Growth precursors and dynamics of dust particle formation in the Ar/CH4 and Ar/C2H2 plasmas

This paper deals with the study of the temporal and spatial evolution of the dust formation in a capacitively coupled standard GEC cell in Ar/C2H2 and Ar/CH4 Mixtures. To initiate the particle growth in the Ar/CH4 discharge, we have either to apply transiently high power to the discharge or to inject transiently a pulse of C2H2. In the Ar/C2H2 discharge, however, the particles are formed spontaneously at constant low power. The experiments underline the importance of acetylenic compounds for the nucleation process, i.e. for the first step of particle growth. Due to the different initiation process, the further temporal evolution of the dust formation is significantly different for both kinds of discharges. The dust particles are detected by means of laser beam scattering and by measuring the extinction of the laser beam after passing the discharge. The response of the plasma to the formation of dust has been analysed by emission spectroscopy and mass spectroscopy. The 7th harmonic signal of the rf driving voltage is a useful indicator for the presence of dust particles and their growth.