Spatial density distributions of C2, C3, and CH radicals by laser-induced fluorescence in a diamond depositing dc-arcjet

Quantitative measurements of C2(a3Πu), C3(X,1Π), and CH(X,2Π) have been made by calibrated linear laser-induced fluorescence in the plume of a dc-arcjet (Ar/H2/CH4 1.1:1:0.005) reactor during the chemical vapor deposition of diamond. The peak number density in the arcjet plume for CH is (3.7±0.8)×1012 molecules/cm3, for C2(3a)(3.1±1.3)×1010 cm−3, and for C3∼3×1012 cm−3 with 25 Torr reactor pressure. The radial spatial distributions for C2 and CH have a maximum in the center of the plume; however, C3 is distributed as a hollow cylinder with a pronounced minimum at the center. The variation in number density and in spatial distribution is investigated for changes in chamber pressure, methane flow, and distance from the nozzle.