Rayon cathodique

thumb|250px|right|Représentation schématique d'un appareillage d'un tube de Crookes. A est une source d'énergie à faible tension pour chauffer la cathode C (une cathode froide fut utilisée par Crookes). B est une source d'énergie à haute tension afin de stimuler l'anode P recouverte de phosphore. Le masque occultant M est connecté au potentiel de cathode et son image est perçue sur le phosphore comme une zone sombre. Un rayon cathodique est un faisceau d'électrons observé dans un tube à vide, c'est-à-dire dans un tube de verre sous vide équipé d'au moins deux électrodes — une cathode et une anode — dans une configuration connue sous le nom de diode. Lorsque la cathode est chauffée, elle émet une radiation, qui voyage jusqu'à l'anode. Si les parois internes du verre se trouvant derrière l'anode sont recouvertes avec un matériau phosphorescent les électrons incidents induisent un scintillement. L'existence des rayons cathodiques fut initialement supposée lors des premières études dans l

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (40)

Publications associées

Chargement

Personnes associées (6)

, , , , ,

Personnes associées

Chargement

Unités associées (3)

Unités associées

Chargement

Concepts associés (62)

Concepts associés

Chargement

Cours associés (56)

Cours associés

Chargement

Séances de cours associées (124)

Afficher plus

Séances de cours associées

Chargement

Femtosecond electron and X-ray source developments for time-resolved applications

Fernando Ardana Lamas

This manuscript summarizes the different technological developments and scientific activities in the field of ultrafast laser and electron physics which I have carried out as part of my PhD thesis. The topics addressed in my thesis range from the development of a novel electron gun to the construction and operation of a coherent X-ray laser, which I used for the study of ultrafast magnetization dynamics. The work was carried out within the frame of SwissFEL at the Paul Scherrer Institute. Electron sources with a very good beam quality are a prerequisite for the realization of compact free electron lasers. In the first part of my work I will describe a novel electron cathode, which is based on a micro-structured surface. The cathode offers a quantum efficiency 2 orders of magnitude larger than what is achieved with conventional metallic cathodes. Then I will describe a table-top soft x-ray source based on HHG where I have played a major role in the construction and commissioning. The generated attosecond pulse train from this source has been characterized by means of a newly developed Terahertz streak camera. Furthermore, first attempts have been made to extend the the spectral range offered by HHG to significantly higher photon energies (up to 400 eV) using an intense mid-infrared laser. Such a source will enable new science applications in near future. Finally, the ultrashort x-ray pulses were used to study ultrafast magnetic dynamics in Cobalt thin films. For this purpose two different techniques, namely XMCD and X-ray magneto-optical effect were implemented and tested at the HHG beamline and first studies on ultrafast magnetization were successfully performed.

EPFL2016

Chargement

Gas-phase volatile organic chloride electroreduction: A versatile experimental setup for electrolytic dechlorination and voltammetric analysis

Christos Comninellis, Henri Encontre

Silver is a well-known and largely studied electrocatalytic material for (hydro)dehalogenation reactions of organic halides, a class which includes several priority pollutants. Silver nanoparticles are particularly attractive since exhibit similar or even better performances than bulk silver allowing a significant reduction of precious metal loading. In this study the hydrodehalogenation of CHCl3 is selected as model reaction in order to evaluate the electrocatalytic activity of 2-15 nm silver nanoparticles. For the electrochemical characterization a versatile experimental setup was purportedly in-house designed and assembled that allows both cyclic voltammetry and electrolysis investigations. All the tests are performed in aqueous solution using a gas diffusion electrode as working cathode. The progressive conversion of gaseous trichloromethane to less chlorinated compounds is quantitatively evaluated in terms of concentration Cl- ions produced in the aqueous electrolyte solution. (C) 2014 Elsevier B.V. All rights reserved.

Elsevier Science Inc2014

Chargement

Electrochemical process for benzanthrones and planar polycyclic aromatic oxo compounds

Christos Comninellis

The title compds., useful in the prodn. of dye intermediates, are prepd. in acid media in an electrolysis cell whose electrodes are sepd. by a membrane. At the cathode, anthraquinones are reductively cyclized with glycerol [56-81-5] to give the corresponding benzanthrones. In the anode chamber the oxidn. state of a transition metal ion is electrochem. increased by 1 and the resulting ion serves as a chem. oxidant for a planar polycyclic arom. compd. Thus, to the cathode chamber contg. 46.8 g anthraquinone [84-65-1] in 1300 g H2SO4, 31.05 g glycerol was added dropwise while the current was running. On the anodic side 10 g MnSO4.H2O was suspended in 130 g 88% H2SO4. benzanthrone [82-05-3] (85%) Was isolated from the cathodic portion, while the anolyte was used to cyclooxidize 10 g 4,4'-bibenzanthrone [116-90-5] to dioxoviolanthrone [64346-54-9] which was reduced with NaHSO3 to dihydroxyviolanthrone (I) [26545-62-0] in 76.4% yield. I was used as an intermediate in the synthesis of vat dyes. [on SciFinder (R)]

(Ciba-Geigy A.-G., Switz.).1982

Chargement

MSE-352: Introduction to microscopy + Laboratory work

Ce cours d'introduction à la microscopie a pour but de donner un apperçu des différentes techniques d'analyse de la microstructure et de la composition des matériaux, en particulier celles liées aux microscopies électronique et optique. Le cours comprend des cours ainsi que des démonstrations.

CH-410: Physical and chemical analyses of materials

The course relates on the use of electromagnetic (X-Ray) and corpuscular (electrons) radiations for physical and chemical analysis of solid materials.

PHYS-405: Experimental methods in physics

The course's objectivs are: Learning several advenced methods in experimental physics, and critical reading of experimental papers.

Électron

L'électron, un des composants de l'atome avec les neutrons et les protons, est une particule élémentaire qui possède une charge élémentaire de signe négatif. Il est fondamental en chimie, car il part

Rayon X

Atome

redresse=1.25|vignette|Représentation d'un atome d' avec, apparaissant rosé au centre, le noyau atomique et, en dégradé de gris tout autour, le nuage électronique. Le noyau d', agrandi à droite, est f