Duck Hyun Lee

Versatile Carbon Hybrid Films Composed of Vertical Carbon Nanotubes Grown on Mechanically Compliant Graphene Films

[*] Prof. S. O. Kim, D. H. Lee, J. E. Kim, T. H. Han, J. W. Hwang, Prof. S. W. Jeon, Prof. S. H. Hong, Prof. W. J. Lee Department of Materials Science and Engineering, KAIST Daejeon 305-701 (Republic of Korea) E-mail: sangouk.kim@kaist.ac.kr Dr. S. Y. Choi Convergence Components and Materials Laboratory Electronics and Telecommunication Research Institute (ETRI) Daejoen 305-700 (Republic of Korea)

Peptide/Graphene Hybrid Assembly into Core/Shell Nanowires

This work was supported by the National Research Laboratory Program (R0A-2008-000-20057-0), the World Class University (WCU) program (R32-2008-000- 10051-0), the Pioneer Research Center Program (2009-0093758), and the National Research Foundation (NRF 2008-0062204) funded by the Korean government. Supporting Information is available online from Wiley InterScience or from the author.

Vertical ZnO nanowires/graphene hybrids for transparent and flexible field emission

We present a transparent and flexible optoelectronic material composed of vertically aligned ZnO NWs grown on reduced graphene/PDMS substrates. Large-area reduced graphene films were prepared on PDMS substrates by chemical exfoliation from natural graphitevia oxidative aqueous dispersion and subsequent thermal reduction. ZnO NWs were hydrothermally grown on the reduced graphene film substrate and maintained their structural uniformity even in highly deformed states. The electrical contact between semiconducting ZnO NWs and the metallic graphene film was straightforwardly measured by electric force microscopy (EFM). It shows a typical metal–semiconductor ohmic contact without a contact barrier. Owing to the mechanical flexibility, transparency, and low contact barrier, the ZnO NWs/graphene hybrids show excellent field emission properties. Low turn-on field values of 2.0 V μm−1, 2.4 V μm−1, and 2.8 V μm−1 were measured for convex, flat, and concave deformations, respectively. Such variation of field emission properties were attributed to the modification of ZnO NWs emitter density upon mechanical deformation.

Flexible room-temperature NO2 gas sensors based on carbon nanotubes/reduced graphene hybrid films

We present a flexible room temperature NO2 gas sensor consisting of vertical carbon nanotubes (CNTs)/reduced graphene hybrid film supported by a polyimide substrate. The reduced graphene film alone showed a negligible sensor response, exhibiting abnormal N–P transitions during the initial NO2 injection. A hybrid film, formed by the growth of a vertically aligned CNT array (with CNTs 20 μm in length) on the reduced graphene film surface, exhibited remarkably enhanced sensitivities with weak N–P transitions. The increase in sensitivity was mainly attributed to the high sensitivity of the CNT arrays. The outstanding flexibility of the reduced graphene films ensured stable sensing performances in devices submitted to extreme bending stress.

Mussel‐Inspired Block Copolymer Lithography for Low Surface Energy Materials of Teflon, Graphene, and Gold

Mussel-inspired interfacial engineering is synergistically integrated with block copolymer (BCP) lithography for the surface nanopatterning of low surface energy substrate materials, including, Teflon, graphene, and gold. The image shows the Teflon nanowires and their excellent superhydrophobicity.

Highly Efficient Vertical Growth of Wall-Number-Selected, N-Doped Carbon Nanotube Arrays

We demonstrate a straightforward approach for rapid growth of wall-number selected, N-doped CNT arrays. Highly uniform nanopatterned iron catalyst arrays were prepared by tilted deposition through block copolymer nanotemplates. PECVD growth of CNTs from the nanopatterned catalysts in an NH(3) environment generated vertical N-doped CNTs with a fine-tunability of their carbon wall numbers. The optimized growth conditions produced 52 microm long N-doped CNTs within 1 min. Owing to N-doping, the wall-number selected CNTs including DWNTs and TWNTs demonstrated enhanced electro-conductivity and chemical functionality. This remarkably fast growth of highly uniform N-doped CNTs, whose material properties and chemical functionalizability are reinforced by N-doping, offers a new area of large-scale nanofabrication, potentially useful for diverse nanodevices.

Flexible Field Emission of Nitrogen-Doped Carbon Nanotubes/Reduced Graphene Hybrid Films

The outstanding flexible field emission properties of carbon hybrid films made of vertically aligned N-doped carbon nanotubes grown on mechanically compliant reduced graphene films are demonstrated. The bottom-reduced graphene film substrate enables the conformal coating of the hybrid film on flexible device geometry and ensures robust mechanical and electrical contact even in a highly deformed state. The field emission properties are precisely examined in terms of the control of the bending radius, the N-doping level, and the length or wall-number of the carbon nanotubes and analyzed with electric field simulations. This high-performance flexible carbon field emitter is potentially useful for diverse, flexible field emission devices.

Surface Energy Modification by Spin-Cast, Large-Area Graphene Film for Block Copolymer Lithography

We demonstrate a surface energy modification method exploiting graphene film. Spin-cast, atomic layer thick, large-area reduced graphene film successfully played the role of surface energy modifier for arbitrary surfaces. The degree of reduction enabled the tuning of the surface energy. Sufficiently reduced graphene served as a neutral surface modifier to induce surface perpendicular lamellae or cylinders in a block copolymer nanotemplate. Our approach integrating large-area graphene film preparation with block copolymer lithography is potentially advantageous in creating semiconducting graphene nanoribbons and nanoporous graphene.

Palladium Nanoparticle Catalyzed Conversion of Iron Nanoparticles into Diameter- and Length-Controlled Fe2P Nanorods

This work was supported by MEST (NRF 2009-0090897, KRF-2008- 314-C00234, NRF 2010-0014807) and MIHWAF (the Korea Health 21 R&D Project: A085136) to K.L., by the NRL program (R0A-2008- 000-20057-0) to S.O.K., and by NRF 2009-0082451 to G.R.Y. We thank KBSI for allowing the usage of their HRTEM, SQUID, GC-MS (operator: Yun Gyong Ahn) instruments and Prof. Sang-Won Lee at Korea Univ for MS measurements.