Characterization of nanoparticles by scanning electron microscopy (SEM)

The samples were dispersed in solution and diluted with demineralized water. Then, the samples were applied to silicon wafers from Siegert Wafer Company and allowed to dry at laboratory temperature (23 °C). This wafer was adhered by a carbon conductive tape to the stub that was inserted into the SEM. The samples were examined by SEM on a Tescan MAIA 3 equipped with an FEG (Tescan Ltd., Brno, Czech Republic). The images were recorded using the In-Lens SE detector at a working distance between 2.92 and 2.99 mm at a 5 kV acceleration voltage under high vacuum conditions. The 768 × 858-pixel images were obtained at 100,000-fold magnification covering a sample area of 2.08 µm. Full frame capture was performed in Ultra Hight (UH) Resolution mode and image shift correction was enabled with accumulation of images, and it took approximately 0.5 min with an ∼0.32 µs/pixel dwell time. The spot size was set at 2.4 nm. The size of the nanoparticles was confirmed by a dynamic light scattering technique (Malvern Instrument Ltd, UK). Zn NPs and SiO₂ NPs were sonicated in distilled water. After this treatment, the larger NPs aggregated into microparticles.