In a distributed antenna array (DAA) reactor, microwave H 2 plasmas with admixtures of 2.5% CH 4 and 1% CO 2 used for the deposition of nanocrystalline diamond films have been studied by infrared absorption and optical emission spectroscopy (OES) techniques. The experiments were carried out in order to analyze the dependence of plasma chemical phenomena on power and pressure at relatively low pressures, up to 0.55 mbar, and power values, up to 3 kW. The evolution of the concentration of the methyl radical, CH 3 , and of five stable molecules, CH 4 , CO 2 , CO, C 2 H 2 and C 2 H 6 , was monitored in the plasma processes by in situ infrared laser absorption spectroscopy using lead salt diode lasers (TDL) and external-cavity quantum cascade lasers (EC-QCL) as radiation sources. OES was applied simultaneously to obtain complementary information about the degree of dissociation of the H 2 precursor gas and of its gas temperature. The experimental results are presented in two separate parts. In Part I, the present paper, the measurement of the gas (T gas ), rotational (T rot ) and vibrational (T vib ) temperatures of the various species in the complex plasma was the main focus of interest. To achieve reliable values for the gas temperature inside and outside the plasma bulk as well as for the rotational and vibrational temperatures in the plasma hot zones, which are of great importance for calculation of species concentrations, five different methods based on the emission and absorption spectroscopy data of H 2 , CH 4 , CH 3 and CO have been used. In these, line profile analysis has been combined with Boltzmann plot methods. Based on the wide tuning range of the EC-QCL, a variety of CO lines in the ground and three excited states was measured enabling extensive temperature analysis providing new insight into the energetic aspects of this multi-component plasma. Depending on the different plasma zones the gas temperature was found to range between about 360 and 1000 K inside the DAA reactor. In Part II, based on detailed concentration measurements general plasma chemical aspects will be analyzed and discussed.

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In a distributed antenna array (DAA) reactor, microwave H 2 plasmas with admixtures of 2.5% CH 4 and 1% CO 2 used for the deposition of nanocrystalline diamond films have been studied by infrared laser absorption and optical emission spectroscopy (OES) techniques. The experiments were carried out in order to analyze the dependence of plasma chemical phenomena on power and pressure at relatively low pressures, up to 0.55 mbar, and power values, up to 3 kW. The evolution of the concentration of the methyl radical, CH 3 , of five stable molecules, CH 4 , CO 2 , CO, C 2 H 2 and C 2 H 6 , and of vibrationally excited CO in the first and second hot band was monitored in the plasma processes by in situ infrared laser absorption spectroscopy using tunable lead salt diode lasers (TDL) and an external-cavity quantum cascade laser (EC-QCL) as radiation sources. OES was applied simultaneously to obtain complementary information about the degree of dissociation of the H 2 precursor and of its gas temperature. The experimental results are presented in two separate parts. In Part I, the first paper in a two-part series, the measurement of the gas (T gas ), rotational (T rot ) and vibrational (T vib ) temperatures of the various species in the complex plasma was the main focus of interest. Depending on the different plasma zones the gas temperature was found to range between about 360 and 1000 K inside the DAA reactor (Nave et al 2016 Plasma Sources Sci. Technol. 25 065002). In Part II, the present paper, taking into account the temperatures determined in the first paper, the concentrations of the various species, which were found to be in a range between 10 11 and 10 15 cm −3 , are the focus of interest. The influence of the discharge parameters power and pressure on the molecular concentrations has been studied. To achieve further insight into general plasma chemical aspects the dissociation of the carbon precursor gases including their fragmentation and conversion to the reaction products has been analyzed in detail.

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Silane (SiH 4 ) plasmas are widely used for the deposition of hydrogenated amorphous silicon (a-Si:H) films. Nevertheless, the chemical processes governing film deposition are still incompletely understood. Moreover, there is still no general method available to determine the absolute concentration of the silyl radical (SiH 3 ), which is the accepted chemical precursor of a-Si:H films. In this study, a 10% silane in helium RF plasma was spectroscopically investigated between 2085 and 2175 cm −1 using an external cavity quantum cascade laser (EC-QCL) based spectrometer. This led to the identification of 4 distinct species from their absorption features: SiH 4 , disilane (Si 2 H 6 ), SiH 3 , and an unassigned short-lived species. Furthermore, 17 absorption features of SiH 3 were identified and unambiguously assigned. Fast spectral scanning of selected absorption features belonging to the four species in a 10 Hz pulsed RF plasma enabled the measurement and interpretation of their temporal behavior in terms of plausible chemical reactions involving silicon containing species. By quantitatively measuring the decay of the SiH 3 a ← a p P 4 (5) transition at 2151.3207 cm −1 after the discharge was stopped, its line strength (S) was determined to be (7.5 ± 5.5) × 10 −20 cm 2 cm −1 mol −1 .

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