Publications

2024

• Gallium nitride deposition via magnetron sputtering: Linking plasma-surface interactions and thin film crystalline features
  
  • Srinivasan Lakshman
  • Gazeli Kristaq
  • Prasanna Swaminathan
  • Invernizzi Laurent
  • Roca I Cabarrocas Pere
  • Lombardi Guillaume
  • Ouaras Karim
  Vacuum, Elsevier, 2024, 224, pp.113185. Ga-atoms dynamic in an Ar/N2 magnetron sputtering discharge for GaN deposition is explored employing plasma diagnostic techniques such as optical emission spectroscopy and microwave interferometry. Through the assessment of gas temperature, electron temperature and density measured from the abovementioned diagnostics, we estimated both the flux and average energy of Ga-atoms impinging on the substrate. Emphasizing the working pressure as a pivotal factor, this study uncovers a correlation between the Ga-atoms flux, their average energy, and the growth rate and crystallinity of the GaN films extracted from ex-situ characterizations. Notably, the pressure value (6.6 Pa) at which both the growth rate and crystalline fraction are the greatest is also the condition at which both the flux and energy of Ga-atoms impinging on the target are maximal. The findings pave the way for improving the understanding and control of the complex interplay between plasma conditions and resulting film properties in the sputtering process. (10.1016/j.vacuum.2024.113185)
  DOI : 10.1016/j.vacuum.2024.113185
• Dimesitylborane as Electron Accepting Unit in High Performance Yellow Single‐Layer Phosphorescent Organic Light Emitting Diode
  
  • Brouillac Clément
  • Lucas Fabien
  • Ari Denis
  • Lebreton Christophe
  • Jeannin Olivier
  • Rault-Berthelot Joëlle
  • Quinton Cassandre
  • Jacques Emmanuel
  • Poriel Cyril
  Small, Wiley-VCH Verlag, 2024, pp.2405312. A new host material for Single‐Layer Phosphorescent Organic Light‐Emitting Diodes (SL‐PhOLED) is reported, namely SPA‐2‐FDMB, using the dimesitylborane (DMB) fragment as an acceptor unit. The molecular design is constructed on the general donor‐spiro‐acceptor architecture, which consists of connecting, via a spiro bridge, a donor and an acceptor units in order to avoid strong interaction between them. The DMB fragment is known for many electronic applications (notably Aggregation‐Induced Emission) but has not been used yet for SL‐PhOLED applications. This appears particularly interesting, as the development of this simplified technology has shown that only a few electron‐accepting fragments such as diphenylphosphine oxide can provide high‐performance devices. Herein, the yellow‐emitting SL‐PhOLED using SPA‐2‐FDMB as host presents an External Quantum Efficiency of 8.1% (Current Efficiency of 24.9 cd.A−1) with a low threshold voltage of 2.6 V. As SPA‐2‐FDMB presents a sharp HOMO/LUMO difference, the good matching of HOMO and LUMO energy levels with the Fermi level of the electrodes is responsible for these performances. The low LUMO level of −2.61 eV also appears particularly important. These performances are, to date, the highest reported for a yellow/orange‐emitting SL‐PhOLED and show the potential of DMB unit in the single‐layer technology. (10.1002/smll.202405312)
  DOI : 10.1002/smll.202405312
• Microlayer evaporation during bubble growth in nucleate boiling
  
  • Tecchio Cassiano
  • Cariteau Benjamin
  • Le Houedec Corentin
  • Bois Guillaume
  • Saikali Elie
  • Zalczer Gilbert
  • Vassant Simon
  • Roca I Cabarrocas Pere
  • Bulkin Pavel
  • Charliac Jérôme
  • Nikolayev Vadim
  International Journal of Heat and Mass Transfer, Elsevier, 2024, 231, pp.125860. We experimentally investigate the near-wall heat transfer at single bubble growth in nucleate saturated pool boiling of water at atmospheric pressure. Our focus is on the evaporation of the micro-metric thin film of liquid (microlayer) that is formed between the heating wall and the bubble. High speed and high resolution optical techniques are employed. Synchronous and simultaneous measurements of the microlayer thickness, wall temperature and bubble macroscopic shape are performed by white light interferometry, infrared thermography and side-wise shadowgraphy, respectively. We measure the wall temperature of an ITO heating film through a transparent to the infrared waves porthole. The heating is provided by an infrared laser. The wall heat flux is numerically reconstructed by using the experimental wall temperature data. We reveal a temporal rise of the thermal resistance of the liquid–vapor interface during the microlayer evaporation, which corresponds to a decrease of the accommodation coefficient. We attribute it to the progressive accumulation of impurities at the interface during evaporation. The contribution of microlayer evaporation to the overall bubble growth is about 18%. (10.1016/j.ijheatmasstransfer.2024.125860)
  DOI : 10.1016/j.ijheatmasstransfer.2024.125860
• Nucleation of nanodiamonds in H-atom rich microplasma
  
