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Pikhitsa, Peter V.,Choi, Mansoo,Kim, Hyung-Jung,Ahn, Sung-Hoon WILEY-VCH Verlag 2009 Physica status solidi. PSS. B, Basic solid state p Vol.246 No.9
<P>Auxetics are novel counterintuitive materials that grow thicker perpendicularly to the applied force when stretched and therefore are described by a negative Poisson's ratio. We show that a regular lattice of individual multipods properly assembled in three dimensions has the ultimate negative Poisson's ratio −1: the lattice expands or contracts uniformly in all directions. Our ball-and-stick working model verifies the mathematical construction. Application of the model to real materials is discussed. Our result is important for understanding the ways to create entangled materials with interesting mechanical properties.</P>
Pikhitsa, Peter V.,Chae, Sukbyung,Shin, Seungha,Choi, Mansoo Hindawi Limited 2017 Journal of spectroscopy Vol.2017 No.-
<P>Mn<SUP>2+</SUP> ion doping is used as an electron paramagnetic resonance (EPR) probe to investigate the influence of low-coordination structural defects such as step edges at the surface of terraced (001) MgO nanoparticles on the electronic properties. Beside the well-known hyperfine sextet of Mn<SUP>2+</SUP> ions in the cubic crystal field of MgO, an additional EPR feature with a striking nonmonotonous temperature dependent shift of the g-factor is observed in terraced nanoparticles in the temperature range from 4 K to room temperature. By linking the difference in the temperature dependence of the Mn<SUP>2+</SUP> sextet intensity in cubic and terraced nanoparticles with the possible s-d exchange shift and enhanced Zeeman splitting we conclude that the novel EPR feature originates from the loosely trapped charge-compensating carriers at the abundant structural defects at the surface of terraced nanoparticles due to their exchange interaction with neighboring Mn<SUP>2+</SUP> ions.</P>
Two-band luminescence from an intrinsic defect in spherical and terraced MgO nanoparticles
Pikhitsa, Peter V.,Kim, Changhyuk,Chae, Sukbyung,Shin, Seungha,Jung, Sekwon,Kitaura, Mamoru,Kimura, Shin-ichi,Fukui, Kazutoshi,Choi, Mansoo American Institute of Physics 2015 Applied Physics Letters Vol.106 No.18
레이저가 조사된 아세틸렌에서의 임계전이를 거쳐서 형성된 쉘 형상 카본 나노입자에 관한 연구
최만수(Mansoo Choi),Igor S.Altman(Igor S. Altman),김영정(Young-Jeong Kim),Peter V.Pikhitsa(Peter V. Pikhitsa),이상훈(Sanghoon Lee) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
Shell shaped hollow carbon nanoparticles are synthesized in the oxygen-hydrogen diffusion flame with C₂H₂ as precursor when it is irradiated with CO₂ laser of certain power. Below this power of laser, we couldn’t get any other but amorphous soot. This shell shaped hollow carbon nanoparticles shows outer wall of high degree of crystallinity with void space inside of itself. And size distribution of these nanoparticles is measured with TEM image analysis. Also the structural comparison between this carbon nanoparticle and soot is done by Raman and XRD measurement. These results show this carbon nanoparticles are of grapheme structure, which means it has good crystallinity when compared with soot.
Ultrasensitive mechanical crack-based sensor inspired by the spider sensory system
Kang, Daeshik,Pikhitsa, Peter V.,Choi, Yong Whan,Lee, Chanseok,Shin, Sung Soo,Piao, Linfeng,Park, Byeonghak,Suh, Kahp-Yang,Kim, Tae-il,Choi, Mansoo Nature Publishing Group, a division of Macmillan P 2014 Nature Vol.516 No.7530
Recently developed flexible mechanosensors based on inorganic silicon, organic semiconductors, carbon nanotubes, graphene platelets, pressure-sensitive rubber and self-powered devices are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints. Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider’s slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0–2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection–reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity.
Three-Dimensional Assembly of Nanoparticles from Charged Aerosols
Lee, Heechul,You, Sukbeom,Pikhitsa, Peter V.,Kim, Junhoi,Kwon, Sunghoon,Woo, Chang Gyu,Choi, Mansoo American Chemical Society 2011 Nano letters Vol.11 No.1
<P>The capability of assembling nanoparticles into a desired ordered pattern is a key to realize novel devices which are based not only on the unique properties of nanoparticles but also on the arrangements of nanoparticles. While two-dimensional arrays of nanoparticles have been successfully demonstrated by various techniques, a controlled way of building ordered arrays of three-dimensional (3D) nanoparticle structures remains challenging. We report that a variety of 3D nanoparticle structures can be formed in a controlled way based on the ion-induced focusing, electrical scaffold, and antenna effects from charged aerosols. Particle trajectory calculations successfully predict the whole process of 3D assembly. New surface enhanced Raman scattering substrates based on our 3D assembly were constructed as an example showing the viability of the present approach. This report extends the current capability of positioning nanoparticles on surface to another spatial dimension, which can serve as the foundation of future optical, magnetic, and electronic devices taking the advantage of multidimensions.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-1/nl103787k/production/images/medium/nl-2010-03787k_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl103787k'>ACS Electronic Supporting Info</A></P>
신승하(Seungha Shin),Peter V. Pikhitsa,김창혁(Changhyuk Kim),최만수(Mansoo Choi) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Magnesium oxide (magnesia, MgO) particle was synthesized by metal combustion method using magnesium powder as precursor. Evolution of morphology and size of magnesia particles synthesized by metal combustion method was studied, and the process of growth of MgO particles in flame was observed by TEM analysis.