Beom Joon Kim

High-Performance Flexible Graphene Field Effect Transistors with Ion Gel Gate Dielectrics

A high-performance low-voltage graphene field-effect transistor (FET) array was fabricated on a flexible polymer substrate using solution-processable, high-capacitance ion gel gate dielectrics. The high capacitance of the ion gel, which originated from the formation of an electric double layer under the application of a gate voltage, yielded a high on-current and low voltage operation below 3 V. The graphene FETs fabricated on the plastic substrates showed a hole and electron mobility of 203 +/- 57 and 91 +/- 50 cm(2)/(V x s), respectively, at a drain bias of -1 V. Moreover, ion gel gated graphene FETs on the plastic substrates exhibited remarkably good mechanical flexibility. This method represents a significant step in the application of graphene to flexible and stretchable electronics.

Stretchable Graphene Transistors with Printed Dielectrics and Gate Electrodes

With the emergence of human interface technology, the development of new applications based on stretchable electronics such as conformal biosensors and rollable displays are required. However, the difficulty in developing semiconducting materials with high stretchability required for such applications has restricted the range of applications of stretchable electronics. Here, we present stretchable, printable, and transparent transistors composed of monolithically patterned graphene films. This material offers excellent mechanical, electrical, and optical properties, capable of use as semiconducting channels as well as the source/drain electrodes. Such monolithic graphene transistors show hole and electron mobilities of 1188 ± 136 and 422 ± 52 cm(2)/(V s), respectively, with stable operation at stretching up to 5% even after 1000 or more cycles.

Low‐Temperature, Solution‐Processed and Alkali Metal Doped ZnO for High‐Performance Thin‐Film Transistors

) and its dep-osition requires a high-cost vacuum process. More importantly, the poor transparency of silicon makes it unsuitable for trans-parent applications, and transparency is one of the key issues for future display technology. Consequently, in a search for alterna-tives for amorphous silicon, considerable interest has focused on metal oxide semiconductors, such as In, Ga, or Zn oxides, as these exhibit high optical transparencies, and have excel-lent electrical properties with high electron mobility, chemical stability, and solution processability. For example, ZnO-based semiconductors have been successfully incorporated into var-ious electronic devices, such as electron transfer layers for solar cells,

Metabolic Syndrome as an Independent Risk Factor of Silent Brain Infarction in Healthy People

Background and Purpose— Metabolic syndrome (MetS) is associated with an increased risk of the subsequent development of cardiovascular disease or stroke. Moreover, a silent brain infarction (SBI) can predict clinical overt stroke or dementia. We examined the associations between SBI and MetS in apparently healthy individuals. Methods— We evaluated 1588 neurologically healthy subjects (927 males and 661 females) who underwent brain MRI at Seoul National University Hospital Healthcare System Gangnam Center. MetS was defined using the criteria of the National Cholesterol Education Program Adult Treatment Panel III. We examined associations between full syndrome (≥3 of the 5 conditions) as well as its components and SBI by controlling possible confounders. Results— Eighty-eight (5.5%) were found to have ≥1 SBI on MRI. Age was found to be significantly related to SBI prevalence (odds ratio [OR], 1.06; 95% CI, 1.04 to 1.09). A history of coronary artery disease was associated with an elevated odds ratio of SBI ...

High-mobility low-temperature ZnO transistors with low-voltage operation

Low voltage high mobility n-type thin film transistors (TFTs) based on sol-gel processed zinc oxide (ZnO) were fabricated using a high capacitance ion gel gate dielectric. The ion gel gated solution-processed ZnO TFTs were found to exhibit excellent electrical properties. TFT carrier mobilities were 13 cm2/V s, ON/OFF current ratios were 105, regardless of the sintering temperature used for the preparation of the ZnO thin films. Ion gel gated ZnO TFTs are successfully demonstrated on plastic substrates for the large area flexible electronics.

Fractional Photothermolysis for the Treatment of Striae Distensae in Asian Skin

AbstractBackground:Striae distensae (SD) are dermal scars characterized by linear atrophic depressions. Fractional photothermolysis (FP) is an effective modality for the treatment of cutaneous scars. Objective:To evaluate the safety and efficacy of FP for the treatment of SD in Asian skin. Methods:Six female volunteers aged between 20 and 35 years with chronic striae albae phase SD on both buttocks were enrolled. SD lesions on the right buttock were irradiated with a 1550-nm FP laser and patients were followed every 4 weeks for a total of 8 weeks. Outcome assessments included serial photographs, erythema index and melanin index tracking, skin elasticity, histologic examination, and the patients’ subjective satisfaction scores. Results:FP treatment was associated with a substantial improvement in the appearance of SD at 8 weeks post-treatment. The erythema index and melanin index of the treated SD lesions tended to converge with those of the control skin at 4-week follow-up. Skin elasticity was found to be partially normalized after FP. In addition, there was a significant increase in epidermal thickness, collagen, and elastic fiber deposition after FP as demonstrated by histologic examination. Adverse effects of FP included mild and transient pain and hyperpigmentation. Conclusion:FP can reduce SD by stimulating new collagen and elastic fiber synthesis. In addition, repetitive treatments might constitute an effective approach to improving the treatment of SD.

