Nanoparticle formation from thin film sputtering: A complex dust cloud structure
Résumé
Dense clouds of nanoparticles can be formed in typical capacitively-coupled radio-frequency discharges operating at low pressure, by sputtering thin films deposited on the electrodes. As the nanoparticle size, and thus mass, are small, gravity is not the dominant force and they can easily occupy most of the plasma volume except the sheathes (where the local electric field repels them) and the void, a dust-free region where the outwards ion flux pushes them away.
The void is a very intriguing structure at the origin of many complex phenomena. For example, it is a region where many instabilities are observed and where new generations of nanoparticles can grow following a cyclic process. The void can grow in size evacuating all nanoparticles from the discharge before a new generation appears, or successive generations can rapidly succeed each other inside the void and coexist. In this last case, clear empty spaces separate the different generations.
Most of the experiments reveal the presence of a single central void. Nevertheless, in a new reactor we observed the existence of two symmetric voids. These voids can stay distinct or merge and form a single one. In both situations, new generations of nanoparticles can emerge from these regions where conditions of fresh nanoparticle nucleation are fulfilled.
In this presentation we will show some particularities of the void formation and how successive generations of nanoparticles can emerge from this region.