  • Siby Abdoulaye Constant
  • Bhakta Arvind K
  • Jeevan Joel
  • Sun Xiaonan
  • Decorse Philippe
  • Ammar Souad
  • Hassouni Khaled
  • Prasanna Swaminathan
  Diamond and Related Materials, Elsevier, 2024. <div><p>In this study, the formation and properties of carbon nanostructures obtained from a low-pressure-low temperature microplasma operated with H$_2$/CH$_4$ gas precursors were investigated. The study reveals gas phase nucleation of nanodiamonds among other phases of carbon such as graphite and amorphous carbon. Raman spectroscopy revealed that the signature of the nanostructures produced was insensitive to the nature of the substrate. The main conclusion of the paper is that nucleating of nanodiamonds is sustained by high densities of H-atoms at moderate gas temperatures and optimum concentrations of hydrocarbon radicals and molecules. High densities of hydrocarbons push the equilibrium towards sp$^2$ and amorphous nanostructures even under high H-atom densities.</p></div> (10.1016/j.diamond.2024.111933)
  DOI : 10.1016/j.diamond.2024.111933
• Stability under electron irradiation of some layered hydrated minerals
  
  • de Noirfontaine Marie-Noëlle
  • Courtial Mireille
  • Alessi A.
  • Tusseau-Nenez Sandrine
  • Garcia-Caurel E.
  • Cavani Olivier
  • Cau Dit Coumes Céline
  • Gorse–pomonti Dominique
  Journal of Solid State Chemistry, Elsevier, 2024, 340, pp.125033. The structural damages caused to some layered hydrated minerals by 2.5 MeV electron irradiation using the SIRIUS platform were studied by powder X-Ray diffraction and, in some cases, by 1H MAS-NMR spectroscopy. It is clearly demonstrated that the radiation damages are distinguishable from the heating effects. It is shown that: i) in all cases electron irradiation leads to distortions of the unit cell and very limited volume expansion, compared to heating; ii) radiation damages increase with increasing the structural complexity of the mineral; iii) portlandite Ca(OH)2 and brucite Mg(OH)2 remain crystalline up to high doses (a few GGy), with appearance of stacking fault disorder especially in brucite; iv) brushite CaHPO4.2H2O and gypsum CaSO4.2H2O undergo a phase transformation of type amorphization for brushite involving the strongest intralayer H bond between the acidic proton and the phosphate tetrahedral, and decomposition for gypsum involving interlayer H bonds between water molecules. (10.1016/j.jssc.2024.125033)
  DOI : 10.1016/j.jssc.2024.125033
• Field emission characterization of field-aligned carbon nanotubes synthesized in an environmental transmission electron microscope
  
