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(322) Production(s) de GIL B.
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High-Pressure Softening of the Out-of-Plane A2u(Transverse-Optic) Mode of Hexagonal Boron Nitride Induced by Dynamical Buckling
Auteur(s): Segura A, Cusco R., Taniguchi T., Watanabe Kanji, Cassabois G., Gil B., Artus L.
(Article) Publié:
The Journal Of Physical Chemistry C, vol. 123 p.17491 (2019)
Texte intégral en Openaccess :
Ref HAL: hal-02192575_v1
DOI: 10.1021/acs.jpcc.9b04582
WoS: 000476693800050
Exporter : BibTex | endNote
6 Citations
Résumé: We investigate the highly anisotropic behavior of the in-plane and out-of-plane infrared-active phonons of hexagonal boron nitride by means of infrared reflectivity and absorption measurements under high pressure. Infrared reflectivity spectra at normal incidence on high-quality single crystals show strict fulfillment of selection rules and an unusually long E1u[transverse-optic (TO)] phonon lifetime. Accurate values of the dielectric constants at ambient pressure ε⊥0 = 6.96, ε⊥∞ = 4.95, ε∥0 = 3.37, and ε∥∞ = 2.84 have been determined from fits to the reflectivity spectra. The out-of-plane A2u phonon reflectivity band is revealed in measurements on an inclined facet, and absorption measurements at an incidence angle of 30° allow us to observe both the transverse- and longitudinal-optic A2u modes. Pressure coefficients and Grüneisen parameters for all infrared-active modes are determined and compared with ab initio calculations. While Grüneisen parameters are generally small in this layered crystal, the A2u(TO) displays an exceptionally large and negative Grüneisen parameter that results in widening of the type I hyperbolic region with increasing pressure. Softening of the A2u(TO) mode is induced by dynamical buckling of the flat honeycomb layers.
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Photonics with hexagonal boron nitride
Auteur(s): Caldwell Joshua David, Aharonovich Igor, Cassabois G., Edgar James H., Gil B., Basov D.N.
(Article) Publié:
Nature Reviews Materials, vol. 8 p.1 (2019)
Ref HAL: hal-02191041_v1
DOI: 10.1038/s41578-019-0124-1
WoS: 000478802800006
Exporter : BibTex | endNote
71 Citations
Résumé: For more than seven decades, hexagonal boron nitride (hBN) has been employed asan inert, thermally stable engineering ceramic; since 2010, it has also been used as the optimal substrate for graphene in nanoelectronic and optoelectronic devices. Recent research has revealed that hBN exhibits a unique combination of optical properties that enable novel (nano) photonic functionalities. Specifically, hBN is a natural hyperbolic material in the mid-IR range,in which photonic material options are sparse. Furthermore, hBN hosts defects that can be engineered to obtain room-temperature, single-photon emission; exhibits strong second-order nonlinearities with broad implications for practical devices; and is a wide-bandgap semiconductor well suited for deep UV emitters and detectors. Inspired by these promising attributes, research on the properties of hBN and the development of large-area bulk and thin-film growth techniques has dramatically expanded. This Review offers a snapshot of current research exploring the properties underlying the use of hBN for future photonics functionalities and potential applications, and covers some of the remaining obstacles.
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Direct band-gap crossover in epitaxial monolayer boron nitride
Auteur(s): Elias C., Valvin P., Pelini T., Summerfeld Alex, Mellor Chris, Cheng T.s., Eaves L., Foxon C.t., Beton Peter, Novikov Sergei, Gil B., Cassabois G.
(Article) Publié:
Nature Communications, vol. 1 p.1 (2019)
Texte intégral en Openaccess :
Ref HAL: hal-02156532_v1
DOI: 10.1038/s41467-019-10610-5
WoS: 000471586700016
Exporter : BibTex | endNote
23 Citations
Résumé: Hexagonal boron nitride is a large band-gap insulating material which complements the electronic and optical properties of graphene and the transition metal dichalcogenides. However, the intrinsic optical properties of monolayer boron nitride remain largely unex- plored. In particular, the theoretically expected crossover to a direct-gap in the limit of the single monolayer is presently not confirmed experimentally. Here, in contrast to the tech- nique of exfoliating few-layer 2D hexagonal boron nitride, we exploit the scalable approach of high-temperature molecular beam epitaxy to grow high-quality monolayer boron nitride on graphite substrates. We combine deep-ultraviolet photoluminescence and reflectance spectroscopy with atomic force microscopy to reveal the presence of a direct gap of energy 6.1eV in the single atomic layers, thus confirming a crossover to direct gap in the monolayer limit.
