Showing papers by "Jong Hyun Ahn published in 2011"

Graphene for Controlled and Accelerated Osteogenic Differentiation of Human Mesenchymal Stem Cells

Abstract: Current tissue engineering approaches combine different scaffold materials with living cells to provide biological substitutes that can repair and eventually improve tissue functions. Both natural and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation into muscles, bones, and cartilages. One of the key objectives for bone regeneration therapy to be successful is to direct stem cells’ proliferation and to accelerate their differentiation in a controlled manner through the use of growth factors and osteogenic inducers. Here we show that graphene provides a promising biocompatible scaffold that does not hamper the proliferation of human mesenchymal stem cells (hMSCs) and accelerates their specific differentiation into bone cells. The differentiation rate is comparable to the one achieved with common growth factors, demonstrating graphene’s potential for stem cell research.

Chemical vapor deposition-grown graphene: the thinnest solid lubricant.

Abstract: As an atomically thin material with low surface energy, graphene is an excellent candidate for reducing adhesion and friction when coated on various surfaces. Here, we demonstrate the superior adhesion and frictional characteristics of graphene films which were grown on Cu and Ni metal catalysts by chemical vapor deposition and transferred onto the SiO2/Si substrate. The graphene films effectively reduced the adhesion and friction forces, and multilayer graphene films that were a few nanometers thick had low coefficients of friction comparable to that of bulk graphite.

High-performance graphene-based transparent flexible heaters.

Abstract: 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.

Stretchable Graphene Transistors with Printed Dielectrics and Gate Electrodes

Abstract: 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 cm2/(V s), respectively, with stable operation at stretching up to 5% even after 1000 or more cycles.

Graphenes Converted from Polymers

Abstract: Because the direct formation of large, patterned graphene layers on active electronic devices without any physical transfer process is an ultimate important research goal for practical applications, we first developed a cost-effective, scalable, and sustainable process to form graphene films from solution-processed common polymers directly on a SiO2/Si substrate. We obtained few-layer graphene by heating the thin polymer films covered with a metal capping layer in a high-temperature furnace under low vacuum in an Ar/H2 atmosphere. We find that the metal capping layer appears to have two functions: prevention of vaporization of dissociated molecules and catalysis of graphene formation. We suggest that polymer-derived graphene growth directly on inert substrates in active electronic devices will have great advantages because of its simple, inexpensive, and safer process.

Graphene-based bimorph microactuators.

Abstract: A novel graphene-on-organic film fabrication method that is compatible with a batch microfabrication process was developed and used for electromechanically driven microactuators. A very thin layer of graphene sheets was monolithically integrated and the unique material characteristics of graphene including negative thermal expansion and high electrical conductivity were exploited to produce a bimorph actuation. A large displacement with rapid response was observed while maintaining the low power consumption. This enabled the successful demonstration of transparent graphene-based organic microactuators.

Wafer-scale graphene/ferroelectric hybrid devices for low-voltage electronics

Abstract: Preparing graphene and its derivatives on functional substrates may open enormous opportunities for exploring the intrinsic electronic properties and new functionalities of graphene. However, efforts in replacing SiO2 have been greatly hampered by a very low sample yield of the exfoliation and related transferring methods. Here, we report a new route in exploring new graphene physics and functionalities by transferring large-scale chemical-vapor deposition single-layer and bilayer graphene to functional substrates. Using ferroelectric Pb(Zr0.3Ti0.7)O3 (PZT), we demonstrate ultra-low-voltage operation of graphene field effect transistors within ±1 V with maximum doping exceeding 1013 cm− 2 and on-off ratios larger than 10 times. After polarizing PZT, switching of graphene field effect transistors are characterized by pronounced resistance hysteresis, suitable for ultra-fast non-volatile electronics.

