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Y M Kim,
S J Uhm,
M K Gupta, J S Yang,
J-G Lim,
Z C Das,
Y T Heo,
H-J Chung,
I-K Kong,
N-H Kim,
H T Lee,
D H Ko
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ABSTRACT: Cryopreservation of bovine embryos can be performed by a variety of methods with variable degree of success. Here, we report a new, easy to perform, simple, inexpensive, and successful method for vitrification of bovine blastocysts. In vitro produced bovine blastocysts were exposed to vitrification solution (5.5 m ethylene glycol, 10% serum and 1% sucrose) in one single step for 20 s, loaded on a paper container prepared from commonly available non-slippery, absorbent writing paper, and then were directly plunged into liquid nitrogen for storage. Vitrified blastocysts were warmed by serial rinsing in 0.5, 0.25 and 0.125 m sucrose solution for 1 min each. Results showed that one step exposure of bovine blastocysts to cryoprotective agents was sufficient to achieve successful cryopreservation. Under these conditions, more than 95% of blastocysts survived the vitrification-warming on paper containers which was significantly higher than those obtained from other containers, such as electron microscope (EM) grid (78.1%), open pulled straw (OPS; 80.2%), cryoloop (76.2%) or plastic straw (73.9%). Embryo transfer of blastocysts vitrified-warmed on paper container resulted in successful conception (19.3%) and full-term live birth of offspring (12.3%) which were lower (P < 0.05) than those obtained from non-vitrified blastocysts (38.0 and 32.7%) but were comparable (P > 0.05) to those obtained from blastocysts vitrified-warmed on EM grid (23.3 and 14.2%). Our results, therefore, suggest that paper may be an inexpensive and useful container for the cryopreservation of animal embryos.
Theriogenology 07/2012; 78(5):1085-93. · 1.96 Impact Factor
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ABSTRACT: We analyze the collective buckling of an array of vertical elastic beams with their lower ends built into an elastic substrate.
The beams interact between themselves through the deformation of the elastic substrate. The present analysis is more sophisticated
than previous ones on rigid beams on an elastic substrate in that the beams are regarded as elastic rather than rigid. From
the linear theory for elastic beam buckling and the linear theory of elasticity, an eigenvalue problem is formulated and solved.
Calculations show that the deformability of the beams lowers the critical height of the beams, but it does not affect the
buckling pattern much. Our work also suggests that the collective buckling is dominated by the interaction of neighboring
beams through the deformation of the substrate rather than whether the beams are rigid or elastic. The results are useful
for the better understanding, design and application of the nanostructures produced by soft lithography.
Acta Mechanica 04/2012; 215(1):235-240. · 1.29 Impact Factor
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ABSTRACT: We investigated the inhomogeneous electronic properties at the surface and interior of VO2 thin films that exhibit a strong first-order metal-insulator transition (MIT). Using the crystal structural change that accompanies a VO2 MIT, we used bulk-sensitive x-ray diffraction (XRD) measurements to estimate the fraction of metallic volume pXRD in our VO2 film. The temperature dependence of the pXRD was very closely correlated with the dc conductivity near the MIT temperature and fitted the percolation theory predictions quite well: σ∼(p−pc)t with t=2.0±0.1 and pc=0.16±0.01. This agreement demonstrates that in our VO2 thin film, the MIT should occur during the percolation process. We also used surface-sensitive scanning tunneling spectroscopy (STS) to investigate the microscopic evolution of the MIT near the surface. Similar to the XRD results, STS maps revealed a systematic decrease in the metallic phase as temperature decreased. However, this rate of change was much slower than the rate observed with XRD, indicating that the electronic inhomogeneity near the surface differs greatly from that inside the film. We investigated several possible origins of this discrepancy and postulated that the variety in the strain states near the surface plays an important role in the broad MIT observed using STS. We also explored the possible involvement of such strain effects in other correlated electron oxide systems with strong electron-lattice interactions.
Phys. Rev. B. 08/2007; 76(7).
