Byung Hyun Kang

Photoresponse of sol-gel-synthesized ZnO nanorods

ZnO nanorods were grown on SiO2/Si substrates by a sol-gel method at low temperatures of around T=95 °C. The diameters and the lengths of ZnO nanorods increased at high concentrations of zinc nitrate hexahydrate and methenamine solution. Current–voltage characteristics of the ZnO nanorods network followed a typical nonlinear behavior with significant photoresponse below λ<400 nm in air, and the conductance was enhanced in vacuum with negligible photoresponse. In photoluminescence (PL) and photocurrent (PC) spectra, the PL peak (λpeak=380 nm and 3.26 eV) did not match the PC edge (λedge=400 nm and 3.1 eV), indicating the nondirect band-gap transition in photocurrent. The origin of the photocurrent was discussed from the point of the influence of the desorption of adsorbed water molecules on the surface or inside the ZnO nanorods.

Detection of a CO and NH3 gas mixture using carboxylic acid-functionalized single-walled carbon nanotubes

Carbon nanotubes (CNT) are extremely sensitive to environmental gases. However, detection of mixture gas is still a challenge. Here, we report that 10 ppm of carbon monoxide (CO) and ammonia (NH3) can be electrically detected using a carboxylic acid-functionalized single-walled carbon nanotubes (C-SWCNT). CO and NH3 gases were mixed carefully with the same concentrations of 10 ppm. Our sensor showed faster response to the CO gas than the NH3 gas. The sensing properties and effect of carboxylic acid group were demonstrated, and C-SWCNT sensors with good repeatability and fast responses over a range of concentrations may be used as a simple and effective detection method of CO and NH3 mixture gas.

Highly Oriented Gold/Nanoclay–Polymer Nanocomposites for Flexible Gas Barrier Films

Layer-by-layer (LBL) assembly, which uses electronic and ionic intermolecular bonding under nonvacuum conditions, is a promising technology for fabricating gas barrier films owing to its simple processing and easy formation of a multilayer structure. In this research, nanoclay-polymer multilayers of Na(+)-montmorillonite (Na-MMT) were fabricated. Particularly, the addition of AuCl3 on fabricated MMT layers caused a reaction with the surface silanol functional groups (Si-O-H) of the MMT platelets, resulting in the formation of Au2O3 on the MMT-polymer multilayers. The Au2O3 filled the vacancies between the MMT platelets and linked the MMT platelets together, thus forming a gas barrier film that reduced the water vapor transmission rate (WVTR) to 3.2 × 10(-3) g m(-2) day(-1). AuCl3-treated MMT-polymer multilayers thus have the potential to be utilized for manufacturing gas barrier films for flexible electronics on a large scale.

Effect of plasma treatment on the gas sensor with single-walled carbon nanotube paste.

The effect of plasma treatment on the gas sensing properties of screen-printed single-walled carbon nanotube (SWCNT) pastes is reported. The gas sensors, using SWCNT pastes as a sensing material, were fabricated by photolithography and screen printing. The SWCNT pastes were deposited between interdigitated electrodes on heater membrane by screen printing. In order to functionalize the pastes, they were plasma treated using several gases which produce defects caused by reactive ion etching. The Ar and O(2) plasma-treated SWCNT pastes exhibited a large response to NO(2) exposure and the fluorinated gas, such as CF(4) and SF(6), plasma-treated SWCNT pastes exhibited a large response to NH(3) exposure.

Percolation network of growing V2O5 nanowires

Percolation network of the growing V2O5 nanowires was demonstrated by devising a simple but practical method to investigate the percolation phenomena. As the reaction proceeded in the ammonium(meta)vanadate solution at room temperature, the lengths of V2O5 nanowires increased at a speed of 0.13μm∕day at an early stage of the growth and 0.03μm∕day on the average up to 3 months. Percolation network was made by abruptly freezing the homogeneously dispersed aqueous solutions of V2O5 nanowires in liquid nitrogen. After 7h of aging time, an abrupt increase of the conductance was observed, revealing the satisfaction of the percolation threshold (pc∼0.17) at the average wire length of 40nm.

Design of a multi-walled carbon nanotube field emitter with micro vacuum gauge

The variation of vacuum level inside a field emission device when electron is emitted from multi-walled carbon nanotubes (MWCNTs) by electric field was measured where MWCNT gauge packaged with a vacuum device was used to measure the degree of a vacuum until the end of the vacuum device life. It was found that the electrical properties of MWCNTs altered with the degree of a vacuum. We fabricated MWCNT gauge which were printed and pasted by the screen printer. In this paper, we report the successful detection of the ionization of gases in vacuum state.

Localized-surface-plasmon-enhanced multifunction silicon nanomembrane Schottky diodes based on Au nanoparticles

Au nanoparticle (NP)-modified Si nanomembrane (Si NM) Schottky barrier diodes (SBDs) were fabricated by using a transfer-printing method to create pedestals using only one photomask on a flexible substrate. The transfer using the pedestals afforded a yield of >95% with no significant cracks. The plasmonic Au NPs can facilitate the improvement of the incident optical absorption. The Au NP-modified Si NM SBD exhibited enhanced photoresponse characteristics with an external quantum efficiency (η(EQE)) of 34%, a photosensitivity (P) of 27 at a voltage bias of -5 V, a light intensity of 1.2 W cm(-2), and a responsivity (R(ph)) of 0.21 A W(-1). Additionally, the mechanical bending characteristics of the device were observed while a compressive strain up to 0.62% was applied to the diode. The results suggest that the Au NP-modified Si NM SBD has great potential for use in multifunction devices as a strain sensor and photosensor.

Carbon nanotube field emitters on KOVAR substrate modified by random pattern

We investigated the field emission characteristics of patterned carbon nanotubes (CNTs) on KOVAR substrates with different surface morphologies. The substrate with a micro-sized random pattern was fabricated through chemical wet etching, whereas the substrate with a nano-sized random pattern was formed by surface roughening process of polymer and chemical wet etching. The field emission characteristics of these substrates were the compared with those of non-treated substrates. It was clearly revealed that the field emission characteristics of CNTs were influenced by the surface morphology of the cathode substrate. When the surface of cathode was modified by random pattern, the modified substrate provided a large surface area and a wider print area. Also, the modified surface morphology of the cathode provided strong adhesion between the CNT paste and the cathode. Particularly, the substrate with the nano-sized random pattern showed that the turn-on field value decreases and the field enhancement factor value improves as compared with non-treated substrate.

Field emission characteristics of patterned carbon nanotubes on metal substrate

Multi-walled carbon nanotubes were fabricated KOVAR substrates using electrophoretic deposition (EPD). The surface treatments of the substrate were performed by palladium coating process which is an activation procedure for electroless plating. Through the surface treatments, the roughness of the surface increased and cathodes which have high roughness factor showed better field emission characteristics compared to non-treated ones.

Effect of surface treatment of substrate on field emission characteristics of carbon nanotubes

The field emission characteristics of patterned carbon nanotubes whose average diameter is 16nm cathodes on substrates with surface treatment were investigated. The surface treatment of the substrate was performed by nickel electroless plating. Carbon nanotubes were patterned on the surface treated substrate with radius of 200μm through conventional photolithography process. It was revealed that the different surface morphologies of the substrates have influence on the field emission characteristics in this study. Through the surface treatment, the roughness of the surface increased and cathode with a high roughness factor showed better field emission characteristics compared to non-treated ones.