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Optimal Moth Eye Nanostructure Array on Transparent Glass Towards Broadband Antireflection
Ji, Seungmuk,Song, Kyungjun,Nguyen, Thanh Binh,Kim, Namsoo,Lim, Hyuneui American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.21
<P>Broadband antireflection (AR) is essential for improving the photocurrent generation of photovoltaic modules or the enhancement of visibility in optical devices. Beyond conventional AR coating methods, moth eye mimicking nanostructures give new directions to enhance broadband antireflection through the selection of geometrical parameters, such as height, periodic distance, shape, and arrangement. This study numerically and experimentally investigates the behavior of light on complex nanostructures designed to mimic the surface of the moth eye with mixed shapes and various arrangements. To obtain broadband AR, we rigorously study the design parameters, such as height, periodic distance, shape, and arrangement, on a transparent quartz substrate. Several kinds of nanopillar arrays are elaborately fabricated including mixed nanostructures comprising pointy and round shapes in ordered and random arrangements via colloidal lithography. The optimal morphology of moth eye nanostructure arrays for broadband antireflection is suggested in view of reflectance and average weight transmittance.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-21/am402881x/production/images/medium/am-2013-02881x_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am402881x'>ACS Electronic Supporting Info</A></P>
Dissipative Hofstadter Model at the Magic Points and Critical Boundary Sine-Gordon Model
Seungmuk Ji,Taejin Lee 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I
The dissipative Hofstadter model describes quantum particles moving in two dimensions subject to a uniform magnetic field, a periodic potential and a dissipative force. We discuss the dissipative Hofstadter model in the framework of the boundary state formulation in string theory and construct exact boundary states for the model at the magic points by using the fermion representation. The dissipative Hofstadter model at magic points is shown to be equivalent to the critical boundary sine-Gordon model.
Controlled Growth of Multi-walled Carbon Nanotubes Using Arrays of Ni Nanoparticles
Seungmuk Ji(지승묵),Taejin Lee(이태진),Jae Ho Bahng(방재호),Young-Kyu Hong(홍영규),Hanchul Kim(김한철),Dong Han Ha(하동한),Chang-Soo Kim(김창수),Ja-Yong Koo(구자용) 한국진공학회(ASCT) 2008 Applied Science and Convergence Technology Vol.17 No.5
화학기상증착법과 Ni 나노입자 배열을 이용한 탄소나노튜브의 최적 성장 조건을 연구했다. Ni 입자의 크기를 변화시키는 방법으로 탄소나노튜브의 직경을 20 ㎚ 이하까지 제어할 수 있었다. 개별 Ni 입자의 크기와 위치는 기존의 식각법 등을 이용하여 웨이퍼 수준의 대면적에서 연속적으로 제어가 가능하였다. 성장온도, 탄소원, 희석가스 등의 비율을 최적화 함으로써 SiO₂/Si 웨이퍼의 넓은 면적에서 각 Ni 입자로부터 단 한 개씩의 탄소나노튜브가 100% 확률로 성장 가능하다는 것을 보였다. 탄소나노튜브의 위치, 직경, 벽두께 등의 특성들은 성장조건을 조정하여 제어가능하다는 것을 보였다. We have investigated the optimal growth conditions of carbon nanotubes (CNTs) using the chemical vapor deposition and the Ni nanoparticle arrays. The diameter of the CNT is shown to be controlled down to below 20 ㎚ by changing the size of Ni particle. The position and size of Ni particles are controlled continuously by using wafer-scale compatible methods such as lithography, ion-milling, and chemical etching. Using optimal growth conditions of temperature, carbon feedstock, and carrier gases, we have demonstrated that an individual CNT can be grown from each Ni nanoparticle with almost 100% probability over wide area of SiO₂/Si wafer. The position, diameter, and wall thickness of the CNT are shown to be controlled by adjusting the growth conditions.
Ji, Seungmuk,Park, Joonsik,Lim, Hyuneui The Royal Society of Chemistry 2012 Nanoscale Vol.4 No.15
<P>The sub-wavelength structures in moth eyes exhibit fascinating antireflective properties over the broadband wavelength region and at large incident angle by generating an air-mixed heterogeneous optical interface. In this work, antireflective behavior of transparent glass is observed with the elaborate controls of the nanopillar morphology. The reflectance spectrum shows a red shift and a notable light scattering with increase of the height of the nanopillars. The nanopillar arrays with a pointed cone shape have better optical performance in visible range than the rounded cone shape which is typical antireflective nanostructures in nature. Based on the observed antireflective behaviors, the flat and low value reflectance spectrum in the visible wavelength range is demonstrated by moth eye mimicking nanostructures on both sides of a glass surface. It is a unique strategy to realize a flat and broadband spectrum in the visible range showing 99% transparency via the appropriate matching of nanopillar height on the front and back sides of glass. The controlled reflection based color tuning on the antireflective and transparent glass is also obtained by adjusting the height of the nanopillar arrays on both sides. The visibility and self-cleaning ability of moth eye mimicking glass are examined for practical applications such as antireflection and self-cleaning.</P>
Density-controlled growth of ZnO nanorods using ZnO nanocrystals-embedded polymer composite
양희선,Ji-Seung Lee,Seungmuk Bae,황진하 한국물리학회 2009 Current Applied Physics Vol.9 No.4
This work focuses on novel synthesis of ZnO nanorods for their potential applications to optoelectronic and electronic nanodevices. The growth density of ZnO nanorods was modulated through controlling of the density of ZnO nanocrystals dispersed on Si substrate. For this, ZnO nanocrystals synthesized via a polyol process were blended with a polymer matrix. ZnO nanocrystals-embedded polymer composite film was generated by spin-coating the mixed solution. Subsequent heat treatment of composite film removed a polymer matrix and left ZnO nanocrystals on the substrate, serving as seeds for the following ZnO nanorod growth. The density of grown ZnO nanorods was well controllable, depending on the density of dispersed ZnO nanocrystals on the substrate, which was varied by the concentration of ZnO nanocrystal- polymer solution.