Papers by Author: Jong Wan Park

Abstract: This study reported the fabrication of tin oxide (SnO2) nanostructures on Co-coated Si substrates by the thermal heating of Sn powders. The microstructures and morphologies of the resultant nanostructures were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning electron microscopy (SEM). The product mainly comprised the tangled nanowires with average diameters in the range of 50-180 nm. The nanostructures were single-crystalline rutile structure of SnO2. The PL measurement with the Gaussian fitting exhibited visible light emission bands centered at 576 nm and 638 nm, respectively. We have discussed the possible growth mechanism of the nanostructures.

Abstract: The crystal defects in diamonds are diverse. In other words, there are almost no perfect diamonds without impurities or dislocations. Most natural diamonds contain a considerable amount of nitrogen impurity in aggregated forms. CVD diamond films also included many crystal defects. We investigated the distribution of luminescence center of natural type Ia diamonds and CVD diamond films by various photoluminescence excitation source. Photoluminescence (PL) spectroscopy is a useful technique to provide information on defects of diamond with high sensitivity.

Abstract: Lithium manganese oxide (LiMn2O4) had been a promising material for lithium-ion and thin film batteries. However, the LiMn2O4 had some problems such as the manganese dissolution into liquid electrolyte. In order to improve cycleability, we introduced SnOx layer as protective layer. This layer was deposited on spinel LiMn2O4 by using radio frequency magnetron sputtering. The deposited SnOx layer fully covered the LiMn2O4 , and didn’t make a change the crystallinity of the spinel films. The SnOx layer prevented direct contact of liquid electrolyte and improved the cycle retention.

Abstract: As the oxygen permeation flux of La0.7Sr0.3Ga0.6Fe0.4O3-δ (LSGF) membranes is lower than commercial membranes, we coated the nano porous La0.6Sr0.4CoO3-δ (LSC) particles to enhance the oxygen permeation flux. The nano porous LSC particles were synthesized in an advanced process to increase the volume fraction of nano pores by ultrasonic spray pyrolysis. The synthesized LSC particles consisted of nano sized primary particles and pores. They also had remarkably high surface area (22 m2/g). It was found that the LSGF membrane coated by the nano porous LSC resulted in significant improvement in the oxygen permeability.

Abstract: In the polymer electrolyte, lots of salt have been studied and synthesized in many laboratories. In the previous our work[1,2], we found that the SiO2 (-7 nm, Degussa-Huls), which had the OH- and (CH3)3 surface groups, could help to enhance the ionic conductivity and the interfacial stability. We used as a plasticizer. It has the four CN groups at the end of chains. It was helpful to enhance the ionic conductivity, as respected. The ionic conductivity of the composite electrolytes was about 5.0ⅹ10-5 S/cm at room temperature. In addition, we conducted the charge/discharge test with LiMn2O4 at room temperature and 45 °C. The retention of 1st cycle to 100th cycle was 74 % at 45°C.

Abstract: We prepared spinel-phase LiMn2O4 layer by using rf magnetron sputtering system. LiMn2O4 films were deposited at room temperature and then annealed at 750°C for crystallization to spinel type. In order to reduce the interface reaction such as Mn dissolution phenomenon during operation, we introduced SnOx (coating-layer) thin film. The SnOx films were deposited on LiMn2O4 films by rf magnetron sputtering system. A SnOx-coated LiMn2O4 film was more stable during the chargingdischarging reaction and maintained good cycle behavior at high temperature conditions of 55°C.

Abstract: We have prepared the Si/Mo multilayer consisting of active/inactive material using rf/dc magnetron sputtering. The pre-treatment using an ECR plasma were introduced at current collector for the adhesion and removal of surface contamination. The structural and electrochemical characteristics of multilayers have been investigated. The multilayer nearly maintained more than 90 % of the initial capacity (2653 mAh/g) after 100 cycles whereas the Si thin film was gradually degraded after 40 cycles.