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Park, Hyungmin,Kim, Jae-Up,Park, Soojin RSC Pub 2012 Nanoscale Vol.4 No.4
<P>A simple, straightforward process for fabricating multi-scale micro- and nanostructured patterns from polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP)/poly(methyl methacrylate) (PMMA) homopolymer in a preferential solvent for PS and PMMA is demonstrated. When the PS-b-P2VP/PMMA blend films were spin-coated onto a silicon wafer, PS-b-P2VP micellar arrays consisting of a PS corona and a P2VP core were formed, while the PMMA macrodomains were isolated, due to the macrophase separation caused by the incompatibility between block copolymer micelles and PMMA homopolymer during the spin-coating process. With an increase of PMMA composition, the size of PMMA macrodomains increased. Moreover, the P2VP blocks have a strong interaction with a native oxide of the surface of the silicon wafer, so that the P2VP wetting layer was first formed during spin-coating, and PS nanoclusters were observed on the PMMA macrodomains beneath. Whereas when a silicon surface was modified with a PS brush layer, the PS nanoclusters underlying PMMA domains were not formed. The multi-scale patterns prepared from copolymer micelle/homopolymer blend films are used as templates for the fabrication of gold nanoparticle arrays by incorporating the gold precursor into the P2VP chains. The combination of nanostructures prepared from block copolymer micellar arrays and macrostructures induced by incompatibility between the copolymer and the homopolymer leads to the formation of complex, multi-scale surface patterns by a simple casting process.</P>
Park, Hyungmin,Li, Xiaxi,Lai, Samson Y.,Chen, Dongchang,Blinn, Kevin S.,Liu, Mingfei,Choi, Sinho,Liu, Meilin,Park, Soojin,Bottomley, Lawrence A. American Chemical Society 2015 NANO LETTERS Vol.15 No.9
<P>Carbon deposition on nickel anodes degrades the performance of solid oxide fuel cells that utilize hydrocarbon fuels. Nickel anodes with BaO nanoclusters deposited on the surface exhibit improved performance by delaying carbon deposition (i.e., coking). The goal of this research was to visualize early stage deposition of carbon on nickel surface and to identify the role BaO nanoclusters play in coking resistance. Electrostatic force microscopy was employed to spatially map carbon deposition on nickel foils patterned with BaO nanoclusters. Image analysis reveals that upon propane exposure initial carbon deposition occurs on the Ni surface at a distance from the BaO features. With continued exposure, carbon deposits penetrate into the BaO-modified regions. After extended exposure, carbon accumulates on and covers BaO. The morphology and spatial distribution of deposited carbon was found to be sensitive to experimental conditions.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-9/acs.nanolett.5b02237/production/images/medium/nl-2015-02237r_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b02237'>ACS Electronic Supporting Info</A></P>
Control of Interfacial Layers for High-Performance Porous Si Lithium-Ion Battery Anode
Park, Hyungmin,Lee, Sungjun,Yoo, Seungmin,Shin, Myoungsoo,Kim, Jieun,Chun, Myungjin,Choi, Nam-Soon,Park, Soojin American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.18
<P>We demonstrate a facile synthesis of micrometer-sized porous Si particles via copper-assisted chemical etching process. Subsequently, metal and/or metal silicide layers are introduced on the surface of porous Si particles using a simple chemical reduction process. Macroporous Si and metal/metal silicide-coated Si electrodes exhibit a high initial Coulombic efficiency of ∼90%. Reversible capacity of carbon-coated porous Si gradually decays after 80 cycles, while metal/metal silicide-coated porous Si electrodes show significantly improved cycling performance even after 100 cycles with a reversible capacity of >1500 mAh g<SUP>–1</SUP>. We confirm that a stable solid-electrolyte interface layer is formed on metal/metal silicide-coated porous Si electrodes during cycling, leading to a highly stable cycling performance.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-18/am5046197/production/images/medium/am-2014-046197_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5046197'>ACS Electronic Supporting Info</A></P>
Park, Hyungmin,Choi, Sinho,Lee, Jung-Pil,Park, Soojin Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.32
<P>We present a new technique to fabricate a highly ordered silicon pin-in-a-hole structure, in which each silicon nanowire is pinned in a hole, by combining polymer sphere arrays induced by Rayleigh instability with chemical etching process. With this process, we were able to create the novel structures that are periodic over very large areas (3 × 3 cm<SUP>2</SUP>), where the length of silicon nanowires can be varied by tuning the etching time. A silicon pin-in-a-hole structure was used as the template for preparing polymer nanotubes. And also these structures exhibited a superior anti-reflection property showing specular reflectance of about 0.2%, nearly three orders of magnitude lower than that of a planar silicon wafer.</P> <P>Graphic Abstract</P><P>We demonstrate a simple route for the fabrication of highly ordered polymer nanosphere arrays by the guiding of saw-toothed PDMS patterns, and subsequent silver deposition and catalytic chemical etching led to the formation of silicon pin-in-a-hole structures. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1jm10812c'> </P>
Park, Hyungmin,Choi, Sinho,Lee, Sung-Jun,Cho, Yoon-Gyo,Hwang, Gaeun,Song, Hyun-Kon,Choi, Nam-Soon,Park, Soojin Elsevier 2016 Nano energy Vol.26 No.-
<P><B>Abstract</B></P> <P>Nanostructured silicon is a promising candidate material for practical use in energy storage devices. However, high temperature operation remains a significant challenge because of severe electrochemical side reactions. Here, we show the design of ultra-durable silicon made by introducing dual coating layers on the silicon surface, allowing stable operation at high temperature. The double layers, which consist of amorphous metal titanate and carbon, provide several advantages including: (i) suppression of volume expansion during Li<SUP>+</SUP> insertion; (ii) creation of a stable solid-electrolyte−interface layer; and (iii) preservation of original Si morphology over 600 cycles at high temperature. The resulting silicon-based anode exhibits a reversible capacity of 990mAhg<SUP>−1</SUP> after 500 cycles at 25°C and 1300mAhg<SUP>−1</SUP> after 600 cycles at 60°C with a rate of 1C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We synthesized a new class of Si-based anode materials by synergistic coupling of amorphous ABO<SUB>x</SUB> and carbon coating. </LI> <LI> ABO<SUB>x</SUB> stabilizes the solid-electrolyte-interphase layers, while carbon acts as an electrical conducting material. </LI> <LI> Si-based anodes show exceptional high-temperature cycling stability with a high specific capacity of 1300mAhg<SUP>−1</SUP> after 600 cycles. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A new class of Si-based materials is fabricated by synergistic coupling of amorphous ABO<SUB>x</SUB> and carbon coating layers onto Si particles. In this system, ABO<SUB>x</SUB> stabilizes the SEI layers, while carbon acts as an electrical conducting material. The resulting Si-based anodes exhibit high specific capacities (1667mAhg<SUP>−1</SUP> (25°C) and 2021mAhg<SUP>−1</SUP> (60°C) at 1C rate) and highly stable cycling performances (capacity retention of 60% after 500 cycles at 25°C and 64% after 600 cycles at 60 °C).</P> <P>[DISPLAY OMISSION]</P>