Plasma‐assisted gas‐phase synthesis and in‐line coating of silicon nanoparticles

This study investigates the feasibility of plasma‐supported in‐line functionalization of silicon nanoparticles (NPs) in an atmospheric pressure gas‐phase reactor. The approach utilizes the synthesis of core silicon NPs and their subsequent coating downstream of the particle formation zone. In‐line coating is accomplished with a cylindrical coating nozzle to achieve homogenous mixing of coating precursor vapors with in‐coming NPs. Multiple siloxanes were tested for their coating suitability and their ability towards coating homogeneity. It was found that tetraethyl orthosilicate is favored for thin layers consisting of almost pure silica while hexamethyldisiloxane and octamethylcyclotetrasiloxane (OMCTS) coatings contained reasonable amounts of hydrocarbons. Moreover, OMCTS showed a pronounced tendency towards homogeneous nucleation, thus leading to the additional formation of silica NPs due to homogeneous nucleation. Gas‐phase synthesis followed by plasma‐assisted in‐line functionalization of silicon nanoparticles is carried out in a plasma reactor under atmospheric pressure. Various coating precursors are used, including tetraethyl orthosilicate, hexamethyldisiloxane, and octamethylcyclotetrasiloxane to obtain distinct core‐shell structures. The plasma generates activated species, which help in the formation of an amorphous, homogeneous SiO2 shell around the crystalline Silicon core in the plasma afterglow. Depending on precursor, composition and concentration, homogeneous nucleation is observed besides homogeneous particle coating via heterogeneous nucleation.