Nano liquid particle monitoring system for colloidal nanoparticle measurement: reducing non-volatile residue via virtual impactor with large-droplet removal

초록

Precise nanoparticle size distribution (PSD) characterization is critical in clean-process applications. This study evaluates a nano liquid particle monitoring system (Nano LPM)-an aerosol-based PSD measurement system-against dynamic light scattering (DLS) and scanning electron microscopy (SEM) for both monodisperse and polydisperse engineered nanoparticles. Standard polystyrene latex (PSL) nanospheres (50-200 nm) were used to calibrate Nano LPM, yielding a near-perfect linear concentration response (R-2 > 0.995). Repeated PSL measurements further showed small combined standard uncertainties for both modal sizing and concentration recovery, confirming the quantitative reliability of the Nano LPM approach. In monodisperse colloidal silica (similar to 120 nm), Nano LPM measured a mode diameter of 120.8 nm, matching SEM (119.8 nm; <1% difference), while DLS reported a slightly higher and broader peak (similar to 126 nm). For a bimodal silica mixture, Nano LPM resolved two distinct particle populations (similar to 55 nm and similar to 121 nm) in agreement with SEM; in contrast, DLS could only detect a single broad mode (similar to 126 nm) and failed to identify the smaller particles. Furthermore, the Nano LPMGen employs a two-stage nebulizer with an integrated virtual impactor to remove larger droplets before downstream drying, and produced much finer transmitted aerosol droplets (geometric mean diameter similar to 0.61 & micro;m at 0.01% solute to similar to 0.39 & micro;m at 0.1% solute) than a conventional atomizer, thereby reducing non-volatile residue (NVR) artifacts. Overall, Nano LPM provided higher-resolution and more accurate PSDs than DLS and matched SEM's accuracy, while reducing residue-related interference through fine-droplet generation and large-droplet removal. It was also observed that larger PSL particles produced larger NVR modes, likely due to the higher amount of surfactants required to stabilize their greater total surface area. These capabilities make Nano LPM a promising inline metrology tool for high-purity nanoparticle process monitoring.

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