Graphene protective film serving as a gas and moisture barrier, method for forming same, and use thereof

Abstract: The present invention relates to a method for forming a graphene protective film having gas and moisture barrier properties, to a graphene protective film formed by the method, and to the use thereof A single-layer or multi-layer graphene protective film can be used as a material for a barrier coating or bags, and improves the gas and moisture barrier properties of a variety of devices in a wide array of industrial fields to thereby maintain the electrical characteristics of devices over a long period of time

Touch sensor using graphene for simultaneously detecting a pressure and a position

Abstract: A touch sensor capable of specifying a touch position and/or a degree of a touch pressure by using graphene as an electrode and/or a strain gauge, and more particular, a touch sensor capable of simultaneously detecting a pressure and a position by means of change in resistance by using graphene is provided.

Touch sensor using graphin for simultaneously detecting pressure and position

Abstract: Provided is a touch sensor for measuring a touch position and/or the degree of touching pressure by using graphin as an electrode and/or a strain gauge, and more particularly, to a touch sensor for simultaneously detecting pressure and position by means of change in resistance by using the graphin.

Graphene roll-to-roll transfer method, graphene roll-to-roll transfer apparatus, and graphene roll

Abstract: PURPOSE: A graphene roll-to-roll transfer method is provided to enable easy transfer a large-sized graphene layer on a flexible substrate through roll-to-roll etching and/or transfer process. CONSTITUTION: A graphene roll-to-roll transfer method comprises the steps of: forming a laminate(50) including a material-graphene layer-first flexible substrate from a graphene layer(20) formed on a substrate(10) and the first flexible substrate(31) contacted with the graphene layer; and removing the substrate from the laminate and transferring the graphene layer on the first flexible substrate by impregnating the laminate in an etchant(60) using a second roller part(120).

Method for preparing graphene, graphene sheet, and device using same

Abstract: The present invention provides a method for preparing graphene by providing a reaction gas including a carbon source and heat onto a substrate, and reacting the same to form a graphene on the substrate, a graphene sheet formed by the method, and a device using the same.

Flexible ferroelectric memory device and manufacturing method for the same

Abstract: The present disclosure relates to a flexible nonvolatile ferroelectric memory device, a 1T-1R (1Transistor-1Resistor) flexible ferroelectric memory device, and a manufacturing method for the same.

A numerical study on the mechanical characteristics of zinc oxide-based transparent thin film transistors.

Abstract: Zinc Oxide (ZnO) based Thin Film Transistors (TFTs) have been fabricated and analyzed to investigate mechanical characteristics regarding the stress, strain and deformation of electro circuits using the Finite Element Method (FEM). As the best compromise between the stretching and bending abilities, the coating thickness of SU-8 can be as important for bendability as a neutral mechanical plane. The neutral mechanical plane in electro circuits was designed for obtaining flexibility, e.g., bendability, in a previous numerical study. After that, through experimental validation, we observed what degree of SU-8 thickness was attributable for improved mechanical stability. The results suggest that not only numerical but also experimental measurements of the deformation and SU-8 coating thickness in electro circuits are useful for enhancing structural stability.

Flexible and transparent heating device using graphene and preparing method of the same

Abstract: PURPOSE: The flexibility transparency heating element using graphene and the manufacturing method thereof are formed differently the floor number of graphene. The calorific efficiency of the heating element is multiplied. CONSTITUTION: A graphene layer(140) is at least formed of a flexibility transparent substrate(100) in a single-side. By offering the reaction gas and the heat including the carbon source on the metallic catalyst and reacting the graphene layer is formed. A electrode(120) more than the pair is formed as long as it is connected to the graphene layer. The protective layer is formed in electrode and the graphene layer. The electrode is patterned to the fine structure.

Plate Girder Bridge Strengthened with Multi-Stepwise Thermal Prestressing Method

Abstract: The strengthening of a plate girder bridge with external prestressing tendons is a commonly used method of upgrading existing bridges. Indeed, it has been known to offer advantages such behaviors as increased elastic behaviors under higher loading, increased ultimate resistance, and reduced deflection under service loads. However, this method has notable disadvantages such as stress concentration at anchorages and inefficient live load-carrying capacity. The thermal prestressing method (TPSM) for steel bridges proposed in this study uses thermal expansion and contraction of a cover-plate to provide a combination with the prestress effects of an external prestressing tendon and the section enlargement benefits of the external bonding method.In this study, the basic concepts of the proposed strengthening protocol using multi-stepwise TPSM are presented. The existence of the strengthening effect is well substantiated and the proposed analytical approach is also rigorously verified. The significant strengthen...

