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Extreme Tech: Nanowire "impossible to replicate" fingerprints could eliminate fraud, counterfeit goods
Research done by Professor Hyun-Joon Song of Chemistry at KAIST on anti-counterfeit, nanoscale fingerprints generated by randomly distributed nanowires was introduced by Extreme Tech, an online global science and technology news. For the articles, please go to: Extreme Tech, March 25, 2014Nanowire ‘impossible to replicate’ fingerprints could eliminate fraud, counterfeit goods http://www.extremetech.com/extreme/179131-nanowire-impossible-to-replicate-fingerprints-could-eliminate-fraud-counterfeit-goods
Rechargeable Lithium Sulfur Battery for Greater Battery Capacity
Professor Do Kyung Kim from the Department of Material Science and Engineering and Professor Jang Wook Choi from the Graduate School of EEWS have been featured in the lead story of the renowned nanoscience journal Advanced Materials for their research on the lithium sulfur battery. This new type of battery developed by Professor Kim is expected to have a longer life battery life and [higher] energy density than currently commercial batteries. With ample energy density up to 2100Wh/kg—almost 5.4 times that of lithium ion batteries—lithium sulfur batteries can withstand the sharp decrease in energy capacity resulting from charging and discharging—which has been considered the inherent limitation of the conventional batteries. Professor Kim and his research team used one-dimensional, vertical alignment of 75nm tick, 15μm long sulfur nanowires to maximize electric conductivity. Then, to prevent loss of battery life, they carbon-coated each nanowire and prohibited direct contact between the sulfur and electrolyte. The result was one of the most powerful batteries in terms of both energy performance and density. Compared to conventional batteries which suffer from continuous decrease in energy capacity after being discharged, the lithium sulfur battery maintained 99.2% of its initial capacity after being charged and discharged 300 times and up to 70% even after 1000 times. Professor Kim claims that his new battery is an important step forward towards a high-performance rechargeable battery which is a vital technology for unmanned vehicles, electric automobiles and energy storage. He hopes that his research can solve the problems of battery-capacity loss and contribute to South Korea’s leading position in battery technology. Professor Kim’s research team has filed applications for one domestic and international patent for their research.
Spintronics: A high wire act by Nanowerk News
An article by Nanowerk News on the integration of ferromagnetic nanowire arrays on grapheme substrates was published. Professor Bong-Soo Kim from the Department of Chemistry, KAIST, led the research in conjunction with Hanyang University and Samsung in Korea. http://www.nanowerk.com/news/newsid=22204.php Posted: Jul 25th, 2011 Spintronics: A high wire act (Nanowerk News) Graphene is a promising material for a wide range of applications due to its remarkable mechanical and electronic properties. An application of particular interest is spin-based electronics, or spintronics, in which the spin orientation of an electron is used to perform circuit functions in addition to its charge. Bongsoo Kim and colleagues from KAIST, Hanyang University and Samsung in Korea now report the integration of ferromagnetic nanowire arrays on graphene substrates, opening up a route for the construction of graphene-based spintronic devices using nanowires as spin-injecting contacts ("Epitaxially Integrating Ferromagnetic Fe1.3Ge Nanowire Arrays on Few-Layer Graphene"). The spin of an electron is a property that, like charge, can be used to encode, process and transport information. However, spin information is easily lost in most media, which has made spintronics difficult to realize in practice. In graphene, on the other hand, spin can be preserved for longer due to its peculiar electron transport properties. "Low intrinsic spin–orbit coupling, long spin diffusion lengths and vanishing hyperfine interaction are features of graphene that make it a promising medium for spin transport," explains Kim. Scanning electron microscopy image of vertical iron germanide nanowires grown on graphene. (© ACS 2011) A prerequisite for the realization of spintronic devices based on graphene is its integration with ferromagnetic contacts to allow spin injection. Kim and his co-workers found that nanowires of iron germanide (Fe1.3Ge) serve as efficient contacts for this purpose. "Iron germanide nanowires show low resistivity and room-temperature ferromagnetism, and they are compatible with existing complementary metal–oxide–semiconductor technologies," says Kim. To produce the atomically well-defined interfacial contact between the nanowires and the graphene surface needed for optimum device performance, the researchers deposited the contacts by an epitaxial method based on chemical vapor transport. Through careful adjustment of deposition parameters such as carrier gas flow rate and reaction temperature, the researchers produced vertically aligned nanowires that are closely lattice-matched to the graphene sheets (see image). Initially preparing the graphene sheets on a substrate of silicon oxide allowed the researchers to isolate the final nanowire–graphene structure by etching and then transfer it to another substrate, greatly expanding the versatility of the approach. It is a delicate process, however. "It is necessary to transfer the graphene films onto the substrate very carefully in order to avoid folding and wrinkling of the graphene," says Kim. Source: Tokyo Institute of Technology
Nanowire crystal transformation method was newly developed by a KAIST research team.
