Social capital refers to potential or actual resources that can be accrued from their embedded relationships, and parents are considered as one of the vital sources from which children can obtain it. Social capital is particularly important in that it can be used to overcome harmful situations faced by children. In the past, social capital had been explored based on the accounts of adults, such as the degree in which parental social capital could be transmitted to children. However, with society's wider acceptance of children as active social agents, children's subjective reports on their social capital have recently gained greater consideration. Professor Yanghee Lee and Dr. Sangwon Kim (the Department of Child Psychology and Education, College of Social Science) stipulated that when parents are the perpetrators of violence, children may lack social capital. Thus, alternatives sources for social capital in children's immediate environment were identified and explored. This study utilized the responses of 4th graders (N= 2,844) from the Korean Youth Panel, and investigated whether social capital from siblings, friends, teachers, neighbors, and online acquaintances mediated the pathway of parental violence leading to aggression or depression. It was found that social capital obtained from siblings, teachers, and neighbors mediated the pathway between parental violence and aggression or depression, and this was consistent in aggression but not in depression. This finding is significant in that other sources of social capital would be crucial in breaking cycle of violence. Social capital obtained from friends did not have a significant mediating effect. It was further confirmed that continuous monitoring should be accompanied because social capital obtained from online acquaintances can lead to increased levels of aggression or depression. Professor Lee explained that this study is noteworthy in that it explored the role of other forms of social capital that can compensate for the lack of parental social capital. She added that it is the responsibility of all of us to protect children from all forms of violence, therefore it is essential to actively seek ways to develop and promote children's social capital. To establish a social safety net for children, Dr. Sangwon Kim said that it is necessary to explore various ways to utilize social capital by considering social capital measured both at the individual and the community level. This study was published in the internationally renowned journal titled Journal of Interpersonal Violence (SSCI, IF=6.144). Professor Lee served as a professor for 30 years and has researched child counseling, play therapy, interventions for children with developmental disabilities, child abuse and neglect, children's rights, and child resilience. She has published more than 100 papers in domestic and international academic journals. She is currently serving as an editorial board member in internationally renowned journals, including Child Abuse & Neglect (SSCI, IF = 3.928), International Journal of Children's Rights (SCOPUS), and others. Also, she served as a Guest editor in Child Abuse & Neglect (2009-2011; 2019-2020) and the International Journal of Children's Rights (2010).
A research team led by Dong ho Kim, an assistant professor in the Department of Education, analyzed account information and behavioral log data collected fromabout 100,000 students using an AI-based math learning platform “Algebra Nation,” by leveraging the learning analytics approach and constructed a prediction model to forecast student dropout in the platform. The team carried out a multilevel-Survival Analysis to explore relationships between student dropout and online activities. Their findings shed light on the behavioral characteristics of at-risk online students. They also provided instructional strategies that can be adopted by teachers who want to boost student engagementin online learning platforms. Their work has recently been published in Computers and Education, one of top journals globally recognized as an outlet for research in education. The workhas received a great deal of attention from researchers as we are in face ofthe rapid growth of online learning in all education sectors. Prof. Dongho Kimhas engaged in the area of AI-based online learning platforms. His work focuses on applying a variety of educational technology theories to find out how to support students in technology-enhanced learning environments. “In the non-contact era, growing attention will be paid to online platformsd esigned to help students who are physically separated from their instructor.” JungwonLee, a graduate student in the Prof. Kim’s research team, said. Jungwon Lee is developing an AI chatbot for pre-service teachers to learn how to teach their students.
