S. Girshick, U. Minnesota Aluminum Nanoparticle Synthesis and Coating Steven L. Girshick University of Minnesota

S. Girshick, U. Minnesota Objectives 1.Synthesize Al nanoparticles using scalable plasma process 3.Coat particles to passivate surfaces 2.Maintain small primary particle size (high specific surface area) for high reactivity

S. Girshick, U. Minnesota Acknowledgments Prof. Michael Zachariah Dr. Feng Liao Mr. Bin Zhang (PhD student) Mr. Bo Liu (MS student) Prof. Jeff Roberts Dr. Ying-Chih Liao

S. Girshick, U. Minnesota Why use thermal plasma? Atmospheric-pressure operation Completely dissociates reactants to elements High energy density  high throughput in small reactor Chemical flexibility Continuous not batch process Environmentally benign Scalable

S. Girshick, U. Minnesota 2000 K 1000 K Complete dissociation Nucleation front Growth & coagulation 5000 K Flow Diffusion & thermophoresis Convection Particle synthesis in a thermal plasma

S. Girshick, U. Minnesota Nanoparticle reactor

S. Girshick, U. Minnesota Plasma torch / nozzle assembly DC plasma torch Injection ring Nozzle holder

S. Girshick, U. Minnesota

plasma Large counterflow plasma counterflow Formation of stagnation layer Small counterflow Al 2 O 3 tube counterflow plasma

S. Girshick, U. Minnesota Experimental Diagnostics Plasma torch Ar/H 2 30/0.5 slm I=200 A, ~10 kW Counter flow Ar, 85 slm Diagnostics port 53kPa Injection Ring 4000 K, 88 kPa Vacuum pump Nozzle Ejector DMA, for size distribution N2N2 Vacuum pump Water cooled substrate, for RBS sample TEM grid, for TEM and EDS Filter holder Sampling probe RBS TEM EDS Size distribution By-pass Glass beads and AlCl 3 powder Heated Ar 100~200 sccm Pressure gauge Vacuum Packed bed Heating cable Thermocouple

S. Girshick, U. Minnesota Particle sampling & measurement Nano DMA TSI CNC 3010A Ejector N2 65 PSI Ejector N2 65 PSI Critical Orifice Critical Orifice Bypass TEM Grid Holder Vacuum Scanning mobility particle sizer (SMPS) Sampled aerosol Dilution

S. Girshick, U. Minnesota Plasma power input 5–10 210–250 A Chamber pressure400Torr Plasma flow rates argon30slm hydrogen0.5–2.0slm AlCl 3 10–20sccm Counterflow argon85slm Operating conditions

S. Girshick, U. Minnesota tapered tube AlCl 3 vapor delivery system Entire vapor flow passage is kept hot to avoid pre- condensation

S. Girshick, U. Minnesota Counterflow reduces particle size SMPS measurements With & w/out counterflow

S. Girshick, U. Minnesota SMPS measurements Effect of Ar carrier gas flow rate Carrier gas   AlCl 3 flow rate   D p  AlCl 3 flow rate  20 sccm

S. Girshick, U. Minnesota Inlet of SMPS sampling probe

S. Girshick, U. Minnesota Particles deposited onto TEM grids Particles are mostly unagglommerated

S. Girshick, U. Minnesota Particle on TEM grid TEM EDS Background from Si 3 N 4 TEM grid is shown in red Al O

S. Girshick, U. Minnesota Particle diameter  125 nm Oxide layer thickness  2-5 nm Oxide layer on particle

S. Girshick, U. Minnesota Lattice fringe spacing = 2.35  Å Al (111) = Å Al particle with surface oxide layer oxide layer crystalline Al core

S. Girshick, U. Minnesota Photoinduced CVD  Gas-phase reactants are activated by UV/VUV photons  Excimer lamps are ideal photon source  Commercially available  Compact, long-life, reliable  UV photons can break most chemical bonds  Many wavelengths available e.g., 172 nm (Xe 2 *), 222 nm (KrCl*)  Increasingly used for CVD of thin films  Not yet used for coating particles Xe 2 *

S. Girshick, U. Minnesota Photoinduced particle coating: tandem DMA experiment

S. Girshick, U. Minnesota Tandem DMA UV lamp Plasma reactor

S. Girshick, U. Minnesota DMA #1: polydisperse aerosol enters, monodisperse aerosol exits

S. Girshick, U. Minnesota In absence of Al particles, UV generates C particles Introduce CH 4 or C 2 H 2, w/o Al particles

S. Girshick, U. Minnesota Al particles + CH 4 + UV

S. Girshick, U. Minnesota Shift in peak due to surface growth? First evidence of UV-induced growth of thin C film on surface

S. Girshick, U. Minnesota Modeling particle nucleation & growth Truhlar: cluster reactivities & free energies Girshick: nucleation & growth model, implemented in reactor flow & temperature field Garrick: effects of turbulence nucleation

S. Girshick, U. Minnesota Summary Developed thermal plasma process and conducted parametric studies of Al nanoparticle production Characterized oxide coating on particles Developed process for photoinduced coating of Al particles with passivating layer In progress: tandem DMA studies. Preliminary results show growth of thin film on particles In progress: particle nucleation model that utilizes ab initio calculations of Truhlar’s group