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Search Results: 1 - 10 of 297852 matches for " Noritaka Usami and Toyohiko J Konno "
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Configuration and local elastic interaction of ferroelectric domains and misfit dislocation in PbTiO3/SrTiO3 epitaxial thin films
Takanori Kiguchi, Kenta Aoyagi, Yoshitaka Ehara, Hiroshi Funakubo, Tomoaki Yamada, Noritaka Usami and Toyohiko J Konno
Science and Technology of Advanced Materials , 2011,
Abstract: We have studied the strain field around the 90° domains and misfit dislocations in PbTiO3/SrTiO3 (001) epitaxial thin films, at the nanoscale, using the geometric phase analysis (GPA) combined with high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark field––scanning transmission electron microscopy (HAADF-STEM). The films typically contain a combination of a/c-mixed domains and misfit dislocations. The PbTiO3 layer was composed from the two types of the a-domain (90° domain): a typical a/c-mixed domain configuration where a-domains are 20–30 nm wide and nano sized domains with a width of about 3 nm. In the latter case, the nano sized a-domain does not contact the film/substrate interface; it remains far from the interface and stems from the misfit dislocation. Strain maps obtained from the GPA of HRTEM images show the elastic interaction between the a-domain and the dislocations. The normal strain field and lattice rotation match each other between them. Strain maps reveal that the a-domain nucleation takes place at the misfit dislocation. The lattice rotation around the misfit dislocation triggers the nucleation of the a-domain; the normal strains around the misfit dislocation relax the residual strain in a-domain; then, the a-domain growth takes place, accompanying the introduction of the additional dislocation perpendicular to the misfit dislocation and the dissociation of the dislocations into two pairs of partial dislocations with an APB, which is the bottom boundary of the a-domain. The novel mechanism of the nucleation and growth of 90° domain in PbTiO3/SrTiO3 epitaxial system has been proposed based on above the results.
Diffraction contrast analysis of 90° and 180° ferroelectric domain structures of PbTiO3 thin films
Kenta Aoyagi, Takanori Kiguchi, Yoshitaka Ehara, Tomoaki Yamada, Hiroshi Funakubo and Toyohiko J Konno
Science and Technology of Advanced Materials , 2011,
Abstract: The ferroelectric domain structure of a PbTiO3 thin film on (100) SrTiO3 has been investigated by transmission electron microscopy (TEM). Two types of a-domain were found: one extended through the film to the surface and another comprised small a-domains confined within the film. Dark-field TEM (DFTEM) observation revealed that 180° domains formed near the substrate and stopped their growth 100 nm away from the substrate. The DFTEM observation also revealed that 90° domain boundaries had head-to-tail structures. To confirm the polarization direction obtained by experiments, diffracted intensities under a two-beam condition were simulated using the extended Darwin–Howie–Whelan equations. On the basis of the obtained results, a ferroelectric domain structure model of PbTiO3 thin films on SrTiO3 is proposed.
90-degree Ferroelectric Domains in PbTiO3: Experimental Observation and Molecular Dynamics Simulations
Kenta Aoyagi,Takeshi Nishimatsu,Takanori Kiguchi,Toyohiko J. Konno,Yoshiyuki Kawazoe,Hiroshi Funakubo,Anil Kumar,Umesh V. Waghmare
Physics , 2012,
Abstract: We report observation of 90-degree ferroelectric domain structures in transmission electron microscopy (TEM) of epitaxially-grown films of PbTiO3. Using molecular dynamics (MD) simulations based on first-principles effective Hamiltonian of bulk PbTiO3, we corroborate the occurance of such domains showing that it arises as metastable states only in cooling simulations (as the temperature is lowered) and establish characteristic stability of 90-degree domain structures in PbTiO3. In contrast, such domains do not manifest in similar simulations of BaTiO3. Through a detailed analysis based on energetics and comparison between PbTiO3 and BaTiO3, we find that 90-degree domain structures are energetically favorable only in the former, and the origin of their stability lies in the polarization-strain coupling. Our analysis suggests that they may form in BaTiO3 due to special boundary condition and/or defect-related inhomogeneities.
TEM and STEM Observations of a Flat Continuous Silicon-Germanium Thin Film Epitaxially Grown on Porous Silicon  [PDF]
Junji Yamanaka, Noritaka Usami, Sevak Amtablian, Alain Fave, Mustapha Lemiti, Chiaya Yamamoto, Kiyokazu Nakagawa
Journal of Materials Science and Chemical Engineering (MSCE) , 2017, DOI: 10.4236/msce.2017.51004
Strain-relaxed SiGe is an attractive material for use as a substrate of strained Si, in which carrier mobility is higher than that of bulk Si. The concept of this study is the use of porous Si as a sponge like substrate so that a SiGe lattice can relax without introducing dislocations. We produced porous Si specimens by electrochemical anodization and annealed them under a H2 atmosphere. Then, SiGe thin films were grown by gas-source molecular beam epitaxy. We observed the microstructure of the specimens using transmission electron microscopy. The result showed that we succeeded in producing a single-crys- tal continuous Si0.73Ge0.27 film with a 10% relaxation ratio and a low dislocation density on porous Si.
