Jae‐Young Choi

Abstract The conductivity of graphite oxide films is modulated using reducing agents. It is found that the sheet resistance of graphite oxide film reduced using sodium borohydride (NaBH 4 ) is much lower than that of films reduced using hydrazine (N 2 H 4 ). This is attributed to the formation of CN groups in the N 2 H 4 case, which may act as donors compensating the hole carriers in reduced graphite oxide. In the case of NaBH 4 reduction, the interlayer distance is first slightly expanded by t

Graphene is a distinct two-dimensional material that offers a wide range of opportunities for membrane applications because of ultimate thinness, flexibility, chemical stability, and mechanical strength. We demonstrate that few- and several-layered graphene and graphene oxide (GO) sheets can be engineered to exhibit the desired gas separation characteristics. Selective gas diffusion can be achieved by controlling gas flow channels and pores via different stacking methods. For layered (3- to 10-n

Large-area, few-layer graphene is grown on a poly-nickel substrate using optimized CVD conditions. High temperature, short growth time, and an optimal gas mixing ratio (C2H2/H2 = 2/45) are found to be necessary to synthesize highly crystalline few-layer grapheme, which may find applications in electronic devices. The wrinkles that are observed under all growth conditions are proposed to be formed by two processes.

Hexagonal boron nitride (h-BN) has received a great deal of attention as a substrate material for high-performance graphene electronics because it has an atomically smooth surface, lattice constant similar to that of graphene, large optical phonon modes, and a large electrical band gap. Herein, we report the large-scale synthesis of high-quality h-BN nanosheets in a chemical vapor deposition (CVD) process by controlling the surface morphologies of the copper (Cu) catalysts. It was found that mor

Transparent flexible charge-generating piezoelectric nanodevices are developed. The resulting integrated nanodevice generates a noticeable current when it is pushed by application of an external load. Piezoelectric ZnO nanorod-based nanodevices with embossed PdAu top electrodes produce the highest output current density of approximately 10 μA cm−2 at a load of 0.9 kgf.

We propose a new method of layer-by-layer (LbL) doping of thin graphene films. Large area monolayer graphene was synthesized on Cu foil by using the chemical vapor deposition method. Each layer was transferred on a polyethylene terephthalate substrate followed by a salt-solution casting, where the whole process was repeated several times to get LbL-doped thin layers. With this method, sheet resistance was significantly decreased up to approximately 80% with little sacrifice in transmittance. Unl

Fully rollable transparent nanogenerators have been developed using chemical vapor deposition-grown large-scale graphene sheets as transparent electrodes and piezoelectric ZnO-nanorod arrays. The electrical and structural stability of the nanogenerators with excellent charge scavenging performance under external mechanical loads such as bending and rolling shows that graphene-based nanogenerators are suitable for self-powered rollable transparent device applications. Detailed facts of importance

This review summarizes organic molecule-based electrode materials for rechargeable batteries.

It is essential to control the electronic structure of graphene in order to apply graphene films for use in electrodes. We have introduced chemical dopants that modulate the electronic properties of few-layer graphene films synthesized by chemical vapor deposition. The work function, sheet carrier density, mobility, and sheet resistance of these films were systematically modulated by the reduction potential values of dopants. We further demonstrated that the power generation of a nanogenerator w

Various viologens have been used to control the doping of single-walled carbon nanotubes (SWCNTs) via direct redox reactions. A new method of extracting neutral viologen (V(0)) was introduced using a biphase of toluene and viologen-dissolved water. A reductant of sodium borohydride transferred positively charged viologen (V(2+)) into V(0), where the reduced V(0) was separated into toluene with high separation yield. This separated V(0) solution was dropped on carbon nanotube transistors to inves

Three-dimensional (3D) structured graphene is a material of great interest due to its diverse applications in electronics, catalytic electrodes, and sensors. However, the preparation of 3D structured graphene is still challenging. Here, we report the fabrication of multilayer graphene balls (GBs) by template-directed carbon segregation using nickel nanoparticles (Ni-NPs) as template materials. To maintain the ball shape of the template Ni-NPs, we used a carburization process using polyol solutio

By introducing the UV beam into our homemade chemical vapor deposition system, we had obtained a well aligned SWNT array on an ST-cut quartz substrate. After transfer onto a SiO(2)/Si substrate, the SWNT array was detected by Raman spectroscopy and electrical measurement, which showed that over 95% of the SWNTs were semiconducting ones. It is proposed that the selection process took place at the very beginning of the SWNT formation rather than destroying the metallic SWNTs after growth. This app

Transparent ZrO2–polydimethylsiloxane (PDMS) nanocomposites with high refractive index were prepared by dispersing ZrO2nanoparticles in a PDMS matrix via ligand molecule engineering. The ligand molecule consists of a diamine head group that adsorbs strongly onto the ZrO2nanoparticles, and a siloxane tail group with a double-tailed structure that can be easily stretched within the PDMS matrix and yields a greater steric hindrance compared to single-tailed structure. The transmission electron micr