Zeolitic imidazolate framework-7 textile-derived nanocomposite fibers as freestanding supercapacitor electrodes

Joshi, Bhavana,Park, Sera,Samuel, Edmund,Jo, Hong Seok,An, Seongpil,Kim, Min-Woo,Swihart, Mark T.,Yun, Je Moon,Kim, Kwang Ho,Yoon, Sam S. Elsevier S.A 2018 Journal of Electroanalytical Chemistry Vol.810 No.-

<P><B>Abstract</B></P> <P>Zeolitic imidazole frameworks (ZIFs) are a class of metal organic frameworks (MOFs) with diverse energy-related applications. High-surface area materials derived from ZIFs can serve as electrodes with good long-term capacity retention. Herein, we demonstrate an electrospun ZIF7/carbon nanofiber (CNF) derived nanocomposite as a freestanding electrode for supercapacitors with excellent capacitance retention. The optimal ZIF7 composite nanofiber carbonized at 950 °C exhibited a specific capacitance of 202 F·g<SUP>−1</SUP> at a current density of 1 A·g<SUP>−1</SUP> and ~98% specific capacitance retention after 5000 charge–discharge cycles. N-doped nanoporous C and the Zn framework of ZIF7 composite fibers delivered an energy density of 42 W·h·kg<SUP>−1</SUP> at a power density of 0.6 kW·kg<SUP>−1</SUP>. These scalable ZIF7/CNF composite textiles (30 × 10 cm<SUP>2</SUP>) can be used as freestanding supercapacitor electrodes without a separate substrate or current collector.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Zeolitic imidazole frameworks-7 nanofiber as a freestanding electrode for supercapacitors is demonstrated. </LI> <LI> The ZIF-7 nanofiber exhibited a specific capacitance of 202 F·g<SUP>−1</SUP> at a current density of 1 A·g<SUP>−1</SUP>. </LI> <LI> The nanofiber exhibited 98% specific capacitance retention after 5000 charge–discharge cycles. </LI> <LI> The well-embedded ZIF-7 that formed pores in the CNF by the removal of Zn increased the electrochemical performance. </LI> <LI> This one-step fabricated method is produced by a commercially scalable process. </LI> </UL> </P>

High-performance glucose biosensor based on green synthesized zinc oxide nanoparticle embedded nitrogen-doped carbon sheet

Muthuchamy, Nallal,Atchudan, Raji,Edison, Thomas Nesakumar Jebakumar Immanuel,Perumal, Suguna,Lee, Yong Rok Elsevier S.A 2018 Journal of Electroanalytical Chemistry Vol.816 No.-

<P><B>Abstract</B></P> <P>A new, highly selective, sensitive and stable enzymatic glucose sensor was fabricated on glassy carbon electrode (GCE) using zinc oxide (ZnO) nanoparticles embedded nitrogen-doped carbon sheets (ZnO@NDCS), glucose oxidase (GOx) (assigned as GCE/ZnO@NDCS/GOx). First, ZnO@NDCS were synthesized by a simple hydrothermal method. Zn powder, aqueous ammonia, and peach extract were served as the precursor for ZnO NPs, nitrogen and carbon, respectively. The fabricated GCE/ZnO@NDCS/GOx biosensor exhibited a high and reproducible sensitivity of 231.7 μA mM<SUP>−1</SUP> cm<SUP>−2</SUP>. Also, showed a wide linear range from 0.2 to 12 mM with a correlation coefficient R<SUP>2</SUP> = 0.998 and lowest detection limit (based on S/N ratio = 3) of 6.3 μM. The GCE/ZnO@NDCS/GOx biosensor is acceptably stable, selective, and it was successfully applied to the quantitative monitoring of glucose in human blood serum. The synthesized ZnO@NDCS nanocomposite may be found useful in other applications in the fields of solar cells and optoelectronic devices. These encouraging results suggest a simple and effective method obtain electrode material for the enzymatic glucose sensor.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZnO@NDCS composite was synthesized from peach fruit by a simple hydrothermal method. </LI> <LI> Fabricated GCE/ZnO@NDCS/GOx sensor delivered a high sensitivity 118.3 μA mM<SUP>−1</SUP> cm<SUP>−2</SUP>. </LI> <LI> This biosensor showed a LOD of 4 μM and fast amperometric current response of (3 s). </LI> <LI> It exhibits a good selectivity, reproducibility, and long term storage stability. </LI> <LI> Moreover, the GCE/ZnO@NDCS/GOx is well suited for the diabetic glucose monitoring. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Low temperature polycrystalline silicon with single orientation on glass by blue laser annealing

