Yumi Ahn

Improved Thermal Oxidation Stability of Solution-Processable Silver Nanowire Transparent Electrode by Reduced Graphene Oxide

Solution-processable silver nanowire-reduced graphene oxide (AgNW-rGO) hybrid transparent electrode was prepared in order to replace conventional ITO transparent electrode. AgNW-rGO hybrid transparent electrode exhibited high optical transmittance and low sheet resistance, which is comparable to ITO transparent electrode. In addition, it was found that AgNW-rGO hybrid transparent electrode exhibited highly enhanced thermal oxidation and chemical stabilities due to excellent gas-barrier property of rGO passivation layer onto AgNW film. Furthermore, the organic solar cells with AgNW-rGO hybrid transparent electrode showed good photovoltaic behavior as much as solar cells with AgNW transparent electrode. It is expected that AgNW-rGO hybrid transparent electrode can be used as a key component in various optoelectronic application such as display panels, touch screen panels, and solar cells.

Highly Conductive and Flexible Silver Nanowire-Based Microelectrodes on Biocompatible Hydrogel

We successfully fabricated silver nanowire (AgNW)-based microelectrodes on various substrates such as a glass and polydimethylsiloxane by using a photolithographic process for the first time. The AgNW-based microelectrodes exhibited excellent electrical conductivity and mechanical flexibility. We also demonstrated the direct transfer process of AgNW-based microelectrodes from a glass to a biocompatible polyacrylamide-based hydrogel. The AgNW-based microelectrodes on the biocompatible hydrogel showed excellent electrical performance. Furthermore, they showed great mechanical flexibility as well as superior stability under wet conditions. We anticipate that the AgNW-based microelectrodes on biocompatible hydrogel substrates can be a promising platform for realization of practical bioelectronics devices.

Highly Sensitive, Transparent, and Durable Pressure Sensors Based on Sea‐Urchin Shaped Metal Nanoparticles

Highly sensitive, transparent, and durable pressure sensors are fabricated using sea-urchin-shaped metal nanoparticles and insulating polyurethane elastomer. The pressure sensors exhibit outstanding sensitivity (2.46 kPa-1 ), superior optical transmittance (84.8% at 550 nm), fast response/relaxation time (30 ms), and excellent operational durability. In addition, the pressure sensors successfully detect minute movements of human muscles.

Enhancement of Interface Characteristics of Neural Probe Based on Graphene, ZnO Nanowires, and Conducting Polymer PEDOT

In the growing field of brain-machine interface (BMI), the interface between electrodes and neural tissues plays an important role in the recording and stimulation of neural signals. To minimize tissue damage while retaining high sensitivity, a flexible and a smaller electrode with low impedance is required. However, it is a major challenge to reduce electrode size while retaining the conductive characteristics of the electrode. In addition, the mechanical mismatch between stiff electrodes and soft tissues creates damaging reactive tissue responses. Here, we demonstrate a neural probe structure based on graphene, ZnO nanowires, and conducting polymer that provides flexibility and low impedance performance. A hybrid Au and graphene structure was utilized to achieve both flexibility and good conductivity. Using ZnO nanowires to increase the effective surface area drastically decreased the impedance value and enhanced the signal-to-noise ratio (SNR). A poly[3,4-ethylenedioxythiophene] (PEDOT) coating on the neural probe improved the electrical characteristics of the electrode while providing better biocompatibility. In vivo neural signal recordings showed that our neural probe can detect clearer signals.

Flexible metal nanowire-parylene C transparent electrodes for next generation optoelectronic devices

We prepared high performance metal nanowire (NW)-parylene C transparent electrodes (TEs) using pyrolytic deposition of a parylene C protection layer onto a silver nanowire (AgNW) or copper nanowire (CuNW) film at room temperature for the first time. The AgNW-parylene C TE showed superior optoelectronic properties such as high optical transmittance (94.7%) and low sheet resistance (41.6 Ω sq−1), comparable to a conventional indium tin oxide (ITO) TE. The AgNW-parylene C TE fabricated on a plastic substrate possessed outstanding flexibility. Moreover, the AgNW-parylene C and CuNW-parylene C TEs exhibited significantly improved oxidation and chemical stability due to the outstanding gas barrier properties of the parylene C protection layer. Furthermore, the potential suitability of the AgNW-parylene C TE was successfully demonstrated by fabricating flexible polymer solar cells. We expect that the flexible metal NW-parylene C TEs can be used as key elements for a variety of next generation optoelectronic devices.

Nanowire based flexible electrode array with pedot film for neural recordings

The electrode-tissue interface plays an important role in neural recordings. Here, we designed and fabricated a flexible electrode array with nanowire structures and poly(3,4-ethylenedioxythiophene) PEDOT on the flexible substrate. ZnO nanowires were used as a nano pillar structure, which increases effective surface area drastically, to decrease electrode impedance. Furthermore, ZnO nanowires was coated with PEDOT to enhance both biocompatibility and charge transfer characteristics. Flexible electrode array with nanowires and PEDOT shows a higher signal-to-noise ratio (SNR).