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(321) Production(s) de GIL B.
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A planar defect spin sensor in a two-dimensional material susceptible to strain and electric fields
Auteur(s): Udvarhelyi Péter, Clua-Provost Tristan, Durand A., Li Jiahan, Edgar James, Gil B., Cassabois G., Jacques V., Gali Adam
(Article) Publié:
Npj Computational Materials, vol. 9 p.150 (2023)
Texte intégral en Openaccess :
Ref HAL: hal-04258308_v1
Ref Arxiv: 2304.00492
DOI: 10.1038/s41524-023-01111-7
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: The boron-vacancy spin defect (V − B) in hexagonal boron nitride (hBN) has a great potential as a quantum sensor in a two-dimensional material that can directly probe various external perturbations in atomic-scale proximity to the quantum sensing layer. Here, we apply first principles calculations to determine the coupling of the V − B electronic spin to strain and electric fields. Our work unravels the interplay between local piezoelectric and elastic effects contributing to the final response to the electric fields. The theoretical predictions are then used to analyse optically detected magnetic resonance (ODMR) spectra recorded on hBN crystals containing different densities of V − B centres. We prove that the orthorhombic zero-field splitting parameter results from local electric fields produced by surrounding charge defects. By providing calculations of the spin-strain and spin-electric field couplings, this work paves the way towards applications of V − B centres for quantitative electric field imaging and quantum sensing under pressure.
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Nanoporous GaN by selective area sublimation through an epitaxial nanomask: AlN versus Si$_x$N$_y$
Auteur(s): Damilano B, Vézian S., Brault J., Ruterana P, Gil B., Tchernycheva M.
(Article) Publié:
Nanotechnology, vol. 34 p.245602 (2023)
Ref HAL: hal-04248760_v1
DOI: 10.1088/1361-6528/acc3a2
Exporter : BibTex | endNote
Résumé: Nanoporous GaN layers were fabricated using selective area sublimation through a self-organized AlN nanomask in a molecular beam epitaxy reactor. The obtained pore morphology, density and size were measured using plan-view and cross-section scanning electron microscopy experiments. It was found that the porosity of the GaN layers could be adjusted from 0.04 to 0.9 by changing the AlN nanomask thickness and sublimation conditions. The room temperature photoluminescence properties as a function of the porosity were analysed. In particular, a strong improvement (>100) of the room temperature photoluminescence intensity was observed for porous GaN layers with a porosity in the 0.4–0.65 range. The characteristics of these porous layers were compared to those obtained with a Si$_x$ N$_y$ nanomask. Furthermore, the regrowth of p-type GaN on light emitting diode structures made porous by using either an AlN or a Si$_x$ N$_y$ nanomask were compared.
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Optically Active Spin Defects in Few-Layer Thick Hexagonal Boron Nitride
Auteur(s): Durand A., Clua-Provost T., Fabre F., Kumar P., Li J., Edgar J. H., Udvarhelyi P., Gali A., Marie X., Robert C., Gérard J. M., Gil B., Cassabois G., Jacques V.
(Article) Publié:
Physical Review Letters, vol. 131 p.116902 (2023)
Texte intégral en Openaccess :
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Stacking-dependent deep level emission in boron nitride
Auteur(s): Rousseau A., Valvin P., Elias C., Xue L., Li J., Edgar J. H., Gil B., Cassabois G.
(Article) Publié:
Physical Review Materials, vol. 6 p.094009 (2022)
Ref HAL: hal-03842086_v1
DOI: 10.1103/PhysRevMaterials.6.094009
WoS: WOS:000860686400005
Exporter : BibTex | endNote
Résumé: We report hyperspectral microscopy in sp2-bonded boron nitride polytypes with a simultaneous inspection of the photoluminescence signal in the UV-C and UV-B spectral ranges. By comparing two different polytypes extracted from the same polycrystalline sample, we reveal that the well-known “4 eV defect” does not emit at the same energy for polytypes in the AB and AA′ stackings. The zero-phonon line is either at 4.14 or 4.16 eV for the noncentrosymmetric AB stacking, instead of the usual 4.09 eV energy in the AA′ stacking. Our results open the way for different characterization methods of the stacking order in sp2-bonded boron nitride, and bring alternative inputs for the elucidation of the atomistic configuration of points defects by advanced ab initio calculations.
