Ion-Induced Nucleation in Nanoparticle Synthesis by Ionization Chemical Vapor Deposition

Particle formation mechanisms in nanoparticle synthesis by ionization chemical vapor deposition (CVD), in which source gases are ionized before being fed into the reactor, were investigated experimentally. First, nonagglomerated nanoparticles were formed from a tetraethylorthosilicate (TEOS)/O ₂ mixture ionized with a sonic-jet ionizer at various furnace temperatures, T _f, and TEOS concentrations, N _TEOS. Then, the electrical mobility of the nanoparticles and ions were measured using a differential mobility analyzer combined with a Faraday cup electrometer, and the particle number concentration by a condensation nucleus counter. Measurements at 293 ≤ T _f ≤ 1173 K and 0 ≤ N _TEOS ≤ 1.38 × 10 ^?5 mol/l showed that (a) negative TEOS and TEOS cluster ions were formed at T _f = 293 K, (b) gas-phase intermediates forming nanoparticles were formed at T _f ≥ 673 K, (c) for T _f = 873 K condensation of the intermediates onto ions (i.e., ion-induced nucleation) started at N _TEOS ≥ 4.48 × 10 ^?7 mol/l, and (d) the growth from ions to nanoparticles was discontinuous for this change in N _TEOS.