Carbonaceous particles produced by atmospheric pressure plasma

Carbonaceous particles produced by atmospheric pressure plasma Ionut Topala Faculty of Physics, Iasi Plasma Advanced Research Center (IPARC), Alexandru Ioan Cuza University of Iasi, Bd. Carol I No. 11, Iasi, 700506, Romania Natural or artificial carbonaceous particulate matter is of great current interest for e.g. atmospheric and environmental sciences, human health, engineering, and astrophysics. Atmospheric carbon-based (nano)particles generally exhibit complex organic architectures, including (poly)aromatics and aliphatics [1,2], while the chemical composition of carbon particulate matter of astrophysical interest may span a broad range of carbon and hydrogen contents, varying with the local astrophysical environments surrounding the particle and formation conditions [3,4]. In order to perform extensive characterization studies and/or realistic in-lab experiments on astrophysical carbon particles, the synthesis of reliable laboratory analogues is of paramount importance. One route to synthetize carbon particles is hydrocarbon plasma-assisted deposition. In this lecture we will be discussing our latest results on the synthesis and characterisation of hydrogenated amorphous carbon (a-C:H) products, deposited using low temperature plasma, at atmospheric pressure [5-7]. Dielectric Barrier Discharge (DBD) is a relatively new method for a-C:H synthesis, and even more so for producing diffuse interstellar medium (DISM) dust analogues. In fact, compared to the materials deposited using other methods (e.g. mechanochemical synthesis, condensation, physical vapour deposition, plasma deposition, combustion and pyrolysis, pulsed laser deposition), the physical and chemical properties, as well as the microscopic aspects of DBD analogues are remarkably different, making them suitable for laboratory astrophysics. Once produced, these dust analogues were thoroughly characterized using a combination of analytical techniques such as Fourier-transform infrared spectroscopy (FTIR), micro-Raman spectroscopy, X-Ray photoelectron spectrometry (XPS), optical microscopy, scanning and transmission electron microscopy (SEM, TEM), or mass spectrometry. Relevant quantities such as CH₂/CH₃ ratio, H/C ratio or sp²/sp³ ratio are calculated and discussed in context of spectral features matching with selected objects in interstellar medium or other dust analogues, by means of spectra comparison and position on ternary diagrams. Further processing of these dust analogues was performed via ion irradiation in the Tandetron^TM beamline (H⁺, 3 MeV, 10¹³ – 10¹⁶ ions/cm²) to assess how ion exposure could modify all the former quantities, as well the microscopic features of the carbon particles. Lastly, we will be discussing the current analyses performed at the PhLAM laboratory using state-of-the art high resolution mass spectrometry to unravel the chemical distribution present at the dust surface. The DBD carbon particles exhibit both spectroscopic and morphological features of carbon cosmic dust observed in aliphatic rich environments, being suitable for laboratory mass production and large laboratory astrophysics experiments. A comparison between DBD carbon dust and other analogues or carbonaceous materials in diffuse interstellar medium will be provided. [1] Duca, D., Rahman, M., Carpentier, Y., Pirim, C., Boies, A., & Focsa, C. (2021). Chemical characterization of size-selected nanoparticles emitted by a gasoline direct injection engine: Impact of a catalytic stripper. Fuel, 294, 120317. [2] Focsa, C., Duca, D., Noble, J. A., Vojkovic, M., Carpentier, Y., Pirim, C. Betrancourt, C., Desgroux, P., Tritscher, T., Spielvogel, J. and Rahman, M (2020). Multi-technique physico-chemical characterization of particles generated by a gasoline engine: Towards measuring tailpipe emissions below 23 nm. Atmospheric Environment, 235, 117642. [3] Chiar, J. E., Tielens, A. G. G. M., Adamson, A. J., & Ricca, A. (2013). The structure, origin, and evolution of interstellar hydrocarbon grains. The Astrophysical Journal, 770(1), 78. [4] Martínez, L., Santoro, G., Merino, P., Accolla, M., Lauwaet, K., Sobrado, J., Sabbah H, Pelaez RJ, Herrero VJ, Tanarro I, Agúndez M. (2020). Prevalence of non-aromatic carbonaceous molecules in the inner regions of circumstellar envelopes. Nature astronomy, 4(1), 97-105. [5] Mihaila, I., Pohoata, V., Jijie, R., Nastuta, A. V., Rusu, I. A., & Topala, I. (2016). Formation of positive ions in hydrocarbon containing dielectric barrier discharge plasmas. Advances in Space Research, 58(11), 2416-2423. [6] Hodoroaba, B., Gerber, I. C., Ciubotaru, D., Mihaila, I., Dobromir, M., Pohoata, V., & Topala, I. (2018). Carbon ‘fluffy’aggregates produced by helium–hydrocarbon high-pressure plasmas as analogues to interstellar dust. Monthly Notices of the Royal Astronomical Society, 481(2), 2841-2850. [7] Gerber, I. C., Chiper, A., Pohoata, V., Mihaila, I., & Topala, I. (2019). Comparative study of 3.4 micron band features from carbon dust analogues obtained in pulsed plasmas. Proceedings of the International Astronomical Union, 15(S350), 237-240.