Different diagnostic techniques are used to monitor the dynamics of electrons and Ar*(1s(5)) metastable atoms in the active plasma phase and in the afterglow of a capacitively coupled radiofrequency (RF) discharge operated in different gas mixtures and at different input powers. Diode laser absorption at 772.38 nm is used to measure the time resolved density of Ar*(1s(5)) atoms in either continuous-wave mode or pulsed RF discharges with 100 Hz pulsing frequency. Simultaneously, microwave interferometry recorded the time dependence of the electron density. Different plasma conditions, namely: (1) pure argon, (2) argon +5.9% acetylene before nanoparticle formation, (3) argon +5.9% acetylene after dust particles have been formed and (4) argon with dust particles remaining in the plasma volume but without acetylene are studied. The measured steady-state Ar*(1s(5)) density in the middle of the reactor is several times larger in the dusty argon plasma than in the pure argon discharge for the same discharge powers. At the same time, the electron density is several times less in the dusty plasma. These changes are caused by dust formation: the electric field in the bulk plasma is enhanced and thus consequently the electron temperature increases. Laser induced fluorescence (LIF) is used to measure the time and space resolved Ar*(1s(5)) axial distribution. In the pure argon discharge, the axial Ar*(1s(5)) metastable distribution has a characteristic saddle-like shape with maxima in the region of the sheaths. With dust particles inside, the axial distribution changes dramatically with the maximum at the discharge mid-plane, revealing an alpha-gamma transition. The spatial distribution and absolute density of metastable atoms are influenced by the formation of a void in the cloud of nanoparticles. Depending on the size of the void, the Ar*(1s(5)) density reduction inside the void is between 30% and 50%. The high Ar*(1s(5)) metastable density in the dusty plasma afterglow strongly influences the time variation of the electron density in the afterglow. The observed increase of the electron density in the afterglow of the Ar/acetylene/dust plasmas is explained by the Penning ionization of acetylene by Ar*(1s(5)) metastable atoms. The time evolution of the electron density in the Ar/dust plasmas reveals that the nowadays assumed rate coefficient for generation of electrons by pooling reaction of Ar* metastable atoms is highly overestimated.

This contribution deals with the nanoparticle distribution inside of plasma with large nanoparticle density. In particular, the formation of voids i.e. dust-free regions in pulsed and CW discharge regime is analyzed. The discharge was ignited in a mixture of argon and acetylene in the conditions favorable for nanoparticles' formation and growth. The temporal evolution of the spatial distribution of nanoparticles during their growth is studied experimentally by means of a laser light scattering technique. The experimental results show that the void expands much faster in the case of pulsed plasma than in the CW plasma operated for the same gas mixture and at the same (average) input power. In the CW plasma, we observed a rapid expansion of the void after some tens of minutes, whereas the corresponding process in the pulsed plasma occurred after some tens of seconds.

The carbon conversion in a N2CH4 radiofrequency (RF) discharge is investigated by analyzing both the gas phase and the dust produced. HCN is identified as the main reactive product and both HCN and NH3 are quantified. This quantification allows determining the carbon conversion yield from CH4 to HCN, which appears to be surprisingly low. The comparison of the infrared absorbance spectra between dust produced in two similar RF plasma setups emphasizes small differences on the CH3/CH2 bonds ratio in the samples. This difference is explained by the aging processes of dust within the plasma.

The carbon conversion in a N2CH4 radiofrequency (RF) discharge is investigated by analyzing both the gas phase and the dust produced. HCN is identified as the main reactive product and both HCN and NH3 are quantified. This quantification allows determining the carbon conversion yield from CH4 to HCN, which appears to be surprisingly low. The comparison of the infrared absorbance spectra between dust produced in two similar RF plasma setups emphasizes small differences on the CH3/CH2 bonds ratio in the samples. This difference is explained by the aging processes of dust within the plasma.

A non-invasive diagnostic technique for measurements of ion fluxes and ion densities in low-pressure pulsed radio-frequency (RF) discharges is described. The ion flux towards an electrode is determined from the change in electrode dc-bias in the plasma afterglow. The measurements in various gas mixtures (Ar, N-2, Ar/C2H2 and Ar with nanoparticles) show an increase in ion flux with the applied RF power. Ion densities are estimated from the ion fluxes and the plasma density at the plasma-sheath boundary, assuming the afterglow electron temperature to be known. Very good agreement between the estimated ion densities and independently measured electron densities is found in the bulk of dust-free plasmas assuming an afterglow electron temperature of 0.05 eV for argon and argon/acetylene plasmas and 0.2 eV for the nitrogen plasma. In dusty plasmas, the ion density at the plasma-sheath boundary can be determined from the measured ion flux and assuming an afterglow electron temperature of 0.05 eV. For the estimation of ion density in the dusty plasma bulk, the ion density distribution, influenced by the negatively charged dust particles, has to be taken into account.

In Ar and He radio-frequency (RF) plasmas with admixtures of C2H2 and CH4 the hydrocarbon chemistry has been studied in relation to dust particle formation by means of infrared tunable diode laser absorption spectroscopy (TDLAS) combined with Fourier transform infrared (FTIR) spectroscopy. The experiments were performed in a RF capacitively coupled parallel plate reactor at a frequency of f = 13.56 MHz, a pressure of p = 0.1 mbar and a flow rate of Φ = 8 sccm of Ar or He with admixtures of 0.5 sccm C2H2 or 1 sccm CH4. The power was P = 15 W. Using TDLAS, the temporal evolution of the concentrations of the methyl radical and of four stable molecules, C2H2, CH4, C2H4 and CO, was monitored in the plasma. Simultaneously, the growth process of the dust particles was analysed by FTIR spectroscopy. The degree of dissociation of the acetylene precursor was found to be nearly constant in the range of 96% under stabilized conditions for both the Ar and He plasmas. In contrast, the degree of dissociation of the methane precursor varied between 45% and 90% depending (i) on the appearance of dust particles in the reactor volume and (ii) on the Ar or He plasma conditions. The methyl radical concentration was found to be in the range of 1011 molecules cm−3. The concentrations of all hydrocarbon species were strongly correlated with the dynamic of the dust formation. Fragmentation efficiencies of acetylene (RF (C2 H2) = 3.2 × 1016 molecules J−1) and of methane (RF (CH4) = (0.16–2.5) × 1016 molecules J−1) and conversion efficiencies to the produced hydrocarbons (RC = (0.23–8.5) × 1014 molecules J−1) could be estimated in dependence on the discharge conditions in the RF plasma.

Metastable and electron densities of pulsed argon plasma containing nano-sized particles were measured by the means of Laser Absorption Spectroscopy and Microwave Interferometry, respectively. Laser Induced Fluorescence was probing the Ar* metastable axial distribution during one dust growing cycle. The experimental results of the dust-free and dusty plasma afterglow were compared to the results obtained by a global model.

The chemical phenomena in hydrocarbon containing Ar /He dusty plasmas have been studied combining MIR tuneable diode laser absorption spect ros opy (TDLAS) and Fourier transform infra-red (FTIR) spectroscopy techniques. The expe riments were done in a rf cc-coupled parallel plate reactor, f = 13.56 MHz. Using TDLAS the tempo ral evolution of C2H2, C2H4, CH3, CH4, CO and CO2 concentrations were measured and the dust particle s formation was monitored with FTIR. The values of the calculated fragmentation of the p recursor molecules and of the conversion rates of the produced hydrocarbons were in a comparable o rd r of magnitude as they were found in surface wave discharges and in planar microwave pla smas.