EXCITED-STATE DENSITY DISTRIBUTIONS OF H, C, C-2, AND CH BY SPATIALLY-RESOLVED OPTICAL-EMISSION IN A DIAMOND DEPOSITING DC-ARCJET REACTOR

Spatially resolved optical emission spectroscopy is used to investigat e excited species in a dc-arcjet diamond depositing reactor. Temperatu re measurements indicate a cold plasma with electrons, excited states, and gas in nonthermal equilibrium. The H, C, C-2, and CH excited stat e number densities decrease exponentially with the distance from the n ozzle and have a pronounced increase in the shock structure above the substrate. The H emission increases throughout the boundary layer to t he substrate surface, whereas emission from other species has a maximu m in the boundary layer and then decreases again towards the substrate . The reconstructed radial distribution of excited state concentration s are Gaussian, with the C and C-2 distributions broader than the H an d CH ones. The optical emission is calibrated with either Rayleigh sca ttering or laser-induced fluorescence to furnish absolute number densi ties. We find all the excited species to be present in concentrations two or more orders of magnitude smaller than the corresponding ground states measured in the same reactor and conditions. We find that C-2(d -a) emission intensity correlates well with laser-induced fluorescence measurements of C-2(a) concentration in the arcjet plume. Ground stat e concentrations of the other species do not vary as their emission in tensity except near the substrate, where the variations of CH(A-X), CH (B-X), and C-2(d-a) emission intensities are good monitors of the corr esponding concentration changes. (C) 1998 American Vacuum Society.