Characterization of Mechanically Attrited Si/SiO_x Nanoparticles and Their Self-Assembled Composite Films

The surface chemistry and structure of nanosized silicon, as obtained by high-energy ball milling and its subsequent dispersion in ethanol, via sonication-assisted oxidation, is presently described. These Si/SiO x suspensions that spontaneously assemble on glass surfaces were investigated as a function of pH in a variety of oxidizing agents and atmospheres. Spectroscopic characterization indicates that at pH 5 or below and in the absence of H 2 O, the Si−OEt groups present on the surface of these nanoparticles get protonated, providing the driving force to assemble on less positively charged glass substrates. X-ray photoelectron spectroscopy concurs with a core/shell (Si/SiO x ) nanoparticle structure, with an average Si-atom ratio of 45/55 and x in the order of 1.5. In addition, Raman investigation suggests that the Si core in these nanoparticles (45% of the total Si-atom content) is composed of crystalline (34%) and amorphous (11%) parts.