  • Vincent Pascal
  • Panciera Federico
  • Florea Ileana
  • Ayari Anthony
  • Perisanu Sorin
  • Cojocaru Costel Sorin
  • Taoum Haifa
  • Wei Chen
  • Saidov Khakimjon
  • Mirsaidov Utkur
  • Aguili Ilias
  • Blanchard Nicholas
  • Legagneux Pierre
  • Purcell Stephen Thomas
  Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics, AVS through the American Institute of Physics, 2024, 42 (2), pp.022802. Optimizing the synthesis of carbon nanotubes (CNTs) for applications like field emission (FE) sources requires a fundamental understanding of the growth kinetics of individual CNTs. In this article, we explore how applying electric fields during CNT synthesis influences the as-grown nanotubes and their FE performance. We observe growth and undertake FE measurements in real time using an environmental transmission electron microscope. This is achieved through a polarizable capacitor gap within a microchip sample heater specifically designed for this purpose. Individual nanotubes are easily resolved and are predominantly single-wall CNTs. At low-applied fields, the growing nanotubes can span the gap and link with the opposite electrode, albeit with some loss due to mechanical failure. With a high-applied field and positive bias for FE, we continue to observe the oriented growth of nanotubes. However, this growth is constrained within the gap due to the possibility of FE occurring during the growth process, which can result in either saturation or damage. At any given time, we have the flexibility to halt the growth process and conduct in situ FE experiments. This approach enables us to comprehensively track the complete development of the CNTs and gain insights into the various mechanisms responsible for limiting the performance of CNT cathodes. Interestingly, we report an original self-oscillation induced destruction mechanism that has not been reported before. (10.1116/6.0003413)
  DOI : 10.1116/6.0003413
• Quinolinoacridine as High Efficiency Building Unit in Single-Layer Phosphorescent Organic Light-Emitting Diodes
  
  • Brouillac Clement
  • Lucas Fabien
  • Ari Denis
  • Tondelier Denis
  • Meot Jonathan
  • Malvaux Marc
  • Jadaud Cyril
  • Lebreton Christophe
  • Rault-Berthelot Joëlle
  • Quinton Cassandre
  • Jacques Emmanuel
  • Poriel Cyril
  Advanced Electronic Materials, Wiley, 2024, 10 (1), pp.2300582. The performances of simplified single-layer phosphorescent organic light-emitting diodes (SL-PhOLEDs) have significantly increased and they now appear to be a promising alternative to multi-layer PhOLEDs. The blue and white emissions, far more challenging than all the other colours, are still particularly desired. Herein, a high efficiency host material for blue emitting SL-PhOLED using the blue emitter FIr6 is reported, which is particularly interesting as it displays an emission at shorter wavelengths than the well-known FIrpic emitter, almost exclusively reported in the SL-PhOLEDs literature. The host material investigated herein is constructed on the electron-rich quinolinoacridine and displays when incorporated in FIr6-based SL-PhOLEDs, an external quantum efficiency (EQE)⟩10% and a low Von of 3.1 V. This is the first work passing an EQE of 10% with FIr6 as an emitter. This host also reaches a very high EQE of 19% when used with the green emitter Ir(ppy)2acac, this performance being among the highest recorded for green SL-PhOLEDs. Finally, as white SL-PhOLEDs involve blue emitting SL-PhOLEDs, this host is also used with a combination of blue and yellow emitters. An extremely high EQE of 24% is reached with CIE coordinates of (0.40;0.48). These findings show the real potential of the quinolinoacridine fragment to reach high performance multi-colour SL-PhOLEDs. A high-efficiency host, constructed on electron-rich quinolinoacridine, for blue and green-emitting simplified single-layer phosphorescent organic light-emitting diodes (SL-PhOLEDs), is reported. The performance is among the highest recorded for green SL-PhOLEDs. To gain insights in the development of challenging white SL-PhOLEDs, this host is also used with a combination of blue and yellow emitters, providing a very high external quantum efficiency of 24%.image (10.1002/aelm.202300582)
  DOI : 10.1002/aelm.202300582
• Insights into the growth of GaN thin films through liquid gallium sputtering: A plasma-film combined analysis
  
  • Srinivasan Lakshman
  • Gazeli Kristaq
  • Prasanna Swaminathan
  • Invernizzi Laurent
  • Roca i Cabarrocas Pere
  • Lombardi Guillaume
  • Ouaras Karim
  The Journal of Chemical Physics, American Institute of Physics, 2024, 161 (15), pp.154709. This study presents the detailed characterization of a magnetron-based Ar–N2 plasma discharge used to sputter a liquid Ga target for the deposition of gallium nitride (GaN) thin films. By utilizing in situ diagnostic techniques including optical emission spectroscopy and microwave interferometry, we determine different temperatures (rotational and vibrational of N2 molecules, and electronic excitation of Ar atoms) and electron density, respectively. Beyond providing insights into fundamental plasma physics, our research establishes a significant correlation between gas-phase dynamics, particularly those of gallium atoms (flux and average energy at the substrate) and deposited GaN thin film properties (growth rate and crystalline fraction). These findings underscore the role of plasma conditions in enhancing thin film quality, highlighting the importance of plasma characterization in understanding and optimizing GaN thin film growth processes. (10.1063/5.0226028)
  DOI : 10.1063/5.0226028
• Microlayer in nucleate boiling seen as Landau-Levich film with dewetting and evaporation
  
