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/C 2 H 2 and Ar/CH 4 mixtures. To initiate the particle growth in the Ar/CH 4 discharge, we have either to apply transiently high power to the discharge or to inject transiently a pulse of C 2 H 2 . In the Ar/C 2 H 2 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.

Reactive plasmas are nowadays widely used for technological applications. The spontaneous formation and growth of dust is a phenomenon frequently observed in such plasmas. The formation of dust particles has been observed in a great variety of different discharge types and in different kind of gases or gas mixtures. Due to the large variety of different phenomena that can be observed in reactive complex plasmas this article will address some selected (general) problems and examples that are specific for the physics and chemistry of such systems. These examples concern the formation and growth of dust particles in reactive plasmas, the mechanisms responsible for that growth processes, the spatial distribution of the dust particles within the discharge, the response of the plasma to the formation and growth of dust particles and some technological aspects.

Zero-dimensional, space-averaged global models of argon dust-free and dusty afterglow plasmas are developed, which describe the time behaviour of electron n e(t) and Ar* metastable n m(t) densities. The theoretical description is based on the assumption that the free electron density is smaller than the dust charge density. In pure argon, fairly good agreement with the experimentally measured densities and their decay times in the afterglow is obtained when the electron energy loss term to the chamber walls is included in the electron energy balance equation. In dusty plasma afterglow, the agreement between theory and experiment is less satisfactory. The calculated metastable density is 3 times smaller than the measured one and the electron decay is much faster in the late afterglows. The difference should probably arise from the assumption that the electron energy distribution function is Maxwellian. Different sources of secondary electrons in the dusty plasma afterglow are analysed. Comparison of the model with experimental results of argon dusty plasma suggests that the metastable pooling could be the source of the experimentally observed electron density increase in the early afterglow but electron generation from metastable–dust interactions cannot be fully discarded.

The electron density in a pulsed complex plasma is measured by means of time resolved microwave interferometry. Depending on the discharge conditions the temporal evolution of the electron density exhibits an anomalous behaviour. The electron density starts to decrease when the rf-power is switched on and it starts to increase when the rf-power is switched off. This anomalous behaviour can be attributed to the charging and decharging of nanoparticles.

We have analyzed the growth process of a-C:H nanoparticles in Ar–C2H2 and Ar–CH4 plasmas by means of in situ Rayleigh-Mie scattering ellipsometry. Complex refractive index (m=n−ki), mean particle radius (r), and particle size distribution (σ) of a-C:H nanoparticles are carefully determined and compared with those of a-C:H thin films deposited at similar conditions. It is found that, in both plasmas, small particles (r<25nm) have graphitelike properties whereas large particles have polymerlike characteristics. These results indicate that the particles have internal structures of a hard core and soft mantles on it. The size distribution of the nanoparticles in both Ar–CH4 and Ar–C2H2 plasmas is essentially monodisperse with a narrow Gaussian size distribution. A systematic comparison between the growth and atomic structure models for a-C:H materials and criteria for interstellar dust (ISD) grains known from astrophysical observations is made. Significant agreement is found in a wide range of radii, supporting earlier findings that plasma-polymerized a-C:H nanoparticles might be a good candidate as an ISD analog.