In this paper, the initial mechanisms of nanoparticle formation and growth in radiofrequency acetylene (C2H2) plasmas are investigated by means of a comprehensive self-consistent one-dimensional (1D) fluid model. This model is an extension of the 1D fluid model, developed earlier by De Bleecker et al. Based on the comparison of our previous results with available experimental data for acetylene plasmas in the literature, some new mechanisms for negative ion formation and growth are proposed. Possible routes are considered for the formation of larger (linear and branched) hydrocarbons C2nH2 (n = 3, 4, 5), which contribute to the generation of C2nH− anions (n = 3, 4, 5) due to dissociative electron attachment. Moreover, the vinylidene anion (H2CC−) and higher anions (n = 2–4) are found to be important plasma species.

The temporal evolution of the neutral plasma chemistry products in a capacitively coupled plasma from argon/helium/acetylene is followed via molecular beam mass spectrometry with a time resolution of 100 ms. Several chemistry pathways are resolved. (i) The formation of C2nH2 (n = 2-5) molecules proceeds via the following sequence: the production of highly reactive C2H radicals in electron impact dissociation of C2H2 is followed by C2H induced chain polymerization of C2nH2 (n = 1-4). (ii) CnH4 (n = 4, 5, 6) compounds are detected already at an early stage of the discharge excluding polymerization reactions with C2H radical being responsible for their formation. Instead, vinylidene reactions with acetylene or mutual neutralization reactions of ionic species are proposed as sources of their formation. (iii) Surface reactions are identified as the source of C8H6. The measured hydrocarbon molecules represents possible precursors for negative ion formation via dissociative electron attachment reactions and can hence play a crucial role in particle nucleation. On the basis of the comparison of our data with available experimental and modeling results for acetylene plasmas in the literature, we propose C2nH2 (n > 1) molecules as important precursors for negative ion formation.

The initial polymerization reactions in particle forming Ar/He/C 2H 2 plasmas are studied using molecular beam mass spectrometry (MBMS). The measured mass spectra are disentangled and quantified with the help of Bayesian probability theory. This approach uses the measured mass spectra and the cracking patterns (CPs) of the species that are formed in the plasma as the main input parameter. The CPs are either taken from calibration measurements or the NIST database or estimated based on a comparison to CPs of similar molecules. These estimated CPs are then modified by Bayesian analysis to fit the measured data. The CPs of C 6H 2, C 6H 4, and C 8H 2, which are not available in the NIST database, are determined in this way and can serve as good estimation until precise data is published. The temporal evolution after plasma ignition of the densities of in total 22 species (hydrocarbons, noble gases, and impurities) are quantified and expressed as partial pressures. The most abundant products in our plasma are C 4H 2 and C 6H 2 molecules with maximum partial pressures of 0.1 and 0.013 Pa, respectively. Our quantitative data can be used to validate plasma chemistry models. First comparison is made to a plasma chemistry model of similar C 2H 2 plasma already available in the literature. The comparison indicates that dissociative electron attachment to C 2 n H 2 ( n > 1) molecules is a dominant source of negative ions in C 2H 2 plasmas. Additionally, the C 2H 4 has been identified as a precursor for C n H 4 molecules.

The initial polymerization reactions in particle forming Ar/He/C 2 H 2 plasmas are studied by means of molecular beam mass spectrometry. The mass spectra are quantified with the help of Bayesian probability theory. The C x H y production in C 2 H 2 plasma is studied by measuring the temporal evolution of the mass spectrometer signal under the influence of added C 2 H 4 to the gas mixture. It is shown that C 4 H 4 is very quickly formed after plasma ignition in reactions of C 2 H 4 with C 2 H radicals. Other C n H 4 molecules, i.e. C 3 H 4 , C 5 H 4 and C 6 H 4 , are formed in reactive pathways involving C 2 H 4 , as well. C 6 H 6 , which could not be uniquely identified as an aromatic or linear molecule, shows a similar trend with additional C 2 H 4 . But in this case more C 2 H 4 is needed to detect the same relative change compared with C 4 H 4 . This is probably because more reaction steps are needed to form C 6 H 6 . It is shown that C 2 H 4 is very likely produced in the acetylene plasma.

The roughness evolution during plasma deposition of amorphous hydrogenated carbon (a-C:H) films is investigated. Films were deposited from an inductively coupled methane plasma using a wide range of process parameters. Plasma deposition is uniquely described by the dissipated energy per source gas molecule Emean. Depending on Emean, a specific set of radicals contributes to film growth causing a characteristic roughness development. The film roughness is measured using atomic force microscopy and spectroscopic ellipsometry and is expressed using the static and dynamic scaling coefficients α and β, respectively. For low Emean<20eV, α∼0.65 and β∼0.19 indicating film deposition via a growth precursor with a large surface diffusion length. For Emean>20eV, α∼0.9 and β∼0.25 indicating film deposition via a growth precursor with a small surface diffusion length.