<Graphical Abstract. Association between adiposity and cardiovascular outcomes: an umbrella review and meta-analysis of observational and Mendelian randomization studies. Eur Heart J. 2021> A research team led by Professor Hong-Hee Won (first author: Minseo Kim, and corresponding author: Hong-Hee Won) of the Samsung Advanced Institute for Health Sciences and Technology (SAIHST), Sungkyunkwan University, and Samsung Genome Institute (SGI), Samsung Medical Center, conducted a comprehensive analysis on adiposity and cardiovascular disease events and mortality, and published results in one of the most prestigious cardiology journals, European Heart Journal (Impact Factor 29.98)'. This study performed a meta-analysis of more than 500 cohorts to comprehensively analyze the effects of adiposity on the risk of nine cardiovascular diseases and mortality. The study design presented in this study enables a higher-resolution analysis for complex epidemiological topics by examining associations using a cohort study and causality through a genomic study. The relationship between adiposity and cardiovascular disease has been continuously studied for a long time, and it is known that adiposity increases the risk of cardiovascular disease. However, each study showed very heterogeneous results according to obesity metrics, ancestry, and cohort characteristics. In addition, obesity has a unique feature that it has a bidirectional interaction with the disease. That is, although the risk of cardiovascular disease is increased by obesity, conversely, the possibility that obesity is increased due to the occurrence of cardiovascular disease cannot be excluded. In the case of such a complex epidemiologic relationship, there is a limitation in that it is difficult to confirm the exact causality or direction of interaction only through observational studies. In interventional studies such as drug research, causality can be confirmed through a study design called a randomized controlled trial. In the case of obesity and cardiovascular disease, however, research mainly relies on observational studies because it is unethical to induce obesity through intervention. Due to the nature of observational studies, it is difficult to fundamentally exclude confounding variables, and in the case of the bidirectional phenotype such as obesity, it becomes more difficult to identify the relationship. To solve this problem, this research team grafted genome-based research to confirm causality to observational research for the first time. Mendelian randomization study used in this study is based on the fact that genetic variants are randomly assigned during meiosis to form groups with high or low genetic risk of obesity. Comparing the difference in the risk of cardiovascular disease for these two groups can evaluate whether obesity causes the disease without intervention. Mendelian randomization studies have the advantage of being able to obtain independent results from confounding variables and reverse causation caused by the environment because groups are randomly divided at the stage of meiosis. This is in contrast to the weakness of epidemiological studies that they can be often affected by confounding factors or reverse causation. This study presents new high-level evidence for the relationship between obesity and cardiovascular disease, which has been studied for a long time, by utilizing both the strength of large-scale observational studies (association confirmation), and the strength of genome-based research (causality confirmation). A researcher, Minseo Kim (graduated from Korea University College of Medicine and a M.A. student at SAIHST, Sungkyunkwan University), said, “There were weaknesses in clinical research while conducting clinical research. We devised a new research design that could augment clinical research with genomic approaches. This was possible because he learned both clinical research and genomics. It is expected that more sophisticated studies will be possible by using this research methodology for many epidemiological research topics in the future.” Professor Hong-Hee Won said, “This study is meaningful that it systematically presented scientific evidence for causality between obesity and the risk of cardiovascular disease by integrating large-scale epidemiological and genomic studies. As obesity has been shown to be responsible for various cardiovascular diseases and mortality risk, it is important to maintain ideal body weight and to adhere to healthy lifestyles to lower the risk of cardiovascular disease." The results of this study, which was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (Information and Communication Technologies) of the Korea government, were published in one of the most prestigious cardiology journals, 'European Heart Journal (Impact Factor 29.98)'. ▲ Prof. Hong-Hee Won, Ph.D. (corresponding author) ▲ Minseo Kim, M.D. (first author) ▲ A research team led by Professor Hong-Hee Won at SAIHST, Sungkyunkwan University, Samsung Medical Center
□ The research team of Prof. Dong-Hwan Kim (1st author: Dr. Byeong-Seok Moon) develop an ever-smaller and ever-more-efficient microlaser using a new upconversion material that has atomic-scale microstructural disorder through the collaboration with Prof. Young-Jin Kim (KAIST) and Prof. Sang Kyu Kwak (UNIST). □ Microlasers are the optical device that can generate laser emission while it is smaller than a few tenths of the thickness of a human hair. Microlasers have attracted a great attention because it can be used as a light source for photonic integrated circuits, for example, an optical communication chip (Intel® Silicon Photonics) for massive data transport. □ To bring the microlasers in our daily life, the researchers around the world have dedicated their efforts to further miniaturize the microlasers and improve their efficiency. However, as we miniaturize the microlasers, they lose their ability to confine and amplify the light. Therefore, the realization of both miniaturization and high laser efficiency has been considered as a challenging task. □ The research team of Prof. Dong-Hwan Kim has overcome this challenge by minimizing the energy loss of gain medium during laser process. □ The developed microlaser in this study has the great potential in next-generation biomedical technologies such like ‘sinlge-molecular biodetection’ and ‘real-time biosensing in live-cells’. Furthermore, since it is feasible for a light source of photonic integrated circuits, it will pave the way for highly-valued industrial applications. □ Prof. Kim said “We for the first time exploited the atomically disordered material for developing microlasers to overcome the conventional limitations of miniaturization and laser efficiency. By automating the fabrication and integrating systems, we are planing to utilize our microlaser as a solution for future technologies.” □ Continuous-wave upconversion lasing with a sub-10 W cm-2 threshold enabled by atomic disorder in the host matrix. Nature Communications, 12, Article number: 4437 (2021), (1st authors: Dr. Byeong-Seok Moon). Published July 21 2021 (IF: 14.919) ※ Title of paper : Continuous-wave upconversion lasing with a sub-10 W cm-2 threshold enabled by atomic disorder in the host matrix Fig. 1: Continuous-wave upconversion lasing in liquid-quenched upconversion microspheres (LQUM). Fig. 2: Ultralow-threshold continuous-wave upconversion lasing. Fig. 3: Theoretical analysis of the enhancement of the upconversion lasing efficiency in the amorphous phase of NaYF4 combined with SiO2.
