The Experts below are selected from a list of 173814 Experts worldwide ranked by ideXlab platform
Koichi Shimakawa - One of the best experts on this subject based on the ideXlab platform.
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Photo-Induced Volume changes in selenium. Tight-binding molecular dynamics study
Journal of Non-crystalline Solids, 2004Co-Authors: J. Hegedüs, Krisztian Kohary, Sándor Kugler, Koichi ShimakawaAbstract:Tight-binding molecular dynamics simulations of photo-excitations in small Se clusters (isolated Se8 ring and helical Se chain) and glassy Se networks (containing 162 atoms) were carried out in order to analyze the photo-Induced instability in amorphous selenium. In the cluster systems after taking an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital a bond breaking occurs. In the glassy networks photo-Induced Volume expansion was observed and at the same time the number of coordination defects changed significantly due to illumination.
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Photo-Induced Volume changes in selenium. Tight-binding molecular dynamics study
Journal of Non-Crystalline Solids, 2004Co-Authors: J. Hegedüs, K. Kohary, S. Kugler, Koichi ShimakawaAbstract:Tight-binding molecular dynamics simulations of photo-excitations in small Se clusters (isolated Se$_8$ ring and helical Se chain) and glassy Se networks (containing 162 atoms) were carried out in order to analyse the photo Induced instability inside the amorphous selenium. In the cluster systems after taking an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital a bond breaking occurs. In the glassy networks photoInduced Volume expansion was observed and at the same time the number of coordination defects changed significantly due to illumination
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In situ measurements of photo-Induced Volume changes in amorphous chalcogenide films
Journal of Non-crystalline Solids, 2000Co-Authors: Ashtosh Ganjoo, Y. Ikeda, Koichi ShimakawaAbstract:Abstract Photo-Induced thickness changes in obliquely deposited amorphous As 2 S 3 and GeSe 2 films have been measured to determine the mechanisms of changes during illumination . For As 2 S 3 , the thickness increases and then decreases and saturates after some time. There is a decrease followed by saturated change even after the illumination is switched off. On the other hand, GeSe 2 has a continuous decrease of thickness with time, which remains constant after the illumination is turned off. The difference in these properties between As 2 S 3 and GeSe 2 films is discussed in terms of different structural units for these films (layered for a-As 2 S 3 and three-dimensional for a-GeSe 2 ).
J. Hegedüs - One of the best experts on this subject based on the ideXlab platform.
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Microscopic and macroscopic models of photo-Induced Volume changes in amorphous selenium
Journal of Materials Science: Materials in Electronics, 2009Co-Authors: Rozalia Lukacs, J. Hegedüs, Sándor KuglerAbstract:We have proposed a new explanation for the photo-Induced Volume changes in chalcogenide glasses. We have found that the covalent bond breaking occurs in these glasses with excited electrons, whereas holes contribute to the formation of inter-chain bonds. We have calculated the charge distribution in a-Se, too.
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Universal feature of photo-Induced Volume changes in chalcogenide glasses
Journal of Non-crystalline Solids, 2006Co-Authors: J. Hegedüs, Krisztian Kohary, Sándor KuglerAbstract:We have investigated in chalcogenide glasses the microscopic processes caused by illumination using tight-binding molecular dynamics computer simulation. After photon absorption we treated the excited electron and hole independently. We found covalent bond breaking in amorphous networks with photo-Induced excited electrons, whereas excited holes contribute to the formation of inter-chain bonds. We also observed a correlated macroscopic Volume change of the amorphous sample. Our results provide a new and universal description, which can explain simultaneously the photo-Induced Volume expansion and shrinkage. This model is supported by the results of recent measurements.
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Light-Induced Volume changes in glassy selenium. II. Kinetics of Volume expansion
Journal of Optoelectronics and Advanced Materials, 2005Co-Authors: J. Hegedüs, Krisztian Kohary, Sándor KuglerAbstract:Based on our previous molecular dynamics simulations we present an universal macroscopic model, which can simultaneously explain the photo-Induced Volume expansion and shrinkage. It is supported by the recent surface height measurements on amorphous selenium.
