Kinetics of boron atoms in Ar- flowing microwave discharges

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Abstract
Production of boron atoms has been investigated in Ar- flowing microwave discharges (2450 MHz) for two different configurations at 700 Pa. In the first one, an Ar-1.5% gas mixture is introduced in the discharge condition, while the same gas mixture is introduced downstream of a pure argon plasma in the second one. Optical emission spectroscopy (OES) has been used to follow the spatial variations of line and band intensities for various excited species (Ar, B, , , BO, Si, Cl and BCl). Variations of electron density along the plasma column, deduced from OES observations, are attributed to electron attachment reactions involving boron trichloride. Excitation processes leading to formation of excited species are discussed by analysing the OES results acquired in the two discharge configurations. For B, , and BCl species, excitation proceeds from electronic collisions with ground states, whereas a complex kinetic process is found for chlorine atom excitation. It is also shown that information on boron atoms could be gained by using the chimiluminescent reaction produced between boron atoms and molecular oxygen. A boron atom lifetime of about s is obtained by introducing an Ar- gas mixture in Ar- post-discharges.