Effect of Physicochemical Properties of Solvents on Microstructure of Conducting Polymer Film for Non-Volatile Polymer Memory

Ungyu Paik,Sangkyu Lee,Jea-Gun Park 대한전자공학회 2008 Journal of semiconductor technology and science Vol.8 No.1

The effect of physicochemical properties of solvents on the microstructure of polyvinyl carbazole (PVK) film for non-volatile polymer memory was investigated. For the solubilization of PVK molecules and the preparation of PVK films, four solvents with different physicochemical properties of the Hildebrand solubility parameter and vapor pressure were considered: chloroform, tetrahydrofuran (THF), 1,1,2,2-tetrachloroethane (TCE), and N,N-dimehtylformamide (DMF). The solubility of PVK molecules in the solvents was observed by ultraviolet-visible spectroscopy. PVK molecules were observed to be more soluble in chloroform, with a low Hildebrand solubility parameter, than solvents with higher values. The aggregated size and micro-/nano-topographical properties of PVK films were characterized using optical and atomic force microscopes. The PVK film cast from chloroform exhibited enhanced surface roughness compared to that from TCE and DMF. It was also confirmed that the microstructure of PVK film has an effect on the performance of non-volatile polymer memory.

Dispersant-Ethyl Cellulose Binder Interactions at the Ni Particle-Dihydroterpineol Interface

Lee, Sangkyu,Paik, Ungyu,Yoon, Seon-Mi,Choi, Jae-Young Wiley (Blackwell Publishing) 2006 JOURNAL OF THE AMERICAN CERAMIC SOCIETY - Vol.89 No.10

Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

Song, Dowon,Paik, Ungyu,Guo, Xingye,Zhang, Jing,Woo, Ta-Kwan,Lu, Zhe,Jung, Sung-Hoon,Lee, Je-Hyun,Jung, Yeon-Gil Elsevier 2016 Surface & coatings technology Vol.308 No.-

<P><B>Abstract</B></P> <P>The effects of microstructure design on the lifetime performance of lanthanum zirconate (La<SUB>2</SUB>Zr<SUB>2</SUB>O<SUB>7</SUB>; LZO)-based thermal barrier coatings (TBCs) were investigated through various thermal exposure tests, such as furnace cyclic thermal fatigue, thermal shock, and jet engine thermal shock. To improve the thermal durability of LZO-based TBCs, composite top coats using two feedstock powders of LZO and 8wt.% yttria-doped stabilized zirconia (8YSZ) were prepared by mixing in different volume ratios (50:50 and 25:75, respectively). In addition, buffer layers were introduced in layered LZO-based TBCs deposited using an air-plasma spray method. The TBC with the double buffer layer showed the best thermal cycle performance among all samples in all tests. For applications with relatively slow cooling rates, the thermal durability in single-layer TBCs is more effectively enhanced by controlling a composition ratio in the blended powder, better than introducing a single buffer layer. For applications with relatively fast cooling rates, the thermal durability can be effectively improved by introducing a buffer layer than controlling a composition in the top coat, since the buffer layer provides fast localized stress relief due to its high strain compliance. These research findings allow us to control the TBC structure, and the buffer layer is efficient in improving thermal durability in cyclic thermal environments.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thermal durability in La<SUB>2</SUB>Zr<SUB>2</SUB>O<SUB>7</SUB> based TBCs has been investigated. </LI> <LI> Cyclic thermal exposure tests were employed in determining thermal durability. </LI> <LI> Buffer layer can improve the thermal durability of TBC in fast cooling rates. </LI> <LI> Blended composition can enhance the thermal durability of TBC in slow cooling rates. </LI> <LI> TBC with a double buffer layer showed the most outstanding thermal durability in all tests. </LI> </UL> </P>

Sb-based electrode materials for rechargeable batteries

Liu, Zhiming,Song, Taeseup,Paik, Ungyu The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.18

