Chul Hee Han

Fabrication of a high-throughput near-field optical probe using a double metal layer

Metal-coated oxide nano-aperture arrays have been fabricated using a micro-fabrication technique including a stress-dependent oxidation, an isotropic wet etching of silicon oxide, and the metal deposition. Au, Al, and Al/Ti double metal layers have been deposited on nano-size oxide aperture arrays in order to provide a better uniformity of the coated metal film and an ideal aperture shape. The introduction of the Ti buffer layer reduced surface roughness during the reflow process of Al deposition and resulted in an ideal circular type aperture shape.

Fabrication of pyramidal probes with various periodic patterns and a single nanopore

The nanometer-scale patterned pyramidal probe with an electron beam-induced nanopore on the pyramid apex is an excellent candidate for an optical biosensor. The nanoapertures surrounded with various periodic groove patterns on the pyramid sides were fabricated using a focused ion beam technique, where the optical characteristics of the fabricated apertures with rectangular, circular, and elliptical groove patterns were investigated. The elliptical groove patterns on the pyramid were designed to maintain an identical distance between the grooves and the apex for the surface waves and, among the three patterns, the authors observed the highest optical transmission from the elliptically patterned pyramidal probe. A 103-fold increase of the transmitted optical intensity was observed after patterning with elliptical grooves, even without an aperture on the pyramid apex. The nanopore on the apex of the pyramid was fabricated using electron beam irradiation and was optically characterized.

Discharged Photoelectrocatalytic System for the Enhancement of Photocatalytic Performance

The photoelectrocatalytic system is a discharge photocatalytic system aimed at enhancing the photocatalytic performance. In this study, we have obtained experimental data revealing the basic mechanism of the photoelectrocatalytic system. We also report removal of xylene isomers in air using the photoelectrocatalytic system, and these data are compared with our previous data on benzene and toluene. Our analysis based on the Lagmuir-Hinshelwood (L-H) kinetic model shows that the rates of degradation are in the order; benzene < toluene < xylene, in the photoelectrocatalytic system, and explanations are given for the trend.

Photocatalytic Activities of Transition Metal-Doped TiO2 Nano-Powders by Sonochemical Method and their Physicochemical Properties

With respect to metal doping into TiO2, the doping limits for V, Cr, Zr, Nb, Mo, and W are predicted to be higher than other transition metals according to the binding energy calculations in a unit cell model of anatase TiO2, which suggests that Cr and W can be doped into anatase structure more easily than Ag or Pt, for example. Our investigation has twofold research objectives. One is to prepare metal-doped TiO2 nano-powders from these transition metals, and the other is to test photocatalytic activity of each resulting powder. For the former, sonochemical process has been used to produce Cr-doped, W-doped, Ag-doped, and Pt-doped TiO2 nanoparticles. For the latter, we have performed photocatalytic oxidation of methylene blue. The combined results of the morphology and photocatalytic activites have enabled characterization of the physicochemical properties of these transition metal-doped nanoparticles.

Fabrication of plasmonic nanopore by using electron beam irradiation for optical bio-sensor

The Au nano-hole surrounded by the periodic nano-patterns would provide the enhanced optical intensity. Hence, the nano-hole surrounded with periodic groove patterns can be utilized as single molecule nanobio optical sensor device. In this report, the nano-hole on the electron beam induced membrane surrounded by periodic groove patterns were fabricated by focused ion beam technique (FIB), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Initially, the Au films with three different thickness of 40 nm, 60 nm, and 200 nm were deposited on the SiN film by using an electron beam sputter-deposition technique, followed by removal of the supporting SiN film. The nanopore was formed on the electron beam induced membrane under the FESEM electron beam irradiation. Nanopore formation inside the Au aperture was controlled down to a few nanometer, by electron beam irradiations. The optical intensities from the biomolecules on the surfaces including Au coated pyramid with periodic groove patterns were investigated via surface enhanced Raman spectroscopy (SERS). The fabricated nanopore surrounded by periodic patterns can be utilized as a next generation single molecule bio optical sensor.

Au particle formation on the electron beam induced membrane

Recently the single molecules such as protein and deoxyribonucleic acid (DNA) have been successfully characterized by using a portable solidstate nanopore (MinION) with an electrical detection technique. However, there have been several reports about the high error rates of the fabricated nanopore device, possibly due to an electrical double layer formed inside the pore channel. The current DNA sequencing technology utilized is based on the optical detection method. In order to utilize the current optical detection technique, we will present the formation of the Au nano-pore with Au particle under the various electron beam irradiations. In order to provide the diffusion of Au atoms, a 2 keV electron beam irradiation has been performed During electron beam irradiations by using field emission scanning electron microscopy (FESEM), Au and C atoms would diffuse together and form the binary mixture membrane. Initially, the Au atoms diffused in the membrane are smaller than 1 nm, below the detection limit of the transmission electron microscopy (TEM), so that we are unable to observe the Au atoms in the formed membrane. However, after several months later, the Au atoms became larger and larger with expense of the smaller particles: Ostwald ripening. Furthermore, we also observe the Au crystalline lattice structure on the binary Au-C membrane. The formed Au crystalline lattice structures were constantly changing during electron beam imaging process due to Spinodal decomposition; the unstable thermodynamic system of Au-C binary membrane. The fabricated Au nanopore with an Au nanoparticle can be utilized as a single molecule nanobio sensor.

