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Ref Arxiv: 2304.00492
DOI: 10.1038/s41524-023-01111-7
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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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Ref Arxiv: 2304.12071
DOI: 10.1103/PhysRevLett.131.116902
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Securing communications over long distances requires bright single photon sources emitting in the telecom band in a well-defined spatial and polarization mode. First, we report our efforts to obtain single photon emission and a Gaussian far-field radiation pattern in the telecom O-band from single quantum dot-nanowires (QD-NWs) monolithically grown on silicon. The InAs/InP QD-NWs were grown on silicon (111) substrates by Vapor-Liquid-Solid assisted solid-source Molecular Beam Epitaxy using In-Au droplets as a catalyst in-situ deposited at 500°C [1]. Low QD-NW density was obtained by a careful control of the In/Au catalyst flux ratio to achieve density <1 NW/μm² [2]. The growth conditions have been tuned (Fig 1.a) to optimize the source brightness and reduce the far-field divergence. The control of the nanowire geometry allows us to demonstrate a Gaussian far field emission profile with an emission angle θ≈30° (Fig 1.c) from a single QD at room temperature in the telecom O-band and the observation of single photon emission with g2(0) = 0.05 (Fig 1.b) at cryogenic temperature [3]. Secondly, we have optimized the growth procedure to achieve InAs/InP QD NWs with an elongated top-view cross-section. Polarization-resolved photoluminescence measurements have revealed a significant influence of the asymmetric shaped NWs on the InAs QD emission polarization with the photons being mainly polarized parallel to the NW long cross section axis [4]. A degree of linear polarization (DLP) up to 91% is obtained, being at the state of the art for the reported DLP values from QD-NWs.\\References:[1] A. Mavel et al, Journal of Crystal Growth, 458 (2017) 96.[2] A. Jaffal et al, Nanotechnology, 31 (2020) 354003.[3] A. Jaffal et al, Nanoscale, 11 (2019) 21847-21855.[4] A. Jaffal et al, Nanoscale, 13 (2021) 16952–16958.

Ref HAL: hal-03951311_v1
Ref Arxiv: 2207.10477
DOI: 10.1103/PhysRevApplied.18.L061002
WoS: WOS:000905309300005
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Optically active spin defects hosted in hexagonal boron nitride (h-BN) are promising candidates for the development of a two-dimensional (2D) quantum sensing unit. Here, we demonstrate quantitative magnetic imaging with h-BN flakes doped with negatively charged boron-vacancy (VB-) centers throughneutron irradiation. As a proof-of-concept, we image the magnetic field produced by CrTe2 , a van der Waals ferromagnet with a Curie temperature slightly above 300 K. Compared to other quantum sensors embedded in 3D materials, the advantages of the h-BN-based magnetic sensor described in this work areits ease of use, high flexibility, and, more importantly, its ability to be placed in close proximity to a target sample. Such a sensing unit will likely find numerous applications in 2D materials research by offering a simple way to probe the physics of van der Waals heterostructures.

Ref HAL: hal-03884890_v1
DOI: 10.1021/acs.inorgchem.2c02430
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Low-dimensional boron nitride (BN) chains were prepared in the one-dimensional pores of the siliceous zeolites theta-one (TON) and Mobil-twelve (MTW) by the infiltration, followed by the dehydrocoupling and pyrolysis of ammonia borane under high-pressure, high-temperature conditions. High-pressure X-ray diffraction in a diamond anvil cell and in a large-volume device was used to follow in situ these different steps in order to determine the optimal conditions for this process. Based on these results, millimeter-sized samples of BN/TON and BN/MTW were synthesized. Characteristic B–N stretching vibrations of low-dimensional BN were observed by infrared and Raman spectroscopies. The crystal structures were determined using a combination of X-ray diffraction and density functional theory with one and two one-dimensional zig-zag (BN)x chains per pore in BN/TON and BN/MTW, respectively. These 1-D BN chains potentially have interesting photoluminescence properties in the far ultraviolet region of the electromagnetic spectrum.

Ref HAL: hal-03842086_v1
DOI: 10.1103/PhysRevMaterials.6.094009
WoS: WOS:000860686400005
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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.

Ref HAL: hal-03837709_v1
Ref Arxiv: 2210.05485
Ref INSPIRE: 2164234
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We report successful incorporation of an ensemble of G centers in silicon-on-insulator (SOI) microrings using ion implantation and conventional nanofabrication. The coupling between the emitters and the resonant modes of the microrings is studied using continuous-wave and time-resolved microphotoluminescence (PL) experiments. We observe the resonant modes of the microrings on PL spectra, on the wide spectral range that is covered by G centers emission. By finely tuning the size of the microrings, we match their zero-phonon line at 1278 nm with a resonant mode of quality factor around 3000 and volume 7.2 (lambda over n)^3. The zero-phonon line intensity is enhanced by a factor of 5, both in continuous-wave and time-resolved measurements. This is attributed to the Purcell enhancement of zero-phonon spontaneous emission into the resonant mode and quantitatively understood considering the distribution of the G centers dipoles. Despite the enhancement of the zero-phonon emission, we do not observe any sizeable decrease of the average lifetime of the G centers, which points at a low radiative yield (<10%). We reveal the detrimental impact of parasitic defects in heavily implanted silicon, and discuss the perspectives for quantum electrodynamics experiments with individual color centers in lightly implanted SOI rings. Our results provide key information for the development of deterministic single photon sources for integrated quantum photonics.