SKKU Advanced Institute of Nanotechnology SAINT

Suigen, South Korea

SKKU Advanced Institute of Nanotechnology SAINT

Suigen, South Korea
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Trung T.Q.,Sungkyunkwan University | Duy L.T.,Sungkyunkwan University | Ramasundaram S.,Korea Institute of Science and Technology | Lee N.-E.,Sungkyunkwan University | And 2 more authors.
Nano Research | Year: 2017

Stretchable and conformal humidity sensors that can be attached to the human body for continuously monitoring the humidity of the environment around the human body or the moisture level of the human skin can play an important role in electronic skin and personal healthcare applications. However, most stretchable humidity sensors are based on the geometric engineering of non-stretchable components and only a few detailed studies are available on stretchable humidity sensors under applied mechanical deformations. In this paper, we propose a transparent, stretchable humidity sensor with a simple fabrication process, having intrinsically stretchable components that provide high stretchability, sensitivity, and stability along with fast response and relaxation time. Composed of reduced graphene oxide-polyurethane composites and an elastomeric conductive electrode, this device exhibits impressive response and relaxation time as fast as 3.5 and 7 s, respectively. The responsivity and the response and relaxation time of the device in the presence of humidity remain almost unchanged under stretching up to a strain of 60% and after 10,000 stretching cycles at a 40% strain. Further, these stretchable humidity sensors can be easily and conformally attached to a finger for monitoring the humidity levels of the environment around the human body, wet objects, or human skin. [Figure not available: see fulltext.] © 2016 Tsinghua University Press and Springer-Verlag Berlin Heidelberg

Trung T.Q.,Sungkyunkwan University | Lee N.-E.,Sungkyunkwan University | Lee N.-E.,SKKU Advanced Institute of Nanotechnology SAINT | Lee N.-E.,Samsung
Journal of Materials Chemistry C | Year: 2017

The development of transparent and stretchable (TS) electronics can enable a plethora of new applications such as TS integrated circuits, displays and sensors where high levels of both optical transparency and stretchability are required for conformal placement of devices on the human body or any arbitrary surface. Over the past decade, there has been enormous progress in the development of new materials, novel structural engineering, and smart fabrication processes for TS electronic devices including TS sensors, field-effect transistors, optoelectronic components, nanogenerators, supercapacitors, and heaters. TS electronic devices can be made by geometric engineering of traditional transparent and flexible electronic materials or developing new materials that are intrinsically transparent and stretchable. Herein, we review recent advances in TS electronic materials (such as conductors, semiconductors, and insulators) and TS electronic devices. Some representative examples that highlight the unique optical, electrical and mechanical properties of TS materials and devices are also discussed in detail. Conclusions and future prospects for the development of TS electronic devices are discussed in the final section. © The Royal Society of Chemistry.

Seo S.-W.,Sungkyunkwan University | Chae H.,Sungkyunkwan University | Seo S.J.,SKKU Advanced Institute of Nanotechnology SAINT | Chung H.K.,SKKU Advanced Institute of Nanotechnology SAINT | Cho S.M.,Sungkyunkwan University
Applied Physics Letters | Year: 2013

We report on an extremely bendable moisture barrier for the thin-film encapsulation of organic light-emitting diodes (OLEDs). Hybrid barriers with various dyads of alternating aluminum oxide (Al2O3) and plasma-polymerized layers, which are utilizable for the thin-film encapsulation of flexible OLEDs, were prepared by atomic layer deposition and plasma chemical vapor deposition, respectively. When the total thickness of Al2O 3 was fixed at 20 nm, an ultimate 200-dyad multilayer barrier showed change of less than 20 in water vapor transmission rate from its initial value of the order of 10-4 g/m2/day, even after 10 000 times of bending with a bending radius of 5 mm. © 2013 AIP Publishing LLC.

Trung T.Q.,Sungkyunkwan University | Ramasundaram S.,Korea Institute of Science and Technology | Hong S.W.,Korea Institute of Science and Technology | Lee N.-E.,Sungkyunkwan University | And 2 more authors.
Advanced Functional Materials | Year: 2014

A new class of temperature-sensing materials is demonstrated along with their integration into transparent and flexible field-effect transistor (FET) temperature sensors with high thermal responsivity, stability, and reproducibility. The novelty of this particular type of temperature sensor is the incorporation of an R-GO/P(VDF-TrFE) nanocomposite channel as a sensing layer that is highly responsive to temperature, and is optically transparent and mechanically flexible. Furthermore, the nanocomposite sensing layer is easily coated onto flexible substrates for the fabrication of transparent and flexible FETs using a simple spin-coating method. The transparent and flexible nanocomposite FETs are capable of detecting an extremely small temperature change as small as 0.1 C and are highly responsive to human body temperature. Temperature responsivity and optical transmittance of transparent nanocomposite FETs were adjustable and tuneable by changing the thickness and R-GO concentration of the nanocomposite. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lee C.,SKKU Advanced Institute of Nanotechnology SAINT | Baik S.,SKKU Advanced Institute of Nanotechnology SAINT
Carbon | Year: 2010

A membrane filter possessing both superhydrophobicity and superoleophilicity is of great interest for the possible separation of oil and water. Such a filter was realized in this study by synthesizing vertically-aligned multi-walled carbon nano-tubes on a stainless steel mesh. The dual-scale structure, nano-scale needle-like tubes on the mesh with micro-scale pores, combined with the low surface energy of carbon amplified both hydrophobicity and oleophilicity. For the tests, diesel was selected as a representative of low viscosity oils. The contact angles for diesel and water were 0° and 163 ± 4°. The nano-tube filter could separate diesel and water layers, and even surfactant-stabilized emulsions. The successful phase separation of the high viscosity lubricating oil and water emulsions was also carried out. The separation mechanism can be readily expanded to a variety of different hydrophobic and oleophilic liquids. The simple nano-tube filter might be practically employed in environmental and chemical separation processes including oil spill cleanup. © 2010 Elsevier Ltd. All rights reserved.