Coordination Always Occurs in a Two-Strategy Pure-Coordination Logit Game on Scale-Free Networks  [PDF]
Tomohiko Konno
Theoretical Economics Letters (TEL) , 2015, DOI: 10.4236/tel.2015.54066
Abstract: We show that coordination always occurs in scale-free networks by social local interactions regardless of the values of parameters, while it occurs in regular networks if and only if the number of links times a payoff parameter exceeds the threshold. Scale-free networks are ubiquitous in the reality. We study a two-strategy pure coordination game on networks that indicate who plays with whom. A player chooses a strategy by Logit choice and the strategies are dynamically updated. Stable steady states are investigated.
Should a New Good Replace Existing Ones? A Network Approach  [PDF]
Tomohiko Konno
Theoretical Economics Letters (TEL) , 2015, DOI: 10.4236/tel.2015.54068
Abstract: We study goods (or service) with network effect. Social network services are examples. An existing service has an advantage over new one because of the network effect. We study the condition that new goods (or service) replace the existing one, and show that the condition depends on the underlying network structures. For this purpose, we study a coordination game with network structure. If more than half of the players change their strategies, then new strategy beats the existing one in regular networks. On the other hand, if very small number of players with large degree changes their strategies, then the new strategy beats the existing one in scale-free networks.
Recent Synthetic Studies Leading to Structural Revisions of Marine Natural Products
Yoshihide Usami
Marine Drugs , 2009, DOI: 10.3390/md7030314
Abstract: Because of the highly unique structures of marine natural products, there are many examples of structures that were originally proposed based on spectral analyses but later proven incorrect. In many cases, the total syntheses of the originally proposed structures of marine natural products has confirmed their incorrectness and the subsequent total syntheses of the newly proposed structures proved the revised structures. This review will show such cases appearing after 2005 and demonstrate how the true structures were elucidated.
Quantum-noise-limited Angular Momentum Measurement for a Micron-sized Dielectric Object
Koji Usami
Physics , 2007,
Abstract: An approach is described for observing quantum features of micron-sized spinning objects. Specifically, we consider a birefringent (uniaxial positive) dielectric object in the shape of an oblate (i.e., frisbee-like) symmetric top. It can be trapped in the air, its extraordinary axis can be aligned, and its angular momentum along the extraordinary axis can be stabilized, all optically. We show that the angular momentum quantum noise of the object perpendicular to the gigantic angular momentum along the extraordinary axis can be measured as a linear birefringent phase shift of a probe laser in an analogous fashion to the spin quantum nondemolition (QND) measurement in atomic physics.
A free-boundary problem for concrete carbonation: Rigorous justification of the $\sqrt{t}$-law of propagation
Toyohiko Aiki,Adrian Muntean
Physics , 2011,
Abstract: We study a one-dimensional free-boundary problem describing the penetration of carbonation fronts (free reaction-triggered interfaces) in concrete. A couple of decades ago, it was observed experimentally that the penetration depth versus time curve (say $s(t)$ vs. $t$) behaves like $s(t)=C\sqrt{t}$ for sufficiently large times $t > 0$ (with $C$ a positive constant). Consequently, many fitting arguments solely based on this experimental law were used to predict the large-time behavior of carbonation fronts in real structures, a theoretical justification of the $\sqrt{t}$-law being lacking until now. %This is the place where our paper contributes: The aim of this paper is to fill this gap by justifying rigorously the experimentally guessed asymptotic behavior. We have previously proven the upper bound $s(t)\leq C'\sqrt{t}$ for some constant $C'$; now we show the optimality of the rate by proving the right nontrivial lower estimate, i.e. there exists $C">0$ such that $s(t)\geq C"\sqrt{t}$. Additionally, we obtain weak solutions to the free-boundary problem for the case when the measure of the initial domain vanishes. In this way, our mathematical model is now allowing for the appearance of a moving carbonation front -- a scenario that until was hard to handle from the analysis point of view.
Large-time asymptotics of moving-reaction interfaces involving nonlinear Henry's law and time-dependent Dirichlet data
Toyohiko Aiki,Adrian Muntean
Mathematics , 2013,
Abstract: We study the large-time behavior of the free boundary position capturing the one-dimensional motion of the carbonation reaction front in concrete-based materials. We extend here our rigorous justification of the $\sqrt{t}$-behavior of reaction penetration depths by including non-linear effects due to deviations from the classical Henry's law and time-dependent Dirichlet data.
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