The research team of Prof. Changhyun Pang (1st authors: Jihyun Lee, Jin Ho Song, and Dr. Sangyul Baik) revealed the structure and principle of the adhesive cup existing on the foreleg of a male diving beetle. A diagnostic patch that can be applied to disease treatment and provide therapeutic feedback was developed for the first time.  Science Advances June 16 (IF: 14.136); Diving beetle–like miniaturized plungers with reversible, rapid biofluid capturing for machine learning–based care of skin disease, 7(25), eabf5695 (2021), (1st authors: Jihyun Lee and Dr. Sangyul Baik)  Chemical Engineering Journal May 7 (IF: 13.273); “Wet soft bio-adhesion of insect-inspired polymeric oil-loadable perforated microcylinders; 423, 130194 (2021) (1st authors: Jin Ho Song) The diving beetle, an aquatic insect, has a unique characteristic that distinguishes males and females, namely, the round sticky cups on its foreleg. This adhesive cup adheres well to the surface of the female's curved and rough back during mating in the water, and serves to detect chemicals required during mating. It is a unique evolutionary product of the male diving beetle species. Prof. Changhyun Pang in the Department of Chemical Engineering at Sungkyunkwan University (SKKU) report the new approach for the diagnosis and treatment of skin in advanced biomedical technologies. Related research papers are published in Science Advances (Impact Factor 14.136) journal and Chemical Engineering Journal (Impact Factor 13.273). Inspired by the male diving beetle, the microscale suction cups achieve repeatable, enhanced, and multidirectional adhesion to human skin in dry/wet environments, revealing the role of the cavities in these architectures. The hydrogels within the suction cups instantaneously absorb liquids from the epidermis for enhanced adhesiveness and reversibly change color for visual indication of skin pH levels. To realize advanced biomedical technologies for the diagnosis and treatment of skin, our suction-mediated device is integrated with a machine learning framework for accurate and automated colorimetric analysis of pH levels. Furthermore, the research team of Changhyun Pang developed omni-directional non-slip and damage-free soft surgical gripper. For this research outcome, the research team of Prof. Changhyun Pang try to mimic the complex adhesion mechanism of underwater insect creatures, which are composed by suction force and mucus (oil) adhesion. This kind of new approach (oil-assisted suction adhesion inspired adhesive) make the adhesive possible to attach on wet, soft organ surface comparing the previous study. Prof. Pang said that the skin diagnosis patch with non-powered body fluid capture system can be used in medical data-based disease diagnosis and self-diagnosis medical devices and services. * From the left Prof. Pang, Jihyun Lee, Jin Ho Song Fig 1. The diving beetle–like reversible microplungers with biofluid-capturing hydrogel Fig 2. Adhesion of the DIAs via structural deformation in dry and wet conditions
As a society of low birthrates and aging populations, capitals and large cities around the world are becoming more concentrated and complex problems are occurring accordingly. As more people flock to the city, the amount of complaints has increased, but there is not enough manpower to respond to them. Kim Jang-hyun, a professor of interaction science at our university proposed an algorithm to automatically classify 160,000 civil texts through machine learning from 2006 to 2017 and published in CITIES (SSCI, JCR 2019 IF= 4.802, Top 2). Based on Word2vec and Random forest, artificial intelligence can automatically