Jeong Min Baik

Hydrophobic Sponge Structure-Based Triboelectric Nanogenerator

Hydrophobic sponge structure-based triboelectric nanogenerators using an inverse opal structured film for sustainable energy harvesting over a wide range of humid atmosphere have been successfully demonstrated. The output voltage and current density reach a record value of 130 V and 0.10 mA cm(-2) , respectively, giving over 10-fold power enhancement, compared with the flat film-based triboelectric nanogenerator.

Highly Stretchable 2D Fabrics for Wearable Triboelectric Nanogenerator under Harsh Environments

Highly stretchable 2D fabrics are prepared by weaving fibers for a fabric-structured triboelectric nanogenerator (FTENG). The fibers mainly consist of Al wires and polydimethylsiloxane (PDMS) tubes with a high-aspect-ratio nanotextured surface with vertically aligned nanowires. The fabrics were produced by interlacing the fibers, which was bonded to a waterproof fabric for all-weather use for fabric-structured triboelectric nanogenerator (FTENG). It showed a stable high-output voltage and current of 40 V and 210 μA, corresponding to an instantaneous power output of 4 mW. The FTENG also exhibits high robustness behavior even after 25% stretching, enough for use in smart clothing applications and other wearable electronics. For wearable applications, the nanogenerator was successfully demonstrated in applications of footstep-driven large-scale power mats during walking and power clothing attached to the elbow.

Mesoporous pores impregnated with Au nanoparticles as effective dielectrics for enhancing triboelectric nanogenerator performance in harsh environments

A facile and scalable synthesis of mesoporous films impregnated with Au nanoparticles (NPs) as effective dielectrics is demonstrated for enhancing the nanogenerator performance based on vertical contact-separation mode. This technique is so simple and scalable, providing a promising solution for developing large-scale and practical self-powered devices. The spatial distribution of Au NPs made it possible to fabricate an Au NP-embedded mesoporous triboelectric nanogenerator (AMTENG) with a high output power of 13 mW under cycled compressive force, giving over 5-fold power enhancement, compared with a flat film-based TENG under the same mechanical force. It is proposed that the presence of aligned dipoles produced due to the charges created by the contact between Au NPs and PDMS inside the pores can influence the surface potential energy of mesoporous films. With such an enhanced power output and unique device design, we demonstrate various applications such as self-powered shape mapping sensors, foot-step driven large-scale AMTENGs, and integrated circuits with capacitors for powering commercial cell phones for realizing self-powered systems from footsteps, wind power, and ocean waves.

Boosted output performance of triboelectric nanogenerator via electric double layer effect

For existing triboelectric nanogenerators (TENGs), it is important to explore unique methods to further enhance the output power under realistic environments to speed up their commercialization. We report here a practical TENG composed of three layers, in which the key layer, an electric double layer, is inserted between a top layer, made of Al/polydimethylsiloxane, and a bottom layer, made of Al. The efficient charge separation in the middle layer, based on Voltas electrophorus, results from sequential contact configuration of the TENG and direct electrical connection of the middle layer to the earth. A sustainable and enhanced output performance of 1.22 mA and 46.8 mW cm−2 under low frequency of 3 Hz is produced, giving over 16-fold enhancement in output power and corresponding to energy conversion efficiency of 22.4%. Finally, a portable power-supplying system, which provides enough d.c. power for charging a smart watch or phone battery, is also successfully developed.

Effect of microstructural change on magnetic property of Mn-implanted p-type GaN

A dilute magnetic semiconductor was achieved by implanting Mn ions into p-type GaN and subsequent annealing. The ferromagnetic property was obtained after annealing at 800 °C. This was attributed to the formation of Ga–Mn magnetic phases. Higher temperature annealing at 900 °C reduced the ferromagnetic signal and produced antiferromagnetic Mn–N compounds such as Mn6N2.58 and Mn3N2, leaving N vacancies. This provides evidence that N vacancies play a critical role in weakening the ferromagnetic property in the Mn-implanted GaN.