Jin, Seonghyun,Hong, Seungpyo,Mativenga, Mallory,Kim, Boram,Shin, Heung Hyun,Park, Jong Kab,Kim, Tae-Woong,Jang, Jin Elsevier S.A. 2016 Thin Solid Films Vol.616 No.-

<P><B>Abstract</B></P> <P>We report the achievement of low-temperature polycrystalline silicon (LTPS) thin-films with a single orientation on glass by using continuous wave blue laser annealing (BLA) of amorphous silicon (a-Si). The BLA is administered in multiple shots and with increasing number of shots, grain size increases and all grains follow a single orientation. Because the absorption coefficient of a blue laser (BL) in poly-Si is less than that in a-Si, the amount of the un-melted Si at the bottom is gradually reduced with increasing number of shots, resulting in near complete melting of the whole Si layer. In this study, irradiation of a 150-nm-thick a-Si film with 200 BL (445nm) shots achieves a poly-Si film having an average grain size of about 4μm and single orientation in the (100) direction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Large grain poly-Si thin films with a single orientation </LI> <LI> Crystallization of a-Si films by using multiple shots of the CW blue laser annealing </LI> <LI> Grain growth mechanism of Si films with increasing number of blue laser shots </LI> </UL> </P>

Transparent SnO_x thin films fabricated by radio frequency reactive sputtering with a SnO/Sn composite target

Kim, Cheol,Kim, Sungdong,Kim, Sarah Eunkyung Elsevier S.A. 2017 Thin Solid Films Vol.634 No.-

<P><B>Abstract</B></P> <P>SnO<SUB>x</SUB> thin films are potentially excellent conductive material with large hole mobility and have attracted ever-increasing attention for next generation electronic applications. In this study, SnO<SUB>x</SUB> thin films were deposited on a borosilicate glass substrate by radio frequency (rf) reactive sputtering using a SnO/Sn (9:1mol% ratio) composite target. The composite target was used to produce a chemically stable composition of SnO<SUB>x</SUB> thin film while controlling structural defects by chemical reaction between tin and oxygen. The effects of oxygen contents and annealing on various properties of SnO<SUB>x</SUB> thin films were studied. The structural analysis was carried out using X-ray photoelectron spectroscopy and X-ray diffraction. The electrical and optical analyses were performed by the Van der Pauw Hall effect measurement and UV/VIS spectrometer, respectively. SnO<SUB>x</SUB> thin films at P<SUB>O2</SUB> =0% (annealed) and 3% (as deposited) exhibited a p-type conductivity of 0.09–0.11Ω<SUP>−1</SUP> cm<SUP>−1</SUP>, a hole mobility of 0.2–1.2cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, and a hole concentration of ~10<SUP>18</SUP> cm<SUP>−3</SUP>. Also, these thin films showed the transmittance of about 70% and an optical bandgap of 2.75–3.01eV.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabrication of p-type transparent SnO<SUB>x</SUB> thin films by rf sputtering </LI> <LI> SnO:Sn composite target effect on electrical properties of p-type SnO<SUB>x</SUB> thin films </LI> <LI> Study of electrical conductivity conversion of p-type SnO<SUB>x</SUB> thin films </LI> <LI> Annealing effect on electrical properties of p-type SnO<SUB>x</SUB> thin films </LI> </UL> </P>

A conducting neural interface of polyurethane/silk-<i>f</i>unctionalized multiwall carbon nanotubes with enhanced mechanical strength for neuroregeneration

Shrestha, Sita,Shrestha, Bishnu Kumar,Lee, Joshua,Joong, Oh Kwang,Kim, Beom-Su,Park, Chan Hee,Kim, Cheol Sang Elsevier S.A. 2019 Materials Science and Engineering C Vol. No.

