Effect of exit-orifice diameter on Cu nanoparticles produced by gas-aggregation source

Gas-aggregation source (GAS) was used to prepare Cu nanoparticles. By changing the diameter of the exit orifice of the aggregation chamber, we were able to isolate and investigate the effect of the flow rate of the working gas at a constant pressure inside the aggregation chamber. We show that the conventional approach of changing pressure by adjusting the flow rate (at a constant orifice diameter) does not significantly influence the nanoparticle size. However, when the pressure is held constant, changing the flow rate has a notable effect. Based on a theoretical study, we suggest that the determining parameter which needs to be considered is the pressure to flow rate ratio. This ratio determines the residence time of the nanoparticles inside the aggregation chamber (and therefore the time available for them to grow) and is constant for a constant orifice diameter. Decreasing the orifice diameter, however, increases the pressure to flow rate ratio, which gives the nanoparticles longer time inside the aggregation chamber and allows them to grow larger. Apart from their size, the orifice diameter also influences the mass flux and its angular distribution.

Automated summary

By changing the diameter of the exit orifice of the gas-aggregation source, the size and growth time of Cu nanoparticles can be influenced. The pressure to flow rate ratio is the key parameter in determining the growth of nanoparticles.