Figure 1 Schematic illustration of NW crystal transformation process. FeSi is converted to Fe3Si by high-temperature thermal annealing in diluted O2 condition and subsequent wet etching by 5% HF. Figure 2 Low-resolution TEM images of FeSi; Fe3Si@SiO2 core—shell; Fe3Si NW after shell-etching; and Scale bars are 20 nm Professor Bongsoo Kim of the Department of Chemistry, KAIST, and his research team succeeded to fabricate Heusler alloy Fe3Si nanowires by a diffusion-driven crystal structure transformation method from paramagnetic FeSi nanowires. This methodology is also applied to Co2Si nanowires in order to obtain metal-rich nanowires (Co) as another evidence of the structural transformation process. The newly developed nanowire crystal transformation method, Professor Kim said, would be valuable as a general method to fabricate metal-rich silicide nanowires that are otherwise difficult to synthesize. Metal silicide nanowires are potentially useful in a wide array of fields including nao-optics, information technology, biosensors, and medicine. Chemical synthesis of these nanowires, however, is challenging due to the complex phase behavior of silicides. The metal silicide nanowires are grown on a silicon substrate covered with a thin layer of silicon oxide via a simple chemical vapor deposition (CVD) process using single or multiple source precursors. Alternatively, the nanowires can be grown on the thin silicon oxide film via a chemical vapor transport (CVT) process using solid metal silicide precursors. The CVT-based method has been highly effective for the syntheses of metal silicide NWs, but changing the composition of metal silicide NWs in a wider range, especially achieving a composition of a metal to silicon, has been quite difficult. Thus, developing efficient and reliable synthetic methods to adjust flexibly the elemental compositions in metal silicide NWs can be valuable for the fabrication of practical spintronic and neonelectronic devices. Professor Kim expliained, “The key concept underlying this work is metal-enrichment of metal silicide NWs by thermal diffusion. This conversion method could prove highly valuable, since novel metal-rich silicide NWs that are difficult to synthesize but possess interesting physical properties can be fabricated from other metal silicide NWs.” The research result was published in Nanao Letters, a leading peer-reviewed journal, and posted online in early August 2010.
KAIST Professor Unveils New Method of Manufacturing Complex Nano-wire
A KAIST research team led by Prof. Sang-Ouk Kim of the Department of Materials Science and Engineering has discovered a new nanowire manufacturing method, university sources said on Monday (May 11). The KAIST researchers successfully demonstrated soft graphoepitaxy of block copolymer assembly as a facile, scalable nanolithography for highly ordered sub-30-nm scale features. Graphoepitaxy is a new technique that uses artificial surface relief structure to induce crystallographic orientation in thin films. Various morphologies of hierarchical block copolymer assembly were achieved by means of disposable topographic confinement of photoresist pattern. Unlike usual graphoepitaxy, soft graphoepitaxy generates the functional nanostrutures of metal and semiconductor nanowire arrays without any trace of structure-directing topographic pattern. The discovery was featured in the May 7 edition of Nano-Letters. Application has been made for the domestic patent of the new method. The new method is expected to be advantageous for multi-layer overlay processing required for complex device architecture, the sources said.
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