S.S. Choi

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.

Nanofabrication of a sub-wavelength size aperture using anisotropic inductively coupled plasma processing

We successfully fabricated a nano-size silicon oxide aperture using inductively coupled plasma (ICP) anisotropic etching as a potential near-field optical probe application. Several other anisotropic semiconductor processes were also utilized for sub-wavelength size aperture fabrication. Initially, a 2 μm size dot array was photolithographically patterned on an Si(100) wafer. After the formation of a hollow pyramid by anisotropic KOH etching, stress-dependent oxide growth was performed at 1000°C to give an oxide etch-mask for dry etching. Reactive ion etching by 100 W, 9 mTorr, 40 sccm Cl2 feed gas using the ICP system with a negatively biased substrate was performed in order to fabricate the nano-size aperture. After etching at the bias voltages of 500 and 540 V, the diameter of the aperture was measured to be ~ 120 and ~ 200 nm, respectively. Finally, the oxide aperture with a sub-wavelength size diameter was obtained after Si bulk micromachining.

The influence of He addition on Cl-etching procedure for Si-nanoscale structure fabrication using reactive ion etching system

Abstract Chlorine-based plasma have been often used to etch several semiconducting materials including Si and III–V materials. The chlorine plasma etching is well suited for fabrication of Si-nanoscale structures due to its good control of undercutting and etch profile. Due to some drawbacks such as trenches and damages on the etch mask from physical ion assisted etching, the Cl2/He gas mixture using a conventional reactive ion etching system was utilized and the optimization procedures were performed. Therefore, the influence of the He flow rate was examined. As the He flow increases over 30% of the total inlet gas flow, the plasma state become stable and the etch rate starts to increase. For high flow rate over 60%, the relationship between the etch depth and the etch time was observed to be nearly linear. In addition, the etch rate has been turned out to be linearly increasing with the He flow rate. With this result, the Cl2/He mixture plasma has been utilized and tested for fabrication of the deep Si sidewall and nanosize Si pillar array.

Effect of acupuncture and its influence on cerebral activity in functional dyspepsia patients: study protocol for a randomized controlled trial.

BackgroundFunctional dyspepsia (FD) is a prevalent gastric disorder that is difficult to manage due to lack of satisfactory treatments. Acupuncture has been studied with regard to the rising need for treating FD, but the mechanism verifying its efficacy has not yet been fully revealed. The aim of this study is to explore the efficacy and mechanism of acupuncture for FD compared with a sham group.Methods/designWe describe a proposal for a randomized, assessor-blind, sham-controlled trial with 70 eligible participants who will be randomly allocated either into an acupuncture or a sham group. Participants in the acupuncture group will receive 10 sessions of real acupuncture treatment and those in the sham group will be treated with identical sessions using a Streitberger needle. Functional magnetic resonance imaging (fMRI) and metabolomics studies will be implemented before and after 4 weeks of treatment to investigate the mechanism of acupuncture. The primary outcome is a proportion of responders with adequate symptom relief and the secondary outcomes include the Nepean Dyspepsia Index - Korean version, Functional Dyspepsia-Related Quality of Life questionnaire, Ways of Coping Questionnaire, Coping Strategies Questionnaire, perception of bodily sensation questionnaire, State-Trait Anxiety Inventory, and the Center for Epidemiological Studies - Depression Scale. The outcomes will be evaluated before and after the treatment.DiscussionThis is the first large-scale trial evaluating the efficacy and mechanism of acupuncture with fMRI and metabolomic methods. We will compare real acupuncture with the Streitberger sham needle to verify the specific effect of acupuncture. The results of this trial are expected to be relevant evidences affecting policy and decision-makers associated with routine healthcare.Trial registrationClinicalTrials.gov Identifier: NCT02358486.Date of Registration: 21 January 2015.

Nanofabrication of sub-wavelength size aperture array for near field optical probe array

Recently there have been tremendous interests about near field optical lithographic techniques for the next generation gigabyte information storage devices. The near field optical lithographic technique will circumvent the classical diffraction limit and can provide the sub-wavelength size patterns less than 100 nm and the parallel data processing has been examined. Therefore, several parallel processing techniques such as multi-cantilever array and the nano-size aperture array have been previously reported. In this work, the nano-fabrication technique for the sub-wavelength size aperture array is presented. Initially, the (50/spl times/50) dot array was patterned on the SiO/sub 2/ thermally grown on Si (100) substrate. Each dot has (5/spl times/5) /spl mu/m/sup 2/ pattern size. The anisotropic TMAH etching of the Si substrate was performed and followed by anisotropic stress-dependent thermal oxidation at 1000/spl deg/C and backside Si etching using TMAH solution. The opening of the nano-size aperture on the oxide pyramid array was carried out using water-diluted (50:1) HF solution. The uniformity of the (50/spl times/50) nano-size aperture array was examined carefully on the four corners of the array patterns. The average diameter of the aperture was -260 nm and its deviation was found to be /spl sim/10%. The optical characterization for the oxide pyramidal array was performed and its diffraction pattern was revealed. In addition, the 50 nm thick Al thin film for the near field probe was deposited and the result of its characterization is reported.

