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Mechanism for Shape Control of Cu Nanocrystals Prepared by Polyol Process
Cha Seung-I.,Kim Kyung-T.,Mo Chan-B.,Jeong Yong-J.,Hong Soon-H. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
This study investigated a mechanism for controlling the shape of Cu nanocrystals fabricated using the polyol process, which considers the thermodynamic transition from a facetted surface to a rough surface and the growth mechanisms of nanocrystals with facetted or rough surfaces. The facetted surfaces were stable at relatively low temperatures due to the low entropy of perfectly facetted surfaces. Nanocrystals fabricated using a coordinative surfactant stabilized the facetted surface at a higher temperature than those fabricated using a non-coordinative surfactant. The growth rate of the surface under a given driving force was dependent on the surface structure, i.e., facetted or rough, and the growth of a facetted surface was a thermally activated process. Surface twins decreased the activation energy for growth of the facetted surface and resulted in rod- or wire-shaped nanocrystals
Cha, Seung I.,Koo, Bo K.,Hwang, Kyu Hyeon,Seo, Seon Hee,Lee, Dong Yoon Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.17
<P>A sinter-free TiO<SUB>2</SUB> electrode for flexible DSSCs was fabricated by utilizing spherical aggregates of pre-sintered TiO<SUB>2</SUB> nanoparticles 2–5 μm in diameter (micro-balls), which are prepared by a spray-drying process. The network of interconnected TiO<SUB>2</SUB> nanoparticles within the pre-sintered TiO<SUB>2</SUB> micro-balls resulted in an electron diffusion path from adsorbed dye to an underlying TCO surface, while the nanoparticles themselves made a porous, high surface area TiO<SUB>2</SUB> structure, hence improved energy conversion efficiency.</P> <P>Graphic Abstract</P><P>A sinter-free TiO<SUB>2</SUB> electrode for flexible DSSCs was fabricated by utilizing spherical aggregates of pre-sintered TiO<SUB>2</SUB> nanoparticles 2–5 μm in diameter (micro-balls), which are prepared by a spray-drying process. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0jm04450d'> </P>
Kinetically controlled fabrication of C60 1-dimensional crystals.
Cha, Seung I,Miyazawa, Kun'ichi,Kim, Yun K,Lee, Dong Y,Kim, Je-Deok American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.4
<P>Considering the current application of fullerenes in the field of organic semiconductor devices, the highly crystalline or single crystal fullerene nanostructures with controlled shape and size contains some breakthrough for improved efficiency. Recently, fullerene 1-dimensional nanostructures, including nanowhiskers and nanotubes, become attractive kind of materials since the development of liquid-liquid interface precipitation (LLIP) process. The LLIP process has critical advantage; the fabrication of highly crystalline, even single crystal, fullerene 1-dimensional nanostructures with simple apparatus. However, the fabrication fullerene 1-dimensional structures by LLIP process requires long process time from one day to several days. In order to overcome this drawback, a modified process from conventional LLIP process is suggested. In the modified LLIP process, the nucleation step and growth step were divided. For the nucleation step, saturated fullerene solution is mixed with small amount of alcohols such as 2-propanol or ethanol. For the controlled growth step, the fullerenes in the nucleated solution are precipitated by addition of alcohol, which is injected to the bottom of the solution with controlled flow rate. In this modified process, the shape of the precipitated fullerene crystals is critically dependent on the nucleation steps and the size is dependent on the precipitation rate. By combination of proper nucleation step and growth rate, a well defined fullerene 1-dimensional structures, of 200-500 nm width and of hundreds microm length can be fabricated within two hours. In addition, by controlling injection rate and degree of supersaturation, several types of 1-dimensional structures including micro-tubes can be prepared and, by changing solvent and alcohol, several shape of C60 crystals including polyhedral particles and plates can be prepared.</P>
Cha, Seung I,Hwang, Kyu Hyeon,Kim, Yu Hyun,Yun, Min Ju,Seo, Seon Hee,Shin, Yun Ji,Moon, Jeong Hyun,Lee, Dong Yoon RSC Pub 2013 Nanoscale Vol.5 No.2
