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Yanggu, South Korea

Gwon H.,KAIST | Kim H.-S.,KAIST | Kim H.-S.,Samsung | Lee K.U.,KAIST | And 6 more authors.
Energy and Environmental Science | Year: 2011

Recently, great interest has been aroused in flexible/bendable electronic equipment such as rollup displays and wearable devices. As flexible energy conversion and energy storage units with high energy and power density represent indispensable components of flexible electronics, they should be carefully considered. However, it is a great challenge to fabricate flexible/bendable power sources. This is mainly due to the lack of reliable materials that combine both electronically superior conductivity and mechanical flexibility, which also possess high stability in electrochemical environments. In this work, we report a new approach to flexible energy devices. We suggest the use of a flexible electrode based on free-standing graphene paper, to be applied in lithium rechargeable batteries. This is the first report in which graphene paper is adopted as a key element applied in a flexible lithium rechargeable battery. Moreover graphene paper is a functional material, which does not only act as a conducting agent, but also as a current collector. The unique combination of its outstanding properties such as high mechanical strength, large surface area, and superior electrical conductivity make graphene paper, a promising base material for flexible energy storage devices. In essence, we discover that the graphene based flexible electrode exhibits significantly improved performances in electrochemical properties, such as in energy density and power density. Moreover graphene paper has better life cycle compared to non-flexible conventional electrode architecture. Accordingly, we believe that our findings will contribute to the full realization of flexible lithium rechargeable batteries used in bendable electronic equipments. © 2011 The Royal Society of Chemistry.


Kim E.,Sejong University | Lee W.-G.,National Nano Fab Center | Jung J.,Sejong University
Electronic Materials Letters | Year: 2011

The agglomeration effect of thin metal catalyst on graphene film grown via CVD was investigated. Among Ni and Co catalysts with 200 nm to 400 nm thickness, 200 nm-Ni exhibits the highest agglomeration and the worst non-uniformity of the synthesized graphene film. Agglomeration induces roughness of catalysts and in turn degrades thickness uniformity of graphene film due to non-uniform dissolution and precipitation of carbon across the catalyst film. Increasing catalyst thickness suppresses the agglomeration and improves uniformity of graphene film. Co shows higher resistant to agglomeration than Ni and improves uniformity of the synthesized graphene film. © 2011 The Korean Institute of Metals and Materials and Springer Netherlands.


Mun J.H.,KAIST | Hwang C.,Korea Research Institute of Standards and Science | Lim S.K.,National Nano Fab Center | Cho B.J.,KAIST
Carbon | Year: 2010

The change of surface roughness during graphene synthesis on evaporated Ni thin films was monitored. It was found that Ni is highly agglomerated during high temperature annealing but the surface roughness is made smoother by the coverage of graphene. It is demonstrated that diffuse reflectance is a fast and convenient technique for evaluating surface roughness over a large area of graphene on a metal film, and specular reflectance is a good indicator of the coverage of graphene on the metal film. © 2009 Elsevier Ltd. All rights reserved.


Lee C.H.,Pusan National University | Jung P.G.,Pusan National University | Lee S.M.,Pusan National University | Park S.H.,Pusan National University | And 5 more authors.
Journal of Micromechanics and Microengineering | Year: 2010

We present the replication of polyethylene (PE) nano-micro hierarchical structures and their application for superhydrophobic surfaces. A commercial ultrasonic welding system was used to apply ultrasonic vibration energy to the forming of nano-micro hierarchical structures. To evaluate ultrasonic formability, Ni nanomold and nano-micro hierarchical mold were designed and fabricated. The optimal weld times were 1.5 s and 3.0 s for PE nanoprotrusions and nano-micro hierarchical structures, respectively. The forming process was conducted at atmospheric pressure. The PE structures were well replicated without a vacuum. The trapped air in the microcavity of the nano-micromold was dispersed and absorbed into the molten PE. Ultrasonic nano-microreplication technology showed an extremely short processing time and did not require a vacuum environment. To investigate the applicability of ultrasonic forming, the fabricated nanoprotrusions and nano-micro hierarchical structures were coated with plasma polymerized fluorocarbon (PPFC) of a hydrophobic nature and were applied to modify superhydrophobic surfaces. The contact angle was increased from 106° (smooth surface) to 125° (nanostructured surface) and finally to 160° (nano-microstructured surface) so that the surface became superhydrophobic. © 2010 IOP Publishing Ltd.


An H.,Institute of Nano and Advanced Materials Engineering | Lee W.-G.,National Nano Fab Center | Jung J.,Institute of Nano and Advanced Materials Engineering
Current Applied Physics | Year: 2012

A new method for implementing graphene ribbons using selective graphene growth on metal-sidewall by chemical vapor deposition has been proposed. In this method, Ni catalyst is pre-patterned before chemical vapor deposition, and graphene film is selectively grown on the sidewall of the nickel for graphene ribbons. The graphene ribbons were confirmed by TEM image and Raman spectroscopy, and the fabricated graphene ribbon transistors showed well gate-modulated output characteristics. We believe this sidewall-graphene could be useful for applications such as graphene sensors which require high surface area of graphene. © 2011 Elsevier B.V. All rights reserved.

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