Nano Analysis Center

KIST, South Korea

Nano Analysis Center

KIST, South Korea
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Ma J.W.,Yonsei University | Lee W.J.,Yonsei University | Bae J.M.,Yonsei University | Jeong K.S.,Yonsei University | And 6 more authors.
Nano Letters | Year: 2013

The Young's modulus and fracture strength of Si1-xGex nanowires (NWs) as a function of Ge concentration were measured from tensile stress measurements. The Young's modulus of the NWs decreased linearly with increasing Ge content. No evidence was found for a linear relationship between the fracture strength of the NWs and Ge content, which is closely related to the quantity of interstitial Ge atoms contained in the wire. However, by removing some of the interstitial Ge atoms through rapid thermal annealing, a linear relationship could be produced. The discrepancy in the reported strength of Si and Ge NWs between calculated and experimented results could be related to SiO2-x/Si interfacial defects that are found in Si 1-xGex NWs. It was also possible to significantly decrease the number of interfacial defects in the NWs by incorporating a surface passivated Al2O3 layer, which resulted in a substantial increase in fracture strength. © 2013 American Chemical Society.

Kang M.,KAIST | Jung S.,Brain Bio | Zhang H.,University of Michigan | Kang T.,Korea Research Institute of Bioscience and Biotechnology | And 8 more authors.
ACS Nano | Year: 2014

Size reduction of neural electrodes is essential for improving the functionality of neuroprosthetic devices, developing potent therapies for neurological and neurodegenerative diseases, and long-term brain-computer interfaces. Typical neural electrodes are micromanufactured devices with dimensions ranging from tens to hundreds of micrometers. Their further miniaturization is necessary to reduce local tissue damage and chronic immunological reactions of the brain. Here we report the neural electrode with subcellular dimensions based on single-crystalline gold nanowires (NWs) with a diameter of ∼100 nm. Unique mechanical and electrical properties of defect-free gold NWs enabled their implantation and recording of single neuron-activities in a live mouse brain despite a ∼50× reduction of the size compared to the closest analogues. Reduction of electrode dimensions enabled recording of neural activity with improved spatial resolution and differentiation of brain activity in response to different social situations for mice. The successful localization of the epileptic seizure center was also achieved using a multielectrode probe as a demonstration of the diagnostics potential of NW electrodes. This study demonstrated the realism of single-neuron recording using subcellular-sized electrodes that may be considered a pivotal point for use in diverse studies of chronic brain diseases. © 2014 American Chemical Society.

Seo J.-H.,Nano Analysis Center | Seo J.-H.,Korea University | Yoo Y.,KAIST | Park N.-Y.,Kookmin University | And 12 more authors.
Nano Letters | Year: 2011

We report that defect-free Au nanowires show superplasticity on tensile deformation. Evidences from high-resolution electron microscopes indicated that the plastic deformation proceeds layer-by-layer in an atomically coherent fashion to a long distance. Furthermore, the stress-strain curve provides full interpretation of the deformation. After initial superelastic deformation, the nanowire shows superplastic deformation induced by coherent twin propagation, completely reorientating the crystal from <110> to <100>. Uniquely well-disciplined and long-propagating atomic movements deduced here are ascribed to the superb crystallinity as well as the radial confinement of the Au nanowires. © 2011 American Chemical Society.

Ma J.W.,Yonsei University | Lee W.J.,Yonsei University | Bae J.M.,Yonsei University | Jeong K.S.,Yonsei University | And 7 more authors.
Nano Letters | Year: 2015

Changes in the carrier mobility of tensile strained Si and SiGe nanowires (NWs) were examined using an electrical push-to-pull device (E-PTP, Hysitron). The changes were found to be closely related to the chemical structure at the surface, likely defect states. As tensile strain is increased, the resistivity of SiGe NWs deceases in a linear manner. However, the corresponding values for Si NWs increased with increasing tensile strain, which is closely related to broken bonds induced by defects at the NW surface. Broken bonds at the surface, which communicate with the defect state of Si are critically altered when Ge is incorporated in Si NW. In addition, the number of defects could be significantly decreased in Si NWs by incorporating a surface passivated Al2O3 layer, which removes broken bonds, resulting in a proportional decrease in the resistivity of Si NWs with increasing strain. Moreover, the presence of a passivation layer dramatically increases the extent of fracture strain in NWs, and a significant enhancement in mobility of about 2.6 times was observed for a tensile strain of 5.7%. © 2015 American Chemical Society.

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