Geun Hoi Gu

Fabrication of graphene flakes composed of multi-layer graphene sheets using a thermal plasma jet system

We have developed a method to fabricate graphene flakes composed of high quality multi-layer graphene sheets using a thermal plasma jet system. A carbon atomic beam was generated by injecting ethanol into Ar plasma continuously; the beam then flowed through a carbon tube attached to the anode. Graphene was made by epitaxial growth where a carbon atomic beam, having the proper energy, collided with a graphite plate. The graphene fabricated was very pure and showed a relatively good crystalline structure. We have demonstrated that the number of layers of graphene sheets could be controlled by controlling the rate of ethanol injection. Our process is a continuous process with a relatively high yield (approximately 8%).

Enhancement at the junction of silver nanorods.

The enhancement of surface enhanced Raman scattering (SERS) at the junction of linearly joined silver nanorods (31 nm in diameter) deposited in the pores of anodic aluminum oxide templates was studied systematically by excitation with a 632.8 nm laser line. The single and joined silver nanorod arrays showed a similar extinction spectrum when their length was the same. Maximum enhancement was observed from the junction system of two nanorods of the same size with a total length of 62 nm. This length also corresponded to the optimum length of single nanorods for SERS by excitation with a 632.8 nm laser line. The enhancement at the junction was approximately 40 times higher than that of the 31 nm single nanorod, while it was 4 times higher than that of the 62 nm single nanorod. The enhancement factor at the junction after oxide removal was approximately 3.9 x 10 (9).

Well-ordered Co nanowire arrays for aligned carbon nanotube arrays

Abstract Well-ordered Co nanowire arrays formed on the porous anodic aluminum oxide (AAO) templates prepared by a two-step anodization technique have been used in the fabrication of well-aligned carbon nanotubes. Designed Co nanowire arrays can be made by controlling the pore arrays on AAO templates. By using them as a catalyst it is possible to fabricate the designed carbon nanotube arrays. Carbon nanotubes fabricated by disproportionation of CO were well graphitized, uniform in diameter and aligned vertically with respect to the plane of the template. It has been suggested that CO is an ideal precursor in fabrication of carbon nanotubes.

Minimum Enhancement of Surface-Enhanced Raman Scattering for Single-Molecule Detections

We have calculated the minimum enhancement factor for single-molecule detections from the surface-enhanced Raman scattering (SERS) data measured from well-defined silver nanorod arrays. Silver nanorods were fabricated by electrodepositing them evenly near the mouth of the pores of anodic aluminum oxide templates with a very shallow depth. The SERS intensity increased almost linearly with an increase in the concentration of the mother solution. From the data of the enhancement and the number of molecules irradiated by the laser beam at the detection limit, the minimum SERS enhancement factor for nonresonant single-molecule detections was calculated to be approximately 10(11).

Anodic aluminum oxide membrane bonded on a silicon wafer for carbon nanotube field emitter arrays

We have developed a method to bond a very thin anodic aluminum oxide membrane (400nm thick) on a Si wafer. Furthermore, we were able to fabricate well-ordered carbon nanotube (CNT) arrays on the membrane at a very high temperature—above 1000°C—without deformation. The CNT arrays fabricated at 800°C exhibited long-term stability and uniform emission. Their current density was higher than 1mA∕cm2; such a density might be required for flat panel displays. When the tip of the CNTs was modified from an open shape to a closed shape by exposure to acetylene gas, the turn-on voltage decreased significantly and the enhancement factor increased significantly.

Electrodeposited Silver Nanoparticles Patterned Hexagonally for SERS

We have fabricated hexagonally patterned silver nanoparticles for surface‐enhanced Raman scattering (SERS) by electrodepositing silver on the surface of an aluminum plate prepared by completely removing the oxide from anodic aluminum oxide (AAO) templates. Even after completely removing the oxide, well‐ordered hexagonal patterns, similar to the shape of graphene, remained on the surface of the aluminum plate. The borders of the hexagonal pattern protruded up to form sorts of nano‐mountains at both the sides and apexes of the hexagon, with the apexes protruding even more significantly than the sides. The aluminum plate prepared by completely removing the oxide has been used in the preparation of SERS substrates by sputter‐coating of gold or silver on it. Instead of sputter‐coating, here we have electro‐deposited silver on the aluminum plate. When silver was electro‐deposited on the plate, silver nanoparticles were made along the hexagonal margins.