Won-Seok Kang

Plasma formation using a capillary discharge in water and its application to the sterilization of E. coli

An underwater electrical discharge in a narrow dielectric capillary provides the details of the evolution of microbubbles to plasma as formed by a tungsten electrode inserted in the capillary. An increase in the applied voltage forms microbubbles after water fills the capillary. A further increase in the voltage generates a surface discharge through the boundary of the bubble, elongating the bubble shape, and eventually forming plasma by electrical breakdown. This produces atomic oxygen, atomic hydrogen, and hydroxyl radicals from dissociation of water vapor. Also, a bactericidal test in normal saline solution showed that more than 99.6% of the bacterial cells were killed within 8 s, resulting from chlorine-containing species, in particular hypochlorous acid as a major bactericidal agent.

Patterning of hierarchically aligned single-walled carbon nanotube Langmuir-Blodgett films by microcontact printing.

We present a patterning method for hierarchically aligned assembly of single-walled carbon nanotubes (SWNTs) using a combination of the Langmuir-Blodgett (LB) technique and soft lithography. The LB technique allows one to control the alignment and the surface density of SWNTs by adjusting surface pressure of the film at the air-water interface. The aligned SWNT Langmuir films are successfully transferred onto the polydimethylsiloxane (PDMS) or silicon substrate with unidirectional alignment, and SWNT patterns with various shapes are fabricated on silicon and flexible poly(ethylene terephthalate) (PET) substrates by contacting and peeling off the PDMS stamp from the substrates via microcontact printing or lift-up methods. The SWNT patterning technique using the combination of soft lithography and the LB method can be applied in various fields, such as flexible high-speed transistors, high-efficiency solar cells, and transparent electrodes.

Fabrication of carbon nanotube AFM probes using the Langmuir-Blodgett technique.

Carbon nanotube (CNT)-tipped atomic force microscopy (AFM) probes have shown a significant potential for obtaining high-resolution imaging of nanostructure and biological materials. In this paper, we report a simple method to fabricate single-walled carbon nanotube (SWNT) nanoprobes for AFM using the Langmuir-Blodgett (LB) technique. Thiophenyl-modified SWNTs (SWNT-SHs) through amidation of SWNTs in chloroform allowed to be spread and form a stable Langmuir monolayer at the water/air interface. A simple two-step transfer process was used: (1) dipping conventional AFM probes into the Langmuir monolayer and (2) lifting the probes from the water surface. This results in the attachment of SWNTs onto the tips of AFM nanoprobes. We found that the SWNTs assembled on the nanoprobes were well-oriented and robust enough to maintain their shape and direction even after successive scans. AFM measurements of a nano-porous alumina substrate and deoxyribonucleic acid using SWNT-modified nanoprobes revealed that the curvature diameter of the nanoprobes was less than 3 nm and a fine resolution was obtained than that from conventional AFM probes. We also demonstrate that the LB method is a scalable process capable of simultaneously fabricating a large number of SWNT-modified nanoprobes.

Random Networks of Single-Walled Carbon Nanotubes Promote Mesenchymal Stem Cell’s Proliferation and Differentiation

Studies on the interaction of cells with single-walled carbon nanotubes (SWCNTs) have been receiving increasing attention owing to their potential for various cellular applications. In this report, we investigated the interactions between biological cells and nanostructured SWCNTs films and focused on how morphological structures of SWCNT films affected cellular behavior such as cell proliferation and differentiation. One directionally aligned SWCNT Langmuir-Blodgett (LB) film and random network SWCNT film were fabricated by LB and vacuum filteration methods, respectively. We demonstrate that our SWCNT LB and network film based scaffolds do not show any cytotoxicity, while on the other hand, these scaffolds promote differentiation property of rat mesenchymal stem cells (rMSCs) when compared with that on conventional tissue culture polystyrene substrates. Especially, the SWCNT network film with average thickness and roughness values of 95 ± 5 and 9.81 nm, respectively, demonstrated faster growth rate and higher cell thickness for rMSCs. These results suggest that systematic manipulation of the thickness, roughness, and directional alignment of SWCNT films would provide the convenient strategy for controlling the growth and maintenance of the differentiation property of stem cells. The SWCNT film could be an alternative culture substrate for various stem cells, which often require close control of the growth and differentiation properties.

Substrate Heated Spray-Deposition Method for High Efficient Organic Solar Cell: Morphology Inspection

We report a general approach involving the heating of glass substrates for fabricating spray-coated organic photovoltaic cells. We heated a substrate was heated to temperatures of 50, 100, and 150 °C during the spray-coating process and observed different morphology of the active layer. It was found that the morphology influenced the performance of the organic solar cell. The solar cell subjected to spray coating at a substrate temperature of 150 °C showed a power conversion efficiency (PCE) of ~3.84%, an open voltage of ~0.61 V, and a short current density of ~20 mA/cm2. After optimizing post annealing, we obtained the PCE up to 4.3%.

Nanorod measurement-layer separate structure for nanorod-character measurement, simulation, and application as sensor devices

This paper reported the simple nanorod characteristic measurement method by layer separated structure. The structures are designed by the ANSYS simulation and they are fabricated by semiconductor fabrications. In the experiment, dielectrophoresis (DEP) principle is used to assemble nanorods which are synthesized by electrochemical deposition (ECD) method. However, it is difficult to make devices without assembly process because nanorods which are synthesized by the ECD method are dispersed in the medium. Therefore, this paper was studied to design and fabricate the nanorod assembly-layer and measurement-layer separation. After assembling the nanorods, I-V characteristics of the nanorods were measured.

Development of multi-layer for Au nanorod assembly

In this study, dielectrophoresis (DEP) principle was used to assemble Au nanorods which were synthesized by electrochemical deposition (ECD) method. The nanorod assembly electrode was designed by considering the simulation and fabricated using semiconductor fabrications. In experiment, only 1st layer and multilayer were experienced to compare the Au nanorod assembly efficiency. First, assembly efficiency was about 20 % when 20 kHz, 20 Vp-p (AC) was applied on the only 1st layer. Second, multi-layer was designed for getting high assembly efficiency. Assembly efficiency was improved by 45 % when 10 V (DC) was applied on the 1st layer electrode and 20 kHz, 20 Vp-p (AC) was applied on the 2nd layer electrode. As a result, the Au nanorod assembly efficiency of the multi-layer was increased about 25 % than assembly efficiency of the only 1st layer.

I-V Characteristic of the Au Nanorod According to the Contact Materials

The authors had manufactured the Au nanorod by electrochemical deposition (ECD) method. ECD method has many advantages that it can make the nanorod using the various materials having the dipole and it can make the hetero structure of nanorod. The nanorods have a good round shape with 7 mum height and 200 nm thick. To measure the characteristics of the nanorod, measurement electrode pattern is fabricated on the oxide layer. Electrode pattern was suggested to catch many nanorods randomly and materials of the pattern were used by the gold and titanium considering the work function of the nanorods. Basically, I-V characteristic of the Au was measured in the state of ohmic contact. The resistance of the Au nanorod was about 280 Omega and I-V curve was not measured over the 0.54 V. Confirming the optical microscope, Au nanorod was broken by the specific factor such as heating or excessive current.

Random network single-walled carbon nanotube biosensor by metal work function modulation

We have fabricated highly sensitive network SWNT devices, which have successfully detected specific adsorptions of streptavidin at 1 pM concentrations.