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Photo-Induced Volume changes in selenium. Tight-binding molecular dynamics study
Journal of Non-crystalline Solids, 2004Co-Authors: J. Hegedüs, Krisztian Kohary, Sándor Kugler, Koichi ShimakawaAbstract:Tight-binding molecular dynamics simulations of photo-excitations in small Se clusters (isolated Se8 ring and helical Se chain) and glassy Se networks (containing 162 atoms) were carried out in order to analyze the photo-Induced instability in amorphous selenium. In the cluster systems after taking an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital a bond breaking occurs. In the glassy networks photo-Induced Volume expansion was observed and at the same time the number of coordination defects changed significantly due to illumination.
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Photo-Induced Volume changes in selenium. Tight-binding molecular dynamics study
Journal of Non-Crystalline Solids, 2004Co-Authors: J. Hegedüs, K. Kohary, S. Kugler, Koichi ShimakawaAbstract:Tight-binding molecular dynamics simulations of photo-excitations in small Se clusters (isolated Se$_8$ ring and helical Se chain) and glassy Se networks (containing 162 atoms) were carried out in order to analyse the photo Induced instability inside the amorphous selenium. In the cluster systems after taking an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital a bond breaking occurs. In the glassy networks photoInduced Volume expansion was observed and at the same time the number of coordination defects changed significantly due to illumination
Gilberto Fabbris - One of the best experts on this subject based on the ideXlab platform.
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different routes to pressure Induced Volume collapse transitions in gadolinium and terbium metals
Physical Review B, 2013Co-Authors: Gilberto Fabbris, Takahiro Matsuoka, Jinhyuk Lim, J R L Mardega, Katsuya Shimizu, D Haskel, J S SchillingAbstract:(Received 3 May 2013; revised manuscript received 16 November 2013; published 3 December 2013) The sudden decrease in molar Volume exhibited by most lanthanides under high pressure is often attributed to changes in the degree of localization of their 4f electrons. We give evidence, based on electrical resistivity measurements of dilute Y(Gd) and Y(Tb) alloys to 120 GPa, that the Volume collapse transitions in Gd and Tb metals have different origins, despite their being neighbors in the periodic table. Remarkably, the change under pressure in the magnetic state of isolated Pr or Tb impurity ions in the nonmagnetic Y host appears to closely mirror corresponding changes in pure Pr or Tb metals. The collapse in Tb appears to be driven by an enhanced negative exchange interaction between 4f and conduction electrons under pressure (Kondo resonance) which, in the case of Y(Tb), dramatically alters the superconducting properties of the Y host, much like previously found for Y(Pr). In Gd, our resistivity measurements suggest that a Kondo resonance is not the main driver for its Volume collapse. X-ray absorption and emission spectroscopies clearly show that 4f local moments remain largely intact across both Volume collapse transitions ruling out 4f band formation (delocalization) and valence transition models as possible drivers. The results highlight the richness of behavior behind the Volume collapse transition in lanthanides and demonstrate the stability of the 4f level against band formation to extreme pressure.
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Pressure-Induced Volume collapse and structural phase transitions in SrRuO3
Journal of Solid State Chemistry, 2013Co-Authors: Mikhail Zhernenkov, Gilberto Fabbris, Omar Chmaissem, J. F. Mitchell, Hong Zheng, Daniel HaskelAbstract:Abstract We report on the low temperature (6 K) structural properties of SrRuO 3 under quasi-hydrostatic pressure studied by synchrotron X-ray powder diffraction in a diamond anvil cell. First principle calculations predict a first-order perovskite (Pv) to post-perovskite (pPv) phase transition at ∼40 GPa accompanied by a 1.9% Volume collapse. Our results rule out the occurrence of a pPv phase to 54 GPa. Instead, we find a Pv to monoclinic to triclinic sequence of phase transitions. The monoclinic to triclinic phase transition at ∼38 GPa is accompanied by a 3.5% Volume collapse. X-ray absorption spectroscopy indicates that this Volume collapse is not accompanied by a change in Ru valence state. Our results should help guide improvements to theoretical treatments of this and other correlated d -electron systems based on density functional theory.
Sándor Kugler - One of the best experts on this subject based on the ideXlab platform.
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Microscopic and macroscopic models of photo-Induced Volume changes in amorphous selenium
Journal of Materials Science: Materials in Electronics, 2009Co-Authors: Rozalia Lukacs, J. Hegedüs, Sándor KuglerAbstract:We have proposed a new explanation for the photo-Induced Volume changes in chalcogenide glasses. We have found that the covalent bond breaking occurs in these glasses with excited electrons, whereas holes contribute to the formation of inter-chain bonds. We have calculated the charge distribution in a-Se, too.
