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Influence of Growth Temperature and Scandium Concentration on the Surface Oxidation of ScAlN Films Grown by Molecular Beam Epitaxy
No full textInternational audienceRecently, there has been a large interest in the ScAlN alloy, thanks to its various applications in high-frequency highpower, acoustoelectric, and ferroelectric devices. Nonetheless, these applications could be impaired by defects present in the ScAlN alloy, such as oxygen impurities, a very prevalent defect due to the high oxygen affinity of scandium. Recent trends in ScAlN growth such as lowering growth and increasing Sc content could have an effect in the appearance of these impurities. Considering this, we have studied the influence of growth temperature and Sc content in the surface oxide and oxygen content of ScAlN films grown by ammonia source molecular beam epitaxy and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and angle resolved-X-ray photoelectron spectroscopy
Stress and doping analysis of low n-doped GaN layers grown on GaN, silicon and sapphire substrates by micro-Raman 2. Physics and characterization
No full textInternational audienceVertical GaN power devices counters the drawbacks of the lateral ones. The best performances are observed with vertical GaN-on-GaN, but the absence of large GaN substrates makes the homoepitaxy option less marketable than the heteroepitaxy one. However, thick heteroepitaxial GaN drift layers must exhibit a low biaxial stress and a low ndoping density. Monitoring these properties of GaN layers are therefore crucial issues for vertical GaN power devices development. Here, a methodology is proposed, using non-destructive micro-Raman, to analyze biaxial stress and ndoping density for low n-doped GaN layers (< 10 17 cm -3 ) independently of the substrate type (GaN, silicon and sapphire).The variation of A 1 (LO) and E 2 H GaN Raman shifts (ω A1 , ω E2 ) due to biaxial stress (σ B ) and the n-doping density (n)Combining these two equations, ω A1 can be linearly correlated to ω E2 , with a slope (S=K B A1 ⁄K B E2 ) independent of the biaxial stress and a y-intercept g(n) increasing with n. Micro-Raman 2D-mapping shows that samples display the expected behavior concerning the biaxial stress: GaN-onsapphire layers exhibit the highest values of the ω A1 and ω E2 (compressive stress) while GaN-on-silicon layers have the lowest ones (tensile tress). In addition, results agree with the proposed relationship between ω A1 and ω E2 , such that regardless of the substrate, the slope S is similar. Hence, this work refines S to 0.78 ± 0.03, compared to the literature (0.28 to 0.80 [1,2]). Moreover, as expected, the y-intercept increases with the sample n-doping level, regardless of its substrate. Present results can then be used as a benchmark for estimating n-doping level and inhomogeneity of low n-doped GaN layers.This study shows that micro-Raman is an effective technique for analyzing the low doped and low strain layers required for the next generation of vertical GaN power devices. Furthermore, the final publication will correlate these micro-Raman results with other electrical and physical characterizations
An elliptical SRR low-profile multiband antenna-backed AMC for wireless applications and satellite communications
No full textInternational audienceAbstract This paper presents a low-profile, triple-band elliptical coplanar waveguide-fed antenna designed using the split-ring resonator technique. An artificial magnetic conductor with three zero-phases of the reflection coefficient is incorporated as a reflector to improve the antenna gain. The results show a gain enhancement of 3.4, 5.65, and 1.5 dBi at the three frequency bands of interest centered on 2.45, 5.2, and 8 GHz, respectively. The first two operational bands are Industrial, Scientific and Medical bands (2.33–2.59 and 4.97–5.48 GHz) that can be particularly used for wireless local area network and Bluetooth applications, while the third band (7.48-8.59 GHz) is suitable for military and satellite communications. The proposed solution that is designed, fabricated, and tested exhibits a good agreement between measured and simulated results
Sprinting performance correlates with composite indices of femoral neck strength in middle-aged active men