classify complaints, including transportation, environment, and culture, with an accuracy of about 70%. Inefficient administrative procedures, which had to be classified by existing civil servants in charge of civil complaints, can be quickly and accurately transformed into efficient civil complaints through machine learning. In addition, we propose a method to analyze automatically complaints using dynamic topic modeling to predict complaints in the future. Finally, the data analysis process was disclosed in github and a book (Urban Data Standards Analysis Model: Civil Petitions Analysis) so that each local government can help build a smart city system in the future. You can find the book that manualized the paper and analysis process through the website below. https://www.sciencedirect.com/science/article/pii/S0264275120312890#f0005 https://github.com/SeoulDigitalFoundation/VoiceOfSeoul_AnalysisGuide https://sdf.seoul.kr/research-report/1241 Image 1. Subway seat care for elderly and preganant women Image 2. Emphasis on fine dust and energy saving issues
This research shows the electrophysiological mechanism of how Korean liberals and conservatives have different moral values given the political confrontation in modern society and how different moral decisions are made in the context of business ethics. Professor Lee Eun-Ju's research team from the Department of Marketing at the SKK Business school published a paper in the Journal of Business Ethics (IF=5.453, Financial Times' Top 50 Journals List) that looked at how liberals and conservatives process dissociable psychological mechanisms in the Korean context of business ethics. The study was led by Jin Ho Yun under the topic of his Ph.D. dissertation. Do liberals’ and conservatives’ brain processes differ in moral reasoning? This research explains these groups’ dissimilar moral stances when they face ethical transgressions in business. Research that explores the effects of ideological asymmetry on moral reasoning processes through moral foundations (i.e., fairness and authority) has been limited. We hypothesize two different moral reasoning processes and test them in the South Korean culture. Study 1 uses the neuroscientific method of event-related potentials (ERP) to explore the dissociable neural mechanisms that underlie Korean liberals’ and conservatives’ moral reasoning processes in business ethical transgressions. Liberals’ early frontal negative-going (EFN) brain waves showed that they are quick to pass negative judgment by intuitively detecting violations of fairness (i.e., moral engagement), while conservatives’ temporoparietal positive-going (TPP) brain waves showed that they have a higher motivation to respect authority (i.e., moral rationalization). Both liberals’ and conservatives’ ERP components occur within the first second of the decision-making phase, suggesting the rapid and intuitive nature of moral reasoning processes. Study 2 tests a mediating process and confirms that Korean liberals (conservatives) exhibit the moral engagement (rationalization) strategy, through the fairness (authority) foundation. These findings from our interdisciplinary research deepen the knowledge of the complexity of human morality in business ethics research. Additionally, the lead author, Jin Ho Yun, has received an offer as an assistant professor by Ecole de Management Léonard De Vinci (EMLV) in Paris, France, but he will shortly join the Wharton Neuroscience Initiative (WiN) at the University of Pennsylvania. As a post-doctoral researcher, he will continue to contribute to the areas of neuroeconomics, consumer neuroscience, and business ethics.