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Spontaneous emission of color centers at 4eV in hexagonal boron nitride under hydrostatic pressure
Auteur(s): Koronski Kamil, Kaminska Agata, Zighadlo Nikolai d, Elias C., Cassabois G., Gil B.
(Article) Publié:
Superlattices And Microstructures, vol. 131 p.1 (2019)
Texte intégral en Openaccess :
Ref HAL: hal-02141847_v1
DOI: 10.1016/j.spmi.2019.05.018
WoS: 000475999900001
Exporter : BibTex | endNote
3 Citations
Résumé: The light emission properties of color centers emitting in 3.3–4 eV region are investigated for hydrostatic pressures ranging up to 5 GPa at liquid helium temperature. The light emission energy decreases with pressure less sensitively than the bandgap. This behavior at variance from the shift of the bandgap is typical of deep traps. Interestingly, hydrostatic pressure reveals the existence of levels that vary differently under pressure (smaller increase of the emission wavelength compared to the rest of the levels in this energy region or even decrease of it) with pressure. This discovery enriches the physics of the color centers operating in the UV in hBN.
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Influence of isotopic substitution on the anharmonicity of the interlayer shear mode of h-BN
Auteur(s): Cusco Ramon, Edgar James H., Liu Song, Cassabois G., Gil B., Artus Luis
(Article) Publié:
Physical Review B, vol. 99 p.085428 (2019)
Texte intégral en Openaccess :
Ref HAL: hal-02086080_v1
DOI: 10.1103/PhysRevB.99.085428
WoS: WOS:000459225100013
Exporter : BibTex | endNote
5 Citations
Résumé: We present a detailed analysis of the temperature dependence of the interlayer shear mode that reveals a variation of the four-phonon scattering coupling with isotopic mass. Phonon anharmonic decay and isotopic disorder effects are very weak for the low-energy interlayer shear mode, and the overall temperature dependence is mainly governed by the thermal lattice expansion. This allows us to observe systematic differences in the temperature dependence of the low-energy mode with the isotopic mass that are related to the four-phonon scattering contribution in quartic anharmonicity. The change in the quartic anharmonicity coefficient between the isotopically pure samples is larger than would be purely expected from the mass variation.
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Structural and Optical Properties of Zn1-xMgxO Prepared by Calcination of ZnO + Mg(OH)2 after Hydro Micro Mechanical Activation
Auteur(s): Vuong Thi Quynh Phuong, Lair Valentin, Lacoste Francois, Halloumi Samy, Coindeau Stéphane, Thiel Julien, Shubina T., Pauthe Monique, Gil B.
(Article) Publié:
Annalen Der Physik, vol. p.1800379 (2019)
Ref HAL: hal-01992435_v1
DOI: 10.1002/andp.201800379
WoS: 000471714300010
Exporter : BibTex | endNote
Résumé: Zn1-xMgxO microcrystals are produced in the 0.15 & x & 1 composition range by calcination of ZnO + Mg(OH)2 after hydro micro mechanical activation according to the patent WO2018065735A1. The structural properties of the samples have revealed the cohabitation of wurtzite and rock-salt phases for x values ranging from 0.15 up to 0.6 with a clear increase of the proportion of cubic phase with x. A single cubic phase is observed in the range 0.66
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Photoluminescence of GaN and AlxGa1-xN (x≤ 0.2) doped with Mg and grown by molecular beam epitaxy
Auteur(s): Leroux Mathieu, Brault Julien, Matta S., Al khalfioui Mohamed, Damilano Benjamin, Contreras S., Juillaguet S., Konczewicz L., Gil B., Brochen S.
(Affiches/Poster)
JNMO (Cap Esterel-Aguay, FR), 2018-06-13
Résumé: Photoluminescence of GaN and AlxGa1-xN (x≤ 0.2) doped with Mg and grown by molecular beam epitaxy
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