The Experts below are selected from a list of 1791 Experts worldwide ranked by ideXlab platform
Tianxiang Xu - One of the best experts on this subject based on the ideXlab platform.
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three dimensional nonlinear photonic crystal in ferroelectric barium Calcium Titanate
Nature Photonics, 2018Co-Authors: Tianxiang Xu, Krzysztof Switkowski, Xin Chen, Kaloian Koynov, Haohai Yu, Huaijin Zhang, Jiyang Wang, Yan ShengAbstract:The performance of many optical devices based on frequency conversion critically depends on spatial modulation of the nonlinear optical response of materials. This modulation ensures efficient energy exchange between optical waves at different frequencies via quasi-phase matching1. In general, quasi-phase-matching structures, also known as nonlinear photonic crystals2–4, offer a variety of properties and functionalities that cannot be obtained in uniform nonlinear crystals5–9. So far, nonlinear photonic crystals have been restricted to one- or two-dimensional geometries owing to a lack of fabrication technologies capable of three-dimensional (3D) nonlinearity engineering. Here, we provide an experimental example of a 3D nonlinear photonic crystal, fabricated in ferroelectric barium Calcium Titanate, by applying an ultrafast light domain inversion approach. The resulting full flexibility of 3D nonlinearity modulation enables phase matching of nonlinear processes along an arbitrary direction, thereby removing constraints imposed by low-dimensional structures. A three-dimensional nonlinear photonic crystal in ferroelectric barium Calcium Titanate that enables phase matching of nonlinear processes along an arbitrary direction, thereby removing constraints imposed by low-dimensional structures, is experimentally realized.
Yan Sheng - One of the best experts on this subject based on the ideXlab platform.
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three dimensional nonlinear photonic crystal in ferroelectric barium Calcium Titanate
Nature Photonics, 2018Co-Authors: Tianxiang Xu, Krzysztof Switkowski, Xin Chen, Kaloian Koynov, Haohai Yu, Huaijin Zhang, Jiyang Wang, Yan ShengAbstract:The performance of many optical devices based on frequency conversion critically depends on spatial modulation of the nonlinear optical response of materials. This modulation ensures efficient energy exchange between optical waves at different frequencies via quasi-phase matching1. In general, quasi-phase-matching structures, also known as nonlinear photonic crystals2–4, offer a variety of properties and functionalities that cannot be obtained in uniform nonlinear crystals5–9. So far, nonlinear photonic crystals have been restricted to one- or two-dimensional geometries owing to a lack of fabrication technologies capable of three-dimensional (3D) nonlinearity engineering. Here, we provide an experimental example of a 3D nonlinear photonic crystal, fabricated in ferroelectric barium Calcium Titanate, by applying an ultrafast light domain inversion approach. The resulting full flexibility of 3D nonlinearity modulation enables phase matching of nonlinear processes along an arbitrary direction, thereby removing constraints imposed by low-dimensional structures. A three-dimensional nonlinear photonic crystal in ferroelectric barium Calcium Titanate that enables phase matching of nonlinear processes along an arbitrary direction, thereby removing constraints imposed by low-dimensional structures, is experimentally realized.
Krzysztof Switkowski - One of the best experts on this subject based on the ideXlab platform.
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three dimensional nonlinear photonic crystal in ferroelectric barium Calcium Titanate
Nature Photonics, 2018Co-Authors: Tianxiang Xu, Krzysztof Switkowski, Xin Chen, Kaloian Koynov, Haohai Yu, Huaijin Zhang, Jiyang Wang, Yan ShengAbstract:The performance of many optical devices based on frequency conversion critically depends on spatial modulation of the nonlinear optical response of materials. This modulation ensures efficient energy exchange between optical waves at different frequencies via quasi-phase matching1. In general, quasi-phase-matching structures, also known as nonlinear photonic crystals2–4, offer a variety of properties and functionalities that cannot be obtained in uniform nonlinear crystals5–9. So far, nonlinear photonic crystals have been restricted to one- or two-dimensional geometries owing to a lack of fabrication technologies capable of three-dimensional (3D) nonlinearity engineering. Here, we provide an experimental example of a 3D nonlinear photonic crystal, fabricated in ferroelectric barium Calcium Titanate, by applying an ultrafast light domain inversion approach. The resulting full flexibility of 3D nonlinearity modulation enables phase matching of nonlinear processes along an arbitrary direction, thereby removing constraints imposed by low-dimensional structures. A three-dimensional nonlinear photonic crystal in ferroelectric barium Calcium Titanate that enables phase matching of nonlinear processes along an arbitrary direction, thereby removing constraints imposed by low-dimensional structures, is experimentally realized.