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ABSTRACT: We investigated the inhomogeneous electronic properties at the surface and interior of VO_{2} thin films that exhibit a strong first-order metal-insulator transition (MIT). Using the crystal structural change that accompanies a VO_{2} MIT, we used bulk-sensitive X-ray diffraction (XRD) measurements to estimate the fraction of metallic volume p^{XRD} in our VO_{2} film. The temperature dependence of the p$^{XRD}$ was very closely correlated with the dc conductivity near the MIT temperature, and fit the percolation theory predictions quite well: $\sigma$ $\sim$ (p - p_{c})^{t} with t = 2.0$\pm$0.1 and p_{c} = 0.16$\pm$0.01. This agreement demonstrates that in our VO$_{2}$ thin film, the MIT should occur during the percolation process. We also used surface-sensitive scanning tunneling spectroscopy (STS) to investigate the microscopic evolution of the MIT near the surface. Similar to the XRD results, STS maps revealed a systematic decrease in the metallic phase as temperature decreased. However, this rate of change was much slower than the rate observed with XRD, indicating that the electronic inhomogeneity near the surface differs greatly from that inside the film. We investigated several possible origins of this discrepancy, and postulated that the variety in the strain states near the surface plays an important role in the broad MIT observed using STS. We also explored the possible involvement of such strain effects in other correlated electron oxide systems with strong electron-lattice interactions. Comment: 27 pages and 7 figures
07/2007;
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T C Kim,
C-M Ghim,
H J Kim,
D H Kim,
D Y Noh,
N D Kim,
J W Chung, J S Yang,
Y J Chang,
T W Noh,
B Kahng,
J-S Kim
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ABSTRACT: We investigate the kinetic roughening of Ar+ ion-sputtered Pd(001) surface both experimentally and theoretically. In situ real-time x-ray reflectivity and in situ scanning tunneling microscopy show that nanoscale adatom islands form and grow with increasing sputter time t. Surface roughness W(t) and lateral correlation length xi(t) follow the scaling laws W(t) approximately t(beta) and xi(t) approximately t(1/z) with the exponents beta approximately 0.20 and 1/z approximately 0.20, for an ion beam energy epsilon=0.5 keV, which is inconsistent with the prediction of the Kuramoto-Sivashinsky (KS) model. We thereby extend the KS model by applying the coarse-grained continuum approach of the Sigmund theory to the order of O(inverted Delta(4),h(2)), where h is the surface height, and derive a new term of the form inverted Delta(2)(inverted Delta h)(2) which plays a decisive role in describing the observed morphological evolution of the sputtered surface.
Physical Review Letters 07/2004; 92(24):246104. · 7.37 Impact Factor
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D. H. Kim, J. S. Yang,
Y. S. Kim,
D.-W. Kim,
T. W. Noh,
S. D. Bu,
Y.-W. Kim,
Y. D. Park,
S. J. Pearton,
Y. Jo,
J.-G. Park
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ABSTRACT: We observed superparamagnetism in Co-ion-implanted anatase TiO <sub>2</sub> thin films on SrTiO <sub>3</sub> (001) substrates. After postannealing under oxygen pressure of 1.0×10<sup>-6</sup> Torr , the blocking temperature increased with increasing annealing temperature. Eventually, the 600 ° C -annealed sample became ferromagnetic at room temperature. These phenomena can be explained by the formation of Co (or ferromagnetic Co compound) particles and their growth during postannealing, as directly observed with transmission electron microscopy. High oxygen pressure during annealing reduced the size of the clusters and saturation magnetization moment, which indicates that cobalt clustering should be the main cause of the room-temperature ferromagnetism in the Co-ion-implanted films. © 2003 American Institute of Physics.
Applied Physics Letters 01/2004; · 3.84 Impact Factor
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ABSTRACT: The surface structure of an anatase Ti0.94Co0.06O2 (001) film, grown epitaxially on a Nb-doped SrTiO3 (001) substrate, was investigated using in situ scanning tunneling microscopy. For the as-grown film, a (1×n) (n = 3, 4, 5, and 6) reconstructed surface was observed that shows (n−2) faint rows between adjacent bright rows. After annealing at 650 °C, nanoparticles appeared, mostly on the step edges. From the I–V curves measured by scanning tunneling spectroscopy, the tunneling gap of Co:TiO2 was estimated to be about 3.0 eV, consistent with the band gap (Eg = 3.2 eV) of pure anatase TiO2. However, on nanoparticles, the I–V curve showed a much smaller gap, suggesting that the particle must be different from TiO2. © 2003 American Institute of Physics.
Applied Physics Letters 05/2003; 82(18):3080-3082. · 3.84 Impact Factor
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J-Y Kim,
J-H Park,
B-G Park,
H-J Noh,
S-J Oh, J S Yang,
D-H Kim,
S D Bu,
T-W Noh,
H-J Lin,
H-H Hsieh,
C T Chen
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ABSTRACT: We investigated ferromagnetism of a newly discovered ferromagnetic semiconductor Co-doped anatase TiO2 thin film, using the magnetic circular dichroism (MCD) at the Co L(2,3) absorption edges. The magnetic moment was observed to be approximately 0.1 micro(B)/Co in the measurements, but the MCD spectral line shape is nearly identical to that of Co metal, showing that the ferromagnetism is induced by a small amount of clustered Co. With thermal treatments at approximately 400 degrees C, the MCD signal increases, and the moment reaches up to approximately 1.55 micro(B)/Co, which is approximately 90% of the moment in Co metal. In the latter case, the cluster size was observed to be 20-60 nm.
