AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Formation of 1.0-10 nm Ni Clusters in an Atmospheric Pressure DC Microplasma
R. MOHAN SANKARAN, Ajay Kumar, Seungkoo Kang, Carlos Larriba-Andaluz, Hui Ouyang, Christopher Hogan Jr., Case Western Reserve University
Abstract Number: 173 Working Group: Nanoparticles and Materials Synthesis
Abstract Microplasmas are a special class of plasmas formed in geometries where at least one dimension is less than 1 mm. Plasma confinement leads to several unique properties, including high-pressure stability and non-equilibrium. Aerosol nanoparticles can be nucleated and rapidly quenched in a microplasma to obtain small (less than 10 nm) clusters. Using a high resolution differential mobility analyzer (1/2-mini DMA, Nanoengineering) coupled to a faraday cage electrometer, we have investigated the formation of Ni clusters through the decomposition of nickelocene (bis(cyclopentadienyl)nickel). Nickelocene vapor was introduced into the microplasma via a heated tube containing nickelocene powder upstream of the plasma electrodes. Prior to mobility measurement, produced clusters were brought to a steady-state charge distribution via diffusion charging with ions produced in a Kr-85 source (TSI, Inc.). Both positive and negative mobility distributions measured exhibited high intensity peaks around ~0.75 nm equivalent “mobility diameter”, corresponding to the ions produced by the Kr-85 source. The introduction of nickelocene vapor in the microplasma resulted in a lower intensity distribution of clusters, spanning from the peaks corresponding to Kr-85 generated ions to 10 nm in mobility size. Under all circumstances, the mobility distribution from the ion peak to the largest produced clusters was continuous, indicating the microplasma reactor can form stable entities below 2.0 nm in size. To obtain structure-mobility relationships, density functional theory and gas molecule scattering calculations were carried out. The clusters were also collected by electrostatic precipitation and further characterized by atomic force microscopy to confirm their size and distribution. These results demonstrate the ability of microplasma reactors to form stable sub-2.0 nm clusters for studies of particle formation in the vapor phase.