Determination of atomic hydrogen density in non-thermal hydrogen plasmas via emission actinometry

Abstract

Atomic hydrogen plays an important role in the chemical vapour deposition of diamond and other functional materials. This paper reports the experimental determinations of atomic hydrogen density in dielectric barrier discharge hydrogen plasmas via optical emission spectrometry using Ar as an actinometer. At certain discharge conditions (ac 24 kHz, 28 kV of peak-to-peak voltage), the approximate hydrogen dissociation fractions calculated from the emission intensities with respect to electron temperatures obtained with the Langmuir probe, are decreased from 0.099 to 0.01 as the gas pressure increases from 2 to 4 Torr. The relative H atom mole fractions as a function of discharge parameters (spatial position and gas flow rate) have been investigated. It is shown that the discharge characteristics strongly depend on the spatial position but not on the gas flow rate. The influences of the above operating parameters on the emission intensities have been discussed.

Production and Detection of H Atoms and Vibrationally Excited H2 Molecules in CVD Processes

“…OES is one of the most sensitive, non‐invasive, simple, and direct ways to identify radical species 78–81. Great care, however, must be taken in quantitative analysis.…”

Use of plasma oxidation for conversion of metal salt infiltrated thin polymer films to metal oxide

“…Atomic oxygen density was monitored using the optical emission spectroscopy (OES) based actinometry technique. This method has been successfully applied to measure the number density of radicals such as O, H and F present in reactive plasma [24,26,27]. Pre-treatment and post-treatment chemical analysis of sample surfaces was performed using XPS to determine the impact of processing on surface layer composition.…”

Depopulation mechanisms of atomic hydrogen in the n = 3 level following two-photon excitation by a picosecond laser

“…Unfortunately, measuring the absolute atomic hydrogen density can be highly challenging, especially when spatial resolution is required to account for temperature and density gradients in the vicinity of the plasma boundaries. Straightforward techniques based on optical emission spectroscopy such as actinometry give only access to the relative variation of the density [13] and a collisional radiative model is required for calibration [14], [15] which affects the robustness and accuracy of the method. Other techniques based on chemical titration such as NO 2 titration are very specific to post-discharge conditions and uniform concentration fields and are mainly suitable for calibration purposes [16], [17].…”