In an aging population, the frequency of patients with spine-related problems such as spinal stenosis, vertebral fractures, progressive deformities, and instability has shown a concerning increase. Due to the superior biological properties, biomimetic bone grafts have been long considered to be the reference standard for successful bone tissue regeneration and spinal fusion. Prof. Geun Hyung Kim and his research team (Hanjun Hwangbo and Dr. Hyeongjin Lee; first author) from the department of biomechatronic engineering / biomedical institute for Convergence at SKKU (BICS) conducted joint research with Prof. In-Bo Han and his research team (Eun Ji Roh; first author) from CHA University School of medicine to develop 4D printing strategy to fabricate biomimetic microchanneled collagen/hydroxyapatite scaffold (MC- scaffold). The fabricated MC- scaffold was further analyzed in a spinal fusion model of a mouse. Consequently, the results indicate significantly higher bone regeneration and rate of spine fusion compared to the conventionally fabricated collagen/hydroxyapatite scaffold. A major drawback of the conventionally used bone grafts is the limited vascular network causing insufficient nutrient and metabolite transfer to the surrounding tissue. To overcome this issue, Prof Geun Hyung Kim and his research team utilized a 4D printing strategy (one-way-shape-morphing) to fabricate a biomimetic microchanneled scaffold composed of collagen and hydroxyapatite (the main component of native bone) to induce a higher degree of osteogenesis and angiogenesis. These findings are owed to the synergistic effects of high infiltration of blood vessels into the microchannels and superior biophysical properties of the microchanneled collagen/hydroxyapatite scaffold. Additionally, Prof. Geun Hyung Kim and his research team (WonJin Kim; first author) collaborated with Prof. SangJin Lee and his research team (Dr. Hyeongjin Lee; first author) from Wake Forest Institute for Regenerative Medicine (WFIRM) applied 4D printing strategy to induce cellular alignment in extracellular matrix (ECM) based scaffold. Subsequently, a significantly higher degree of muscle regeneration was observed via implantation of the 4D printed bioconstruct into a muscle defect in the rat model. Currently, mimicking the uniaxial alignment of muscle cells as presented in the native skeletal muscle is often a challenging and difficult task to accomplish with conventional 3D printing. To overcome this issue, Prof. Geun Hyung Kim and his research team utilized developed a composite bioink composed of natural polymer (ECM) and synthetic polymer (Polyvinyl alcohol, PVA), and a 4D printing strategy to provide topographical cue in ECM-based scaffold to induce cellular alignment of primary human muscle progenitor cell (hMPC). Various process parameters such as PVA molecular weight and pneumatic pressure have been analyzed to optimized to obtain the best biological factors such as cellular alignment and differentiation of the host cells. In addition, to conduct in vivo investigations into muscle regeneration, the bioconstruct sized 15 × 7 × 3 mm3 have been printed and implanted into the tibialis anterior (TA) muscle defect. The cell viability of the fabricated bioconstruct was measured to be around 90%. After 8 weeks of implantation, the muscle regeneration on rats that received the 4D bioprinted structure was significantly higher compared to the conventional 3D printed structure. The presented 4D printing strategy enables versatility of designing various biological and physical factors of the implant grafts for effective tissue regeneration. Moreover, the introduced 4D printing strategy is believed to have multiple applications such as tendon, nerve, or cardiac. These studies were supported by a grant from the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology and by an NRF grant funded by the Ministry of Science and ICT for the Bioinspired Innovation Technology Development Project. In addition, both studies were published in “Applied Physics Reviews” (IF = 17.05) and were selected as a featured paper. Figure 1. Schematical illustration and SEM images of microchanneled collagen/HA scaffold. Figure 2. Immunofluorescent images of the retrieved TA muscles for MRPL12 (green)/MHC (red) at 8 weeks after implantation. Professor Geun Hyung Kim Professor Geun Hyung Kim and his research team (From right) Prof. Geun Hyung Kim, Dr Hyeongjin Lee, Mr WonJin Kim, Mr Hanjun Hwangbo (From left) Prof. Geun Hyung Kim, Dr Hyeongjin Lee, Mr WonJin Kim, Mr Hanjun Hwangbo
A research collaboration team led by Prof.Daeil Kwon (Dept. of Systems Management Engineering) and Prof. Jooho Choi(Korea Aerospace University) developed a remaining useful life predictionmethod for secondary batteries with state changes. This research was publishedIEEE Transactions on Industrial Electronics (IF=7.515, Instruments &Instrumentation, JCR top 0.78% in instruments & instrumentation) Most cell phone users may have noticed overthe lifetime that the usage time of their cell phones is becoming short,compared to that of a new phone, even after the phone is fully charged. Thisphenomenon is known as capacity fade, the capacity of li-ion batteriesgradually decreases over repeated charge and discharge cycles. While capacityfading for most batteries is fairly consistent, some batteries show significantcapacity drop after a certain charge and discharge cycles, sometimes resultingin consumer claims. This research developed an advanced methodto accurately predict remaining useful life of secondary batteries even withstate changes. Particle filter, a popular model-based method for battery lifeprediction, may be inappropriate for batteries with state changes. The proposedmethod demonstrated accurate remaining useful life prediction performance bycontinuously learning the changes in battery capacity behavior, and by updatingthe prediction model accordingly. The proposed method is expected to apply tosystems with state changes in analyzing system behavior, as well as predictingremaining useful life, and thus to contribute effective and efficientmanagement of engineering assets.
