Platinum-decorated reduced graphene oxide/polyaniline:poly(4-styrenesulfonate) hybrid paste for flexible dipole tag-antenna applications.

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>

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>

Solvent-free synthesis of Cu2ZnSnS4 nanocrystals: a facile, green, up-scalable route for low cost photovoltaic cells.

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>

Effect of core quantum-dot size on power-conversion-efficiency for silicon solar-cells implementing energy-down-shift using CdSe/ZnS core/shell quantum dots.

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>

Investigation of ultraviolet optical properties of semiconducting-enriched and metal-enriched single-walled carbon nanotube networks using spectroscopic ellipsometry.

Park, Young Ran,Kim, Woo-Jae,Ko, Min Jae,Min, Nam Ki,Lee, Cheol Jin RSC Pub 2012 Nanoscale Vol.4 No.20

<P>The ultraviolet optical properties of semiconducting-enriched and metallic-enriched single-walled carbon nanotube (semi-enriched and m-enriched SWCNT) networks were studied using spectroscopic ellipsometry. According to calculated energy loss function, the energy loss peak assigned to the maximum intensity of π-plasmon energy was found to increase from 4.5 eV to 5.0 eV as SWCNT network composition was changed from m-SWCNT enriched to semi-SWCNT enriched. These results clearly demonstrate that the dielectric response in the 4-6 eV range is sensitive to changes in the surrounding dielectric environment depending on the semi-/m-SWCNT content. Therefore, the spectral shift of this energy loss is attributed to the enhanced electron confinement by the presence of the surface plasmon due to a small amount of m-SWCNT, which is an important phenomenon at the SWCNT network.</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>

Nanoprobe arrays for multiple single cell insertion using heterogeneous nanosphere lithography (HNSL).

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>

Cellular interactions of doxorubicin-loaded DNA-modified halloysite nanotubes.

Lee, Yeonju,Jung, Goo-Eun,Cho, Sang Joon,Geckeler, Kurt E,Fuchs, Harald RSC Pub 2013 Nanoscale Vol.5 No.18

<P>Halloysite nanotube (HNT)-based supramolecular complexes are synthesized and evaluated with respect to their cytotoxicity and effects on cellular structures. As HNTs are water-insoluble, DNA is applied for wrapping the surface of HNTs to enhance their water-dispersibility. To investigate the potential of DNA-wrapped HNTs (HD) as a promising drug delivery carrier, doxorubicin (DOX) is introduced as a model anticancer agent and loaded onto HD. The DOX-loaded, DNA-wrapped HNTs (HDD) show sustained DOX release over two weeks without initial burst of DOX indicating delayed DOX release inside cells. In addition, effects of DNA-wrapped HNTs (HD) or HDD on the cytoskeleton organization of A549 cells are studied by visualizing the distribution of F-actin filaments using confocal laser scanning microscopy, and cellular morphological changes are observed by scanning electron microscopy and scanning ion conductance microscopy.</P>

A simple self-assembly route to single crystalline SnO2 nanorod growth by oriented attachment for dye sensitized solar cells.

Song, Hui,Lee, Kwang-Ho,Jeong, Huisu,Um, Soong Ho,Han, Gil-Sang,Jung, Hyun Suk,Jung, Gun Young RSC Pub 2013 Nanoscale Vol.5 No.3

<P>One-dimensional (1-D) SnO(2) nanorods (NRs) with a rutile structure are grown on various substrates regardless of the lattice-mismatch by using a new nutrient solution based on tin oxalate, which generated supersaturated Sn(2+) sources. These affluent sources are appropriate for producing a large number of SnO(2) nanoparticles, sufficient for stacking on a substrate surface by gravity, which then acts as a seed layer for subsequent nanorod growth. Single crystalline nanorods are grown along the [001] direction by the oriented attachment phenomenon in which the attached nanoparticles were rearranged to reduce the overall surface energy through sharing thermodynamically unstable crystal (001) planes. Furthermore, the grown SnO(2) NRs are covered with a TiO(2) particulate film and utilized as a photoanode in DSSCs. The power conversion efficiency is 8.61%, enhanced by 14.2% compared to the photoanode with only a TiO(2) particulate film.</P>