Highly efficient organic light-emitting diodes with hole injection layer of transition metal oxides

We report on the advantage of interlayers using transition-metal oxides, such as iridium oxide (IrOx) and ruthenium oxide (RuOx), between indium tin oxide (ITO) anodes and 4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl (α-NPD) hole transport layers on the electrical and optical properties of organic light-emitting diodes (OLEDs). The operation voltage at a current density of 100mA∕cm2 decreased from 17to11V for OLEDs with 3-nm-thick IrOx interlayers and from 17to14V for OLEDs with 2-nm-thick RuOx ones. The maximum luminance value increased about 50% in OLED using IrOx and 108% in OLED using RuOx. Synchrotron radiation photoelectron spectroscopy results revealed that core levels of Ru 3d and Ir 4f shifted to high binding energies and that the valence band was splitting from metallic Fermi level as the surface of the transition metal was treated with O2 plasma. This provides evidence that the transition-metal surface transformed to a transition-metal oxide. The surface of the transition metal became smoother ...

Self-Assembled and Highly Selective Sensors Based on Air-Bridge-Structured Nanowire Junction Arrays

We describe a strategy for creating an air-bridge-structured nanowire junction array platform that capable of reliably discriminating between three gases (hydrogen, carbon monoxide, and nitrogen dioxide) in air. Alternatively driven dual nanowire species of ZnO and CuO with the average diameter of ∼30 nm on a single substrate are used and decorated with metallic nanoparticles to form two-dimensional microarray, which do not need to consider the post fabrications. Each individual nanowires in the array form n-n, p-p, and p-n junctions at the micro/nanoscale on single substrate and the junctions act as electrical conducting path for carriers. The adsorption of gas molecules to the surface changes the potential barrier height formed at the junctions and the carrier transport inside the straight semiconductors, which provide the ability of a given sensor array to differentiate among the junctions. The sensors were tested for their ability to distinguish three gases (H2, CO, and NO2), which they were able to do unequivocally when the data was classified using linear discriminant analysis.

Hierarchically Driven IrO2 Nanowire Electrocatalysts for Direct Sensing of Biomolecules

Applying nanoscale device fabrications toward biomolecules, ultra sensitive, selective, robust, and reliable chemical or biological microsensors have been one of the most fascinating research directions in our life science. Here we introduce hierarchically driven iridium dioxide (IrO(2)) nanowires directly on a platinum (Pt) microwire, which allows a simple fabrication of the amperometric sensor and shows a favorable electronic property desired for sensing of hydrogen peroxide (H(2)O(2)) and dihydronicotinamide adenine dinucleotide (NADH) without the aid of enzymes. This rational engineering of a nanoscale architecture based on the direct formation of the hierarchical 1-dimensional (1-D) nanostructures on an electrode can offer a useful platform for high-performance electrochemical biosensors, enabling the efficient, ultrasensitive detection of biologically important molecules.

Incorporation of Oxygen Donors in AlGaN

The chemistry of oxygen atoms at the surface of an AlGaN layer for Al 0.35 Ga 0.65 N/GaN heterostructures was investigated by scanning photoemission microscopy (SPEM) using synchrotron radiation. SPEM imaging and space-resolved photoemission spectroscopy showed that the oxygen atoms were preferentially incorporated into AlGaN rather than GaN due to the high reactivity of Al with oxygen. In situ annealing at 1000°C could lead to the outdiffusion of oxygen impurities from the bulk AlGaN, resulting in a significant increase in the intensity of Al-O bonds at the AlGaN surface. Therefore, it is suggested that the unintentional doping of oxygen impurities in AlGaN could yield a heavily doped n-type AlGaN layer, resulting in a drastic reduction in effective Schottky barrier heights of metal contacts on AlGaN/GaN heterostructures.

Single carbon fiber decorated with RuO2 nanorods as a highly electrocatalytic sensing element.

We demonstrate highly efficient electocatalytic activities of single crystalline RuO(2) nanorods grown on carbon fiber (CF), i.e., RuO(2) nanorod-CF hybrid microelectrode, prepared by a simple thermal annealing process from the Ru(OH)(3) precursor at 300 °C. The general electrochemical activity of a RuO(2) nanorod-CF microelectrode represents faster electron transfer for the [Fe(CN)(6)](3-/4-) couple than that of the bare CF microelectrode which are confirmed from the cyclic voltammetry (CV) measurement. Also, the amperometric response for the H(2)O(2) oxidation is remarkably facilitated at the RuO(2) nanorod-CF microelectrode by not only the enlarged surface area but the high electrocatalytic activity of the RuO(2) nanorod material itself. Furthermore, a single microelectrode of RuO(2) nanorod-CF exhibits the superior tolerance to Cl(-) ion poisoning unlike Pt-based electrocatalysts, indicating the promising sensor candidate in physiological conditions.