Micro- and Nanostructured Semiconductor Materials for Flexible and Stretchable Electronics

Abstract: In this chapter, the authors review some recent work in the area of micro/nanostructured materials (including wires, ribbons, and single-walled carbon nanotubes) for high-performance devices and circuits on flexible and even stretchable substrates, in two- or three-dimensional layouts. Approaches, ranging from self-assembly to dry transfer printing, for fabricating a variety of micro/nanostructured materials are discussed. These methods enable high-performance electronics on plastic or elastomer substrates, as demonstrated in several different application examples. Successful commercial implementation of such techniques represents a significant engineering challenge, but could create interesting opportunities for developing electronic systems such as personal health monitors and hemispherical electronic eye imagers.

Inorganic Semiconductor Nanomaterials for High‐Performance Flexible Electronics

Abstract: This article reviews several classes of high-quality inorganic semiconductor nanomaterials for high-performance flexible and stretchable electronics in two- or three-dimensional layouts Approaches for fabricating inorganic semiconductors in the forms of wires, ribbons, and membranes, and methods for integrating these materials on flexible substrates are presented Finally, perspectives on the trends for future work related to flexible electronics are described Keywords: flexible electronics; inorganic semiconductor nanomaterials; top-down approach; dry transfer printing; thin-film transistor; stretchable electronics; 3-D heterogeneous integrated circuits

Chemical Vapor Deposition-Grown Graphene: The Thinnest Solid

Abstract: As an atomically thin material with low surface energy, graphene is an excellent candidateforreducingadhesionandfrictionwhencoatedonvarioussurfaces.Here,wedemonstrate thesuperioradhesionandfrictionalcharacteristicsofgraphene filmswhichweregrownonCuandNi metal catalysts by chemical vapor deposition and transferred onto the SiO2/Si substrate. The graphene films effectively reduced the adhesion and friction forces, and multilayer graphene films that were a few nanometers thick had low coefficients of friction comparable to that of bulk graphite.

The mechanical reliability of transparent ZnO TFT transfer printed on the flexible substrate

Abstract: In this study, we investigated the bendablity and reliability of transparent ZnO TFTs. Transfer printing method was used to make flexible ZnO TFTs. The PET was used as the transparent and flexible plastic substrate which thickness was 188 μm. The bending test and fatigue test were performed to evaluate the mechanical reliability. After reliability tests, the failure mode of ZnO TFTs was analyzed and its results were also confirmed by stress/strain simulation analysis.

Deformation characteristics of an organic thin film transistor.

Abstract: An organic thin film transistor (OTFT) on a flexible substrate with electroplated electrodes has many advantages in the fabrication of low cost sensors, e-paper, smart cards, and flexible displays. In this study, we simulated the mechanical characteristics of an OTFT with various compressive stress conditions using COMSOL. An analysis model, which was limited to channel, source, and drain, was used to investigate deformation and internal stress concentrations. The channel length is 40 m and the OTFT structure is a top-contact structure. The OTFT was fabricated using pentacene as a semiconducting layer and electroplated Ni as a gate electrode. The deformation characteristics of the fabricated OTFT were predicted in terms of strain and internal stress.

Study on Design of ZnO-Based Thin-Film Transistors With Optimal Mechanical Stability

Abstract: ZnO-based thin-film transistors (TFTs) have been fabricated and the mechanical characteristics of electric circuits, such as stress, strain, and deformation are analyzed by the finite element method (FEM). In this study, a mechanical-stability design guide for such systems is proposed; this design takes into account the stress and deformation of the bridge to estimate the stress distribution in an film with 0 to 5% stretched on 0.5--thick. The predicted buckle amplitude of bridges agrees well with experimental results within 0.5% error. The stress and strain at the contact point between bridges and a pad were measured in a previous structural analysis. These structural analysis suggest that the numerical measurement of deformation, SU-8 coating thickness for Neutral Mechanical Plane (NMP) and ITO electrode size on a dielectric layer was useful in enhancing the structural and electrical stabilities.