Synthesis of Functionalized Few-Layer Graphene Through Fast Electrochemical Expansion of Graphite

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Transport property study of MgO-GaAs(001) contacts for spin injection devices

International audienceThe electrical properties of Au/MgO/n-GaAs(001) tunnel structures have been investigated with capacitance-voltage and current-voltage measurements at room temperature with various MgO thicknesses between 0.5 and 6.0nm. For an oxide thickness higher than 2nm and for low bias voltages, the voltage essentially drops across the oxide and the structure progressively enters the high-current mode of operation with increasing reverse bias voltage, the property sought in spin injection devices. In this mode, we demonstrate that a large amount of charge accumulates at the MgO/GaAsinterface in interface traps located in the semiconductor band gap

DMTs and Covid-19 severity in MS: a pooled analysis from Italy and France

We evaluated the effect of DMTs on Covid-19 severity in patients with MS, with a pooled-analysis of two large cohorts from Italy and France. The association of baseline characteristics and DMTs with Covid-19 severity was assessed by multivariate ordinal-logistic models and pooled by a fixed-effect meta-analysis. 1066 patients with MS from Italy and 721 from France were included. In the multivariate model, anti-CD20 therapies were significantly associated (OR = 2.05, 95%CI = 1.39–3.02, p < 0.001) with Covid-19 severity, whereas interferon indicated a decreased risk (OR = 0.42, 95%CI = 0.18–0.99, p = 0.047). This pooled-analysis confirms an increased risk of severe Covid-19 in patients on anti-CD20 therapies and supports the protective role of interferon

Electrical and thermal spin injection in semiconductors

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Electrical and thermal spin injection in semiconductors

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Barrière tunnel épitaxiées de MgO sur GaAs(001) (croissance, propriétés électroniques et électriques)

Cette thèse a pour cadre l effort réalisé actuellement pour injecter un courant polarisé en spin dans un semiconducteur. Le moyen le plus prometteur pour cela est l utilisation d une électrode métallique magnétique déposée sur une barrière tunnel de MgO épitaxié sur GaAs. Nous déposons les couches de MgO sur des surfaces de GaAs(001) sous ultravide ou sous atmosphère d O2, à température ambiante. Les propriétés structurales telles que la relations d épitaxie, la réactivité aux interfaces ou les offsets de bande ont été étudiés par RHEED et XPS. Des mesures de transport (I-V, C-V) sur des jonctions Au/MgO/GaAs nous ont permis de mieux comprendre les mécanismes de transport mais ont montré que notre structure ne remplissait pas les critères énoncés par Fert pour une injection efficace de courant polarisé dans GaAs. Pour s approcher de ces critères d injection, des modifications des conditions de dépôt et/ou de l architecture de nos structures ont alors été avancées puis testée.The background of this work is the growing development of spintronic devices combining ferromagnetic materials (spin source) and semi-conductors (spin manipulation medium). The main goal of this thesis is the study of the growth, physical-chemical properties and tunnel spin injection into the Fe/MgO/GaAs(001) system. Structure properties, chemical reactivity and band offsets have been studied by RHEED and XPS. Transport measurement (I-V, C-V) on Au/MgO/GaAs structures have been achieved to better understand the transport mechanisms through the barrier but showed the interface resistance does not fulfil Fert s criteria for efficient spin injection. Modifications of the growth conditions and/or our structures design have therefore been proposed and tested.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Thermal creation of a spin current by Seebeck spin tunneling

International audienceThe thermoelectric analog of spin-polarized tunneling, namely Seebeck spin tunneling, is a recently discovered phenomenon that arises from the spin-dependent Seebeck coefficient of a magnetic tunnel contact. In a tunnel junction with one ferromagnetic electrode and one non-magnetic electrode, a temperature difference between the two electrodes creates a spin current across the contact. Here, the basic principle and the observation of Seebeck spin tunneling are described. It is shown how it can be used to create a spin accumulation in silicon driven by a heat flow across a magnetic tunnel contact, without a charge tunnel current. The sign of the spin current depends on the direction of the heat flow, whereas its magnitude is anisotropic, i.e., dependent on the absolute orientation of the magnetization of the ferromagnet. The connection between Seebeck spin tunneling and the tunnel magneto-Seebeck effect, observed in metal magnetic tunnel junctions, is also clarified. Seebeck spin tunneling may be used to convert waste heat into useful thermal spin currents that aid or replace electrical spin current, and thereby improve the energy efficiency of spintronic devices and technologies. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Transport properties study of MgO/GaAs(001) contacts for spin injection in unipolar devices

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