<P><B>Abstract</B></P> <P>A fibrous scaffold, fully assimilating polyurethane (PU) and silk fibroin associated with functionalized multi-walled carbon nanotubes (<I>f</I>MWCNTs) was developed by electrospinning technique. Herein, we engineered the PU/Silk fibroin-<I>f</I>MWCNTs-based biomaterial that shows great promise as electrospun scaffolds for neuronal growth and differentiation, because of its unique mechanical properties, hydrophilicity, and biodegradability, with outstanding biocompatibility in nerve tissue engineering. The morphology and structural properties of the scaffolds were studied using various techniques. In particular, the presence of <I>f</I>MWCNTs enhances the electrical conductivity and plausible absorption of sufficient extracellular matrix (ECM). The <I>in vitro</I> tests revealed that the aligned scaffolds (PU/Silk-<I>f</I>MWCNTs) significantly stimulated the growth and proliferation of Schwann cells (S42), together with the differentiation and spontaneous neurite outgrowth of rat pheochromocytoma (PC12) cells that were particularly guided along the axis of fiber alignment. The conductive PU/Silk-<I>f</I>MWCNTs scaffold significantly improves neural expression <I>in vitro</I> with successful axonal regrowth, which was confirmed by immunocytochemistry and qRT-PCR analysis. Inspired by the comprehensive experimental results, the <I>f</I>MWCNTs-based scaffold affords new insight into nerve-guided conduit design from both conductive and protein rich standpoints, and opens a new perspective on peripheral nerve restoration in preclinical applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Polyurethane-silk/multiwall carbon nanotubes based aligned electrospun scaffold was fabricated. </LI> <LI> A protein rich biomaterial showed high mechanical strength and good electrical conductivity. </LI> <LI> PC12 cells are well proliferated and differentiated on scaffold along with fibers orientation. </LI> <LI> The scaffold exhibited strong bioactivity, suited for <I>in vitro</I> nerve cell regeneration. </LI> </UL> </P>

Preparation of SnS₂ thin films by conversion of chemically deposited cubic SnS films into SnS₂

U., C.,B., P.,B., P.R.,Park, S.H. Elsevier S.A. 2017 Thin Solid Films Vol.640 No.-

We report the growth of SnS<SUB>2</SUB> thin films by annealing chemically deposited cubic SnS films under a sulfur atmosphere in a graphite box. The chemically deposited SnS films were annealed in the temperature range of 200-550<SUP>o</SUP>C to understand its influence on the conversion of SnS into SnS<SUB>2</SUB>. In the X-ray diffraction analysis, the as-deposited SnS films annealed in the temperature range of 200-250<SUP>o</SUP>C showed the formation of a minor SnS<SUB>2</SUB> phase along with the dominant SnS phase. The films annealed at 300<SUP>o</SUP>C contained mixed phases of SnS and SnS<SUB>2</SUB>. Increasing the annealing temperature from 350 to 500<SUP>o</SUP>C led to the formation of only the dominant SnS<SUB>2</SUB> phase. Further increasing the annealing temperature to 550<SUP>o</SUP>C gave rise to the formation of a highly oriented SnS<SUB>2</SUB> film with hexagonal structure having (001) as the preferred orientation. The crystallite size of the SnS<SUB>2</SUB> films was found to increase from 17nm to 25nm with increasing annealing temperature from 350<SUP>o</SUP>C to 550<SUP>o</SUP>C. The lattice parameters were found to be a=0.365nm and c=0.592nm. Raman spectroscopy analysis confirmed the formation of single phase SnS<SUB>2</SUB> films at annealing temperatures above 350<SUP>o</SUP>C. The morphological studies showed the conversion of the round shaped grains into flake-like ones on annealing at temperatures above 350<SUP>o</SUP>C. These flakes increased in size on increasing the annealing temperature from 350<SUP>o</SUP>C to 500<SUP>o</SUP>C. The direct optical band gap of these SnS<SUB>2</SUB> films was found to be 2.58eV.

Bandgap-controlled non-equilibrium ZnO_1−xS_x thin films grown by pulsed laser deposition method

Choi, H.I.,Kim, S.W.,Lee, M.H.,Kim, D.J.,Han, S.-J.,Lee, W.,Song, T.K.,Kim, M.-H.,Jeong, I.-K.,Kim, W.J. Elsevier S.A. 2015 Thin Solid Films Vol.589 No.-

<P><B>Abstract</B></P> <P>Although ZnO and ZnS are chemically and structurally similar, these binary compounds do not form a solid solution at room temperature for all proportions of sulfur (S) and oxygen (O) due to solubility limits of S in ZnO and O in ZnS in equilibrium states. To fabricate ZnO<SUB>1−x</SUB>S<SUB>x</SUB> thin films with 0<x<1, films were intentionally deposited in a non-equilibrium state using pulsed laser deposition while controlling oxygen pressures. The deposited ZnO<SUB>1−x</SUB>S<SUB>x</SUB> thin film structures were investigated by X-ray diffraction, confirming the formation of hexagonal wurtzite structures with c-axis lattice constants larger than that of ZnO and smaller than that of ZnS. Furthermore, phase segregation to ZnO and ZnS was observed by increasing the temperature of the ZnO<SUB>0.5</SUB>S<SUB>0.5</SUB> thin film, suggesting non-equilibrium state of the deposited film. The observed optical energy bandgaps of the ZnO<SUB>1−x</SUB>S<SUB>x</SUB> thin films were smaller than those of both ZnO (~3.3eV) and ZnS (~3.68eV), suggesting a bandgap bowing effect due to valance and conduction band shifts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We successfully deposited a II–VI type of semiconductors, ZnO<SUB>1−x</SUB>S<SUB>x</SUB> thin films. </LI> <LI> We study about ZnO<SUB>0.5</SUB>S<SUB>0.5</SUB> phase with temperature dependent XRD. </LI> <LI> The contents of ZnO<SUB>1−x</SUB>S<SUB>x</SUB> thin films are from 1(ZnS) to 0(ZnO). </LI> </UL> </P>