The effect of carbon mesh on the electric property of α-carbon films

Abstract The solid state amorphous carbon films have been deposited by the method of plasma enhanced chemical vapor deposition (PECVD). The structural features have been characterized using FT-IR spectroscopy, Raman scattering, and I–V measurement. The film is considered to be composed of microcrystalline diamond domains and graphite-like carbon domains, which are interconnected by hydrogenated sp 3 tetrahedral carbons. In I–V measurement, the sudden increase of current at a certain critical voltage has been observed and this phenomenon is understood to be due to the effect of charge tunneling through carbon mesh between graphite-like domains.

Electromagnetic wave funneling through nano-gaps and nano-antennas

We show that accumulation of charges at the metal edges via light-induced currents creates large horizontal electric field, which in effect attracts the incoming light. The enhanced field is fully propagating towards the far-field because no cut-off exists. With the amplitude enhancement in the range of 1,000, the intensity enhancement of 106, and the nonlinear enhancement of 1012, this structure can be an excellent launching pad for inducing broad-band nonlinearity, small signal detection in astronomy or biology, and for surface enhanced Raman scattering.

Controlling the nanopore fabrication using high energy electron beam exposure

Recently there has been tremendous interest about the dynamical sequence of fabrication of the solid state nanopore due to its capability of the nanosize solid state biosensor as a single molecule sensor. Depending upon the instruments such as transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM), the dynamics of nanopore formation present different physical mechanisms. In this report, formation of the nanopores was examined. Metallic nanopores with ~ 50 nm diameter on top of the oxide pyramid were fabricated using conventional Si microfabrication techniques followed by wet isotropic etching of the oxide; sputter metal deposition followed by the focused ion beam (FIB) techniques. No shrinking phenomena were observed for the nanopore diameter greater than 50 nm under electron beam irradiation using TEM. However, for high scanning electron beam irradiation using FESEM, shrinking of the Au nanopore was always observed. We do believe that these phenomena can be attributed to the liquid phase surface modification for TEM electron beam and adiabatic solid state phase surface modification for high scanning FESEM. For a huge amount of energy input from high scan rate and the poor thermal conduction to its surrounding area, the energy spike inside the electron penetration area would occur. However, a TEM electron beam irradiation without repetitive scan can provide the liquid phase surface modification.

Dynamical sequence of Au plasmonic nanopore formation using high energy electron beam exposure

Recently there have been tremendous interests about the fabrication of the solid state nanopore due to the capability of the solid state nanopore as a single molecule sensor. The SiN nanopore and the SiO2 nanopore have been fabricated with high energy electron beam exposure such as transmission electron microscopy, field emission electron microscopy, and focused ion beam sculpting. However, the plasmonic Au nano-pore can be utilized as a nanobio optical sensor due to the 106 fold increase of the Raman signal intensity. Hence, in this report, the fabrication of the plasmonic nanopore with less than ~ 10 nm on the apex of the micronsize pyramidal structure using various high energy electron beam exposure. Under the electron beam exposure of FESEM followed by EPMA, the widening and the shrinking of the Au nanopore were observed depending upon the EPMA probe current. The diameters of the Au nanopore was also reduced successively from ~ 5 nm down to zero using 200 keV TEM. From these experimental results, the dynamics of the nanopore formation are found to depend on the viscosity of the membrane, radiation damage, and evaporation of the materials under high vacuum condition. This fabricated plasmonic nano-pore device can be utilized as geneome sequencing device or a single-molecule sensor.

Superfocusing the light through nanosize circular aperture

e macro size pyramidal horn probe such as klystron horn antenna has been used to provide the excellent focusing capabilities in microwave region. In the similar way, the pyramidal probe with the micron size mirror (pyramidal horn probe) has been fabricated with a nano-size aperture with diameter ranging from 30 to 330 nm on its apex. Light transmission through the micro-fabricated pyramidal horn probe has been measured to enhance the light transmission due to resonant effects between the cavity mode and the slit modes in the probe, along with directionality of the transmitted beam. The resonant tunneling between two standing waves in the input groove and in the output groove can provide the transmission enhancements. Below ~170 nm, the output power normalized to the input power (ratio) has been increased with decreasing diameter. On the other hand, for the diameter ranging from 330 to 170 nm, the ratio has been decreased with decreasing diameter. The transmission (T) is measured to be inversely proportional to the area (A), and TA value for input wavelength 532 nm is found to be constant, 0.136 for the diameter below 160 nm, and to be 0.053 for diameter greater than 160 nm.