A LUMINESCENT SILICON NANOCRYSTAL COLLOID VIA A HIGH-TEMPERATURE AEROSOL REACTION

We describe a high-temperature aerosol apparatus for the synthesis of 3-8-nm, surface-oxidized Si crystallites. The particles are made by homogeneous gas-phase nucleation following pyrolysis of dilute disilane in He. The particles are collected as a robust ethylene glycol colloid, and characterized by transmission electron microscopy, X-ray powder Bragg scattering, IR, high-pressure liquid chromatography, and optical spectroscopy. The particles exhibit a shell structure, with a crystalline Si core, of bulk lattice constant, capped with an approximately 1.2-nm shell of silicon dioxide. After acidic reflux, the particles luminesce with 5% net quantum yield. As the Si core decreases to about 2 nm the emission shifts 0.5 eV above the bulk Si band pp. This red luminescence appears consistent with a predicted quantum size effect in crystalline silicon.