NMR Study of the Synthesis of Alkyl-Terminated Silicon Nanoparticles from the Reaction of SiCl4with the Zintl Salt, NaSi

Abstract

The synthesis of silicon nanoclusters and their characterization by multinuclear solid-state nuclear magnetic resonance (NMR) is presented. A combination of 23Na, 29Si, and 13C magic angle spinning with and without cross polarization to 1H nuclei have been used to investigate the reaction of sodium silicide (NaSi) with silicon tetrachloride (SiCl4) followed by varying degrees of surface passivation. The 23Na and 29Si NMR spectra of NaSi distinguish the two crystallographically inequivalent sites for each, consistent with the crystal structure. This compound exhibits extreme diamagnetic chemical shifts for 29Si of −361 and −366 ppm. NaSi is reacted with SiCl4 in refluxing ethylene glycol dimethyl ether to produce both amorphous and crystalline Si nanoparticles with surfaces capped by chlorine. This reaction produces new 29Si resonances that survive subsequent capping and oxidation reactions. The 29Si NMR spectrum shows that the product is incompletely passivated with butyl groups and gives several peaks lying between −67 and −81 ppm that can be attributed to surface silicon atoms. Further reaction of this product with water produces a new NMR spectrum consistent with further termination of the surface by −OH groups.