<P>The demand for green energy conversion and storage for various applications, such as portable electronics, electric vehicles, and large-scale power stations, has boosted the exploration of advanced energy storage technologies. Lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and liquid-metal batteries (LMBs) meet the different requirements of high-energy density, low cost, and large-scale energy storage, respectively. Currently, designing and synthesizing appropriate electrode materials with high performance, abundant natural availability, and low cost are the main challenges for rechargeable battery technology. Recent studies have demonstrated that Sb-based materials are promising electrode candidates for LIBs, SIBs, and LMBs because of their relatively low cost and high electrochemical performance. This review critically presents recent developments in Sb-based electrode materials, including storage mechanisms, synthesis strategies, and applications in LIBs, SIBs, and LMBs. It also presents challenges and prospects on further improving Sb-based electrode materials for real applications.</P>

Dielectric Polarization of a High-Energy Density Graphite Anode and Its Physicochemical Effect on Li-Ion Batteries

Park, Hyunjung,Shin, Donghyeok,Paik, Ungyu,Song, Taeseup American Chemical Society 2017 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.56 No.46

<P>The high energy density graphite anode for the commercial LIBs has critical problems on Li<SUP>+</SUP>-ion kinetics due to decreases both in electrode porosity and electrolyte permeability. To overcome issues, interfaces of graphite particles in the anode are polarized using poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) with the high dielectric constant (ε = 8.4), high solubility with lithium salt, and ability to trap a large amount of liquid electrolyte. The PVDF-HFP treatment promoted electrolyte permeability into the graphite electrode with a high mass loading of 13.8 mg cm<SUP>–2</SUP> and a density of 1.7 g cc<SUP>–1</SUP> (a current density over 5 mA cm<SUP>–2</SUP>) which particularly leads to an improvement of capacity retention from 77% of a bare electrode to 95% over 40 cycles. These achievements were attributed not only to the enhancement of the lithium-ion kinetics but also to the stable formation of a solid electrolyte interface (SEI) layer on the graphite surface.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/iecred/2017/iecred.2017.56.issue-46/acs.iecr.7b03797/production/images/medium/ie-2017-03797q_0010.gif'></P>

Nature of Surface and Bulk Defects Induced by Epitaxial Growth in Epitaxial Layer Transfer Wafers

Suk-Goo Kim,박재근,Ungyu Paik 한국전기전자재료학회 2004 Transactions on Electrical and Electronic Material Vol.5 No.4

Surface defects and bulk defects on SOI wafers are studied. Two new metrologies have been proposed to characterize surface and bulk defects in epitaxial layer transfer (ELTRAN) wafers. They included the following: i) laser scattering particle counter and coordinated atomic force microscopy (AFM) and Cu-decoration for defect isolation and ii) cross-sectional transmission electron microscope (TEM) foil preparation using focused ion beam (FIB) and TEM investigation for defect morphology observation. The size of defect is 7.29 um by AFM analysis, the density of defect is 0.36 /cm2 at as-direct surface oxide defect (DSOD), 2.52 /cm2 at ox-DSOD. A hole was formed locally without either the silicon or the buried oxide layer (Square Defect) in surface defect. Most of surface defects in ELTRAN wafers originate from particle on the porous silicon.

Nanoscale printing simplified

Rogers, John A.,Paik, Ungyu Springer Science and Business Media LLC 2010 Nature nanotechnology Vol.5 No.6

Exfoliation of titanium oxide powder into nanosheets using hydrothermal reaction and its reassembly into flexible papers for thin-film capacitors

Lee, Sangkyu,Park, Hun,Paik, Ungyu,Han, Tae Hee Elsevier 2015 Journal of solid state chemistry Vol.224 No.-

