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Shim, Ee Le,Lee, Min Ho,Lu, Ming-Yen,Kang, Chi Jung,Lee, Kyu-Wang,Choi, Young Jin American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.12
<P>Boron-doped microcrystalline diamond (BMD) and nanocrystalline diamond (BND) thin films were grown on Si substrates by microwave-assisted chemical vapor deposition, and their field emission properties were evaluated. BND exhibited a lower turn-on field and higher field enhancement factor than BMD. Furthermore, in a long-term emission stability test, BND showed only a 4% increase in the current density after 12 h of emission, whereas the current density of BMD decreased by - 59%. These results indicate that BND is a more stable and viable current emitter than BMD.</P>
Formation of ZnO nanocones using wet chemical etching of ZnO nanorods in an aqueous solution of HCl.
Bae, Joonho,Shim, Ee-Le,Park, T Y,Kang, C J,Choi, Young Jin American Scientific Publishers 2009 Journal of Nanoscience and Nanotechnology Vol.9 No.12
<P>In this report, a simple wet chemical etching of ZnO nanorods to fabricate large area ZnO nanocones is demonstrated. The cone-like morphology formation utilizes anisotropic etching rate on the different crystal planes of ZnO nanorods in an aqueous solution of HCl (HCl [aq]). To form ZnO nanocones, single crystalline ZnO nanorods with a flat hexagonal shape are synthesized on p-Si(100) using hydrothermal method at 90 degrees C and then, are immersed in HCl [aq]. Electron microscopy reveals that the HCl [aq] treatment of ZnO nanorods significantly etched sidewalls of nanorods, resulting in the cone-like morphology formation. The nanocone formation is the most noticeable when the etching occurred in HCl [aq] with a pH of 2.5-3.0 for 5 min etching time. Geometrical analysis using the electron microscopy reveals that the sidewall of a ZnO nanocone have formed a plane indexed as (0-111) after the etching process.</P>
Bae, Joonho,Shim, Ee Le,Park, Yeonsang,Kim, Hyunjin,Kim, Jong Min,Kang, C J,Choi, Y J IOP Pub 2011 Nanotechnology Vol.22 No.28
<P>We report, for the first time, direct observation of enhanced cathodoluminescence (CL) emissions from ZnO nanocones (NCs) compared with ZnO nanowires (NWs). For direct and unambiguous comparison of CL emissions from NWs and nanocones, periodic arrays of ZnO NW were converted to nanocone arrays by our unique HCl [aq] etching technique, enabling us to compare the CL emissions from original NWs and final nanocones at the same location. CL measurements on NW and nanocone arrays reveal that emission intensity of the nanocone at ∼ 387 nm is over two times larger than that of NW arrays. The enhancement of CL emission from nanocones has been confirmed by finite-difference time-domain simulation of enhanced light extraction from ZnO nanocones compared to ZnO NWs. The enhanced CL from nanocones is attributed to its sharp morphology, resulting in more chances of photons to be extracted at the interface between ZnO and air. </P>
Kim, Kyu Young,Le Shim, Ee,Choi, Young Jin American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10
<P>The resistive switching characteristics in resistive random access memory (RRAM) devices based on metal oxide materials are strongly influenced by the qualities of the metal oxide film, such as the defect density and grain size. In this report, we demonstrate the deposition-temperature-dependence of the resistive switching properties of the ZnO active layer in an AZO/ZnO/ITO transparent RRAM device. As we increase the deposition temperature of ZnO to 300 degrees C, the forming voltage and the resistance in the low resistance state increase from 2 V and 0.3 m Omega to 6 V and 4.3 m Omega, respectively, owing to the decrease of oxygen vacancies that play a critical role in the conduction mechanism. However, the stability of the device improves owing to the enhancement of the crystallinity of the ZnO thin film. For the film deposited at 450 degrees C, the resistance in the low resistance state decreases to the value of the sample prepared at room temperature and the resistance ratio between the high resistance state and the low resistance state is fairly depressed, which results from inter-diffusion of indium or tin atoms into the ZnO layer at high deposition temperatures. Our devices have potential for transparent nonvolatile memory applications because the transmittance is measured to be approximately 80% in all cases.</P>
Giant enhancement of the Raman response due to one-dimensional ZnO nanostructures.
