Determination of molecular temperatures within inductively coupled plasmas is critical to understanding the reactions that drive the chemistry of these systems and the mechanisms involved in surface processing. To investigate such interactions, a dual, in situ broadband absorption and optical emission spectroscopy system was designed; providing insight into neutral and excited state species energetics, specifically rotational (T R ) and vibrational (T V ) temperatures across a broad spectral range (>800 nm). Nitric oxide plasmas have been investigated, where measured T V values were higher than T R values, indicating rotational degrees of freedom are more easily thermalized. Using the imaging of radicals interacting with surfaces technique, surface scatter coefficients were measured for NO radicals, which are discussed in relation to energy partitioning in these systems. K E Y W O R D Sbroadband absorption spectroscopy, energy partitioning, inductively coupled plasmas, nitrogen oxides, optical emission spectroscopy (OES)

Understanding energy distributions and kinetic processes in NO plasma systems is vital to realizing their potential in a range of applications, including pollution abatement. Energy partitioning between degrees of freedom and multiple molecules formed within NO plasma systems (N, NO, N/O) was investigated using both optical emission and broadband absorption spectroscopies. Specifically, we determined electron temperatures (T) as well as rotational (T) and vibrational (T) temperatures for various N (BΠ and CΠ) and NO (XΠ and AΣ) states. T and T for both molecules (regardless of state) show a strong positive correlation with applied plasma power, as well as a negative correlation with system pressure. In all cases, T values are significantly higher than T for both species, suggesting vibrational modes are preferentially excited over rotational degrees of freedom. Time-resolved optical emission spectroscopy was utilized to determine rate constants, providing mechanistic insight and establishing the relationships between system parameters and plasma chemistry. Ultimately, the combination of these data allows us to glean information regarding both the kinetics and energetics of N and NO molecules formed within nitrogen- and oxygen-containing plasma systems for potential applications in gas remediation of pollutants.

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Understanding fundamental plasma–surface interactions remains an important component of increasing the utility of plasma systems in a range of applications including plasma-assisted catalysis (PAC). A key element in realizing the potential of these applications is understanding the foundational data that control the overall process. Here, fundamental gas-phase and film chemistry trends in methane inductively coupled plasmas are studied to model PAC systems for decomposition of volatile organic compounds. Specifically, energy partitioning trends are presented in conjunction with surface characterization data to elucidate processes occurring at the plasma–surface interface. Optical emission spectroscopy yields rotational and vibrational distribution measurements that can be converted to temperatures (TR and TV) for CH in 100% CH4 and CH4/Ar plasmas as a function of pressure (50–200 mTorr) and applied rf power (25–150 W). Under these conditions, TV ranges from ∼3000 to ∼5000 K, whereas TR has values of 1500–2500 K. These are considerably above room temperature, even at pressures of 200 mTorr and Ar content as high as 25% of total precursor feed. Surface characterization of plasma-treated substrates yields minimal changes in chemical composition but more significant variations in film morphology as functions of plasma pressure and applied rf power. Collectively, these data aim to unravel the complex chemistry of plasma systems for PAC.

The contributions of various gas-phase species in surface reactions are of significant value to assess and improve catalytic substrates for abatement of vehicular emissions. The impact of ions on surface scatter of NO radicals is investigated with an aim toward improving and tailoring surfaces for the reduction or removal of nitrogen oxide (N(x)O(y)) species via inductively coupled plasmas (ICPs). Nascent ions are monitored via mass spectrometry and energy analysis for a variety of N(x)O(y) precursor gases. The total average ion energy ((total)) determined for all ions within each respective plasma system shows a strong positive correlation with applied rf power and a negative correlation with system pressure. The imaging of radicals interacting with surfaces (IRIS) technique was used to determine the role ions play in the surface scatter of NO radicals. The net effect of ions on substrate processing is largely dependent upon (total). Scatter coefficients (S), determined for ion-limited and ion-rich plasma systems were used to correlate (total) and scatter. The resultant effect is that ions play a substantial role in scatter of NO only when (total) > ~50 eV. The majority of systems studied contained ions below this energy threshold, suggesting knowledge of ion energies is integral to appropriately controlling the chemistry occurring between the gas-phase and surface.