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Fabrice Donatini

Publications and source records attributed to Fabrice Donatini.

9 recordsLinked to original sources
arXiv2026

Maskless Electron Beam-Induced Etching of Diamond in Air: A Secondary Electron-Driven Mechanism

We report a direct, maskless electron beam-induced etching (EBIE) process for diamond in air, enabling high-precision patterning without lithography or plasma processing. Through a comprehensive analysis of electron-gas, electron-diamond, and gas-surface interactions in the SEM environment, we demonstrate that etching is predominantly governed by low-energy secondary electrons, which drive gas dissociation and radical generation. The resulting oxygen- and nitrogen-based radicals chemisorb on the diamond surface, form volatile carbon-containing species, and desorb under continued electron irradiation, enabling controlled material removal. The process exhibits two distinct regimes: a molecule-limited regime governed by gas flux and an electron-limited regime controlled by current density. Etch depths up to 212 nm and lateral resolution down to 200 nm are achieved. Time-dependent anisotropy is observed, with (100) surfaces transitioning to (111)-faceted morphologies, enhancing etch yield. These results establish a general secondary electron-driven mechanism for EBIE in gas environments, providing a maskless, damage-free nanofabrication route for diamond semiconductor and other chemically inert materials.

cond-mat.mtrl-sci↗
arXiv2025

Cathodoluminescence Study of a Quantum Dot in a Nanowire for Single-Photon Emission

Cathodoluminescence in a scanning electron microscope was applied to a semiconductor quantum dot in a nanowire able to emit single photons. We show that cathodoluminescence can be used not only for imaging and spectroscopy, but also to measure the correlation function and characterize the purity of the single-photon emitter. The electron beam can be manipulated to minimize the collection of parasitic luminescence. At cryogenic temperatures, we observed that the thermal budget, as measured via the phonon sidebands, is close to that of non-resonant micro-photoluminescence. This makes cathodoluminescence an efficient tool in the quest of novel single-photon sources.

physics.optics↗
arXiv2023

AlGaN/AlN Stranski-Krastanov quantum dots for highly efficient electron beam pumped emitters: The role of miniaturization and composition to attain far UV-C emission

Conventional ultraviolet (UV) lamps for disinfection emit radiation in the 255-270 nm range, which poses a high risk of causing cancer and cataracts. To address these concerns, solid-state far UV-C sources emitting below 240 nm are gaining attention as a safe and sustainable disinfection solution for occupied spaces. Here, we delve into the extension of the AlxGa1-xN/AlN quantum dot (QD) technology towards the far UV-C range, which presents various challenges associated with the reduction of the lattice mismatch and band offset when Al is incorporated in the QDs. We explore the structural and optical impact of increasing the Al content through the increase of the Al flux and eventual correction of the Ga flux to maintain a constant metal/N ratio. We also examine the impact of extreme miniaturization of the QDs, achieved through a reduction of their growth time, on the spectral behavior and internal quantum efficiency (IQE). The high Al content results in QDs with a reduced aspect ratio (height/diameter) and thicker wetting layer when compared to the GaN/AlN system. Self-assembled QDs grown with a metal/N ratio ranging from 0.5 to 0.8 show an IQE around 50%, independent of the Al content (up to 65%) or emission wavelength (300-230 nm). However, samples emitting at wavelengths below 270 nm exhibit a bimodal luminescence associated with inhomogeneous in-plane emission attributed to fluctuations of the QD shape associated with extended defects. Reducing the QD size exacerbates the bimodality without reducing the emission wavelength. The power efficiencies under electron beam pumping range from 0.4% to 1%, with clear potential for improvement through surface treatments that enhance light extraction efficiency.

physics.app-ph↗
arXiv2021

AlGaN/GaN asymmetric graded-index separate confinement heterostructures designed for electron-beam pumped UV lasers

