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On the importance of Ni-Au-Ga interdiffusion in the formation of a Ni-Au / p-GaN ohmic contact
No full textInternational audienceThe Ni-Au-Ga interdiffusion mechanisms taking place during rapid thermal annealing (RTA) under oxygen atmosphere of a Ni-Au/p-GaN contact are investigated by high-resolution transmission electron microscopy (HR-TEM) coupled to energy dispersive X-ray spectroscopy (EDX). It is shown that oxygen-assisted, Ni diffusion to the top surface of the metallic contact through the formation of a nickel oxide (NiOx) is accompanied by Au diffusion down to the GaN surface, and by Ga out-diffusion through the GaN/metal interface. Electrical characterizations of the contact by Transmission Line Method (TLM) show that an ohmic contact is obtained as soon as a thin, Au-Ga interfacial layer is formed, even after complete diffusion of Ni or NiOx to the top surface of the contact. Our results clarify that the presence of Ni or NiOx at the interface is not the main origin of the ohmic-like behavior in such contacts. Auto-cleaning of the interface during the interdiffusion process may play a role, but TEM-EDX analysis evidences that the creation of Ga vacancies associated to the formation of a Ga-Au interfacial layer is crucial for reducing the Schottky barrier height, and maximizing the amount of current flowing through the contact
Thickness Dependence in Phase Formation and Properties of TaSe2 Layers Grown on GaP(111)B
No full textA CC-BY public copyright license has been applied by the authors to the present document and will be applied to all subsequent versions up to the Author Accepted Manuscript arising from this submission, in accordance with the grant’s open access conditions.International audienceThe effect of growth temperature and subsequent annealing on the epitaxy of both single- and few-layer TaSe2 on Se-terminated GaP(111)B substrates is investigated. The selective growth of the 1T and 1H phases is shown up to 1 ML according to X-ray and ultraviolet photoelectron spectroscopies. The 1H monolayer, favored at low temperatures, exhibits a very homogeneous coverage after annealing, while the 1T ML, grown at high temperatures, is characterized by a better in-plane orientation. Moreover, X-ray photoelectron diffraction spectroscopy performed on 1T submonolayers shows a negligible amount of mirror twins. By contrast, in multilayers, scanning transmission electron microscopy always reveals a mixture of 2Ha and 3R polytypes with very few 1T. In addition, the multilayers become Se-deficient above 500 °C, and a new interfacial phase identified as Ta1+xSe2 or TaP appears. Finally, the optimized multilayers grown between 250 and 500 °C exhibit a similar metallic behavior with a resistivity comparable to the bulk one with valuable outcomes in the formation of electrical contacts for two-dimensional (2D) material-based devices
The electrochemical performance of Ta2O5 thin films in ionic liquid and ionogel electrolytes
No full textInternational audienceIn this work, we present a new cell design for miniaturized energy storage devices by realizing a hybrid microcapacitor, which uses for the first time a TaN/ Ta 2 O 5 thin film electrode in combination with a MnO 2 composite electrode. In this proof of concept study, the electrochemical performance of the dielectric material Ta 2 O 5 was of main interest. Therefore, various tantalum oxide films with different thicknesses from 23 to 80 nm have been tested in combination with a pseudocapacitive oversized MnO 2 composite electrode. This was done with two model electrolytes, namely the ionic liquid Emim FSI and the solid-state ionogel Emim FSI: PVdF 80:20. Surface capacitance values up to 1.94 µF cm -2 in Emim FSI and 2.84 µF cm -2 in IG Emim TFSI: PVdF 80:20 have been reached at high scan rates (100 mV s -1 ) with no significant distortion of the voltammograms. When films of 47 and 80 nm thickness of Ta 2 O 5 are used, stable cycling with scan rates of up to 5000 mV s -1 at a cell voltage of 20 V can be achieved even in solid-state ionogel electrolyte. This performance highlights the promising characteristics of these materials and cell concept for miniaturized high power energy storage application and opens the way for further investigations to improve this needed technology
Fe3O4 decorated hexagonal boron nitride nanosheets enhanced surface-assisted laser desorption/ionization mass spectrometry & mass spectrometry imaging for rapid and sensitive detection of synthetic antioxidants
No full textInternational audienceSynthetic antioxidants have become increasingly common pollutants across various environmental matrices, raising concerns about their potential migration into food and subsequent ingestion by humans. In this work, Fe3O4@hexagonal boron nitride nanosheets (Fe3O4@BN) composite was fabricated by a hydrothermal method and applied as inorganic matrix for the analysis of various synthetic antioxidants (2,6-di-tert-butyl-hydroxytoluene, dibenzothiazine, Irganox 2246, Irganox 565, and tns-(2.4-di-tert-butyl)-phosphite) by surface-assisted desorption/ionization mass spectrometry (SALDI-MS). The limit of detection of 2,6-di-tert-butyl-hydroxytoluene (BHT) in aquaculture wastewater and Irganox 565 in human serum were 0.25 and 1 µg/L, respectively. Moreover, quantitative detection of tns-(2.4-di-tert-butyl)-phosphite (AO 168) in exposed cactus samples was assessed by laser desorption/ionization mass spectrometry imaging (LDI-MSI) using Fe3O4@BN inorganic matrix. AO 168 was determined within the 10–1000 µg/L linear range with a limit of detection of 2.5 µg/L. The results demonstrated that the Fe3O4@BN nanocomposite offers excellent sensitivity and effectively detect synthetic antioxidants when applied to real-world samples using SALDI-MS & MSI
Introducing the Essays in Cultural, Fundamental and Technological Frameworks. Part I
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Papers submitted by the PhD candidate: AI-based Driving Assistance: Deliverable 9.1
No full textWork Package 9 has started with the recruitment of Jean-Valentin Merlevede who is working at UPHF since October 1st 2023 and supervision with SUPSI has been initiated at this date. Unfortunately, no collaboration has been achieved with SNCF nor RAILENIUM during M1 to M24. However, a new industrial partner (ALSTOM Italy) has participated in several remote meetings (in March, June and December 2024) to discuss the opportunity of research challenges raised by the project. A 2 months visiting scholar has been organized at SUPSI for co-supervision of PhD activities. Partner has offered seminar and access to laboratory to increase AI knowledge of PhD student.Scientific contributions (M1 to M24) can be summarized into two points:1. State-of-the-art about key concepts. The step has consisted in identifying the main scientific advances about the development of ICT for train cabin, of train driving assistances, and of their impact on drivers’ behaviours. The research has selected the disruptive supports that can be usedfor the PhD thesis and the driving tasks to be assisted on GoA.2. Implementation of configurations of GoA integrating driving assistance and ICT. With regard to the outputs of the first step, this part of the thesis has developed models for assisting drivers and for monitoring them.The lack of financial support has led partners to find external possibilities to organize long visiting scholar. Many student mobility calls have been answered successfully by M. Merlevede to reach this objective. The 2-months visiting scholar at SUPSI was financed by a French regional project andSUPSI funding. We cannot be sure that new visiting period will be organized till the end of the project.A new contribution is now under investigation by PhD candidate. It concerns proposal for new ways to design and validate AI-based driving assistance. The models of the second step of the project could be used to propose new ways for designing and validating driving assistances in railway (M24 to M42)
Tribological characterization of contacts in the temporomandibular joint
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