Yong Ju Yun

Ultrasensitive and Highly Selective Graphene-Based Single Yarn for Use in Wearable Gas Sensor

Electric components based on fibers or textiles have been investigated owing to their potential applications in wearable devices. High performance on response to gas, drape-ability and washing durability are of important for gas sensors based on fiber substrates. In this report, we demonstrate the bendable and washable electronic textile (e-textile) gas sensors composed of reduced graphene oxides (RGOs) using commercially available yarn and molecular glue through an electrostatic self-assembly. The e-textile gas sensor possesses chemical durability to several detergent washing treatments and mechanical stability under 1,000 bending tests at an extreme bending radius of 1u2009mm as well as a high response to NO2 gas at room temperature with selectivity to other gases such as acetone, ethanol, ethylene, and CO2.

Local doping of graphene devices by selective hydrogen adsorption

N-type graphene fabricated by exposure to hydrogen gas has been previously studied. Based on this property of graphene, herein, we demonstrate local doping in single-layer graphene using selective adsorption of dissociative hydrogen at 350 K. A graphene field effect transistor was produced covered with PMMA on half of the graphene region. The charge neutrality point of the PMMA-window region shifted to a negative gate voltage (VG) region prominently compared with that of the PMMA-covered region. Consequently, a single graphene p-n junction was obtained by measuring the VG-dependent resistance of the whole graphene region. This method presents opportunities for developing and controlling the electronic structure of graphene and device applications.

Solution-processed Au–Ag core–shell nanoparticle-decorated yarns for human motion monitoring

Wearable strain sensors based on Au–Ag core–shell nanoparticle decorated yarns were fabricated by a solution-based approach. Smart wearable systems with our strain sensors that can monitor various human motions, including finger motion, marching and squatting, and transmit the information of human motion in real time to an LED light was demonstrated.

Highly stretchable, mechanically stable, and weavable reduced graphene oxide yarn with high NO2 sensitivity for wearable gas sensors

Stretchable gas sensors are important components of wearable electronic devices used for human safety and healthcare applications. However, the current low stretchability and poor stability of the materials limit their use. Here, we report a highly stretchable, stable, and sensitive NO2 gas sensor composed of reduced graphene oxide (RGO) sheets and highly elastic commercial yarns. To achieve high stretchability and good stability, the RGO sensors were fabricated using a pre-strain strategy (strain-release assembly). The fabricated stretchable RGO gas sensors showed high NO2 sensitivity (55% at 5.0 ppm) under 200% strain and outstanding mechanical stability (even up to 5000 cycles at 400% applied strain), making them ideal for wearable electronic applications. In addition, our elastic graphene gas sensors can also be woven into fabrics and clothes for the creation of smart textiles. Finally, we successfully fabricated wearable gas-sensing wrist-bands from superelastic graphene yarns and stretchable knits to demonstrate a wearable electronic device.

Dew point temperature as an invariant replacement for relative humidity for advanced perovskite solar cell fabrication systems

The ambient environment plays a pivotal role in the formation of organic–inorganic halide perovskite films. In particular, a certain level of humidity during the fabrication process can promote the crystallization of perovskites, resulting in better film morphologies and enhanced photovoltaic performances. Here, we unravel the importance of thermal equilibrium on the effect of relative humidity during perovskite film fabrication. We show that crystal quality is highly influenced by the dew point even when the relative humidity is unchanged. Observations related to the importance of the dew point on the material morphology, crystal quality, and resultant photovoltaic properties shed light on the dew point as a universal parameter affecting perovskite film fabrication.