Study of initial dust formation in an Ar-SiH4 discharge by laser induced particle explosive evaporation

TLDR

Dust formation in low‑pressure RF discharges involves particulate growth that differs from Rayleigh scattering, which scales as r⁶. The study employed laser‑induced particle explosive evaporation (LIPEE) to observe nanometer‑sized particles, with a model indicating that LIPEE continuum emission scales as r⁴. LIPEE proved far more efficient than conventional light scattering for detecting nanometer particles, revealing that dust formation begins with clustering of nanometer‑scale crystallites that subsequently coalesce into larger particles.

Abstract

The initial step of particulate growth in a dust forming low pressure radio-frequency discharge has been studied in situ by laser induced particle explosive evaporation (LIPEE). With respect to the conventional light scattering, this method has been found much more efficient to observe small nanometer size particles, especially in the case of UV excimer laser radiation. Experimental results interpreted by a simple model of laser-particle interaction show that the intensity of LIPEE continuum emission depends on the particle radius roughly as r4. This interaction is essentially different from Rayleigh scattering, as the latter varies as r6. A study of time evolution of powder formation by LIPEE emission reveals the initial formation of nanometer size crystallites and the coalescence process leading to larger scale particles. It could be demonstrated that the critical step of dust formation is the initial clustering process leading to nanometer scale crystallites.