Jang-Hee Yoon

Water sensor for a nonaqueous solvent with poly(1,5-diaminonapthalene) nanofibers.

A water sensor for a nonaqueous solvent was fabricated using poly(1,5-diaminonapthalene (DAN) nanofibers, which were prepared through a catalytic chemical polymerization of the DAN monomer using Fe(III) salt as the catalyst. Poly(1,5-DAN) nanofibers were characterized by atomic force microscope (AFM), transmission electron microscope (TEM), scanning electron microscope (SEM), and UV-vis spectroscopy. The electrochemical properties of poly(1,5-DAN) nanofibers were investigated using cyclic voltammetry (CV). The electrochemical activity of poly(1,5-DAN) nanofibers was utilized for water sensing. The fabrication of water sensor was followed by placing one drop (about 2 microL) of 0.01% poly(1,5-DAN) nanofibers solution in the gap between two split gold electrodes (PBSA) and completely dried. The response of the water sensor in an acetonitrile solution was evaluated under optimized conditions. The linear dynamic range was from 0.05 to 20%, and the detection limit was determined to be 0.01%. The response of this sensor was shown to be comparable to that obtained with the Karl Fischer titration method.

Towards Vaporized Molecular Discrimination: A Quartz Crystal Microbalance (QCM) Sensor System Using Cobalt-Containing Mesoporous Graphitic Carbon

A recent study on nanoporous carbon based materials (J. Am. Chem. Soc. 2012, 134, 2864) showed that the presence of abundant graphitized sp(2) carbon species in the frameworks led to higher affinity for aromatic hydrocarbons than their aliphatic analogues. Herein, improved understanding of the sensitive and selective detection of aromatic substances by using mesoporous carbon (MPC)-based materials, combined with a quartz crystal microbalance (QCM) sensor system, was obtained. MPCs were synthesized by direct carbonization of mesoporous polymers prepared from resol through a soft templating approach with Pluronic F127. The carbon-based frameworks can be graphitized through the addition of a cobalt source to the precursor solution, according to the catalytic activity of the cobalt nanoparticles formed during the carbonization process. From the Raman data, the degree of the graphitization was clearly increased by increasing the cobalt content and elevating the carbonization temperature. From a QCM study, it was proved that the highly graphitized MPCs exhibited a higher affinity for aromatic hydrocarbons than their aliphatic analogues. By increasing the degree of graphitization in the carbon-based pore walls, the MPCs showed both larger adsorption uptake and faster sensor response towards toxic benzene and toluene vapors.

A potentiometric non-enzymatic glucose sensor using a molecularly imprinted layer bonded on a conducting polymer.

A non-enzymatic potentiometric glucose sensor for the determination of glucose in the micomolar level in saliva was developed based on a molecularly imprinted polymer (MIP) binding on a conducting polymer layer. A MIP containing acrylamide, and aminophenyl boronic acid, as a host molecule to glucose, was immobilized on benzoic acid-functionalized poly(terthiophene) (pTBA) by the amide bond formation onto a gold nanoparticles deposited-screen printed carbon electrode (pTBA/AuNPs/SPCE). Aromatic boronic acid was incorporated into the MIP layer to stably capture glucose and create a potentiometric signal through the changed pKa value of polymer film by the formation of boronate anion-glucose complex with generation of H+ ions by the cis-diol reaction. Reversible binding and extraction of glucose on the sensor surface was observed using a quartz crystal microbalance. Each layer of the sensor probe was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The potentiometric response at the optimized conditions exhibited a wide linear dynamic range of 3.2×10-7 to 1.0×10-3M, with a detection limit of 1.9 (±0.15)×10-7M. The sensor probe revealed an excellent selectivity and sensitivity for glucose compared to other saccharides. In addition, the reliability of the proposed glucose sensor was evaluated in physiological fluid samples of saliva and finger prick blood.

Development of compact linear accelerator in KBSI.

The compact linear accelerator using a 28 GHz ECRIS is under construction in KBSI, South Korea. The main capability of this facility is the production of fast neurons for the neutron radiography. The designing of a superconducting magnet, microwave transmission system, beam extraction, and plasma chamber of ECRIS were finished. The nominal axial design fields of the magnets are 3.6 T at injection and 2.2 T at extraction; the nominal radial design field strength at the plasma chamber wall is 2.1 T. We already installed 10 kW, 28 GHz gyrotron, and tested a microwave power from gyrotron using a dummy load. The current status will be discussed in this paper.

Manufacturing of a superconducting magnet system for 28 GHz electron cyclotron resonance ion source at KBSIa)

A magnet system for a 28 GHz electron cyclotron resonance ion source is being developed by the Korea Basic Science Institute. The configuration of the magnet system consists of 3 solenoid coils for a mirror magnetic field and 6 racetrack coils for a hexapole magnetic field. They can generate axial magnetic fields of 3.6 T at the beam injection part and 2.2 T at the extraction part. A radial magnetic field of 2.1 T is achievable at the plasma chamber wall. A step type winding process was employed in fabricating the hexapole coil. The winding technique was confirmed through repeated cooling tests. Superconducting magnets and a cryostat system are currently being manufactured.

