Soft Nanoelectronic Devices Based on Novel 2D Nanomaterials and Self-assembled Organic Semiconductors

Department of Energy EngineeringRecent advances in electronic device are focused on a fabrication of flexible and stretchable electronic gadgets in a low-cost and sustainable ways. The fabrication of flexible and stretchable electronic devices is highly challenging using inorganic or Si-based electronic materials due to its fragile nature upon a strain. Utilization of solution-processable organic materials including small molecules and polymer in organic field effect transistors (OFETs), light emitting diodes, and solar cells, facilitates a low-cost, large-area, cheap, and environment-friendly mass production for the fabrication of flexible and stretchable electronic devices. Conjugated small molecules and polymers continue to be studied intensively as semiconducting and conducting materials due to its tunability of their electronic and optoelectronic properties. Graphene, a single layer of two-dimensional (2D) carbon atoms in a honeycomb lattice, has attracted enormous attention due to its unique electronic, optical, thermal, and mechanical properties. It has an extremely high charge carrier mobility (~ 200,000 cm2V???1s???1), an optical transmittance of 97.7%, a theoretical sheet resistance of 30 ??/sq, a high fracture strain resistance greater than 20%, and chemical stability. These features make it highly promising for applications in flexible electronics and energy conversion devices, including touch screens, field-effect transistors (FETs), capacitors, batteries, solar cells, and light-emitting diodes (LEDs). However, the zero-band gap, small optical absorption, and chemical inertness have limited its practical application in switching and optoelectronic devices. Similar to graphene, transition metal dichalcogenides (TMDCs) are 2D materials stacked by van der Waals forces. Contrary to graphene, which does not have a bandgap energy, TMDCs have tunable bandgaps unlike to graphene. Typically, bulk TMDCs show indirect bandgap. On the other hand, the bandgap of TMDCs gradually decrease to one monolayer. Herein, I present a forward-looking my research results which are mainly focused on the interface studies between organic electronic materials and 2D nanomaterials including graphene and MoSe2, because of the importance of the mechanism and the behavior of electrical property change when organic electronic materials and 2D nanomaterials comes together in the electronic device system. When it comes to the interface study between heterogeneous electronic materials, doping of organic semiconductor and 2D nanomaterials is one of the important steps to enhance the electrical performance. Especially, n-doping of organic semiconductor is more challenging than p-doping because the n-dopants have to show a very low ionization potential to enable electrons to be transferred effectively, which renders most possible candidates unstable in air. Among the various doping strategies, surface transfer doping technique has been investigated for graphene and MoSe2 to modify or enhance their electrical or optoelectrical properties without severe damage on the surface of matrix. In addition, new carbon-based materials with honey comb structure or graphitic structure applying heterogenous atoms such as nitrogen (nitrogen doped reduced graphene oxide and 2D polyaniline) are explored to figure out their unique electrical properties and potential of electronic application. The experimental results and discussion in this thesis represent a forward-looking insight in charge transport behavior when organic electronic materials and 2D nanomaterials make junction together and pave the way of the applicability of organic semiconductors in conventional microelectronic infrastructures, which will lead to progress in the realization of soft nanoelectronic devices.ope

Grazing-Incidence X-ray Diffraction을 이용한 유기반도체 구조 분석과 양극성 유기트랜지스터 어레이 응용

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THE EFFECTS OF SUSPENSION FUNCTION OF HIKING BOOTS ON THE STABILITY OF THE FOOT

The purpose of this study is to investigate the effects of suspension function of hiking boot on the stability of foot. 8 participants free from injury to the triceps surae muscle group in recent years and able to perform jumping participated in this test. 2-D kinematic analysis and kinetic analysis were conducted for the data acquisition. The maximum suspension angle of suspension boot was greater than that of normal boot for eversion condition; on the contrary the maximum loading rate of normal boot was greater than that of suspension boot for inversion condition. These results meant that the suspension function helps the boot keep stable shortly after landing through the control of rearfoot angle. Moreover, if we apply a lower threshold level at medial part of boot, suspension function will show its ability even though at medial landing. It was concluded that an improved suspension function may help to reduce fatigue and prevent injury such as ankle sprain in hiking on uneven surface

Advanced Materials and Assembly Strategies for Wearable Biosensors: A Review

Recent technological advances of soft functional materials and their assembly into wearable (i.e., on-skin) biosensors lead to the development of ground-breaking biomedical applications ranging from wearable health monitoring to drug delivery and to human-robot interactions. These wearable biosensors are capable of unobtrusively interfacing with the human skin and enabling long-term reliable monitoring of clinically useful biosignals associated with health and other conditions affecting well-being. Scalable assembly of diverse wearable biosensors has been realized through the elaborate combination of intrinsically stretchable materials including organic polymers or/and low-dimensional inorganic nanomaterials. In this Chapter, we review various types of wearable biosensors within the context of human health monitoring with a focus of their constituent materials, mechanics designs, and large-scale assembly strategies. In addition, we discuss the current challenges and potential future research directions at the end of this chapter

