Mass spectrometric investigations of plasma chemical reactions in a radiofrequency discharge with Ar/C2H2 and Ar/C2H2/O2 gas mixtures

Abstract

Plasma chemical reactions in complex Ar/C2H2 and Ar/C2H2/O2 radiofrequency plasmas with formation of nano-particles are investigated. Growing nano-particles cause a growth instability, which leads to temporal variations and a cyclic behaviour of plasma properties. Mass spectrometric observations show the consumption of C2H2 and the formation of polyacetylene C2nH2 molecules which increases with acetylene gas flow. The cycle frequency is a decreasing function of acetylene consumption. The addition of oxygen to the discharge reduces the cycle frequency and the formation of nano-particles and leads to the formation of CO and CO2 molecules presumably through the oxidation of C2H radicals which are formed in the discharge.

Effects of process conditions on the chemistry of an Ar/C2H2 dust‐forming plasma

“…As C 2 H 2 is mainly lost in collisions with Ar* atoms, the C 2 H 2 density evolves inversely to n m . In turn, the C 4 H 2 production is related to the C 2 H 2 density, and, as a result, the n d ‐dependencies of both molecules are similar.…”

“…Since both, the anion and hydrocarbon molecule densities, are small at large n e ( P abs ), an Ar/C 2 H 2 plasma with low or moderate electron density is, in our opinion, more suitable for nanoparticle production than one with large n e . It may be a reason why most of the nanoparticle growth experiments in Ar/C 2 H 2 are performed at relatively low power The densities of plasma species also depend on the shape of the EEDF.…”

“…The experiments have shown that dust particle growth strongly depends on the concentrations of C 2 H − ions, which are supposed to act as the main species for the initiation of dust formation and C 2 H neutral radicals . The experiments also revealed that the formation of dust particles in Ar/C 2 H 2 plasmas is accompanied by a decrease of the electron and acetylene densities and by an increase of the electron temperature and the density of metastable argon atoms . Numerical simulations of the nucleation of nanoparticles in C 2 H 2 and Ar/C 2 H 2 plasmas showed that positive and negative ions, as well as hydrocarbon radicals, may take part in the initial stage of particle formation …”

“…In the past two decades, plasmas used for the formation of carbonaceous dust particles have been intensively investigated both by experimental measurements and numerically . The experiments have shown that dust particle growth strongly depends on the concentrations of C 2 H − ions, which are supposed to act as the main species for the initiation of dust formation and C 2 H neutral radicals .…”

Infrared gas phase study on plasma-polymer interactions in high-current diffuse dielectric barrier discharge

“…This suggests that in the etching process, small (less than 10 nm) partially oxidized polymer fragments are produced and agglomerated during transport in the gas flow forming bigger particles (> 100 nm). 40 The initially airborne particles may attach on the inner surface of the FTIR system (memory effect) and further decompose into CO x species and thus artificially enhance the FTIR absorption signal. However, not much is known in the polymer interactions with the oxygencontaining plasma.…”