Preparation and characterization of Ce-doped ZnO nanofibers by an electrospinning method

ZnO and Ce-doped ZnO Nanofibers on (111) Pt/SiO2/Si substrates were produced using an electrospinning technique. The as-prepared composite fibres were subjected to high-temperature calcination to produce inorganic fibers. After calcining at a temperature of 500 o C, the average diameter of the ZnO and Ce-doped ZnO nanofibers were determined to be 170 nm and 225 nm, respectively. The average grain size of the ZnO and Ce-doped ZnO nanofibers were about 50 nm and 57 nm, respectively. The microstructure, chemical bonding state and photoluminescence of the produced ZnO and Ce-doped ZnO nanofibers were investigated. The Cedoped ZnO nanofiber can be assigned to the presence of Ce ions on substitutional sites of Zn ions and the Ce 3+ state from X-ray photoelectron spectra. Compared with PL spectra of ZnO nanofibers, the peak position of the UV emission of the Ce-doped ZnO nanofibers is sharply suppressed while the green emission band is highly enhanced.

Nitrogen ion implantation into various materials using 28 GHz electron cyclotron resonance ion source

The installation of the 28 GHz electron cyclotron resonance ion source (ECRIS) ion implantation beamline was recently completed at the Korea Basic Science Institute. The apparatus contains a beam monitoring system and a sample holder for the ion implantation process. The new implantation system can function as a multipurpose tool since it can implant a variety of ions, ranging hydrogen to uranium, into different materials with precise control and with implantation areas as large as 1-10 mm(2). The implantation chamber was designed to measure the beam properties with a diagnostic system as well as to perform ion implantation with an in situ system including a mass spectrometer. This advanced implantation system can be employed in novel applications, including the production of a variety of new materials such as metals, polymers, and ceramics and the irradiation testing and fabrication of structural and functional materials to be used in future nuclear fusion reactors. In this investigation, the first nitrogen ion implantation experiments were conducted using the new system. The 28 GHz ECRIS implanted low-energy, multi-charged nitrogen ions into copper, zinc, and cobalt substrates, and the ion implantation depth profiles were obtained. SRIM 2013 code was used to calculate the profiles under identical conditions, and the experimental and simulation results are presented and compared in this report. The depths and ranges of the ion distributions in the experimental and simulation results agree closely and demonstrate that the new system will enable the treatment of various substrates for advanced materials research.

First results of 28 GHz superconducting electron cyclotron resonance ion source for KBSI accelerator.

The 28 GHz superconducting electron cyclotron resonance (ECR) ion source has been developed to produce a high current heavy ion for the linear accelerator at KBSI (Korea Basic Science Institute). The objective of this study is to generate fast neutrons with a proton target via a p(Li,n)Be reaction. The design and fabrication of the essential components of the ECR ion source, which include a superconducting magnet with a liquid helium re-condensed cryostat and a 10 kW high-power microwave, were completed. The waveguide components were connected with a plasma chamber including a gas supply system. The plasma chamber was inserted into the warm bore of the superconducting magnet. A high voltage system was also installed for the ion beam extraction. After the installation of the ECR ion source, we reported the results for ECR plasma ignition at ECRIS 2014 in Russia. Following plasma ignition, we successfully extracted multi-charged ions and obtained the first results in terms of ion beam spectra from various species. This was verified by a beam diagnostic system for a low energy beam transport system. In this article, we present the first results and report on the current status of the KBSI accelerator project.

Recondensation performance of liquid helium cryostat for a 28 GHz electron cyclotron resonance ion sourcea)

Cryostat performance is essential for the stable operation of a superconducting magnet. A closed-cycle liquid helium cryostat was adopted for use for a superconducting electron cyclotron resonance (ECR) ion source by recondensing liquid helium vapor. The goal was to maintain the liquid helium filled reservoir at a constant level without transferring any liquid helium during the normal operation of the ECR ion source. To accomplish this, Gifford-McMahon (GM) refrigerators, which have two cold heads, were installed on the top of the cryostat. The cooling power of the GM cryocooler is 1.5 W at the second stage and 50 W at the first stage. Each stage was connected to the liquid helium reservoir, a radiation shield including high-Tc current lead, and related items. Before commissioning the ECR ion source, a preliminary evaluation of the recondensation performance was carried out with the magnet in partial operation. The design of the cryostat, its fabrication, and the experimental results are reported.

Magnetic lens effect using Gd-Ba-Cu-O bulk superconductor in very high magnetic field

We investigate the performance of a magnetic lens in very high magnetic fields exceeding 24 T. The magnetic lens is composed of Gd-Ba-Cu-O superconducting bulk materials. The unique configuration of the magnetic field amplifier, which consists of slits and electrical insulation in the bulk, allows the magnetic flux density to be further enhanced by a background magnet. In field cooling operation, the external magnetic field was varied ∼4 T from 24.2 to 28.3 T and a total magnetic flux density of 30.35 T was found at the center of the device with a background magnet. The magnetic lens additionally increased the magnetic flux density by 2.05 T due to the lens effect. However, it was also observed that the bulk was partially quenched when the external field was varied. This partial quench and recovery of the bulk magnet is considered to be one factor that limits the performance of the lens effect. Finally, we are able to generate a substantial magnetic flux density of 2 T under very high magnetic field becau...