No full textInternational audienceThe aim of the current study was to explore the relationships between 20-meter sprinting time and composite indices of femoral neck strength (compression strength index (CSI), bending strength index (BSI) and impact strength index (ISI)) in a group of middle-aged active men. 50 middle-aged active men voluntarily participated in this study. Their mean age was 45 ± 8.6 years. Body composition, total hip bone mineral density (TH BMD) and femoral neck bone mineral density (FN BMD) were evaluated by DXA. Sprinting time was negatively correlated to CSI (r = -0.52; p < 0.001), BSI (r = -0.43; p < 0.01) and ISI (r = -0.47; p < 0.001). The significant correlations between sprinting time and composite indices of femoral neck strength (CSI, BSI and ISI) remained significant after controlling for body weight, age and maximum oxygen consumption using multiple linear regressions. In conclusion, the current study suggests that sprinting performance (m/sec) is a positive determinant of CSI, BSI and ISI in middle-aged men
PEPR ADICT: Fabrication of RF switches based on MoS and WS
No full textNational audienceIn the framework of the ADICT project, the partner IEMN-CARBON aims to produce components based on 2D materials [1-3], for targeted PEPR projects. The aim is to extract their electrical properties and propose applications for high-frequency analogue electronics.The first components to be explored are RF switches based on 2D materials.Our work has led us to develop technological processes that are compatible with those of our partners (CEA Leti). The material used is MoS2 by ALD (Atomic Layer Deposition) growth, requiring a wet or dry transfer step. The growth and the fabrication process are managed on a 200 mm silicon substrate.This approach will be compatible with materials obtained by MBE (Molecular Beam Epitaxy) growth.A second approach has been developed with our partners at LAF, where 2D materials (WS2) are obtained by PLD (Pulse Laser Deposition) growth, requiring no transfer step, given the lower thermal budget.The performance of the devices obtained is in line with the simulations carried out at IEMN. The performances obtained are already state-of-the-art for this type of component
Nanoconfinement‐Induced Electrochemical Ion‐Solvent Cointercalation in Pillared Titanate Host Materials
No full textInternational audienceAbstract Electrochemical ion‐solvent cointercalation reactions are an avenue to reach improved kinetics compared to the corresponding intercalation of desolvated ions. Here, we demonstrate the impact of different structural pillar molecules on the electrochemical Li + intercalation mechanism in expanded hydrogen titanate (HTO) electrode materials. We show that interlayer‐expansion of HTO with organic pillars can enable cointercalation reactions. Their electrochemical reversibility is drastically improved when non‐cross‐linking pillars are employed that expand and separate the host material's individual layers, underlining the impact of the electrochemo‐mechanics of the nanoconfined interlayer space. This pillared HTO structure results in an increased Li + storage capacity and reversibility compared to pristine HTO. We derive structural models of the pillared HTO host materials based on combined experiments and theoretical calculations, and employ electrochemical operando experiments to unambiguously demonstrate the nanoconfinement‐induced cointercalation mechanism in pillared HTO electrode materials. The work demonstrates the potential of nanoconfined pillar molecules to modify host materials and enable highly reversible cointercalation reactions with improved capacity and kinetics
Orbiting, colliding and merging droplets on a soap film: toward gravitational analogues
No full textModern telescopes provide breathtaking images of nebulae, clouds and galaxies shaped by gravity-driven interactions between complex bodies. While such structures are prevalent on an astrophysical scale, they are rarely observed at the human scale. In this letter, we report the observations of the complex orbits, collision, and coalescence of droplets on a soap film, forming structures such as bridges and spiral arms, reminiscent of their astrophysical counterparts. These dynamics emerge from attractive forces caused by gravito-capillary-driven distortions of the supporting soap film. Long orbits and intricate coalescence mechanisms are enabled by the small dissipation in the soap film and the fluidic nature of the droplets and supporting film, respectively. The existence of stable droplets within the soap film featuring a universal radius, as well as the attractive potentials, are explained through a careful comparison of experimental data with models computing the distortions of the supporting soap film. This work opens perspectives to study analogies between phenomena occurring at dramatically different length and time scales
IDTC Special Issue. Newton's Principia & Newtonian Mechanics: Foundations, Heritage, Methodology, Editions, Popularization and Nature of Science Teaching
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