The formation of dust particles in argon diluted C2H2 plasmas was studied by means of Fourier transform infrared absorption spectroscopy and mass spectroscopy. The detection limit for infrared absorption was significantly improved by the use of a multipass technique. Measuring the intensity of the Rayleigh/Mie scattering of the infrared signal we found a periodicity of dust formation/vanishing (period of about 35 min in our experimental conditions). The fast disappearance of the dust from the plasma region at the end of every period is the evidence of a narrow particle size distribution, as confirmed by secondary electron micrographs of the collected powder. Characteristic infrared absorption features have their origin in absorption within the dust particles. Besides the strong presence of aliphatic hydrocarbons characteristic for amorphous hydrocarbon films, a significant amount of aromatic structures was detected. Heavy positive ions measured by ion-mass spectroscopy originate from polyacetilenic (C2nH2) and aromatic compounds. Time resolved mass spectra gave insight into the plasma response to the dust formation.

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.

Carbonaceous compounds are a significant component of interstellar dust, and the composition and structure of such materials is therefore of key importance. We present 1.5-15 m spectra of a plasma-polymerized carbonaceous material produced in radio-frequency discharge under low pressure, using C 2 H 2 as a precursor component. The infrared spectra of the resulting spheroidal carbonaceous nanoparticles reveal a strong aliphatic band (3.4 m feature), weak OH and carbonyl bands, and traces of aromatic compounds, all characteristics identified with dust in the diffuse interstellar medium of our Galaxy. The plasma polymerization process described here provides a convenient way to make carbonaceous interstellar dust analogs under controlled conditions and to compare their characteristics with astronomical observations. Here we focus on a comparison with the IR spectra of interstellar dust. The IR spectrum of carbonaceous dust in the diffuse interstellar medium is characterized by a strong 3.4 m CÀH stretching band and weak 6.8 and 7.2 m CÀH bending bands, with little evidence for the presence of oxygen in the form of carbonyl (C = O) or hydroxide (OH) groups. The plasma polymerization products produced under oxygen-poor conditions compare well with the peak position and profiles of the observed IR spectrum of diffuse dust. In addition, we find that addition of nitrogen to the plasma results in bands at 6.15 m (C = N band) and at 3 m (NH band). We note that, with the addition of nitrogen, the 3.4 m hydrocarbon band diminishes greatly in strength as the NH band grows. This may have implications for the puzzling absence of the 3.4 m hydrocarbon bands in the IR spectra of dust in dense molecular clouds, given that the presence of nitrogen-related bands has been established in dense-cloud dust.

The properties of an Ar/C 2 H 2 dusty plasma (ion, electron and neutral particle densities, effective electron temperature and dust charge) in glow and afterglow regimes are studied using a volumeaveraged model and the results for the glow plasma are compared with mass spectrometry measurements. It is shown that dust particles affect essentially the properties of glow and afterglow plasmas. Due to collection of electrons and ions by dust particles, the effective electron temperature, the densities of argon ions and metastable atoms are larger in the dusty glow plasma comparing with the dust-free case, while the densities of most hydrocarbon ions and acetylene molecules are smaller. Because of a larger density of metastable argon atoms and, as a result, of the enhancement of electron generation in their collisions with acetylene molecules, the electron density in the afterglow dusty plasma can have a peak in its time-dependence. The results of numerical calculations are in a good qualitative agreement with experimental results.