Plasma grown particles: From injected gases to nanoparticles and nanomaterials, from injected particles to dust clouds in the PKE experiment

This paper will be focused on two specific examples related to particle growth phenomena in low pressure plasmas. The first one concerns the formation of nanometer size silicon particles and their impact on plasma processing of thin films where the deposition of these particles leads to a significant improvement of quality or to the opening of new windows in thin films technologies. Solar cells based on 'polymorphorphous silicon' , based on nanoparticles grown in Silane-Hydrogen plasmas will illustrate the first point, while nanometer crystals of silicon, deposited in SiF4-H2 plasmas and not embedded in an amorphous matrix, evidence attractive phototoluminescence properties. The second illustration is related to the growth of particles in an RF argon plasmas, where externally injected polymer particles represent the primary source for dust growth. Particle growth process, as observed in preliminary laboratory studies, evidences successive growth-etching phenomena reported here. These studies lead to optimized conditions for growing dust clouds in the PKE-NEFEDOF experiments, achieved in microgravity conditions on board of ISS. In these experiments the size of grown particles was not available by ex-situ measurements and laser scattering data suggest only the existence of at a dense cloud of particles too small to be observed individually. We will show that particle size and density can be estimated from macroscopic data such as the RF discharge impedance and the propagation across the cloud of low frequency mechanical excitation driven by sheath width modulations