Park J.,Center for Superfunctional Materials | Lee W.H.,Pohang University of Science and Technology | Huh S.,Center for Superfunctional Materials | Sim S.H.,SKKU Advanced Institute of Nanotechnology SAINT | And 6 more authors.
Journal of Physical Chemistry Letters | Year: 2011

We have devised a method to optimize the performance of organic field-effect transistors (OFETs) by controlling the work functions of graphene electrodes by functionalizing the surface of SiO2 substrates with self-assembled monolayers (SAMs). The electron-donating NH2- terminated SAMs induce strong n-doping in graphene, whereas the CH 3-terminated SAMs neutralize the p-doping induced by SiO2 substrates, resulting in considerable changes in the work functions of graphene electrodes. This approach was successfully utilized to optimize electrical properties of graphene field-effect transistors and organic electronic devices using graphene electrodes. Considering the patternability and robustness of SAMs, this method would find numerous applications in graphene-based organic electronics and optoelectronic devices such as organic light-emitting diodes and organic photovoltaic devices. © 2011 American Chemical Society.

Ni G.-X.,National University of Singapore | Zheng Y.,National University of Singapore | Bae S.,SKKU Advanced Institute of Nanotechnology SAINT | Kim H.R.,SKKU Advanced Institute of Nanotechnology SAINT | And 8 more authors.
ACS Nano | Year: 2012

The technical breakthrough in synthesizing graphene by chemical vapor deposition methods (CVD) has opened up enormous opportunities for large-scale device applications. To improve the electrical properties of CVD graphene grown on copper (Cu-CVD graphene), recent efforts have focused on increasing the grain size of such polycrystalline graphene films to 100 Î/m and larger. While an increase in grain size and, hence, a decrease of grain boundary density is expected to greatly enhance the device performance, here we show that the charge mobility and sheet resistance of Cu-CVD graphene is already limited within a single grain. We find that the current high-temperature growth and wet transfer methods of CVD graphene result in quasi-periodic nanoripple arrays (NRAs). Electron-flexural phonon scattering in such partially suspended graphene devices introduces anisotropic charge transport and sets limits to both the highest possible charge mobility and lowest possible sheet resistance values. Our findings provide guidance for further improving the CVD graphene growth and transfer process. © 2012 American Chemical Society.

Lai S.,SKKU Advanced Institute of Nanotechnology SAINT | Lai S.,Center for Human Interface Nanotechnology | Kyu Jang S.,SKKU Advanced Institute of Nanotechnology SAINT | Jae Song Y.,SKKU Advanced Institute of Nanotechnology SAINT | And 4 more authors.
Applied Physics Letters | Year: 2014

We report a simple and accurate method for detecting graphene defects that utilizes the mild, dry annealing of graphene/Cu films in air. In contrast to previously reported techniques, our simple approach with optical microscopy can determine the density and degree of dislocation of defects in a graphene film without inducing water-related damage or functionalization. Scanning electron microscopy, confocal Raman and atomic force microscopy, and X-ray photoelectron spectroscopy analysis were performed to demonstrate that our nondestructive approach to characterizing graphene defects with optimized thermal annealing provides rapid and comprehensive determinations of graphene quality. © 2014 AIP Publishing LLC.

Kang J.,SKKU Advanced Institute of Nanotechnology SAINT | Kim H.,Korea Electronics Technology Institute | Kim K.S.,Sejong University | Lee S.-K.,Sungkyunkwan University | And 9 more authors.
Nano Letters | Year: 2011

We demonstrate high-performance, flexible, transparent heaters based on large-scale graphene films synthesized by chemical vapor deposition on Cu foils. After multiple transfers and chemical doping processes, the graphene films show sheet resistance as low as ∼43 Ohm/sq with ∼89% optical transmittance, which are ideal as low-voltage transparent heaters. Time-dependent temperature profiles and heat distribution analyses show that the performance of graphene-based heaters is superior to that of conventional transparent heaters based on indium tin oxide. In addition, we confirmed that mechanical strain as high as ∼4% did not substantially affect heater performance. Therefore, graphene-based, flexible, transparent heaters are expected to find uses in a broad range of applications, including automobile defogging/deicing systems and heatable smart windows. © 2011 American Chemical Society.

Kim B.J.,Soongsil University | Jang H.,SKKU Advanced Institute of Nanotechnology SAINT | Jang H.,Sungkyunkwan University | Lee S.-K.,SKKU Advanced Institute of Nanotechnology SAINT | And 6 more authors.
Nano Letters | Year: 2010

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 cm2/(V•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. © 2010 American Chemical Society.

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