<P><B>Abstract</B></P> <P>We have discovered a methodology to realize the fabrication of flexible metal oxide film using two-dimensional (2D) nanosheets. Atomic scale titanium oxide (TiO<SUB> <I>x</I> </SUB>) nanosheets were exfoliated from bulk TiO<SUB> <I>x</I> </SUB> powder that had a layered structure via the modified Sasaki’s method. The vacuum-assisted filtration generates films with laterally aligned TiO<SUB> <I>x</I> </SUB> nanosheets. The 2D sheet-like structure and hydrophilic nature of TiO<SUB> <I>x</I> </SUB> nanosheets enables the film consisting of TiO<SUB> <I>x</I> </SUB> nanosheets to be bendable. Also, we demonstrate the fabrication of electrochemical capacitors using this film. The mechanically flexible metal oxide film is expected to open up the possibility of fabricating flexible energy storage devices from 2D metal oxide nanosheets.</P> <P><B>Highlights</B></P> <P> <UL> <LI> TiO<SUB> <I>x</I> </SUB> single sheets, a novel 2-dimensional material, were exfoliated from bulk powders via the modified Sasaki’s method. </LI> <LI> In our method, the acid treatment of TiO<SUB> <I>x</I> </SUB> bulk powders was simply modified by applying the hydrothermal reaction. </LI> <LI> Then, the delamination procedures of large cation exchange were conducted following the method proposed by Sasaki et al. </LI> <LI> Reassembly of TiO<SUB> <I>x</I> </SUB> sheets into flexible free-standing films was simply achieved via vacuum assisted filtration method. </LI> <LI> TiO<SUB> <I>x</I> </SUB> films were used as a flexible supercapaictor electrode material. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The modified Sasaki’s method, combined process of hydrothermal reaction and bulky ion exchange, enables to obtain TiO<SUB> <I>x</I> </SUB> monolayer nanosheets. The vacuum-assisted filtration generates bendable films with laterally aligned TiO<SUB> <I>x</I> </SUB> nanosheets. Also, we demonstrate the fabrication of electrochemical capacitors using this film.</P> <P>[DISPLAY OMISSION]</P>

Porous TiNb₂O₇ nanofibers decorated with conductive Ti_1−xNb_xN bumps as a high power anode material for Li-ion batteries

Park, Hyunjung,Song, Taeseup,Paik, Ungyu The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.16

<▼1><P>Porous TiNb2O7 nanofibers with metal nitride bumps show ultra-fast rate capability even at 100 C.</P></▼1><▼2><P>Titanium niobium oxide (TiNb2O7) has been reported recently as an attractive anode material for lithium ion batteries due to its practical capacity of ∼280 mA h g<SUP>−1</SUP>, which is much higher than those of well-known metal oxide materials such as TiO2 and Li4Ti5O12. However, low electronic conductivity and poor lithium diffusivity limit its practical use as the active material in lithium ion batteries. Here, we synthesized porous TiNb2O7 nanofibers decorated with Ti1−xNbxN bumps <I>via</I> electro-spinning and thermal ammonia gas treatment. As-prepared nanofibers have one-dimensional geometry with an average diameter of ∼110 nm, and consist of ∼70 nm crystallites and pores in the range of 0–40 nm, shortening pathways for Li<SUP>+</SUP> ion migration into the host material. Furthermore, conductive Ti1−xNbxN bumps with a particle size of ∼5 nm were formed on the surface <I>via</I> thermal ammonia gas treatment which render fast electron transport along the longitudinal direction. The fibers have a specific discharge capacity of ∼254 mA h g<SUP>−1</SUP> at 1 C and a superior rate capability (∼183 mA h g<SUP>−1</SUP> at 100 C). They also show a robust cycle performance over 500 cycles. These dramatic achievements are attributed to heterogeneous nano-structuring creating a porous structure, and the conductivity of the metal nitride achieved by optimal synthetic conditions.</P></▼2>

Si nanotubes array sheathed with SiN/SiOxNy layer as an anode material for lithium ion batteries

Song, Taeseup,Jeon, Yeryung,Paik, Ungyu Springer-Verlag 2014 JOURNAL OF ELECTROCERAMICS Vol.32 No.1