We present a study of undoped AlGaN/GaN separate confinement heterostructures designed to operate as electron beam pumped ultraviolet lasers. We discuss the effect of spontaneous and piezoelectric polarization on carrier diffusion, comparing the results of cathodoluminescence with electronic simulations of the band structure and Monte Carlo calculations of the electron trajectories. Carrier collection is significantly improved using an asymmetric graded-index separate confinement heterostructure (GRINSCH). The graded layers avoid potential barriers induced by polarization differences in the heterostructure and serve as strain transition buffers which reduce the mosaicity of the active region and the linewidth of spontaneous emission.

physics.optics↗
arXiv2019

Light / heavy hole switching with correlated characterization on a single quantum dot : Probing the light hole / heavy hole switching with correlated magneto-optical spectroscopy and chemical analysis on a single quantum dot

A whole series of complementary studies have been performed on the same, single nanowire containing a quantum dot: cathodoluminescence spectroscopy and imaging, micro-photoluminescence spectroscopy under magnetic field and as a function of temperature, and energy-dispersive X-ray spectrometry and imaging. The ZnTe nanowire was deposited on a Si 3 N 4 membrane with Ti/Al patterns. The complete set of data shows that the CdTe quantum dot features the heavy-hole state as a ground state, although the compressive mismatch strain promotes a light-hole ground state as soon as the aspect ratio is larger than unity (elongated dot). A numerical calculation of the whole structure shows that the transition from the heavy-hole to the light-hole configuration is pushed toward values of the aspect ratio much larger than unity by the presence of a (Zn,Mg)Te shell, and that the effect is further enhanced by a small valence band offset between the semiconductors in the dot and around it.

cond-mat.mes-hall↗
arXiv2018

Shot noise limited nanomechanical detection and radiation pressure backaction from an electron beam

Detecting nanomechanical motion has become an important challenge in Science and Technology. Recently, electromechanical coupling to focused electron beams has emerged as a promising method adapted to ultra-low scale systems. However the fundamental measurement processes associated with such complex interaction remain to be explored. Here we report highly sensitive detection of the Brownian motion of um-long semiconducting nanowires (InAs). The measurement imprecision is found to be set by the shot noise of the secondary electrons generated along the electromechanical interaction. By carefully analysing the nano-electromechanical dynamics, we demonstrate the existence of a radial backaction process which we identify as originating from the momentum exchange between the electron beam and the nanomechanical device, which is also known as radiation pressure.

cond-mat.mes-hall↗
arXiv2013

Optical properties of single ZnTe nanowires grown at low temperature

Optically active gold-catalyzed ZnTe nanowires have been grown by molecular beam epitaxy, on a ZnTe(111) buffer layer, at low temperature 350\degree under Te rich conditions, and at ultra-low density (from 1 to 5 nanowires per micrometer^{2}. The crystalline structure is zinc blende as identified by transmission electron microscopy. All nanowires are tapered and the majority of them are <111> oriented. Low temperature micro-photoluminescence and cathodoluminescence experiments have been performed on single nanowires. We observe a narrow emission line with a blue-shift of 2 or 3 meV with respect to the exciton energy in bulk ZnTe. This shift is attributed to the strain induced by a 5 nm-thick oxide layer covering the nanowires, and this assumption is supported by a quantitative estimation of the strain in the nanowires.

cond-mat.mtrl-sci↗
arXiv2012

Structural recovery of ion implanted ZnO nanowires

Ion implantation is an interesting method to dope semiconducting materials such as zinc oxide provided that the implantation-induced defects can be subsequently removed. Nitrogen implantation followed by anneals under O2 were carried out on zinc oxide nanowires in the same conditions as in a previous study on bulk ZnO [J. Appl.Phys. 109, 023513 (2011)], allowing a direct comparison of the defect recovery mechanisms. Transmission electron microscopy and cathodoluminescence were carried out to assess the effects of nitrogen implantation and of subsequent anneals on the structural and optical properties of ZnO nanowires. Defect recovery is shown to be more effective in nanowires compared with bulk material due to the proximity of free surfaces. Nevertheless, the optical emission of implanted and annealed nanowires deteriorated compared to as-grown nanowires, as also observed for unimplanted and annealed nanowires. This is tentatively attributed to the dissociation of excitons in the space charge region induced by O2 adsorption on the nanowire surface.

cond-mat.mtrl-sci↗