Nataf, Guillaume F. - One of the best experts on this subject based on the ideXlab platform.
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Nouvelles approches pour comprendre les parois de domaines conductrices et les parois de domaines polaires par spectroscopie Raman et microscopie électronique de faible énergie
HAL CCSD, 2016Co-Authors: Nataf, Guillaume F.Abstract:We investigate the structural and electronic properties of domain walls to achieve a better understanding of the conduction mechanisms in domain walls of lithium niobate and the polarity of domain walls in Calcium Titanate. In a first part, we discuss the interaction between defects and domain walls in lithium niobate. A dielectric resonance with a low activation energy is observed, which vanishes under thermal annealing in monodomain samples while it remains stable in periodically poled samples. Therefore we propose that domain walls stabilize polaronic states. We also report the evolution of Raman modes with increasing amount of magnesium in congruent lithium niobate. We identified specific frequency shifts of the modes at the domain walls. The domains walls appear then as spaces where polar defects are stabilized. In a second step, we use mirror electron microscopy (MEM) and low energy electron microscopy (LEEM) to characterize the domains and domain walls at the surface of magnesium-doped lithium niobate. We demonstrate that out of focus settings can be used to determine the domain polarization. At domain walls, a local stray, lateral electric field arising from different surface charge states is observed. In a second part, we investigate the polarity of domain walls in Calcium Titanate. We use resonant piezoelectric spectroscopy to detect elastic resonances induced by an electric field, which is interpreted as a piezoelectric response of the walls. A direct image of the domain walls in Calcium Titanate is also obtained by LEEM, showing a clear contrast in surface potential between domains and walls. This contrast is observed to change reversibly upon electron irradiation due to the screening of polarization charges at domain walls.Ce travail de thèse porte sur les propriétés structurales et électroniques des parois de domaines ferroïques ; il a pour objectif une meilleure compréhension des mécanismes de conduction dans les parois de domaines du niobate de lithium d’une part, et de la polarité des parois de domaine dans le Titanate de Calcium d’autre part. La première partie est consacrée aux interactions entre les défauts et les parois de domaine dans le niobate de lithium. L’observation d’une relaxation diélectrique de faible énergie d’activation et l’analyse de son comportement sous l’effet d’un recuit dans des échantillons avec et sans parois nous conduisent à proposer que les parois de domaines stabilisent des états polaroniques. Nous rapportons aussi l'évolution de modes Raman dans des échantillons congruents de niobate de lithium dopés de manière croissante en magnésium. Nous identifions des décalages en fréquence spécifiques aux parois de domaines. Les parois de domaines apparaissent alors comme des lieux de stabilisation des défauts polaires. Nous utilisons la microscopie électronique miroir (MEM) et la microscopie électronique de faible énergie (LEEM) pour caractériser les domaines et parois de domaines à la surface du niobate de lithium dopé magnésium. Nous démontrons que les réglages de la distance focale peuvent être utilisés pour déterminer la polarisation du domaine. Aux parois de domaines, un champ électrique latéral, provenant de différents états de charge de surface, est mis en évidence. Dans une seconde partie, nous étudions la polarité des parois de domaine dans le Titanate de Calcium. Nous utilisons la spectroscopie de résonance piézo-électrique pour mettre en évidence l’excitation de résonances élastiques par un signal électrique, ce qui est interprété comme une réponse piézoélectrique des parois de domaines. Une image directe des parois de domaine du Titanate de Calcium est obtenue par LEEM, et montre une différence de potentiel de surface entre domaines et parois. Ce contraste peut être modifié sous l’effet d’injection d’électrons, par un effet d’écrantage des charges de polarisation aux parois
Hisao Yoshida - One of the best experts on this subject based on the ideXlab platform.