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Superradiance of optical phonons in two-dimensional materials
Auteur(s): Cassabois G., Fugallo G, Gil B.
(Article) Publié:
Physical Review Research, vol. 4 p.L032040 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03794436_v1
DOI: 10.1103/PhysRevResearch.4.L032040
Exporter : BibTex | endNote
Résumé: We study the superradiance of optical phonons during the two- to three-dimensional (2D-3D) crossover of the light-matter interaction in multilayers of atomic crystals. We show the emergence of a superradiant regime with a mode having a linewidth first increasing linearly with the number N of monolayers, and then decreasing as N^{−3} to zero because of the formation of stationary phonon polaritons. The linewidth culminates to values of the order of the longitudinal-transverse splitting. We estimate the extremum of the radiative efficiency for various 2D materials in the superradiant regime. We predict radiative efficiencies larger than 50% for optical phonons emitting between 6 and 165 μm. Superradiance appears as a key resource for mid- and far-infrared optophononics and advanced thermal management using multilayers of 2D materials as the active medium.
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Determination of the direct bandgap value in In4Se3 thin films
Auteur(s): De Brucker L., Moret M., Gil B., Desrat W.
(Article) Publié:
Journal Of Physics: Condensed Matter, vol. 34 p.425703 (2022)
Ref HAL: hal-03780298_v1
DOI: 10.1088/1361-648X/ac895f
Exporter : BibTex | endNote
Résumé: The value and the nature of the bandgap of In4Se3 are still not well defined, with a large spread of the experimental data between 0.42 and 1.68 eV and an uncertain nature, predicted to be indirect by ab initio band structure calculations. Here we report on the optical transmission and photoluminescence (PL) performed in In4Se3 thin films grown by coevaporation on (0001)-oriented sapphire wafers. The quality of the polycrystalline layers allows the first detection of the excitonic-like transition in the optical absorption of this compound at low temperature. The PL detected under weak laser excitation shows a bound exciton emission at 0.75 eV. Strong laser irradiation reveals a quadratic dependence of the PL intensity on the optical excitation, which demonstrates a stimulated emission at 0.79 eV in relation with an exciton–exciton scattering process. On the basis of a reasonable estimate of the exciton energy, equal to 10 − 15 meV, we evaluate the direct bandgap of In4 Se3 to 0.82 ± 0.01 eV at low temperature.
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Phonon-assisted broadening in Bernal boron nitride: A comparison between indirect and direct excitons
Auteur(s): Rousseau A., Valvin P., Xue L., Li J., Edgar J. H., Gil B., Cassabois G.
(Article) Publié:
Physical Review B, vol. 106 p.035203 (2022)
Ref HAL: hal-03767169_v1
DOI: 10.1103/PhysRevB.106.035203
WoS: WOS:000832496600004
Exporter : BibTex | endNote
Résumé: We study the deep-ultraviolet emission in Bernal boron nitride as a function of temperature. The quasidegeneracy of indirect and direct excitons in Bernal boron nitride leads to their simultaneous recombination, allowing a comparison of phonon-assisted broadening in the two cases. Temperature-dependent measurements reveal that below 200 K, the efficiency of phonon-assisted broadening is one order of magnitude lower for the direct transition at 6.035 eV than for the phonon replicas of the indirect exciton. This striking effect results from the inhibition of quasielastic acoustic phonon scattering in the strong-coupling regime of the light-matter interaction, where the density of final states is reduced by the curvature of the polaritonic dispersion.
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