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(419) Production(s) de l'année 2017
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Core-Shell structure induces new ground states in strontium titanate 
Auteur(s): Hehlen B. , Kiat Jean-Michel, Al-Sabbagh A, Anoufa Mickaël, Bogicevic Christine, Al-Zein A.
Conférence invité: 12th Pacific Rim Conference on CEramics and Glass Technology (PACRIM) (Waikoloa - Hawaï, US, 2017-05-22)
Texte intégral en Openaccess : 
Ref HAL: hal-01937924_v1
Exporter : BibTex | endNote
Résumé: Hyper-Raman scattering (HRS) is a non-linear spectroscopy sensitive to all polar excitations, in particular the soft modes inactive in Raman. HRS has been applied to nano-ceramics of strontium titanate (SrTiO3) of controlled grain size. Contrary to infrared absorption which sees an average medium, the vibrational responses of the core and the shell(s) are split in HRS, allowing thereby probing the structural and dielectric properties of the two subsystems. The resulting structural model successfully reproduces the effective dielectric permittivity measured by dielectric experiments [1]. These results confirm the strong, but still under-exploited, potentialities of HRS for the investigation of polar materials [2].We also demonstrate that a new ground state can be obtained by tailoring the core-shell structure of the particles. High energy X-rays at synchrotron combined to neutron diffraction and HRS revealed a lowering of the ferroelastic ground state towards a new antiferrodistortive phase, accompanied with strong shift of the critical temperature [3,4]. This new phase is discussed within the Landau theory, and the crucial competition between particle shape anisotropy, surface tension, and shear strain is analyzed as well. This shows that controlling the core-shell structure provides an easy way to stabilize new phases that cannot exist in bulk material, just like film deposition on a substrate.
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Ab-Initio modeling of vibrational spectra of silicate glasses and decomposition into principal structural components.
Auteur(s): Kilymis D., Hehlen B., Peuget S., Delaye Jean-Marc, Ispas S.
Conference: Glass & Optical Material Division, Annual Meeting 2017 (GOMD) (Waikoloa - Hawaï, US, 2017-05-21)
Texte intégral en Openaccess :
Ref HAL: hal-01937865_v1
Exporter : BibTex | endNote
Résumé: Density functional theory is used to calculate the vibrational properties of pure silica and sodo-silicateglasses with 20, 25, and 33 mol% of Na2O. The infrared and Raman spectra are calculated and the full responses aredecomposed into principal structural components (PSC). Those are for example the SiO4n--tetrahedra with n nonbrigdingoxygens defining the Qn-species at the origin of the structured feature at high frequency, and the Si-O-Sibridges leading the broad Raman R-band at intermediate frequencies. Our results confirm that Si-O-Si bending inbridges with large angle vibrate preferentially at lower frequencies than those with low angle. In addition, the spectralresponse of the Q2-species is bimodal and overlaps with that of the Q3, while the Q4 response covers almost all ofthe spectral range of the Qn-band. The ab-initio individual spectral responses of the PSC are used to reconstruct theexperimental Raman responses. Contrary to the commonly used multi-Gaussian decomposition, this approachprovides unambiguous band-assignments and hence a more accurate way to probe the structural and chemicalproperties of glasses from their spectroscopic signature.
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Quantum Dot based UV Light Emitting Diodes
Auteur(s): Brault Julien, Matta S., Al Khalfioui Mohamed, Leroux Mathieu, Damilano Benjamin, Chenot S., Korytov M, Peyre H., Konczewicz L., Contreras S., Chaix C., Massies Jean, Gil B.
(Affiches/Poster)
12th international conference on nitride semiconductors (STRASBOURG, FR), 2017-07-24
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High Temperature Electrical Transport Study of MBE grown Mg-doped AlGaN
Auteur(s): Contreras S., Konczewicz L., Juillaguet S., Peyre H., Al khalfioui Mohamed, Matta S., Leroux Mathieu, Damilano Benjamin, Brault Julien
(Affiches/Poster)
12th international conference on nitride semiconductors (STRASBOURG, FR), 2017-07-24
Résumé: High Temperature Electrical Transport Study of MBE grown Mg-doped AlGaN
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High temperature electrical transport study of n-type Si-doped AlN
Auteur(s): Contreras S., Konczewicz L., Peyre H., Juillaguet S., Weyher J.l., Dziecielewski I, Al khalfioui Mohamed, Matta S., Leroux Mathieu, Damilano Benjamin, Brault Julien, Gil B.
(Affiches/Poster)
International Workshop on Ultraviolet Materials and Devices (FUKUOKA, JP), 2017-11-14
Résumé: High temperature electrical transport study of n-type Si-doped AlN
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HgCdTe as a playground for massless fermions
Auteur(s): Teppe F., Krishtopenko S.
Conférence invité: 7th International Symposium on Terahertz Nanosciences (Porquerolles, FR, 2017-10-02)
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