Modeling Nanoparticle Synthesis by Gas Condensation in a Nanocluster Source for Applications in Photovoltaic and Hydrogen Fuel Cells

One challenging and relatively cost-effective alternative to MOCVD-deposited nanoparticles (NPs) is the synthesis of nano-aggregates by inert-gas condensation of a sputtered vapor in a dedicated magnetron-based reactor. By tuning the collision path length and hence the time of residence of NPs in the carrier gas phase, spherical aggregates with well-controlled nanometer-scale diameters and relatively narrow size dispersion are produced from various materials. Such aggregates exhibit interesting properties related to their high surface-to-volume ratio and surface reactivity (e.g. in catalysis applications). On the basis of experimental results, a detailed modeling of NP nucleation and growth based on the classical nucleation theory was developed taking the peculiar geometry and thermal profile of the NP reactor into account. The simulated curves, calculated by a matlab program developed for that purpose, exhibit a good qualitative agreement with experiment and highlight the role of the process parameters and reactor temperature profile on the NP size distribution. Such calculations underline the possible optimization of the NP source design in order to improve its efficiency and reproducibility. The model may also yield a feasibility criterion and facilitate process development for costly materials by limiting the range of investigated parameters.