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Universal feature of photo-Induced Volume changes in chalcogenide glasses
Journal of Non-crystalline Solids, 2006Co-Authors: J. Hegedüs, Krisztian Kohary, Sándor KuglerAbstract:We have investigated in chalcogenide glasses the microscopic processes caused by illumination using tight-binding molecular dynamics computer simulation. After photon absorption we treated the excited electron and hole independently. We found covalent bond breaking in amorphous networks with photo-Induced excited electrons, whereas excited holes contribute to the formation of inter-chain bonds. We also observed a correlated macroscopic Volume change of the amorphous sample. Our results provide a new and universal description, which can explain simultaneously the photo-Induced Volume expansion and shrinkage. This model is supported by the results of recent measurements.
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Light-Induced Volume changes in glassy selenium. II. Kinetics of Volume expansion
Journal of Optoelectronics and Advanced Materials, 2005Co-Authors: J. Hegedüs, Krisztian Kohary, Sándor KuglerAbstract:Based on our previous molecular dynamics simulations we present an universal macroscopic model, which can simultaneously explain the photo-Induced Volume expansion and shrinkage. It is supported by the recent surface height measurements on amorphous selenium.
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Photo-Induced Volume changes in selenium. Tight-binding molecular dynamics study
Journal of Non-crystalline Solids, 2004Co-Authors: J. Hegedüs, Krisztian Kohary, Sándor Kugler, Koichi ShimakawaAbstract:Tight-binding molecular dynamics simulations of photo-excitations in small Se clusters (isolated Se8 ring and helical Se chain) and glassy Se networks (containing 162 atoms) were carried out in order to analyze the photo-Induced instability in amorphous selenium. In the cluster systems after taking an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital a bond breaking occurs. In the glassy networks photo-Induced Volume expansion was observed and at the same time the number of coordination defects changed significantly due to illumination.
Andrij Pich - One of the best experts on this subject based on the ideXlab platform.
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Heterogeneous Morphology of Random Copolymer Microgels as Reflected in Temperature‐Induced Volume Transition and 1H High‐Resolution Transverse Relaxation NMR
Macromolecular Chemistry and Physics, 2011Co-Authors: Andreea Balaceanu, Dan E. Demco, Martin Möller, Andrij PichAbstract:The Flory temperature-Induced Volume transition theory for copolymer microgels is generalized for the case of a bimodal heterogeneity of the crosslink density in the microgel particles and applied to PVCL–PNIPAAm and PVCL–PNIPMAAm systems. The most probable morphological parameters are selected from the microscopic and thermodynamic constraints imposed by 1H transverse relaxation NMR data and the Flory equation of state in the approximation of a homogeneous morphology. NMR proves the existence of a bimodal heterogeneous morphology of the copolymer microgel particles. Although the systems are different in chemical structure, the heterogeneity parameters obtained from Flory transition theory and NMR transverse relaxation are not essentially different.
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Microgel Heterogeneous Morphology Reflected in Temperature-Induced Volume Transition and 1H High-Resolution Transverse Relaxation NMR. The Case of Poly(N-vinylcaprolactam) Microgel
Macromolecules, 2011Co-Authors: Andreea Balaceanu, Dan E. Demco, Martin Möller, Andrij PichAbstract:The Flory temperature-Induced Volume transition theory for homopolymer microgels was generalized for the case of bimodal heterogeneous morphology. The most probable morphological parameters were selected from the microscopic and thermodynamic constraints imposed by 1H transverse relaxation NMR and Flory equation of state in the approximation of a homogeneous morphology. Proton transverse magnetization relaxation NMR proved directly the existence of a bimodal heterogeneous morphology of the PVCL microgel particle. The Volume polymer fractions in the deswollen state and the number of subchains for the core and corona were obtained from size−temperature data for a series of differently cross-linked microgels made of poly(N-vinylcaprolactam) (PVCL) in water. The cross-link density effect given by the different amounts of cross-linker used was investigated using dynamic light scattering. From the combination of Flory heterogeneous theory and NMR transverse relaxation, the number of polymer subchains in core an...