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Cathode rays or electron beam (e-beam) are streams of electrons observed in discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the cathode (the electrode connected to the negative terminal of the voltage supply). They were first observed in 1859 by German physicist Julius Plücker and Johann Wilhelm Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays. In 1897, British physicist J. J. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the electron. Cathode-ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen. Description Cathode rays are so named because they are emitted by the negative electrode, or cathode, in a vacuum tube. To release electrons into the tube, they f

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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

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

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

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