"Morphological and Electronic Study of Au Nanoparticles on SiO₂/Si Using MEIS, XPS, and TEM"

The growing demand for metallic nanoparticles[1] in medicine and electronics drives the development of precise synthesis and characterization techniques. This work presents a morphological and electronic properties study of gold nanoparticles (Au NPs) synthesized and deposited on a SiO₂/Si substrate. Characterization was performed using Medium-Energy Ion Scattering (MEIS)[2], complemented by X-ray Photoelectron Spectroscopy (XPS)[2] and Transmission Electron Microscopy (TEM). XPS analysis determined the chemical environment of the Au NPs in colloids, the precursor salt (KAuCl₄), and in an aqueous salt solution, while also evaluating X-ray radiation effects from the Al Kα source. In the colloids, Au⁰ and Au¹⁺ oxidation states predominated in the Au 4f transition. For the precursor solution, X-ray exposure induced an reduction reaction from Au³⁺ to Au¹⁺, tracking the expected reduction sequence toward Au⁰, whereas the dry salt showed no significant modifications. Subsequently, the spin-coated samples were analyzed by MEIS using 150 keV alpha particles. Experimental spectra were fitted using PowerMEIS software, evaluating different surface morphological models via the reduced χ² test. The statistical analysis indicated that a spherical geometry best described the supported Au NPs. Finally, TEM micrographs confirmed this spherical morphology, showing excellent agreement with the MEIS reconstructions. These results highlight the capability of MEIS as a precise, non-destructive tool for reconstructing the morphology of supported nanostructures.