(479d) Non-Thermal Plasmas and Semiconductor Nanocrystals

Many of the processes of technological interest involving the use of plasmas are negatively affected by the nucleation and growth of particles in the gas-phase. Much of the research in the area of particles and plasmas, as a consequence, has focused on the elimination of particles from these processes. A radically new approach will be presented, in which nanoparticles are deliberately synthesized in a plasma and studied for a class of novel technological applications. In particular, this work focuses on the synthesis of silicon quantum dots, small silicon nanocrystals whose electronic and optical properties strongly deviate from those of the bulk material. A continuous flow non-thermal plasma reactor will be described in detail. In non-thermal plasmas, the gas temperature remains close to room temperature while the presence of energetic free-electrons triggers the nucleation and growth of nanocrystals. Moreover, the electrostatic charging of the particles slows down agglomeration, making this process ideal for the synthesis of small particles. For the first time, we have studied the nanoparticle energy balance in the discharge and shown that there is a significant non-equilibrium between the particle temperature and the background gas temperature, likely leading to the formation of high quality nanocrystals. This work also addresses the passivation and functionalization of the nanoparticles, with the goal of (1) maximizing the fluorescence efficiency of the crystals and (2) providing a good dispersion of particles in the desired solvent, enabling the formulation of inks for various applications, such as printed electronics or roll-to-roll fabrication of solar cells. In particular, I intend to highlight the importance of these novel nanomaterials for energy-related applications, such as photovoltaics.