Publications: Articles

Resume: Discharges in heptane in pin-to-plate configuration are produced between a platinum wire and a (100)-oriented silicon wafer coated by a carbon nanotube (CNT) carpet. This carpet is used to simulate the behavior of a nanostructured surface in electro-discharge machining (EDM) where small protrusions on the surface could play a similar role. CNTs behave like simple electrical conductors between the discharge and the silicon wafer. They act as if they would focus the current on smaller areas. The average diameter of impacts is about five times smaller if the silicon wafer is coated by a CNT carpet. The underlying silicon surface is heated by the plasma and melts, forming a central spot surrounded by a serrated trailing edge. The current density being about one order of magnitude larger when a CNT carpet is present, the induced magnetic field stirs the molten silicon, creating serrations all around the impact. Hot nanoparticles of carbon coming from the plasma fall and roll randomly on the silicon surface where they create wavy micro-channels. Nanowires that are detached from the surface are covered by nanoparticles of platinum in the plasma and embedded within an amorphous carbon layer deposited on the nanotube. However, these effects can only be observed if the current density is high enough (>approximate to 10A mu m(-2) depending on the material) like in micro-EDM but not in nano-EDM.

Equipe: Centre de Compétences : ERMIONE informatique et calcul

Resume: Interaction of discharges in heptane with magnetron-sputtered thin films made of aluminum, copper or iron is studied in a pin-to-plate configuration. The behavior of discharges on thin films can be used to better understand the interaction of discharges with given surfaces and it might also improve the reproducibility of the impacts in order to better control their shape. Single layers and bilayers of metals are characterized after impact by SEM, AFM, micro-EDX and nano-SIMS analyses. Discharges last typically for a few hundreds of nanoseconds and dissipated energies range between 1 and 100 mJ. We show that at low impact energy, copper and aluminum are heated and stretched by surface stress. At intermediate energy, melting occurs, leading to the synthesis of external beads by Marangoni's convection. At high energy, the shape of the impact is defined by the pressure release when the discharge stops. When iron is deposited onto silicon, dewetting is an important mechanism. The columnar structure of the deposit may have two distinct roles. On the one hand, gases trapped in intercolumnar boundaries can produce tiny holes. On the other hand, the shock wave can abrade the outermost and less cohesive part of the film if it is made of columns separated by large porosities. (C) 2013 Elsevier B.V. All rights reserved.

Equipe: Département CP2S : Expériences et Simulations des Plasmas Réactifs - Interaction plasma-surface et Traitement des Surfaces ESPRITS

Resume: Interaction of discharges in heptane with magnetron-sputtered thin films made of aluminum, copper or iron is studied in a pin-to-plate configuration. The behavior of discharges on thin films can be used to better understand the interaction of discharges with given surfaces and it might also improve the reproducibility of the impacts in order to better control their shape. Single layers and bilayers of metals are characterized after impact by SEM, AFM, micro-EDX and nano-SIMS analyses. Discharges last typically for a few hundreds of nanoseconds and dissipated energies range between 1 and 100 mJ. We show that at low impact energy, copper and aluminum are heated and stretched by surface stress. At intermediate energy, melting occurs, leading to the synthesis of external beads by Marangoniâ??s convection. At high energy, the shape of the impact is defined by the pressure release when the discharge stops. When iron is deposited onto silicon, dewetting is an important mechanism. The columnar structure of the deposit may have two distinct roles. On the one hand, gases trapped in intercolumnar boundaries can produce tiny holes. On the other hand, the shock wave can abrade the outermost and less cohesive part of the film if it is made of columns separated by large porosities.

Equipe: Département CP2S : Expériences et Simulations des Plasmas Réactifs - Interaction plasma-surface et Traitement des Surfaces ESPRITS

Equipe: Département SI2M : Microstructures et Contraintes

Equipe: Centre de Compétences : X-Gamma rayons X et spectroscopie