<P>Crystal splitting and enhanced photocatalytic activities caused by implied dislocations were observed in hierarchical TiO(2) nano-architectures prepared by one-pot hydrothermal synthesis in concentrated HCl. Microstructural observation revealed that the nanowires formed by continuous splitting of TiO(2) nano-belts, which is caused by a lattice misorientation of about 6, were generated by an array of dislocations. In addition, the larger amount of dislocations implied in TiO(2) nano-architectures induces higher photocatalytic activities under ultra-violet illumination.</P>
Cha, Seung I,Hwang, Kyu Hyun,Kim, Yuhyun,Seo, Sean Hee,Lee, Dong Yoon American Scientific Publishers 2012 Journal of nanoscience and nanotechnology Vol.12 No.9
<P>TiO2 nanostructures have been studied intensively for decades for their photocatalytic properties. Recently, several interesting TiO2 nanostructures with controlled surface facets or shapes were reported. However, systemic approaches to obtain designed nanostructures are still rare. Here, various hierarchical 1D TiO2 nanostructures, including TiO2 nanorods, echinoid-shaped TiO2, and labyrinth-structured TiO2, were fabricated by a one-pot hydrothermal process. Concentrated HCl was added to a solution having a Ti4+/H+ ratio that ranged from 1/4 to 1/8. The highly concentrated acid stabilized hydrolysis and hindered condensation, thereby balancing nucleation and growth of TiO2 nanostructures in the hydrothermal treatment step. Dye-sensitized solar cells prepared using the hierarchical 1D TiO2 nanostructures have shown higher photon to current conversion efficiency in the wavelength over 600 nm compared to those prepared with TiO2 nanoparticles.</P>
Cha, Seung I.,Kim, Yuhyun,Hwang, Kyu Hyeon,Shin, Yun-Ji,Seo, Seon Hee,Lee, Dong Yoon The Royal Society of Chemistry 2012 ENERGY AND ENVIRONMENTAL SCIENCE Vol.5 No.3
<P>Dye-sensitized solar cells (DSSCs) are considered a suitable photovoltaic system for urban applications and highly bendable DSSCs can be expanded to applications such as dispensable DSSCs for commercial advertising and small portable power sources. However, although many reports have shown flexible or highly bendable photoelectrodes using TCO-coated polymeric substrates or metal meshes, until now, few have shown highly bendable DSSCs using electrodes because the flexibility of a single electrode is not a critical issue for highly bendable DSSCs. Here, we report a new DSSC design, inspired by the traditional Korean door structure consisting of a paper-bonded wooden frame, and a process for TCO-free highly bendable DSSCs utilizing glass paper and metal mesh. In the new DSSC design, constituents such as stainless steel mesh and mesoporous TiO<SUB>2</SUB> loaded with a Ru-complex dye were bonded on the glass paper, which was sputter-coated with Pt on one side and filled with electrolyte. The glass-paper-based flexible DSSCs showed 2% energy-conversion efficiency, which was maintained under bending until the radius of curvature reached 2 cm. The new glass-paper-based flexible DSSCs may have potential applications as low-cost highly bendable solar cells to overcome the limitations of conventional sandwich-type DSSCs.</P> <P>Graphic Abstract</P><P>New TCO free, highly bendable dye-sensitized solar cells (DSSCs) are designed by utilizing glass paper inspired from Korean traditional door structures. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2ee03096a'> </P>
Fabrication Process and Properties of Carbon Nanotube/Cu Nanocomposites
Cha Seung-I.,Kim Kyung-T.,Mo Chan-B.,Hong Soon-H. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Carbon nanotubes (CNTs) have attracted remarkable attention as reinforcement for composites owing to their outstanding mechanical properties. The CNT/Cu nanocomposite is fabricated by a novel fabrication process named molecular level process. The novel process for fabricating CNT/Cu composite powders involves suspending CNTs in a solvent by surface functionalization, mixing Cu ions with CNT suspension, drying, calcination and reduction. The molecular level process produces CNT/Cu composite powders whereby the CNTs are homogeneously implanted within Cu powders. The mechanical properties of CNT/Cu nanocomposite, consolidated by spark plasma sintering of CNT/Cu composite powders, shows about 3 times higher strength and 2 times higher Young's modulus than those of Cu matrix.