Ho Young Jang

All Graphene-Based Thin Film Transistors on Flexible Plastic Substrates

High-performance, flexible all graphene-based thin film transistor (TFT) was fabricated on plastic substrates using a graphene active layer, graphene oxide (GO) dielectrics, and graphene electrodes. The GO dielectrics exhibit a dielectric constant (3.1 at 77 K), low leakage current (17 mA/cm(2)), breakdown bias (1.5 × 10(6) V/cm), and good mechanical flexibility. Graphene-based TFTs showed a hole and electron mobility of 300 and 250 cm(2)/(V·s), respectively, at a drain bias of -0.1 V. Moreover, graphene TFTs on the plastic substrates exhibited remarkably good mechanical flexibility and optical transmittance. This method explores a significant step for the application of graphene toward flexible and stretchable electronics.

Synthesis of bimetallic Pt/Pd nanotubes and their enhanced catalytic activity in methanol electro-oxidation

In this work, we successfully synthesized a vertically-aligned bimetallic Pt/Pd nanotube array by using anodic aluminum oxide (AAO) template-assisted electro-deposition. The resulting nanostructures exhibited higher catalytic activity in methanol oxidation than either individual constituent (Pt or Pd). The facile synthesis of the Pt/Pd tubular nanostructure was inspired by the previously developed thin-walled Pd nanotube formation mechanism, which takes advantage of the surface hydroxyl chemistry of the AAO template. The content of Pt in the bimetallic Pt/Pd nanotubes could reach up to 50%. The inner and outer walls of the perpendicular open Pt/Pd nanotubes increased the ratio of the surface area to the mass relative to the solid nanorod structure, resulting in a higher current density in methanol oxidation. More importantly, the synergistic electronic effect between Pt and Pd gave rise to the enhanced catalytic activity in methanol oxidation, as evidenced from comparisons of the onset potentials and CO oxidation behaviors. Thus, vertically-aligned bimetallic Pt/Pd nanotubes may act as a better catalyst in methanol oxidation than the single-component Pt counterpart.

Direct growth of graphene nanomesh using a Au nano-network as a metal catalyst via chemical vapor deposition

Herein, we report a simple and facile method on the direct formation of graphene nanomesh (GNM) on insulating substrates by chemical vapor deposition using the Au metal nano-network as a metal catalyst. Well-ordered hexagonal honeycomb shapes of Au nano-network films synthesized using an anodized aluminum oxide template, served as catalysts for the growth of GNM. As-prepared GNM was characterized by various techniques and fabricated as a conducting channel in field effect transistors. Enhanced mobility and a relatively high ON/OFF ratio confirmed our synthetic strategy of the fabrication of GNM as an alternative to a conventional top-down lithographic approach.

Close‐Packed Two‐Dimensional Silver Nanoparticle Arrays: Quadrupolar and Dipolar Surface Plasmon Resonance Coupling

Silver nanoparticles (NPs) ranging in size from 40 to 100 nm were prepared in high yield by using an improved seed-mediated method. The homogeneous Ag NPs were used as building blocks for 2D assembled Ag NP arrays by using an oil/water interface. A close-packed 2D array of Ag NPs was fabricated by using packing molecules (3-mercaptopropyltrimethoxysilane) to control the interparticle spacing. The homogeneous 2D Ag NP array exhibited a strong quadrupolar cooperative plasmon mode resonance and a dipolar red-shift relative to individual Ag NPs suspended in solution. A well-arranged 2D Ag NP array was embedded in polydimethylsiloxane film and, with biaxial stretching to control the interparticle distance, concomitant variations of the quadrupolar and dipolar couplings were observed. As the interparticle distance increased, the intensity of the quadrupolar cooperative plasmon mode resonance decreased and dipolar coupling completely disappeared. The local electric field of the 2D Ag NP array was calculated by using finite difference time domain simulation and qualitatively showed agreement with the experimental measurements.