Fluorescence of silicon nanoparticles suspended in water: reactive co-deposition for the control of surface properties of clusters

Abstract

Abstract. Fluorescent silicon nanoparticles have been produced in a two-step process in ultra high vacuum. First, silicon clusters were produced in the gas phase in a molecular beam. At the end of the cluster beam machine the cluster were co-deposited with water onto a cold target. Melting of the ice yields a suspension that fluoresces at 420 nm when excited with ultraviolet light. The fluorescence intensity remains constant over a period of more than a year. Photo-absorption and photo-luminescence spectra provide evidence of a Si/SiO 2 core-shell structure having a silicon core size of at least 1.4 nm in diameter and oxygen deficient O-Si-O defects as the origin of the deep-blue fluorescence. Furthermore, the fluorescent suspension was deposited on freshly cleaved highly oriented pyrolytic graphite (HOPG). AFM images recorded in UHV showed networks of agglomerated clusters, their smallest units having a diameter of typically 0.7 nm.

Size-selecting effect of water on fluorescent silicon clusters

“…We have recently reported on a new production method for fluorescent silicon nanoparticles in water in which silicon clusters are produced in a molecular beam in the gas phase and then co-deposited with a beam of water vapour onto a cold target [24][25][26]. After deposition the ice is melted which produces a suspension of nanoparticles in water.…”