C.J. Kang

The interlayer screening effect of graphene sheets investigated by Kelvin probe force microscopy

We report on the interlayer screening effect of graphene using Kelvin probe force microscopy (KPFM). By using a gate device configuration that enables the supply of electronic carriers in graphene sheets, the vertical screening properties were studied from measuring the surface potential gradient. The results show layer-dependence of graphene sheets, as the number of graphene layers increases, the surface potential decreases exponentially. In addition, we calculate the work function-related information of the graphene layers using KPFM.

Dynamic Characteristics of the Micro-Fluidic Systems Actuated by Thermopneumatic-Method

We investigated the dynamic characteristics of microfluidic systems under various operating conditions for micropump and microvalve. The pumping rates of the micropump are dependent on a frequency, a duty ratio of applied voltage, a poly(dimethylsiloxane) (PDMS) membrane thickness, and a channel depth. The maximum pumping rate of 64 nl/min was obtained at the applied frequency of 5 Hz and duty ratio of 4% for a PDMS membrane thickness of 450 µm and a channel depth of 100 µm. The flow rates of the microvalve with a 300 µm PDMS membrane thickness are measured as a function of an applied power. The flow rate is easily controlled by the on/off alternation with the applied power of 400 mW. The in-channel structured PDMS micropump and microvalve are fabricated with the same fabrication procedure on the same substrate.

A Novel Electrochemical Detector using Prussian Blue Modified Indium Tin Oxide Electrode

We propose a novel electrochemical detector (ECD) to catalyze redox efficiently by electrodepositing Prussian blue (PB, ferric hexacyanoferrate) on the indium tin oxide (ITO) electrode. Capillary electrophoresis (CE) and amperometric methods were used. We investigated the PB surface properties by topography from atomic force microscopy (AFM). The PB film on dense and smooth surfaces could catalyze redox reaction efficiently. Compared with CE-ECD microchips using a bare-ITO electrode, the proposed CE-ECD microchip using a PB modified electrode has shown better sensitivity of the electropherograms. It has been verified that wide-ranging detection can be performed under the limits of 0.01 mM of dopamine and catechol respectively when we use a PB modified electrode.

Microcantilever-Based Biosensor for Detection of Various Biomolecules

We propose an optical and an electrical methods for detecting various biomolecules effectively with microcantilevers. The microcantilevers were fabricated employing surface micromachining technique that has attractive advantages in terms of cost efficiency, simplicity and ability of fabricating in array. The fluid cell system for injection of biomolecular solution is fabricated using poly(dimethylsiloxane) (PDMS) and a fused silica glass. The microcantilever is deflected with respect to the difference of the surface stress caused by the formation of self-assembled biomolecules on the gold coated side of the microcantilever. It detected cystamine dihydrochloride and glutaraldehyde molecules and analyzed individual concentrations of the cystamine dihydrochloride solution. We confirm that the deflections of bending-up or bending-down are occurred by the biomolecule adsorption and microcantilever can be widely used to a micro total analysis system (µ-TAS) and a lab-on-a-chip for a potential detection of various biomolecules.

Resistive switching characteristics of a compact ZnO nanorod array grown directly on an Al-doped ZnO substrate

ZnOs resistive switching properties have drawn much attention because ZnO has a simple chemical composition and is easy to manipulate. The propulsion mechanism for resistive switching in ZnO is based on a conducting filament that consists of oxygen vacancies. In the case of film structure, the random formation of the conducting filaments occasionally leads to unstable switching characteristics. Limiting the direction in which the conducting filaments are formed is one way to solve this problem. In this study, we demonstrate reliable resistive switching behavior in a device with an Au/compact ZnO nanorod array/Al-doped ZnO structure with stable resistive switching over 105 cycles and a long retention time of 104 s by confining conducting filaments along the boundaries between ZnO nanorods. The restrictive formation of conducting filaments along the boundaries between ZnO nanorods is observed directly using conductive atomic force microscopy.

