Preparation of nanoparticle-embedded thin films by simultaneous feeding of gaseous and solid raw materials in plasma-enhanced chemical vapor deposition process

Titania (TiO2) films in which silica (SiO2) nanoparticles are embedded (SiO2/TiO2 films) are prepared by a combination of a novel aerosolization technique and plasma-enhanced chemical vapor deposition (PECVD). Using titanium tetraisopropoxide (TTIP) in a microwave plasma field, anatase films are prepared on silicon and quartz-glass substrates. By utilizing Coulomb explosion of charged droplets in the plasma field, an aerosol with well-dispersed SiO2 nanoparticles is obtained from the breakup of sprayed droplets of a nanoparticle suspension. Simultaneous feeding of the TTIP vapor as a gaseous raw material and the SiO2 nanoparticle aerosol as a solid raw material enables preparation of the SiO2/TiO2 films with many protrusions. The number and size of the protrusions increase with increasing concentration of the nanoparticle suspension and increasing size of the nanoparticles, respectively. The size of the nanoparticles is related to the surface roughness of the SiO2/TiO2 films. Quantitative evaluation of the protrusions suggests that the mechanism of the protrusion evolution on SiO2 nanoparticles varies with the size of the nanoparticles. Embedding SiO2 nanoparticles into the TiO2 films enhances the photocatalytic activities compared to that of a TiO2-only film probably because the protrusions increase the surface area of the films.