Constriction requirement for nanoparticle crystallization in a non-thermal atmospheric pressure plasma

Plasmas have emerged as among the most promising methods to synthesize nanoparticles, including from high-crystallization-temperature materials such as silicon. Recent work in the area of flow-through low-temperature plasma synthesis of nanoparticles has indicated that the assumptions of plug flow and diffuse plasma properties are not entirely supported by experimental evidence. Here, we report on an atmospheric pressure, non-thermal plasma reactor for silicon nanocrystal synthesis, together with our findings that the plasma is not diffuse but instead is a dynamic constricted discharge. Furthermore, we find that this constriction is dependent on the silane concentration in the reactor and also plays a role in nanoparticle crystallization. This work highlights the complexity of this process, and the need for further work to understand how nanoparticles are synthesized and crystallized in flow-through non-thermal plasma reactors.