Silicon improves growth and antioxidative defense system in salt-stressed Kentucky bluegrass (Poa pratensis L.), ‘Perfection’ and ‘Midnight’

After 400 mM of NaCl treatment, 0.1 and 1.0 mM of silicon (Si) were added to Kentucky bluegrass, ‘Perfection’ and ‘Midnight,’ to identify the effect of Si on the antioxidant defense mechanisms and inorganic ions as a parameter in the salt stress on grass. Compared to the control, the NaCl treatment caused a significant decrease in the shoot length and the fresh and dry weight of shoot and root of the both types of Kentucky bluegrass. Adding Si after the NaCl treatment increased the growth and dry and fresh weight of shoot and root in the grass. In both types, the Na+ concentration significantly increased after the NaCl-only treatment compared to control and decreased dramatically after 0.1 and 1.0 mM Si were added following the NaCl treatment compared to the NaCl-only treatment. K+ and Si concentrations remarkably increased in the shoot and root when Si was added after NaCl treatment. There was a significant reduction in the oxygen radical absorption capacity and the total phenolic compounds in the both types. Compared to the NaCl-only treatment, higher glutathione and lower proline concentrations were observed in the plant treated with Si after NaCl treatment. These results suggest that, even though Si is not generally classified as ‘essential element’, Si may have a significant involvement in the antioxidant defense mechanisms and inorganic ions in the salt stress on grass.Key words: diphenyl-1-picrylhydrazyl (DPPH), total phenolic concentration, proline, salt stress

Antioxidant compounds from marine seaweeds and their mechanism of action

Investigation of natural products has moved toward marine environments as they are a source of many biologically active agents. The natural antioxidant compounds isolated from seaweeds provide a valuable contribution to the innovation of new drugs for chronic diseases associated with oxidative stress. While the antioxidant activity and nutritional benefits of various seaweed products are well recognized, their proper utilization as antioxidants remains at initial stages that require further investigative studies. This review provides a detailed study of isolated antioxidant compounds from seaweeds and their major mechanism of action by focusing on the reports from 2015 to 2019. The report discusses various active antioxidant compounds, including phenolics (e.g., phlorotannins), polysaccharides, and pigments with proven benefits against oxidative stress-related diseases, especially carotenoids, from the aspect of benefits to human health

Psycho-oncology in Korea: Past, present and future

Background: Psycho-oncology in Korea was introduced among the circle of consultation-liaison psychiatrists, in the 1990s. For almost 25 years, the field has been developing at a steady pace as the psychosocial needs of patients with cancer continue to increase. In this study, we review the history of psycho-oncology in Korea, in a chronological order, within the domains of clinical practice, research activity, training, and public policy. Main body: Before the 1990s, patients with cancer with psychiatric comorbidities were usually taken care of by consultation-liaison psychiatrists in general hospitals. In 1993, psycho-oncology was first introduced by psychiatrists. Psychologists, nurses, and social workers have also been increasingly involved in providing psychosocial care for patients with cancer. Professionals from various disciplines began to communicate, and agreed to found the Korean Psycho-Oncology Study Group (KPOSG) in 2006, the first academic society in this field. In 2009, National Cancer Center published the Recommendations for Distress Management in Patients with Cancer, which are consensus-based guidelines for Korean patients. In 2014, the KPOSG was dissolved and absorbed into a new organization, the Korean Psycho-Oncology Society (KPOS). It functions as a center of development of psycho-oncology, publishing official journals, and hosting annual conferences. There are many challenges, including, low awareness of psycho-oncology, presence of undertreated psychiatric disorders in patients with cancer, shortage of well-trained psycho-oncologists, stigma, and suicide risk. It is important to improve the cancer care system to the extent that psycho-oncology is integrated with mainstream oncology. Considering the socio-cultural characteristics of Korean cancer care, a Korean model of distress management is being prepared by the KPOS. Conclusion: This article provides an overview of the development, current issues, and future challenges of psycho-oncology in Korea. Through its long journey to overcome the many barriers and stigmas of cancer and mental illnesses, psycho-oncology is now acknowledged as an essential part of integrated supportive care in cancer. Active research and international cooperation can gradually shape the Korean model of distress management.ope