Active Matrix Electronic Skin Strain Sensor Based on Piezopotential‐Powered Graphene Transistors

Dr. Q. Sun, B. J. Kim, Prof. S.-W. Kim, Prof. J. H. Cho SKKU Advanced Institute of Nanotechnology (SAINT) Sungkyunkwan University Suwon 440-746 , South Korea E-mail: kimsw1@skku.edu; jhcho94@skku.edu W. Seung, Prof. S.-W. Kim School of Advanced Materials Science and Engineering Sungkyunkwan University Suwon 440-746 , South Korea Prof. J. H. Cho School of Chemical Engineering Sungkyunkwan University Suwon 440-746 , South Korea Prof. S. Seo College of BioNano Technology Gachon University Seongnam 461-701 , South Korea

Coplanar-Gate Transparent Graphene Transistors and Inverters on Plastic

Transparent flexible graphene transistors and inverters in a coplanar-gate configuration were presented for the first time using only two materials: graphene and an ion gel gate dielectric. The novel device configuration simplifies device fabrication such that only two printing steps were required to fabricate transistors and inverters. The devices exhibited excellent device performances including low-voltage operation with a high transistor-on-current and mobility, excellent mechanical flexibility, environmental stability, and a reasonable inverting behavior upon connecting the two transistors.

Secular Trends in Ischemic Stroke Characteristics in a Rapidly Developed Country Results From the Korean Stroke Registry Study (Secular Trends in Korean Stroke)

Background— A dynamic change in industry, lifestyle, and healthcare structure brings a corresponding change in disease patterns. Limited data exist with respect to secular trends in stroke epidemiology in Korea, a rapidly developed country. Methods and Results— We analyzed individual patient data registered the Korean Stroke Registry, a nationwide hospital-based stroke database, between January 2002 and November 2010. Mortality data were obtained from a national death certificate system. Linear or logistic regression analyses were performed to assess secular trends. A total of 46 098 patients were included in this study. Mean±SD age was 66.1±12.3 years, and 57.6% of the patients were men. Over the 9-year period, patient ages steadily increased by 0.24 year annually (P<0.001). Risk factor proportions of hypertension, diabetes, smoking, and prior stroke declined slightly (P<0.05 for all). However, dyslipidemia frequency showed a complex pattern of an initial decline and then an increase. For relative proportions of subtypes, cardioembolism increased, small vessel occlusion decreased, and large artery atherosclerosis remained stable. Still, intracranial stenosis overwhelms extracranial stenosis, but extracranial stenosis is on the rise. Arrival within 3 hours increased from 20% to 29%, and reperfusion therapy increased from 5.3% to 7.0%. Age-adjusted all-cause mortality did not decrease at 30 days but decreased at 1 year over time. Conclusions— During the first decade of 21st century, stroke characteristics in Korea changed, likely because of increased lifespan, westernized lifestyle, and improved public awareness. Stroke experts need to cope with these distinguishing trends to establish a better strategy for prevention and acute therapy.

Multiple Pass Ultrasound Tightening of Skin Laxity of the Lower Face and Neck

BACKGROUND Skin laxity is a common complaint of patients who request skin rejuvenation. Radiofrequency and infrared light are widely used for nonablative treatment of skin laxity. Intense focused ultrasound (IFUS) has been investigated as a tool for the treatment of solid benign and malignant tumors for many decades but is only now beginning to emerge as a potential noninvasive alternative to conventional nonablative therapy. OBJECTIVES To evaluate the efficacy of IFUS for the treatment of face and neck laxity. METHODS Twelve female volunteers were enrolled in the study, and 10 were ultimately evaluated. The device under investigation was an IFUS. Areas treated included the face and neck. For treatment, the 4‐MHz, 4.5‐mm probe was used first, followed by the 7‐MHz, 3.0‐mm probe. Two blinded, experienced clinicians evaluated paired pretreatment and post‐treatment (day 90) photographs. Patient self‐assessments were also obtained. RESULTS On the first primary outcome measure, two blinded clinicians felt that 8 of 10 subjects (80%) showed clinical improvement 90 days after treatment. Nine of 10 subjects (90%) reported subjective improvement. CONCLUSIONS IFUS has many advantages for skin tightening.