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Lee, Jun Seop,Kim, Minkyu,Lee, Choonghyeon,Cho, Sunghun,Oh, Jungkyun,Jang, Jyongsik RSC Pub 2015 Nanoscale Vol.7 No.8
<P>With recent developments in technology, tremendous effort has been devoted to producing materials for flexible device systems. As a promising approach, solution-processed conducting polymers (CPs) have been extensively studied owing to their facile synthesis, high electrical conductivity, and various morphologies with diverse substrates. Here, we report the demonstration of platinum decorated reduced graphene oxide intercalated polyanililne:poly(4-styrenesulfonate) (Pt_rGO/PANI:PSS) hybrid paste for flexible electric devices. First, platinum decorated reduced graphene oxide (Pt_rGO) was fabricated through the chemical reduction of platinum cations and subsequent heat reduction of GO sheets. Then, the Pt_rGO was mixed with PANI:PSS solution dispersed in diethylene glycol (DEG) using sonication to form a hybrid PANI-based paste (Pt_rGO/PANI:PSS). The Pt_rGO/PANI:PSS was printed as a micropattern and exhibited high electrical conductivity (245.3 S cm(-1)) with flexible stability. Moreover, it was used in a dipole tag antenna application, where it displayed 0.15 GHz bandwidth and high transmitted power efficiency (99.6%).</P>
Shin, Jungwoo,Park, Kyusung,Ryu, Won-Hee,Jung, Ji-Won,Kim, Il-Doo RSC Pub 2014 Nanoscale Vol.6 No.21
<P>Carbon nanofibers encapsulating Si nanoparticles (CNFs/SiNPs) were prepared via an electrospinning method and chemically functionalized with 3-aminopropyltriethoxysilane (APS) to be grafted onto graphene oxide (GO). As a result, the thin and flexible GO, which exhibits a negative charge in aqueous solution, fully wrapped around the APS-functionalized CNFs with a positive surface charge via electrostatic self-assembly. After the formation of chemical bonds between the epoxy groups on GO and the amine groups in APS via an epoxy ring opening reaction, the GO was chemically reduced to a reduced graphene oxide (rGO). Electrochemical and morphological characterizations showed that capacity loss by structural degradation and electrolyte decomposition on Si surface were significantly suppressed in the rGO-wrapped CNFs/SiNPs (CNFs/SiNPs@rGO). Superior capacities were consequently maintained for up to 200 cycles at a high current density (1048 mA h g(-1) at 890 mA g(-1)) compared to CNFs/SiNPs without the rGO wrapping (304 mA h g(-1) at 890 mA g(-1)). Moreover, the resistance of the SEI layer and charge transfer resistance were also considerably reduced by 24% and 88%, respectively. The described graphene wrapping offers a versatile way to enhance the mechanical integrity and electrochemical stability of Si composite anode materials.</P>
Ryu, Won-Hee,Jung, Ji-Won,Park, Kyusung,Kim, Sang-Joon,Kim, Il-Doo RSC Pub 2014 Nanoscale Vol.6 No.19
<P>A tailored conversion-reaction anode material of 1-D MoS2 nanofibers with a vine-like shape composed of MoS2 nanoflakes delivers exceptionally high Na capacity and exhibits excellent rate properties. The improved cycleability of the MoS2 nanofiber electrode is achieved by a uniform TiO2 coating, which effectively minimized the sulfur dissolution.</P>
Fast synthesis of high-quality reduced graphene oxide at room temperature under light exposure.
Some, Surajit,Kim, Sungjin,Samanta, Khokan,Kim, Youngmin,Yoon, Yeoheung,Park, Younghun,Lee, Sae Mi,Lee, Keunsik,Lee, Hyoyoung RSC Pub 2014 Nanoscale Vol.6 No.19
<P>An approach of presenting new reducing reagents, sodium-benzophenone (Na-B) or Na-B in the presence of the hydrazine (Na-B-H) system under light exposure could produce rGOs with/without N-doping at room temperature in both the solution phase and on a solid substrate. Benzophenone activated those solutions acting as a photosensitizer under light. It was assumed that the newly generated radical anions with electrons from Na-B under light can reduce GO to rGO sheets (rGONa-B1). In addition, the Na-B-H system can allow a higher degree of reduction with the doping of nitrogen atoms by the introduction of hydrazine to produce radical anions and electrons with a sodium hydrazide complex, which helps decrease the sheet resistance of the as-made rGONa-B-H2. The excellent properties (very low oxygen content (C/O 16.2), and low sheet resistance (130 ω square(-1))) of the rGOs were confirmed by XPS, XRD, IR, Raman spectroscopy, TGA, wettability, and sheet resistance measurements. High-quality rGO films on flexible substrates could be prepared by directly immersing the GO films in these solutions for several minutes.</P>
Park, Bo-In,Hwang, Yoonjung,Lee, Seung Yong,Lee, Jae-Seung,Park, Jong-Ku,Jeong, Jeunghyun,Kim, Jin Young,Kim, BongSoo,Cho, So-Hye,Lee, Doh-Kwon RSC Pub 2014 Nanoscale Vol.6 No.20
<P>Efficient Cu2ZnSnSe4 (CZTSe) solar cells were fabricated with a simple, environmentally friendly, and scalable synthetic method for Cu2ZnSnS4 (CZTS) nanocrystals. CZTS nanoparticles were mechanochemically synthesized from elemental precursors on a relatively large scale (20 g), during which no solvents or additives were used, thus alleviating the complex process of particle synthesis. An analysis of the time evolution of the crystalline phase and morphology of precursor powders revealed that the formation of the CZTS compound was completed in 0.5 h once initiated, suggesting that the mechanochemically induced self-propagating reaction prevails. CZTS ink was prepared by dispersing the as-synthesized nanoparticles in an environmentally benign solvent (160 mg mL(-1) in ethanol) without using any additives, after which it was cast onto Mo-coated glass substrates by a doctor-blade method. Subsequent reactive annealing at 560 C under a Se-containing atmosphere resulted in substantial grain growth along with the nearly complete substitution of Se. The CZTSe solar cells therefrom exhibited power conversion efficiency levels as high as 6.1% (based on the active area, 0.44 cm(2)) with a relatively high open-circuit voltage (0.42 V) in comparison with the bandgap energy of 1.0 eV.</P>
Direct growth of patterned graphene on SiO2 substrates without the use of catalysts or lithography.
