensors to break away from the conventional technology where force touch sensors need to have air-gaps between electrodes for high sensitivity and flexibility.
The proposed non air-gap force touch sensor is based on a transparent nanocomposite insulator containing metal nanoparticles which can maximize the capacitance change in dielectrics according to the pressure, and a nanograting substrate which can increase transparency as well as sensitivity by concentrating pressure. As a result, the team succeeded in fabricating a highly sensitive, transparent, flexible force touch sensor that is mechanically stable against repetitive pressure.
Furthermore, by placing the sensing electrodes on the same plane as the neutral plane, the force touch sensor can operate, even when bending to the radius of the ballpoint pen, without changes in performance levels.
The proposed force touch has also satisfied commercial considerations in mass production such as large-area uniformity, production reproducibility, and reliability according to temperature and long-term use.
Finally, the research team applied the developed sensor to a pulse-monitoring capable healthcare wearable device and detected a real-time human pulse. In addition, the research team confirmed with HiDeep, Inc. that a seven-inch large-area sensor can be integrated into a commercial smartphone.
The team of Professor Jun-Bo Yoon, PhD student Jae-Young Yoo, and Dr. Min-Ho Seo from the School of Electrical Engineering carried out this study that was featured as a back cover in Advanced Functional Materials Journal.
PhD student Jae-Young Yoo who led this research said, "We successfully developed an industrial-grade force touch sensor by using a simple structure and fabrication process. We expect it to be widely used in user touch interfaces and wearable devices."
This research was supported by the Basic Research Program through the National Research Foundation of Korea funded by the Ministry of Science and ICT, and also supported by the Open Innovation Lab Cooperation Project funded by the National Nano Fab Center.
Figure 1. Schematic illustration of a transparent, flexible force touch sensor (upper image) and sensitivity enhancement by using stress concentration (lower image).
2018.10.15 View 6140