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Platinum Cocatalyst Loaded on Calcium Titanate Photocatalyst for Water Splitting in a Flow of Water Vapor
Chemsuschem, 2019Co-Authors: Hisao Yoshida, Ryoko Yamada, Tomoko YoshidaAbstract:In water splitting by using heterogeneous photocatalysts, the use of a suitable cocatalyst has been recognized as one of the key factors in enhancing the photocatalytic activity. Although platinum is a representative cocatalyst for many heterogeneous photocatalytic reactions, it has not been used for photocatalytic water splitting, owing to its high catalytic activity for the reverse reaction of water splitting. In the present study, platinum nanoparticles were loaded as a cocatalyst on a Calcium Titanate photocatalyst by a conventional impregnation method and a photodeposition method and examined for photocatalytic water splitting in a flow of water vapor. Platinum nanoparticles loaded by the impregnation method were found to retain the oxidized form on the Calcium Titanate photocatalyst, even under photoirradiation, and promoted hydrogen and oxygen production by photocatalytic water vapor splitting without promoting the reverse reaction.
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highly selective photocatalytic reduction of carbon dioxide with water over silver loaded Calcium Titanate
Catalysis Communications, 2017Co-Authors: Akihiko Anzai, Naoto Fukuo, Akira Yamamoto, Hisao YoshidaAbstract:Abstract The once reported Ag-modified CaTiO 3 photocatalyst was reexamined by optimizing the Ag loading amount and using a conventional photochemical reactor. This revealed that the Ag-modified CaTiO 3 photocatalyst actually showed both high production rate of CO (54 μmol h −1 ) and excellent selectivity towards CO formation (94%) by suppressing the H 2 production via water splitting. It is suggested that the high photocatalytic performance originates from not only the optimized amount of cocatalyst and the high irradiation light intensity but also the high concentration of dissolved CO 2 that was achieved by a bubbling flow of CO 2 at the lower reaction temperature. These reaction conditions provided ca. 40 times higher CO formation rate. It was proposed that the deposited small Ag nanoparticles are the selective active sites for CO formation and the CaTiO 3 crystal surface produces H 2 preferably.
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Calcium Titanate photocatalyst prepared by a flux method for reduction of carbon dioxide with water
Catalysis Today, 2015Co-Authors: Hisao Yoshida, Like Zhang, Masumi Sato, Takeshi Morikawa, Tsutomu Kajino, Takeshi Sekito, Matsumoto Shinichi, Hirohito HirataAbstract:Abstract Several Calcium Titanate samples were prepared by a flux method with various flux salts and various substrate concentration and also by a solid state reaction method. The prepared Calcium Titanate of various morphologies were loaded with Ag cocatalyst, and examined for the photocatalytic reduction of carbon dioxide with water. A sample prepared with a NaCl flux with a moderate concentration of solute exhibited the highest and stable photocatalytic activity for carbon monoxide production among the prepared samples. It is revealed that the large and flat facets could stabilize the Ag cocatalyst nanoparticles on the surface to enhance the photocatalytic activity for the carbon monoxide production.
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hydrogen production from water and methane over pt loaded Calcium Titanate photocatalyst
Energy and Environmental Science, 2010Co-Authors: Katsuya Shimura, Hisao YoshidaAbstract:Pt/CaTiO3 photocatalysts exhibited a higher production rate of hydrogen in a flowing mixture of water vapour and methane than that in a flow of water vapour only, since both photocatalytic steam reforming of methane and photocatalytic water decomposition simultaneously proceeded.