Contact electrification is a well-known phenomenon in physics, in which opposite charges are created at surfaces due to continuous contact and separation processes occurring between two materials, followed by the generation of electric potentials between them. Triboelectric nanogenerators based on the phenomenon have not only been successfully demonstrated for use as power sources that are sufficient for powering small electronic devices, but they have also been used for sensing momentary stimuli in electronic skin, touch screens, healthcare devices, and habit-recognition security systems. However, the physical contact between two surfaces may have some big drawbacks in TENGs, such as decreases in their output power due to the wear of materials, the need to replace the device, and noise resulting from its operation. Sungkyunkwan University (President Dong Ryeol Shin) has developed a non-contact mode triboelectric nanogenerator with a new dielectric, a C60-containing block polyimide (PI-b-C60). compared with perfluoroalkoxy alkane film-based TENGs, the TENG based on PI-b-C60 generated 4.3 times higher output power and a superior charge density of over 300 μC m−2 with a 3 times slower charge decay rate. With the superior characteristics, a keyless electronic door lock system and a speed sensor with a tone wheel for a car with very sensitive and reliable operations, were developedfor the first time. Team also for the first time suggested a new paradigm to increasing the output voltage of a thermoelectric generator that does not involve material modification by introducing the contact electrification. Thermoelectric energy harvesting is a technology that generates useful energy by utilizing the temperature difference generated at both ends of a material when heat is applied from the outside. But there was still a difficulty in commercialization due to the very low output voltage. As a solution to these challenges, the research team created a polyimide-based polymer layer having negative charges as a triboelectric effect in the cold side of the BiSbTe-based thermoelectric device, which has the highest ZT value at room temperature. As a result, the output power has more than doubled and the world's highest output voltage (50% increase over the previous version) has been achieved. Prof. Baik said “These accomplishments by introducing the contact electrification is the breakthrough technologies for sustainable energy generation in energy harvesting research area.” These studies were published online in Energy & Environmental Science (IF 30.287) and ACS Energy Letters (IF: 19.003).
Professor Joo Sang Lee’s research team (Next-Gen Medicine Lab, Department of Artificial Intelligence and School of Medicine) demonstrated that they can identify which therapies may be particularly beneficial for individual patients by only looking at the patients’ molecular markup before treatment. When applied to data from a wide panel of different cancer targeted and immunotherapy clinical trials, the approach termed SELECT was successfully predictive of patient responses to these therapies in about 80 percent of the trials. These findings were reported April 13, 2021, in Cell. The study is based on identifying synthetic lethal interactions – a functional interaction between two genes whose co-inactivation leads to cancer cell death. Over 20 years ago, synthetic lethality has been proposed to have a great potential to revolutionize cancer treatment. This is partly because these interactions provide an opportunity to selectively kill only tumor cells while sparing normal cells by targeting synthetic lethal pairs of specific genes inactivated in a tumor. It has been investigated as a means to treat cancer, with some specific treatment regimens already used in the clinic. However, it is thought that many such treatment opportunities remain to be discovered and SELECT offers a computational method for identifying such treatment options for individual patients. By analyzing tumor transcriptomics data, this approach can identify actionable tumor vulnerabilities that are not readily evident by traditional mutational- and gene fusion-based sequencing approaches. In collaboration with Eytan Ruppin (Cancer Data Science Laboratory at National Cancer Institute), Joo Sang Lee together with his students Youngmin Chung and Dasol Kim has been leading the development of computational tools to identify synthetic lethality. In this most recent study, they assembled a broad collection of 35 published transcriptomic datasets from targeted and immunotherapy cancer clinical trials across 10 different cancer types. They applied SELECT to predict the treatment response of the patients, given their tumor molecular data, finding the SELECT signatures to be highly accurate in 80 percent of the trials. “To the best of our knowledge, SELECT is the first approach that systematically achieves these moderate, but helpful levels of accuracy across many different therapies and cancer types,” Lee says. Further investigation is now underway in collaboration with several clinical teams at the NIH Clinical Center to bring SELECT into clinic. The team hopes these prospective studies will further improve SELECT in the next few years, and if successful, establish SELECT as a complementary precision oncology approach for enhancing cancer-patient care.
