Boundary Layer Profiles in Plasma Chemical Vapor Deposition

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Science  19 Mar 1993:
Vol. 259, Issue 5102, pp. 1726-1729
DOI: 10.1126/science.259.5102.1726


A nonlinear optical spectroscopy based on degenerate four-wave mixing has made possible direct measurements of species temperature and concentration profiles through the boundary layer of a reactive plasma at atmospheric pressure. Spectra were obtained for CH and C2 radicals over a range of conditions including those for the plasma chemical vapor deposition of diamond films. Numerical simulations based on a one-dimensional stagnation-point flow model are in good agreement with the measurements. The CH mole fraction is shown to rise and fall as a function of distance from the substrate, which is compelling experimental evidence for the complex chemistry that is occurring in the plasma boundary layer.