Expansion of the ablation plume created by ultraviolet laser irradiation of various target materials

The plasma plume created during photoablation of various targets by an excimer KrF laser beam is studied in typical conditions of pulsed laser film deposition. For the examination of transport phenomena of ejected species, the space and time resolved evolution of the luminous plume is investigated by fast imaging as a function of laser fluence (from 7 to $200~\mathrm{J/cm}^{2}$) and nitrogen background pressure (from 5 × 10−3 to 500 Pa) for five different target materials (boron nitride, graphite, alumina, molybdenum, a superconducting oxide YBCO). Under "vacuum" (5 × 10−3 Pa and for nitrogen background pressures up to 10−1−1 Pa, the plume expands freely. For higher background pressures $(\geq 10~\mathrm{Pa})$, three successive regions above the target can be distinguished: at first the expansion is free, then the plume expands according to a shock wave-like behaviour, and lastly a drag force model correctly describes the plume shape evolution. Velocities of the luminous plasma front and of the "mass center" of the plume are determined versus laser fluence and background nitrogen gas pressure

In situ growth of YBaCuO superconducting thin films by excimer laser ablation: influence of deposition and cooling parameters

International audienceIn situ YBaCuO thin films are deposited on MgO single-crystal by pulsed laser ablation using an excimer laser (KrF, 248 nm). Deposition and cooling conditions are investigated in order to obtain c-oriented samples. The influence of substrate temperature and oxygen pressure during both deposition and post-deposition processes on the structural (orientation, lattice parameters) and electrical (resistivity at 300 K, critical temperature, transition width) film properties is analyzed. These studies lead to reproducible high quality c-oriented thin films which exhibit a critical temperature of 90 K, a superconducting transition width less than 1 K and a good behavior in the normal state

AMORPHOUS SILICON NITRIDE THIN FILMS PERFORMED IN TWO PECVD EXPERIMENTAL DEVICES

Les films de nitrure de silicium sont réalisés par deux procédés de PECVD différents. Dans le premier, ces films sont formés dans une décharge à courant continu dans un plasma d'argon-silane-azote alors que dans le second dispositif, une espèce active d'azote est créée sélectivement dans une post-décharge d'azote et réagit avec le silane dans une zone de réaction où est positionné le substrat. Dans les deux cas, les films réalisés sont sous-stoechiométriques en azote. Leurs caractéristiques : morphologie, structure et composition sont étudiées et comparées.Silicon nitride thin films are obtained using two different PECVD devices. In the first one, these thin films are created in a DC discharge in an argon-silane-nitrogen gas mixture whereas in the second, nitrogen active species are selectively produced in a flowing nitrogen post-discharge and then react with silane in a reaction region where is positioned the substrate. In both cases, the obtained films are substoichiometric in nitrogen. Their characteristics : morphology, structure and composition are studied and compared

Plasma and material surface investigations in a nitriding process of thin molybdenum films using an expanding (Ar-N2-H2) plasma

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