ITO-coated glass/polydimethylsiloxane continuous-flow PCR chip

We propose a continuous-flow polymerase chain reaction (PCR) chip using indium-tin-oxide (ITO)-coated glass/polydimethylsiloxane (PDMS) materials for DNA amplification. The continuous-flow PCR chip enables fast thermal cycling and series amplification, which are difficult to achieve in a conventional PCR or micro-chamber PCR chip. Six heaters of ITO thin films were fabricated on glass for the thermal cycling of the flowing PCR sample. The PDMS microchannel was fabricated using a negative molding method. The width and depth of the microchannel are 250 mum and 200 mum, respectively, with a total channel length of 1340 mm. The PCR chip can perform 20 cycles of amplifications. The ratio of the channel lengths for three different temperature zones, namely denaturation, annealing, and extension, is 2:2:3, respectively. Using the fabricated continuous-flow PCR chip, two DNA plasmids (720-bp pKS-GFP and 300-bp PG-noswsi) were successfully amplified.

Nanoporous Titania by Embossing with PMMA Nanopoles Made from Nanoporous Alumina Template

We produced highly uniform nanoporous thin films of the dense array of titania (TiO2) pores of 70~80 nm in diameter with nanoimprinting method. Titania in HCl and 2-propanol solution was coated on an indium tin oxide (ITO) surface and embossed with an array of PMMA nanopoles which was produced using a nanoporous alumina (Al2O3) template. Two-step anodization was introduced to produce highly uniform and dense nanopores on the aluminum surface. The polymethyl methacrylate (PMMA) was poured onto and infiltrated into the nanoporous alumina surface which was heated at 150 oC. The alumina nanopores and aluminum plate were removed by wet-etching leaving an array of PMMA nanopoles. These highly uniform nanostructured titania films will be very useful for photovoltaic and photocatalytic applications where nanostructuring of surface with controlled dimensions are essential.

Thermopneumatic-Actuated Polydimethylsiloxane (PDMS) Microfluidic System

We propose a new PDMS microfluidic system including microvalves and a micropump that are easily integrated on the same substrate with the same process steps. The pumping rate of the fabricated microfluidic system was measured under various frequency and duty-ratio of applied power. The maximum pumping rate of about 26 nl/min is measured under the duty ratio of 1 % at 2 Hz of the applied pulse voltage. The dynamic response of the microvalve in the microfluidic system is measured under the on/off alternation with the applied power of 100 mW.

Fabrication of Titania Nanopoles by Nanoporous Alumina Template

The paper demonstrate a formation of thin film titania (TiO2) with dense array of nanopoles and nanopores. The heights of poles and pores are 180 nm and 130 nm, respectively. In order to get titania nanopoles and nanopores, the authors make a nanoporous alumina (A12O3) template through a two-step anodization process, which is essential for the uniform and densified nanopores on aluminum surface. Nano-structured titania films were spin-coated under sol-gel state. The spin-coated titania films were then uniformly patterned by nanoimprinting lithography technique with textured PMMA mold or nanoporous alumina template. These fabricated titania films are very useful for solar cells, photocatalytic and sensing applications wherein nano-structuring of surface with controlled dimensions are vital.

Fabrication and characteristics of microcantilever-based biosensor for detection of the protein-ligand binding

This paper describes a proposal for a microcantilever-based biosensor that can be used in investigating the adsorption characteristics of protein-ligand binding on a silicon nitride/gold coated surface. We have detected streptavidin-ligand binding using this microcantilever detection system. The microcantilevers can be mass-produced by a conventional surface micromachining technique. This technique has advantages of cost efficiency, simplicity, and the ability to be fabricated in an array. A transparent fluid cell system, where a gold coated microcantilever was mounted for the injection of bio-molecular solution, was fabricated using polydimethylsiloxane (PDMS) and fused silica glass. The microcantilever was deflected as a result of the difference of surface stress caused by the formation of the self-assembly monolayers (SAMs) of biomolecules on the gold coated side of the microcantilever. The sequential specific interactions of cystamine dihydrochloride/ glutaraldehyde/streptavidin were detected by both optical and electrical methods. We confirmed that the deflections were induced by biomolecular adsorption on the gold coated microcantilever. This study proved to be applicable to real-time monitoring of biological interactions such as specific DNA sequences, proteins, and so on.