Electrical measurements for the control of nanoparticle growth in an acetylene plasma

Nanoparticles are not only of fundamental interest due to their remarkable properties but also of practicle importance in material processing. Controlling their growth in plasmas is regarded as a new route to prepare nanoparticles of well defined size and composition. However, the processes during their formation are yet to be fully understood. Especially the early stages of the particle growth are not well investigated since they are experimentally inaccessible by standard methods like Mie-scattering. A novel collection method based on neutral drag was tested in order to get a better insight into the early stages of particle growth. The experiments were performed in a capacitively coupled discharge, where multiple growth cycles can be obtained. Size distributions of the nanoparticles at different stages of the growth cycle were determined ex-situ by electron microscopy. The obtained size distributions were correlated with in-situ measurements of the bias voltage and the phase angle between discharge current and voltage. The observed correlations, which can be used for prediction of the particle growth, are qualitatively explained.