  • Tecchio Cassiano
  • Zhang Xiaolong
  • Cariteau Benjamin
  • Zalczer Gilbert
  • Roca I Cabarrocas Pere
  • Bulkin Pavel
  • Charliac Jérôme
  • Vassant Simon
  • Nikolayev Vadim
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2024, 989, pp.A4. Both experimental and theoretical studies of fast and microscale physical phenomena occurring during the growth of vapour bubbles in nucleate pool boiling are reported. The focus is on the liquid film of micrometric thickness (a ‘microlayer’) that can form between the heater and the liquid–vapour interface of a bubble. The microlayer strongly affects the macroscale heat transfer and is thus important to be understood. The microlayer appears as a result of the inertial forces that cause the hemispherical bubble shape. It is shown that the microlayer can be seen as the Landau–Levich film deposited by the bubble foot edge during its receding. Paradoxically, the deposition is controlled by viscosity and surface tension. The microlayer profile measured with white-light interferometry, the temperature distribution over the heater, and the bubble shape are observed with synchronised high-speed cameras. According to the numerical simulations, the microlayer consists of two regions: a dewetting ridge near the contact line, and a longer and flatter bumped part. It is shown that the ridge cannot be measured by interferometry because of its intrinsic limitation on the interface slope. The ridge growth is linked to the contact line receding. The simulated dynamics of both the bumped part and the contact line agrees with the experiment. The physical origin of the bump in the flatter part of microlayer is explained. (10.1017/jfm.2024.488)
  DOI : 10.1017/jfm.2024.488
• Reducing two-level system dissipations in 3D superconducting Niobium resonators by atomic layer deposition and high temperature heat treatment
  
  • Kalboussi Yasmine
  • Delatte Baptiste
  • Bira Sarra
  • Dembele Kassiogé
  • Li Xiaoyan
  • Miserque Frederic
  • Brun Nathalie
  • Walls Michael
  • Maurice Jean-Luc
  • Dragoe Diana
  • Leroy Jocelyne
  • Longuevergne David
  • Gentils Aurélie
  • Jublot-Leclerc Stéphanie
  • Julien Gregoire
  • Eozenou Fabien
  • Baudrier Matthieu
  • Maurice Luc
  • Proslier Thomas
  Applied Physics Letters, American Institute of Physics, 2024, 124 (13), pp.134001. Superconducting qubits have arisen as a leading technology platform for quantum computing which is on the verge of revolutionizing the world's calculation capacities. Nonetheless, the fabrication of computationally reliable qubit circuits requires increasing the quantum coherence lifetimes, which are predominantly limited by the dissipations of two-level system (TLS) defects present in the thin superconducting film and the adjacent dielectric regions. In this paper, we demonstrate the reduction of two-level system losses in three-dimensional superconducting radio frequency (SRF) niobium resonators by atomic layer deposition (ALD) of a 10 nm aluminum oxide Al2O3 thin films followed by a high vacuum (HV) heat treatment at 650 {\deg}C for few hours. By probing the effect of several heat treatments on Al2O3-coated niobium samples by X-ray photoelectron spectroscopy (XPS) plus scanning and conventional high resolution transmission electron microscopy (STEM/HRTEM) coupled with electron energy loss spectroscopy (EELS) and (EDX) , we witness a dissolution of niobium native oxides and the modification of the Al2O3-Nb interface, which correlates with the enhancement of the quality factor at low fields of two 1.3 GHz niobium cavities coated with 10 nm of Al2O3. (10.1063/5.0202214)
  DOI : 10.1063/5.0202214