Fil métallique | EPFL Graph Search

Un fil métallique est un type de fil formé de métal par tréfilage, c'est-à-dire l'étirage d'une matière ductile. Une argue est l'appareil traditionnel servant à filer l'or et l'argent. Les fils métalliques sont constitués de diverses matières, pour différents usages :

"fil de fer", en général en acier ;
fil de cuivre ;
fil d'étain ;
fil d'or ;
fil d'argent ;
fil de tungstène ;

Fil de fer Le fil de fer est formé de fer ou d'acier. Il est résistant en traction, mais aussi déformable. Fil de fer Fil de cuivre vignette|Fils électriques en cuivre Appelé aussi fil d'archal. Le fil de cuivre est utilisé comme conducteur électrique. Il sert aussi à mettre en forme les bonsaïs. Fil d'étain Il est utilisé pour la brasure de composants électriques ou électroniques. Il se présente sous forme de bobine. Fil d'or On retrouve le fils d'or dans la trame de certains tissus ou tapisseries. Le fil d'or peut être utilisé pour la broderie

Fluctuations de l'aimantation induites par des courants de haute densité dans des vannes de spin électrodéposées

Andrea Fabian Montabert

Copper wires each one containing a pseudo-spin valve of Co/Cu/Co were produced by electrodeposition inside nanoporous polycarbonate membranes. These wires have a diameter of 40 nm and a length of 6000 nm of which only 50 nm relates to the spin valve. In order to be able to measure the magnetic behavior of a single wire, the entire deposition was carried out in a Co/Cu multibath and then electrical contact of a single wire was done with a special equipment using a pure Copper bath. Knowing that such wire has a resistance of the order of 500 Ω, with a Giant Magneto-Resistance ratio of about 0.2 %, one needs a sufficiently sensitive measuring apparatus be able to detect such variations. After having carried out a magnetoresistive characterization, we used a set-up built with a Wheatstone bridge in which the sample is integrated. The resistance variation associated with the magnetization reversal being weak, we were very concerned with the sample quality during these three years of research. As high current densities are injected, a behavior of "Two Level Fluctuation" appeared between parallel and antiparallel states. Such phenomena can be treated only by statistics. Therefore, several thousands of measurements were taken in order to be able to understand the statistical behaviors of the current induced magnetization switching. To better understand the mechanisms of the reversal, we studied its dynamics with a model of double potential well by measuring the average time of residence in parallel (respectively in antiparallel) state as a function of current and applied field for different amplitudes and signs. From our analyses, it arises clearly that the dynamics of the magnetization reversal induced by a high current density, in pseudo-spin valves, could be formulated in terms of Spin-Transfer-Torque. We show that the agreement with this model is remarkable.

EPFL2004

Synthesis and characterization of group II-Vi semiconductor nanowires

Holger Jens Böttcher

Semiconductor nanowires are an emerging class of nanostructures that represent attractive building blocks for nanoscale electronic and photonic devices. To the present, nanowires are synthesized on a small scale by experimentally demanding gas phase deposition techniques. This thesis describes a simple and cost-efficient solution-based synthesis towards high-quality nanowires of Group II-VI compound semiconductors. The effects of various reaction parameters and of doping on the wires' structural, electrical and magnetic properties are investigated. The first part of this thesis is dedicated to a novel variant of the solvothermal synthesis of CdS nanowires employing a single-source precursor. The wires are of single-crystalline quality and can be indexed to wurtzite-type bulk CdS with the preferential growth direction along the axis. As-grown nanowires have a smooth surface, are up to 40 µm long and exhibit aspect ratios up to 1000. The wires' aspect ratio can be increased by choosing a low precursor concentration. Time-dependent experiments reveal the wires to axially grow at a rate of ≈1µm/h while lateral growth only occurs during the initial reaction phase. As shown by photoluminescence spectroscopy the surface defect density can be significantly lowered by raising the reaction temperature from 180 to 200 °C. Electrically contacted CdS nanowires are highly resistive in the dark, but become more conductive by 4 orders of magnitude upon illumination above the bandgap energy (λ

EPFL2010

Metal-wire-embedded alumina insulating material using micro- and nanoscale 3D printing for surface flashover mitigation in a vacuum

Guang-Yu Sun

A micro- and nanoscale 3D printing technique is applied to fabricate a functional insulating material that mitigates surface discharge in a vacuum based on microscopic electron multipactor suppression. The proposed alumina ceramic insulator design consists of surface-embedded thin metal wires that introduce a local gradient of secondary electron emission (SEE) yield, such that the trajectories of multipactor electrons are distorted by accumulated negative surface charge and the SEE avalanche across the insulator surface becomes intermittent. Considerable increases of surface flashover threshold and surface charging reduction are verified by the experiment. Also, additional efforts are made to determine the optimal size and spatial distribution of the metal wire. A convex-shape flashover voltage trace is observed when increasing the width of the wire, suggesting a trade-off between the multipactor mitigation and the insulator strength. The wire's position between the adjacent cathode triple junction and the middle of the insulator is proved to be favorable for flashover mitigation. The physical details of surface flashover mitigation by the proposed insulator design are revealed by an ab initio particle-in-cell simulation code, corroborating the experiment from a microscopic aspect.

2022

Fluctuations de l'aimantation induites par des courants de haute densité dans des vannes de spin électrodéposées

Andrea Fabian Montabert

EPFL2004