Flexible NO2 gas sensor using multilayer graphene films by chemical vapor deposition

We report a highly sensitive NO2 gas sensor based on multi-layer graphene (MLG) films synthesized by a chemical vapor deposition method on a microheater-embedded flexible substrate. The MLG could detect low-concentration NO2 even at sub-ppm (<200 ppb) levels. It also exhibited a high resistance change of ~6% when it was exposed to 1 ppm NO2 gas at room temperature for 1 min. The exceptionally high sensitivity could be attributed to the large number of NO2 molecule adsorption sites on the MLG due to its a large surface area and various defect-sites, and to the high mobility of carriers transferred between the MLG films and the adsorbed gas molecules. Although desorption of the NO2 molecules was slow, it could be enhanced by an additional annealing process using an embedded Au microheater. The outstanding mechanical flexibility of the graphene film ensures the stable sensing response of the device under extreme bending stress. Our large-scale and easily reproducible MLG films can provide a proof-of-concept for future flexible NO2 gas sensor devices.clos

Complex Hand Interaction Authoring Tool for User Selective Media

Nowadays, with the advancement of the Internet and personal mobile devices, many interactive media are prevailing, where viewers make their own decisions on the story of the media based on their interactions. The interaction that the user can make is usually pre-programmed by a programmer. Therefore, interactions that users can make are limited to programmable areas. In comparison, in this paper, we propose an Interactive media authoring tool which can compose diverse two-hand interactions from several one-hand interactive components. The aim is to provide content creators with a tool to produce multiple hand motions so that they can design a variety of user interactions to stimulate the interest of content viewers and increase their sense of immersion. Using the proposed system, the content creator can gain greater freedom to create more diverse and complex interactions than programmable ones. The system is composed of a complex motion editor that edits one-hand motions into complex two-hand motions, a touchless sensor that senses the hand motion and a metadata manager that handles the metadata, which specify the settings for the interactive functions. To our knowledge, the proposed system is the first web-based authoring tool that can authorize complex two-hand motions from single hand motions, and which can also control a touchless motion control device

Complex Hand Interaction Authoring Tool for User Selective Media

Nowadays, with the advancement of the Internet and personal mobile devices, many interactive media are prevailing, where viewers make their own decisions on the story of the media based on their interactions. The interaction that the user can make is usually pre-programmed by a programmer. Therefore, interactions that users can make are limited to programmable areas. In comparison, in this paper, we propose an Interactive media authoring tool which can compose diverse two-hand interactions from several one-hand interactive components. The aim is to provide content creators with a tool to produce multiple hand motions so that they can design a variety of user interactions to stimulate the interest of content viewers and increase their sense of immersion. Using the proposed system, the content creator can gain greater freedom to create more diverse and complex interactions than programmable ones. The system is composed of a complex motion editor that edits one-hand motions into complex two-hand motions, a touchless sensor that senses the hand motion and a metadata manager that handles the metadata, which specify the settings for the interactive functions. To our knowledge, the proposed system is the first web-based authoring tool that can authorize complex two-hand motions from single hand motions, and which can also control a touchless motion control device

Ion-Gel-Gated Graphene Optical Modulator with Hysteretic Behavior

We propose a graphene-based optical modulator and comprehensively investigate its photonic characteristics by electrically controlling the device with an ion-gel top-gate dielectric. The density of the electrically driven charge carriers in the ion-gel gate dielectric plays a key role in tuning the optical output power of the device. The charge density at the ion-gel–graphene interface is tuned electrically, and the chemical potential of graphene is then changed to control its light absorption strength. The optical behavior of the ion-gel gate dielectric exhibits a large hysteresis which originates from the inherent nature of the ionic gel and the graphene–ion-gel interface and a slow polarization response time of ions. The photonic device is applicable to both TE- and TM-polarized light waves, covering two entire optical communication bands, the O-band (1.26–1.36 μm) and the C-band (1.52–1.565 μm). The experimental results are in good agreement with theoretically simulated predictions. The temporal behavior of the ion-gel–graphene-integrated optical modulator reveals a long-term modulation state because of the relatively low mobility of the ions in the ion-gel solution and formation of the electric double layer in the graphene–ion-gel interface. Fast dynamic recovery is observed by applying an opposite voltage gate pulse. This study paves the way to the understanding of the operational principles and future applications of ion-gel-gated graphene optical devices in photonics

Hot carrier multiplication on graphene/TiO2 Schottky nanodiodes.

Carrier multiplication (i.e. generation of multiple electron-hole pairs from a single high-energy electron, CM) in graphene has been extensively studied both theoretically and experimentally, but direct application of hot carrier multiplication in graphene has not been reported. Here, taking advantage of efficient CM in graphene, we fabricated graphene/TiO2 Schottky nanodiodes and found CM-driven enhancement of quantum efficiency. The unusual photocurrent behavior was observed and directly compared with Fowler's law for photoemission on metals. The Fowler's law exponent for the graphene-based nanodiode is almost twice that of a thin gold film based diode; the graphene-based nanodiode also has a weak dependence on light intensity-both are significant evidence for CM in graphene. Furthermore, doping in graphene significantly modifies the quantum efficiency by changing the Schottky barrier. The CM phenomenon observed on the graphene/TiO2 nanodiodes can lead to intriguing applications of viable graphene-based light harvesting

Graphene–Semiconductor Catalytic Nanodiodes for Quantitative Detection of Hot Electrons Induced by a Chemical Reaction

Direct detection of hot electrons generated by exothermic surface reactions on nanocatalysts is an effective strategy to obtain insight into electronic excitation during chemical reactions. For this purpose, we fabricated a novel catalytic nanodiode based on a Schottky junction between a single layer of graphene and an n-type TiO₂ layer that enables the detection of hot electron flows produced by hydrogen oxidation on Pt nanoparticles. By making a comparative analysis of data obtained from measuring the hot electron current (chemicurrent) and turnover frequency, we demonstrate that graphene’s unique electronic structure and extraordinary material properties, including its atomically thin nature and ballistic electron transport, allow improved conductivity at the interface between the catalytic Pt nanoparticles and the support. Thereby, graphene-based nanodiodes offer an effective and facile way to approach the study of chemical energy conversion mechanisms in composite catalysts with carbon-based supports

Reliable seawater battery anode: controlled sodium nucleation via deactivation of the current collector surface

Seawater battery, which consists of a Na metal anode and a seawater cathode, has highly attractive features because of its eco-friendliness in use of seawater and cost-effectiveness in the use of Na, the 6th most abundant element of the Earth's crust. Herein, we demonstrate a reliable Na metal anode for the seawater battery by covering the Cu current collector with a graphene monolayer. The surface of the chemically uniform graphene-coated current collector facilitates control of the nucleation rate of surficial Na metal at the initial stage and enhances the coulombic efficiency in current collector|separator|Na metal cells by lowering the nucleation and plating potentials. Further deliberate modification of the graphene surface by using O2 plasma and thermal treatments supports the significance of the homogeneity of the interface of the current collector. Problematically, heterogeneous Cu surfaces covered with islands of oxide layers significantly altered the surface morphology of plated Na metal and consequently resulted in the decrease in electrochemical performance due to the impeding effect on Na ion diffusion near the current collector surface. Through successful implantation of the graphene-coated Cu current collector as an anode in the seawater battery, the battery performance drastically improved, which was confirmed by monitoring the discharge/charge performance and durability of LED lighting