Shin, Hae-Young,Shim, Ee-Le,Choi, Young-Jin,Park, Jong-Hyurk,Yoon, Seokhyun RSC Pub 2014 Nanoscale Vol.6 No.24
<P>We observed giant enhancement of the Raman intensity from 4-Mpy molecules adsorbed on semiconducting one-dimensional ZnO nanostructures, nanowires and nanocones, without involving any noble metals. Interestingly, the enhancement is strongly dependent on the geometry of ZnO nanostructures and can mainly be explained by the cavity-like structural resonance of the electric field. Our results can be applied to systematically create hot spots for Raman signal enhancement using one-dimensional semiconducting nanomaterials.</P>
Kim, Kyu Young,Cho, Chi Heon,Le Shim, Ee American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10
<P>Formation of the active layer in transparent resistive random access memory (ReRAM) devices is affected by working pressure during sputter of the insulator layer. As the working pressure of the sputtering method changes, the ZnO thin film changes morphology in grain size and various other properties. In general, structural changes of active layers closely relate to the resistive switching characteristics of the ReRAM device. In this study, the dependence of the resistive switching characteristics of ReRAM devices with ITO/ZnO/ITO structures on the various working pressures of the ZnO active layer was evaluated. The ReRAM device with a ZnO film deposited at 50 mTorr showed the best performance and high stability. Forming at a low voltage, the working voltage occurred between -2 V and 2 V.</P>
Nikolay V. Shadrinov,Marina D. Sokolova,A. A. Okhlopkova,Jungkeun Lee,정대용,Ee-Le Shim,조진호 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.12
This article examines the modification of surface properties of ultrahigh-molecular-weight polyethylene (UHMWPE) with nanoscale ceramic particles to fabricate an improved composite with butadiene–nitrile rubber (BNR). Adhesion force data showed that ceramic zeolite particles on the surface of UHMWPE modulated the surface state of the polymer and increased its compatibility with BNR. Atomic force microscopy phase images showed that UHMWPE made up the microphase around the zeolite particles and formed the evolving layer with a complex interface. The complex interface resulted in improvements in the mechanical properties of the composite, especially its low-temperature resistance coefficients, thereby improving its performance in low-temperature applications.
Effect of Carbon Black Activation on Physicomechanical Properties of Butadiene-nitrile Rubber
Shadrinov, N.V.,Kapitonov, E.A.,Sokolova, M.D.,Okhlopkova, A.A.,Shim, Ee Le,Cho, Jin-Ho Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.10
The effects of mechanical activation of carbon black on the processing and properties of butadiene nitrile rubber were studied. Mechanical activation of carbon black caused an improvement in the physical and mechanical properties of the butadiene-nitrile rubber, BNR-18AMN. The optimum activation time that would afford rubber with improved properties was established.
Okhlopkova, A.A.,Sleptsova, S.A.,Alexandrov, G.N.,Dedyukin, A.E.,Shim, Ee Le,Jeong, Dae-Yong,Cho, Jin-Ho Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.5
We investigated the tribochemical and wear properties of Polytetrafluoroethylene (PTFE) based polymer matrix composites with nanoceramic (NC) ${\beta}$-sialon, and $Al_2O_3$ particles for the mechanical seal applications at low temperature. SEM showed that NC particles were homogeneously distributed in the polymer matrix and initiated the formation of the supramolecular spherulites around NC. From the temperature stimulated depolarization (TSD) current results, it was analyzed that the surface charge on nanoceramic affected the formation of the spherulites structure. 2 wt % $Al_2O_3$ NC did not degrade the mechanical properties of PTFE so that composites showed the similar values of tensile strength, elongation at the rupture and friction coefficient as those of neat PTFE. However, the composite with 2 wt % $Al_2O_3$ NC revealed the improved wear resistance, wear rate of 0.4-1.2 mg/h at room temperature and 0.28 mg/h at $-40^{\circ}C$, respectively, while the neat PTFE the 70-75 mg/h at room temperature and 70.3 mg/h at $-40^{\circ}C$.