STUDY OF INITIAL DUST FORMATION IN AN AR-SIH4 DISCHARGE BY LASER-INDUCED PARTICLE EXPLOSIVE EVAPORATION

The initial step of particulate growth in a dust forming low pressure radio-frequency discharge has been studied in situ by laser induced pa rticle explosive evaporation (LIPEE). With respect to the conventional light scattering, this method has been found much more efficient to o bserve small nanometer size particles, especially in the case of UV ex cimer laser radiation. Experimental results interpreted by a simple mo del of laser-particle interaction show that the intensity of LIPEE con tinuum emission depends on the particle radius roughly as r4. This int eraction is essentially different from Rayleigh scattering, as the lat ter varies as r6. A study of time evolution of powder formation by LIP EE emission reveals the initial formation of nanometer size crystallit es and the coalescence process leading to larger scale particles. It c ould be demonstrated that the critical step of dust formation is the i nitial clustering process leading to nanometer scale crystallites.