Physical Review Letters 02/2003; 90(1):017401. · 7.37 Impact Factor
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D. H. Kim, J. S. Yang,
K. W. Lee,
S. D. Bu,
T. W. Noh,
S.-J. Oh,
Y.-W. Kim,
J.-S. Chung,
H. Tanaka,
H. Y. Lee,
T. Kawai
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ABSTRACT: Anatase Ti <sub>0.96</sub> Co <sub>0.04</sub> O <sub>2</sub> films were grown epitaxially on SrTiO <sub>3</sub> (001) substrates by using pulsed laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, P<sub> O <sub>2</sub></sub>, during the growth was systematically varied. As P<sub> O <sub>2</sub></sub> decreased, the growth behavior was changed from a two-dimensional layer-by-layer-like growth to a three-dimensional island-like one, which resulted in an increase in the saturation magnetization. These structural and magnetic changes were explained in terms of the formation of cobalt clusters whose existence was proved by transmission-electron-microscope studies. Our work clearly indicates that the cobalt clustering will cause room-temperature ferromagnetism in the Co-doped TiO <sub>2</sub> films. © 2002 American Institute of Physics.
Applied Physics Letters 10/2002; · 3.84 Impact Factor
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D H Kim, J S Yang,
K W Lee,
S. D. Bu,
T. W. Noh,
S J Oh,
Y W Kim,
J S Chung,
H Tanaka,
H Y Lee,
T Kawai
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ABSTRACT: Anatase Ti0.96Co0.04O2 films were grown epitaxially on SrTiO3 (001) substrates by using plused laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, PO2, during the growth was systematically varied. As PO2 decreased, the growth behavior was changed from a 2-dimensional layer-by-layer-like growth to a 3-dimensional island-like one, which resulted in an increase in the saturation magnetization. These structural and magnetic changes were explained in terms of the formation of cobalt clusters whose existence was proved by transmission-electron-microscopie studies. Our work clearly indicates that the cobalt clustering will cause room-temperature ferromagnetism in the Co-doped TiO2 films. Comment: 8 pages, 3 figures
08/2002;
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D H Kim, J S Yang,
K W Lee,
S D Bu,
D.-W Kim,
T W Noh,
S.-J Oh,
Y.-W Kim,
J.-S Chung,
H Tanaka,
H Y Lee,
T Kawai,
J Y Won,
S H Park,
J C Lee
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ABSTRACT: High-quality epitaxial thin films of Co-doped anatase TiO 2 Co:TiO 2) were grown epitaxially on SrTiO 3 001 substrates by using pulsed laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, P O2 , during the growth was systematically varied. As P O2 decreased, the growth behavior altered from a two-dimensional layer-by-layer-like growth to a three-dimensional island-like pattern. Electrical conductivity and saturation magnetization increased, seemingly consistent with the picture of carrier-induced ferromagnetism. However, we also found that the spatial distribution of Co ions became highly nonuniform and the chemical state of Co ions changed from ionic to metallic. All of these P O2 dependences, even including the transport and the magnetic properties, can be explained in terms of the formation of cobalt clusters, whose existence was clearly demonstrated by transmission–electron–microscope studies. Our work clearly indicates that the cobalt clustering will result in the room-temperature ferromagnetism observed in our Co:TiO 2 films. To check the possible spin polarization of carriers in Co:TiO 2 films, we also fabricated a heterojunction composed of a ferromagnetic Co:TiO 2 , an insulating SrTiO 3 , and a ferromagnetic half-metallic La,BaMnO 3 layer. When the magnetic field was varied, we could not observe any changes in its I–V characteristic curves, which suggests that there might be little spin-polarization effect in the anatase Co:TiO 2 layer. © 2003 American Institute of Physics.
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ABSTRACT: Vanadium dioxide (VO2) shows a metal–insulator transition (MIT) near room temperature, accompanied by an abrupt resistivity change. Since the MIT of VO2 is known to be a first order phase transition, it is valuable to check metallic and insulating phase segregation during the MIT process. We deposited (100)-oriented epitaxial VO2 thin films on R-cut sapphire substrates. From the scanning tunneling spectroscopy (STS) spectra, we could distinguish metallic and insulating regions by probing the band gap. Optical spectroscopic analysis also supported the view that the MIT in VO2 occurs through metal and insulator phase coexistence.
Thin Solid Films 486:46-49. · 1.89 Impact Factor
