Time filter

Source Type

Kim S.Y.,KAIST | Ahn C.H.,Sungkyunkwan University | Lee J.H.,Korea Electronics Technology Institute | Kwon Y.H.,Sungkyunkwan University | And 4 more authors.
ACS Applied Materials and Interfaces | Year: 2013

Cu2O thin films were synthesized on Si (100) substrate with thermally grown 200-nm SiO2 by sol-gel spin coating method and postannealing under different oxygen partial pressure (0.04, 0.2, and 0.9 Torr). The morphology of Cu2O thin films was improved through N2 postannealing before O2 annealing. Under relatively high oxygen partial pressure of 0.9 Torr, the roughness of synthesized films was increased with the formation of CuO phase. Bottom-gated copper oxide (CuxO) thin film transistors (TFTs) were fabricated via conventional photolithography, and the electrical properties of the fabricated TFTs were measured. The resulting Cu2O TFTs exhibited p-channel operation, and field effect mobility of 0.16 cm2/(V s) and on-to-off drain current ratio of ∼1 × 102 were observed in the TFT device annealed at P O2 of 0.04 Torr. This study presented the potential of the solution-based process of the Cu2O TFT with p-channel characteristics for the first time. © 2013 American Chemical Society. Source

Ahn H.B.,KAIST | Lee J.Y.,Center for Nanomaterials and Chemical Reactions | Lee J.Y.,KAIST
CrystEngComm | Year: 2013

We report on the microstructural characterization of ZnO nanowires during a low-temperature sulfidation process. The morphology of ZnO-ZnS core-shell nanowires obtained for different reaction times was observed. After sulfidation, two different interfaces were observed between the crystalline ZnO core and nanostructured ZnS shell. One is flat {1010} planes covered with a dense ZnS NP layer and the other is rough {1010} planes covered with two porous layers of ZnO and ZnS NPs. Voids were formed inside the crystalline ZnO core, resulting in Kirkendall voids with a hexagonal shape and six symmetrically located {1010} planes, which have lower surface energy compared to {1120}. It is believed that these Kirkendall voids are considerably affected by surface energy. © 2013 The Royal Society of Chemistry. Source

Gang M.G.,Chonnam National University | Gurav K.V.,Chonnam National University | Shin S.W.,Center for Nanomaterials and Chemical Reactions | Hong C.W.,Chonnam National University | And 5 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2015

Cu2ZnSnS4 (CZTS) absorber thin films are prepared by sulfurization of sputtered Cu/Sn/Zn (CZT) stacked metallic precursor. The modified sulfurization process is adapted to prepare photovoltaic quality CZTS films. Specifically, sputtered CZT precursor films are sulfurized in sulfur powder contained graphite box using rapid thermal processing furnace at 580 °C for 10 min, in N2(95%) + H2S (5%) atmosphere. The Cu-poor CZTS films with various Cu/(Zn+Sn) ratio are prepared by varying Cu layer deposition time. The effect of Cu/(Zn+Sn) ratio on the properties of CZTS films is investigated. The CZTS thin film solar cells with Cu/(Zn+Sn)=0.76 shows best conversion efficiency of 5.1% (Voc: 573 mV, Jsc: 18.38 mA/cm2, FF: 0.48%, and active area: 0.31 cm2). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Home > Press > IBS team detects hot electrons in real time: The Center for Nanomaterials and Chemical Reactions fabricated a graphene-semiconductor catalytic nanodiode for improved conductivity of graphene-based nanostructures Abstract: From converting vehicle exhaust fumes into less harmful gases to refining petroleum, most commercial chemical applications require nanocatalysts since they can reduce the required time and costs by controlling the rate of chemical reactions. The catalytic activity and selectivity largely depends on their physical properties (size, shape, and composition) as well as the electronic characteristics; the dynamics of hot (high energy) electrons on the surface and interface of catalysts. Though the catalyst industry is constantly growing, it's challenging to permit electric currents to nanocatalysts in order to detect hot electrons and measure the catalytic efficiency. In a new study, the Institute for Basic Science (IBS) team working under the Center's group leader, Professor PARK Jeong Young, created a catalytic nanodiode composed of a single layer of graphene and titanium film (TiO2) that enabled the detection of hot electrons on platinum nanoparticles (Pt NPs). This breakthrough research developed a catalytic nanodiode that allowed the team to observe in real time the flow of hot electrons generated by chemical reactions. Since hot electrons are created when excess energy from the surface of a chemical reaction is permitted to dissipate in femtosecond, they are deemed as an indicator for the catalystic activity. However, the quick thermalization of hot electrons makes the direct detection of hot electrons quite difficult for clarifying the electronic effect on catalytic activity on metal nanoparticles. In this study, researchers extracted 'hot carriers' from a metal catalyst using a graphene-semiconductor junction. A new approach The scientific team experiments differed to previous attempts where gold was used which proved to be inefficient, unstable and expensive. The team from the Center for Nanomaterials and Chemical Reactions experimented on a single layer of graphene, grown on a copper film before being transported to TiO2 where Pt NPs were later deposited. Graphene, the 2D wonder material, was used because of its unique electronic and chemical properties. When integrated with metal NPs, tremendous improvements in the conductivity performance between the supporting material and the platinum NPs were observed by the team. The catalytic activity and amount of hot electrons were measured; the results showed that the catalytic activity and the generation of hot electrons are well-matched and the reaction mechanism can be studied with hot electrons dynamic. "Graphene-based nanostructures, such as ours are promising detectors for the study of hot electron dynamics on metal NPs during the course of catalytic reactions" confirmed the team's paper. The team's work, according to their paper, highlights the lowered contact resistance at the Pt NPs/ graphene interface is the main characteristic leading to efficient hot electron detection on the nanocatalysts in the graphene- based catalytic nanodiode. By utilizing a single layer of graphene for electrical connection of the Pt NPs it allowed for easier observation of hot electrons because of both the atomically thin nature of graphene and the reduced height of the potential barrier existing at the Pt NPs/ graphene interface. The research conducted at IBS can, potentially, help design catalytic and energy materials with improved performances and lower costs. First author and Ph.D. student Hyosun LEE stated: "Even though there is still the potential for improving the quality of the graphene layer itself and its contact with the TiO2, the approach presented here offers a new way to study the roles of graphene during heterogeneous catalysis." For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Suga M.,JEOL Ltd. | Asahina S.,JEOL Ltd. | Sakuda Y.,JEOL Ltd. | Kazumori H.,JEOL Ltd. | And 21 more authors.
Progress in Solid State Chemistry | Year: 2014

Research concerning nano-materials (metal-organic frameworks (MOFs), zeolites, mesoporous silicas, etc.) and the nano-scale, including potential barriers for the particulates to diffusion to/from is of increasing importance to the understanding of the catalytic utility of porous materials when combined with any potential super structures (such as hierarchically porous materials). However, it is difficult to characterize the structure of for example MOFs via X-ray powder diffraction because of the serious overlapping of reflections caused by their large unit cells, and it is also difficult to directly observe the opening of surface pores using ordinary methods. Electron-microscopic methods including high-resolution scanning electron microscopy (HRSEM) have therefore become imperative for the above challenges. Here, we present the theory and practical application of recent advances such as through-the-lens detection systems, which permit a reduced landing energy and the selection of high-resolution, topographically specific emitted electrons, even from electrically insulating nano-materials. © 2014 Elsevier Ltd. All rights reserved. Source

Discover hidden collaborations