Evaluation of the factors that influence the fabrication of porous thin films by deposition of aerosol nanoparticles

• Nonagglomerated TiO2 and SiO2 nanoparticles are generated in a plasma reactor.
• Electrostatic deposition enables fast fabrication of films with highly uniform pore structures.
• Particle agglomeration strongly affect the pore structure of film.
• Pore sizes of films can be tuned by only changing the diameter of nanoparticles.

In this study, porous films were fabricated by gas-phase deposition of nonagglomerated metal oxide nanoparticles generated in a plasma field. The effects of several factors including the deposition mechanism, nanoparticle dispersibility, and nanoparticle diameter on the porous morphology were investigated systematically. Careful tuning of the generation conditions led to the generation of nonagglomerated TiO2 and SiO2 nanoparticles, with diameters ranging from 8 to 36 nm. The electrostatic deposition of the nonagglomerated, negatively charged nanoparticles onto a substrate to which a DC positive bias voltage was applied enabled fast fabrication of porous films as well as highly uniform pore structures, which was theoretically explained by estimating the rate of particle deposition. The deposition of agglomerated nanoparticles resulted in films with greater porosity and more random structures compared with those resulting from nonagglomerated nanoparticles. These increases in porosity and randomness were caused by a large area for the interception of agglomerated nanoparticles that led to a steric hindrance for the agglomerates being deposited. The pore sizes of the films increased as the diameters of the nanoparticles increased, whereas the composition of the nanoparticles did not affect the film morphology. Therefore, this study provides useful information for the fabrication of porous thin films with well-controlled structures from various nanoparticles.