Kim, Yong Seung,Joo, Kisu,Jerng, Sahng-Kyoon,Lee, Jae Hong,Yoon, Euijoon,Chun, Seung-Hyun RSC Pub 2014 Nanoscale Vol.6 No.17
<P>We demonstrate a one-step fabrication of patterned graphene on SiO2 substrates through a process free from catalysts, transfer, and lithography. By simply placing a shadow mask during the plasma enhanced chemical vapor deposition (PECVD) of graphene, an arbitrary shape of graphene can be obtained on SiO2 substrate. The formation of graphene underneath the shadow mask was effectively prevented by the low-temperature, catalyst-free process. Growth conditions were optimized to form polycrystalline graphene on SiO2 substrates and the crystalline structure was characterized by Raman spectroscopy and transmission electron microscopy (TEM). Patterned graphene on SiO2 functions as a field-effect device by itself. Our method is compatible with present device processing techniques, and should be highly desirable for the proliferation of graphene applications.</P>
Axially twinned nanodumbbell with a Pt bar and two Rh@Pt balls designed for high catalytic activity.
Khi, Nguyen Tien,Yoon, Jisun,Kim, Heonjo,Lee, Sangmin,Kim, Byeongyoon,Baik, Hionsuck,Kwon, Seong Jung,Lee, Kwangyeol RSC Pub 2013 Nanoscale Vol.5 No.13
<P>A fail-proof synthetic strategy has been developed for a multiply twinned dumbbell-shaped Rh@Pt nanostructure, which exhibits a superior electrocatalytic activity for methanol oxidation reaction. The unusually high electrocatalytic activity has been attributed to the synergistic effects of crystal twinning and core-shell structure.</P>
Baek, Seung-Wook,Shim, Jae-Hyoung,Seung, Hyun-Min,Lee, Gon-Sub,Hong, Jin-Pyo,Lee, Kwang-Sup,Park, Jea-Gun RSC Pub 2014 Nanoscale Vol.6 No.21
<P>Silicon solar cells mainly absorb visible light, although the sun emits ultraviolet (UV), visible, and infrared light. Because the surface reflectance of a textured surface with SiNX film on a silicon solar cell in the UV wavelength region (250-450 nm) is higher than 27%, silicon solar-cells cannot effectively convert UV light into photo-voltaic power. We implemented the concept of energy-down-shift using CdSe/ZnS core/shell quantum-dots (QDs) on p-type silicon solar-cells to absorb more UV light. CdSe/ZnS core/shell QDs demonstrated clear evidence of energy-down-shift, which absorbed UV light and emitted green-light photoluminescence signals at a wavelength of 542 nm. The implementation of 0.2 wt% (8.8 nm QDs layer) green-light emitting CdSe/ZnS core/shell QDs reduced the surface reflectance of the textured surface with SiNX film on a silicon solar-cell from 27% to 15% and enhanced the external quantum efficiency (EQE) of silicon solar-cells to around 30% in the UV wavelength region, thereby enhancing the power conversion efficiency (PCE) for p-type silicon solar-cells by 5.5%.</P>
Enhanced overcharge performance of nano-LiCoO2 by novel Li3VO4 surface coatings.
Pu, Xiong,Yu, Choongho RSC Pub 2012 Nanoscale Vol.4 No.21
<P>LiCoO(2) nanoparticles were coated with 3.4 and 5.5 wt% of lithium vanadate (Li(3)VO(4)) by a wet-chemical and sintering method. When the electrode containing 5.5-wt% Li(3)VO(4)-coated LiCoO(2) was overcharged to 4.5 V at a current of 30 mA g(-1) (0.2 C), 85% of the initial discharge capacity after 100 charge-discharge cycles was maintained, compared to only 67% for the electrode with bare LiCoO(2) nanoparticles. The electrode with 5.5 wt% coating can also deliver 115 mA h g(-1) discharge capacity at a current of 1200 mA g(-1) (8 C) and a discharge-charge voltage of 4.5 V, which is twice the capacity of the bare LiCoO(2) sample. The improvement of overcharge cyclability and high-rate capability was believed to be due to the structurally protective Li(3)VO(4) surface coating with good Li-ion conductivity.</P>
Seo, Yoon Ho,Kim, Lo Hyun,Kim, Young-Beom,Ryu, WonHyoung RSC Pub 2013 Nanoscale Vol.5 No.17
<P>Nanoprobe arrays for multiple single cell insertion were developed using heterogeneous nanosphere lithography. Using two heterogeneous nanoparticles as sacrificial and masking particles, high aspect ratio Si nanoprobes were fabricated in an array with spacing between the nanoprobes ranging from a few to tens of micrometers. For registered single cell analysis, multiple and precise insertion of nanoprobes into multiple single cells in a parallel fashion was demonstrated using micropipette suction and micromanipulators.</P>