Nano+Letter
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KAIST Research Team Discovers Process for Rapid Growth of N-Doped CNT Arrays
A team of scientists led by Profs. Sang-Ouk Kim, Won-Jong Lee and Duck-Hyun Lee of the Department of Materials Science and Engineering has found a straightforward process for rapid growth of wall-number selected, nitrogen-doped carbon nanotube (CNT) arrays, university officials said on Monday (March 16).
KAIST researchers prepared highly uniform nanopatterned iron catalyst arrays by tilted deposition through block copolymer nanotemplates. This remarkably fast growth of highly uniform N-doped CNTs, whose material properties and chemical functionalizability are reinforced by N-doping, offers a new area of a large-scale nanofabrication, potentially useful for diverse nano-devices.
Carbon nanotubes (CNTs) are of broad technical interest in electronics, photonics, energy devices, and other applications. However, establishing a straightforward process for mass production of uniform CNTs with desired structure and properties has been a long-standing challenge.
In particular, it was strongly desired to precisely control the numbers of walls and diameter of CNTs, which are decisive parameters for the physical properties of CNTs. In this respect, the preparation of monodisperse catalyst array having a narrow size distribution is generally considered an effective pathway to produce well-defined CNTs, since the number of walls and diameter of the produced CNTs are closely related to the catalyst size.
The finding was featured in the March 13 edition of Nano Letters, a leading journal in the nano technology field.
2009.03.20 View 13138 -
Method to Synthesize New Lithium Ion Battery Cathode Material Identified
A KAIST research team headed by Prof. Do-Kyung Kim at the Department of Materials Science and Engineering developed a technology to synthesize a new lithium ion battery spinel cathode which is regarded as a core part of hybrid and lithium battery cars.
The research was conducted in collaboration with a research team of Prof. Yi Cui at Stanford University"s Department of Chemistry. Their findings were introduced in the November issue of Nano Letters, one of the leading academic journals in nano-science.
The newly synthesized lithium ion battery spinel cathode known as spinel LiMn2O4 nanorods is attracting interests as an alternative cathode material since it is a low-cost, environmentally friendly substance for Li-ion battery cathodes. Its raw material is also highly available.
Lithium ion batteries with high energy and power density are important for consumer electronic devices, portable power tools, and vehicle electrification. LixCoO2 is a commonly used cathode material in commercial lithium iron batteries. However, the high cost, toxicity, and limited abundance of cobalt have been recognized to be disadvantageous.
2008.11.20 View 11811 -
KAIST Team Identifies Nano-scale Origin of Toughness in Rare Earth-added Silicon Carbide
A research team led by Prof. Do-Kyung Kim of the Department of Materials Science and Engineering of KAIST has identified the nano-scale origin of the toughness in rare-earth doped silicon carbide (RE-SiC), university sources said on Monday (Oct. 6).
The research was conducted jointly with a U.S. team headed by Prof. R. O. Ritchie of the Department of Materials Science and Engineering, University of California, Berkeley.
The findings were carried in the online edition of Nano Letters published by the American Chemical Association.
Silicon carbide, a ceramic material known to be one of the hardest substances, are potential candidate materials for many ultrahigh-temperature structural applications. For example, if SiC, instead of metallic alloys, is used in gas-turbine engines for power generation and aerospace applications, operating temperatures of many hundred degrees higher can be obtained with a consequent dramatic increase in thermodynamic efficiency and reduced fuel consumption. However, the use of such ceramic materials has so far been severely limited since the origin of the toughness in RE-SiC remained unknown thus far.
In order to investigate the origin of the toughness in RE-SiC, the researchers attempted to examine the mechanistic nature of the cracking events, which they found to occur precisely along the interface between SiC grains and the nano-scale grain-boundary phase, by using ultrahigh-resolution transmission electron microscopy and atomic-scale spectroscopy. The research found that for optimal toughness, the relative elastic modulus across the grain-boundary phase and the interfacial fracture toughness are the most critical material parameters; both can be altered with appropriate choice of rare-earth elements.
In addition to identifying the nano-scale origin of the toughness in RE-SiC, the findings also contributed to precisely predicting how the use of various rare-earth elements lead to difference in toughness.
University sources said that the findings will significantly advance the date when RE-SiC will replace metallic alloys in gas-turbine engines for power generation and aerospace applications.
2008.10.08 View 13910