Microstructure-controlled deposition of yttria-stabilized zirconia electrolyte for low temperature solid oxide fuel cell performance stability enhancement

Hong, S.,Yang, H.,Lim, Y.,Kim, Y.B. Elsevier S.A. 2016 Thin Solid Films Vol.618 No.1

Yttria-stabilized zirconia thin films were deposited with a controlled argon flow rate via DC reactive magnetron sputtering processes. Typically, thin film electrolytes fabricated by physical vapor deposition onto nano-porous substrates generate pinholes due to their columnar grain structure. The grain boundaries between these columnar grains can be considered as structural defects and can cause voltage drops due to electrical shorting when used as thin film electrolytes in energy conversion systems. By controlling the argon flow rate of the reactive sputtering method, YSZ thin films with dense and restrained columnar grains were fabricated. Scanning electron microscopy inspection was conducted to analyze the surface morphologies, grain structures, and nano-defects in the interior of YSZ thin films. X-ray photoelectron spectroscopy revealed that the composition of the YSZ electrolyte is determined by the flow rate of the oxygen-reactive gas. In addition, X-ray diffractometry was conducted to verify the crystalline phase of the YSZ films; it was determined that a lower argon flow rate produces a better crystalline phase. The films also showed high ionic conductivity compared to the reference data, and the restrained columnar structure had higher conductivity due to a reduction in the ion transport blockage. Furthermore, the fuel cell with the YSZ electrolyte fabricated under a low argon flow rate, which had restrained columnar grains, showed a higher peak power density and superior open circuit voltage performance compared to the fuel cell with a higher argon flow rate.

Poly(aniline‑<i>co</i>‑pyrrole)-spaced graphene aerogel for advanced supercapacitor electrodes

Tran, Van Chinh,Sahoo, Sumanta,Hwang, Jinho,Nguyen, Van Quang,Shim, Jae-Jin Elsevier S.A 2018 Journal of Electroanalytical Chemistry Vol.810 No.-

<P><B>Abstract</B></P> <P>Polyaniline (PANI) and polypyrrole (PPy) are conducting polymers used widely in Supercapacitor applications because of their facile synthesis, low cost, and good pseudo-capacitive performance. In this study, PANI and PPy were combined with reduced graphene oxide (RGO) to form a new 3D hybrid aerogel, poly(aniline‑co‑pyrrole)/graphene aerogel (PGA), which was assessed as a promising material for supercapacitor electrodes. A one-step hydrothermal co-assembly method was adopted to synthesize the active electrode materials. The PGA exhibited a high specific capacitance of 675F/g at a current density of 0.5A/g with excellent cycling stability (97.5% capacitance retention and near 100% coulombic efficiency after 1000charge/discharge cycles).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Poly(aniline-co-pyrrole)-spaced graphene aerogel (PGA) was prepared. </LI> <LI> PGA exhibited a highly porous nanoarchitecture. </LI> <LI> PGA achieved a good specific capacitance of 675F/g at a density of 0.5A/g. </LI> <LI> PGA showed a good stability (97.5% capacitance retention after 1000cycles). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Thick tungsten layer coating on ferritic-martensitic steel without interlayer using a DC vacuum plasma spray and a RF low pressure plasma spray method

Kim, H.S.,Hong, B.G.,Moon, S.Y. Elsevier S.A. 2017 Thin Solid Films Vol.623 No.-

Tungsten has been attracted as one of promising candidates for plasma-facing materials in a next fusion reactor because of its many advantages. However, since the tungsten is difficult to machine and requires high cost techniques for joining to various substrates, alternative methods such as plasma spray coating have been developed. In this work, therefore, we coated thick tungsten layer on a ferritic-martensitic steel by a 60kW radio-frequency low pressure plasma spray system and a 55kW direct-current vacuum plasma spray system. Thick tungsten coating over 2mm using both systems without any interlayer was obtained by inserting a substrate preheating process. We also discussed the characteristics of coated tungsten layers such as hardness, micro-structure, porosity, surface morphology, and crystal structure which were investigated using Vickers hardness tester, field emission scanning electron microscopy, microscope, 3-dimensional surface measuring system, and X-ray diffraction, respectively.