In recent years, numerous electronics engineers worldwide have been trying to develop new semiconductor heterostructure devices using atomically thin materials. Among the many devices that can fabricated using these materials are resonant tunnelling diodes, which typically consist of a quantum-well structure placed between two barrier layers. Past research has shown that stacking two-dimensional (2D) layers that are twisted in relation to each other can enhance or suppress the interlayer coupling at their interface. This suppression or enhancement can in turn modulate the electronic, optical and mechanical properties of the resulting device. For instance, some studies found that the intralayer current transport in small angle twisted bilayer graphene prompted some exotic phenomena, such as superconductivity and ferromagnetism. These observations inspired a fundamentally new approach to device engineering, known as ‘twistronics’ (i.e., twist electronics). Researchers at Sungkyunkwan University in South Korea have recently carried out a study aimed at evaluating the potential of a twistronics design for developing resonant tunnelling diodes based on black phosphorus homostructures. The resulting twisted black phosphorus-based resonant tunneling diodes, presented in a paper published in Nature Electronics, exhibit a higher tunnelling conductance than resonant tunnelling diodes based on van der Waals heterostructures. “Interlayer current transport through twisted junctions could also be an intriguing topic of research that has not yet been explored,” Budhi Singh, one of the researchers who carried out the study, said. “This motivated us to investigate interlayer current-transport behavior in twisted black phosphorus-based homostructures.” In a series of laboratory experiments, Singh and his research team identified a number of valuable features that characterize black phosphorus, including its highly anisotropic nature, a thickness-dependent workfunction/2D-carrier density and a twist angle-dependent interlayer coupling. The highly anisotropic nature of black phosphorus ultimately enables a vanishing interlayer coupling strength at specific twist angles. “Interestingly, we found that the interlayer current-transport in such twisted junctions could be controlled even at higher twist angles,” Singh said. “The decoupled interface and momentum mismatch created through twisted Fermi surfaces could also affect the interlayer current-transport behavior and is a part of our primary investigation. In contrast, observation of exotic phenomena in intralayer current transport in twisted junctions is limited to smaller twist angles." To evaluate the potential of the design strategy they devised, the researchers fabricated a black phosphorus tri-layer homojunction, by integrating a thin layer of black phosphorus between two thicker layers. The middle and thinner layer is twisted in relation to the top and bottom black phosphorus layers. “Due to the twisted structure in our devices, the decoupled interfaces behave like a tunnel barrier for interlayer charge carrier transport,” Singh explained. “If we compare this structure with the conventional double barrier resonant tunnelling diode, middle black phosphorus serves as an analogue of the quantum well.” In the device fabricated by Singh and his colleagues, the emergence of a negative differential resistance and the evolution of peak position with a varying thickness of the middle black phosphorus layer produced a signature typically associated with resonant tunnelling diodes. Resonant tunnelling occurs when the energy and momenta of the top and bottom black phosphorus layers match those of the quantum well states, due to processes of energy and momentum conservation. “Whenever we talk about tunnelling phenomena, there has to be a physical barrier (i.e., materials with large energy bandgaps),” Singh said. “In general, this architecture is achieved in a heterostructures assembly, but we demonstrated resonant tunnelling through a homostructure without the need of any physical tunnel barrier.” The twistronics design strategy introduced by Singh and his colleagues could soon inspire the fabrication of other devices that exhibit remarkable tunnelling conductance. In the device created by the researchers, the tunnelling mechanism is dominated by a twist-controlled interlayer coupling, which results in a high tunnelling current density. Their diode device and other twist-controlled tunnel devices with high current densities could ultimately be used to realize a variety of high speed electronics, including THz oscillators and ultrafast switches. “In the near future, we would like to perform experiments to realize twisted black phosphorus homostructures in practical applications, such as THz devices and applications in superconducting spectroscopy.” Image Captions: Figure. (Left) Illustration of the twisted black phosphorus trilayer homojunction device in which a thin black phosphorus is 90o sandwiched between two thick black phosphorus. (Right) Interlayer tunnelling current (ID) through quantum well states revealed the characteristics of a resonant tunnelling diode. References: Resonant tunnelling diodes based on twisted black phosphorus homostructures. <i>Nature Electronics</i>(2021). DOI: 10.1038/s41928-021-00549-1. https://www.nature.com/articles/s41928-021-00549-1