Investigation of Soot Deposition and Composition in a Radio Frequency Plasma of Benzene

A radio frequency (rf) discharge has been utilized to study the decomposition of benzene. SEM inspection has shown that the size of soot particles ranged from 0.5 to several μm. The soot deposited on silicon wafers was analyzed by gas chromatography/mass spectrometry (GC/MS). It was shown that the main components of the soot are polyphenyls (biphenyl and terphenyls) and a trace amount of polycyclic aromatic hydrocarbons (PAHs). Acetylene and hydrogen have been detected by plasma diagnostics techniques using Fourier transform infrared (FTIR) and optical emission spectroscopic techniques. However, GC/MS analysis has shown that the relative yields of PAHs are much less than those of polyphenyls, which indicates that the conventional hydrogen abstraction-acetylene addition (HACA) model for soot formation is not applicable to the benzene plasma due to the reason of temperature. The rf power, the carrier gas flow-rate, the relative yields of polyphenyls, and plasma temperatures were correlated. The reaction pathways of benzene elimination and soot formation in plasma are discussed. This study has provided a new route to control the contamination due to PAHs.