Formation mechanisms of carbon dimer in excimer laser produced plasma
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Formation mechanisms of carbon dimer in excimer laser produced plasma Petru-Edward Nica1 and Cristian Ursu2,a 1 2
Department of Physics, “Gheorghe Asachi” Technical University, Bd. Mangeron, Nr. 67, Iasi 700050, Romania “Petru Poni” Institute of Macromolecular Chemistry, 41 A Gr. Ghica Voda Alley, Iasi 700487, Romania Received 29 June 2020 / Received in final form 1 September 2020 / Accepted 1 September 2020 Published online 6 October 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. Fundamental physical processes involved in carbon excimer laser produced plasma were investigated through high resolution spectroscopic measurements. The spectral emitting features near the target (within 1 mm from it) of different plasma components were recorded at various instants from the laser pulse, with a special emphasis on the carbon dimer known to have a major influence in the synthesis of high-quality carbon-based materials. The dominance of the recombination processes in the dimer formation is deduced from: (i) the existence of multiple time-decay constants evidenced for the spectral lines belonging to various plasma species. These parameters are attributed to the formation of the respective species through different and complex mechanisms, and they are discussed from the perspective of possible deviations from the local thermodynamic equilibrium; (ii) the longer emission time of the carbon dimer compared with singly charged ion or of the neutral. (iii) the increase in time of the vibrational temperature that associated to the carbon molecule.
1 Introduction Investigation of laser produced carbon plasma is of great interest since 90s [1–3] due to its versatility in synthesizing novel materials that are employed in various applications [4,5]. The aim is to correlate the plasma parameters (the nature of the involved species, their kinetic and thermal energies, and the overall plume dynamics) or the chemistry with the surrounding atmosphere, with the characteristics of the deposited materials. Optical emission spectroscopy of ionic, atomic, and molecular species has been largely used as diagnostic tool [6]. For example, when the kinetic energy in the expanding plume is about 100 eV, diamond-like carbon films containing a high percent of sp3 bonds are deposited [7]. The spectroscopic methods are useful for providing features at atomic level, but they are limited to a single location at a specific time, without the possibility of monitoring the plasma global emission evolution in the absence of multiple measurements. Therefore, they are usually accompanied with the time-resolved imaging technique of the plasma plume (e.g., ICCD fast imaging). This combination of methods allows a better understaning of the physical processes occurring during the plasma evolution from the target vicinity toward the deposition substrate. Using such investigation techniques, an excimer laser produced carbon plasma of a V-like
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