Temperature dependence of nucleation and growth of nanoparticles in low pressure Ar/CH4 RF discharges

The gas temperature (T-g) dependence of nucleation and growth processes of hydrocarbon nanoparticles in low pressure Ar/CH4 RF discharges has been investigated. Measuring the electron density with the microwave cavity resonance technique allowed us to monitor nucleation processes on small (mu s) time scales. On larger time scales, coagulation times and growth rates are determined by means of measuring the phase angle between the RF voltage and current in correlation with laser light scattering. The experimental results show a significant gas temperature dependence of both powder nucleation and growth processes. Within the measured gas temperature range (20-130 degrees C) the particle growth rate decreases by a factor of similar to 3.7, while the coagulation time increases by a factor of similar to 6.5 with increasing T-g. Moreover, in this paper we present a simplified model which uses the experimentally determined growth rates and coagulation times to predict the value of the critical density of nanometre sized neutral particles, necessary to initiate coagulation. This model estimates a critical density of 3.5 x 10(15) m(-3) at room temperature which decreases with increasing temperature.