Au cluster formation on a pore containing membrane under the various surface treatments

In this report, the authors will investigate the formation of Au clusters on the nanoscale membrane formed during various surface treatments such as electron beam irradiations, Ga ion focused ion beam (FIB) technique, and thermal treatment. Nanoapertures on the freestanding Au film were fabricated by using FIB technique, and a nanometer scale membrane created in the aperture by various surface treatments. Transmission electron microscopy reveals that Au clusters has formed on the membrane after the sample storage at room temperature for several months. In addition, Au clusters on the carbon-containing membrane were also observed after surface treatments of Ga ion beam etching, and thermal heating of freestanding 40 nm thick Au film at temperatures ranging from 400 to 800 °C. Spinodal decomposition, spinodal dewetting, and coalescence of the Au particles on the carbon-containing membrane were also observed.In this report, the authors will investigate the formation of Au clusters on the nanoscale membrane formed during various surface treatments such as electron beam irradiations, Ga ion focused ion beam (FIB) technique, and thermal treatment. Nanoapertures on the freestanding Au film were fabricated by using FIB technique, and a nanometer scale membrane created in the aperture by various surface treatments. Transmission electron microscopy reveals that Au clusters has formed on the membrane after the sample storage at room temperature for several months. In addition, Au clusters on the carbon-containing membrane were also observed after surface treatments of Ga ion beam etching, and thermal heating of freestanding 40 nm thick Au film at temperatures ranging from 400 to 800 °C. Spinodal decomposition, spinodal dewetting, and coalescence of the Au particles on the carbon-containing membrane were also observed.

Nanopore integrated with Au clusters formed under electron beam irradiation for single molecule analysis

Recently the single molecules such as protein and deoxyribonucleic acid (DNA) have been successfully characterized using a solidstate nanopore with an electrical detection technique. However, the optical plasmonic nanopore has yet to be fabricated. The optical detection technique can be better utilized as next generation ultrafast geneome sequencing devices due to the possible utilization of the current optical technique for genome sequencing. In this report, we have investigated the Au nanopore formation under the electron beam irradiation on an Au aperture. The circular-type nanoopening with ~ 5 nm diameter on the diffused membrane is fabricated by using 2 keV electron beam irradiation by using field emission scanning electron microscopy (FESEM). We found the Au cluster on the periphery of the drilled aperture under a 2 keV electron beam irradiation. Immediately right after electron beam irradiation, no Au cluster and no Au crystal lattice structure on the diffused plane are observed. However, after the sample was kept for ~ 6 months under a room environment, the Au clusters are found on the diffused membrane and the Au crystal lattice structures on the diffused membrane are also found using high resolution transmission electron microscopy. These phenomena can be attributed to Ostwald ripening. In addition, the Au nano-hole on the 40 nm thick Au membrane was also drilled by using 200 keV scanning transmission electron microscopy.

Investigation of electron beam irradiation effect on pore formation for single molecule bio-sensor fabrication

There have been tremendous interests about the fabrication of the Au plasmonic nanopore due to its capability of the nanosize optical biosensor. We have investigated the influence of low energy electron beam irradiation on an Au nanomembrane during Au nanopore formation. In this report, the influence of electron beam irradiation on the Au nanopore formation will be reported. The nanopores on the 200 nm thick Au membrane were initially fabricated using focused ion beam (FIB) and high energy electron beam techniques such as transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). During high energy electron beam by using TEM, either a “shrinking” or a “opening” phenomenon is reported dependent on the ratio of thickness to aperture diameter. However, for a FESEM electron beam irradiation, a shrinking phenomenon is always observed. In this report, the nanopore formation during FESEM electron beam irradiation will be reported depending upon energy absorption and thermal diffusivity.

Preparation and Photocatalytic Performance of Nano Titania-Coated Beads

Fluidized Bed Chemical Vapor Deposition (FB-CVD) method offers advantages over conventional Chemical Vapor Deposition method in coating three dimensional objects. In addition, catalysts prepared by FB-CVD method often show improved physicochemical properties. Thus, FB-CVD seems a useful method for coating TiO2 onto small beads, in view of their photocatalytic application in aqueous environment, for example. In this work, we produced TiO2 coated beads (1~2mm in diameter) of alumina, silica-gel, and glass in ~35nm thickness using FB-CVD method, and examined photocatalytic performance of TiO2 coated beads in the photocatalytic decomposition reaction of methylene blue solution. Based on the combined results of the decomposition reaction kinetics of methylene blue and FE-SEM images of the surface morphology of TiO2 coated beads, we were able to account for the photocatalytic performance with respect to characteristic features detected in the surface morphology.