A New Synthetic Route to Alkyl Terminated Silicon Nanoparticles.
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A New Synthetic Route to Alkyl Terminated Silicon Nanoparticles. Katherine A. Pettigrew, Philip P. Power, and Susan M. Kauzlarich* Department of Chemistry, One Shields Ave University of California, Davis, CA 95616 ABSTRACT This paper describes the preparation of alkyl terminated silicon nanoparticles that are air and moisture stable by the oxidation of magnesium silicide with bromine and then the subsequent termination with an alkyl Grignard reagent. The nanoparticles have been characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, and fluorescence spectroscopy. INTRODUCTION Research in the synthesis of silicon nanoparticles by solution routes [1-7] has been an active area of research. There have been recent demonstrations of silicon nanoparticles fluorescing in the blue, green, yellow, and red from various groups [8-10]. This group has been exploring various routes to the production of surface-capped silicon nanoparticles [4,5,8,11-15]. In particular, we have explored the use of metal silicides [16] as a precursor to silicon nanoparticles, which can be further surface passivated with organic ligands. The synthesis involves reacting metal silicides with silicon tetrachloride through a metathesis reaction and then subsequent termination with alkyl groups. Stable nanoparticles are obtained; however, high yields and narrow size distributions have not been forthcoming. A new method for the solution synthesis of silicon nanoparticles is presented in this paper. It involves the oxidation of magnesium silicide with bromine and subsequent termination of the nanoparticles with use of a Grignard reagent. It is hypothesized that with the covalent bonding of silicon, it will be possible to control the size of the nanoparticles by controlling the surface area of the nanoparticles, by the amount of bromine introduced during the synthesis. The yields are improved over the metathesis reaction and there is a narrower size distribution. EXPERIMENTAL PROCEDURE Chemicals: All reagents and materials were handled either in a nitrogen-dry box or in a Schlenk line using standard anaerobic techniques. Magnesium flake (99.9%) was purchased from Strem Chemical. Silicon (99.999+%) was obtained from J. Matthey. Anhydrous ethylene glycol dimethyl ether (glyme) (99.5%, Aldrich) was dried by distillation over sodium-potassium alloy in an argon atmosphere. n-Butyl magnesium chloride (n-BuMgCl, 2.0M in tetrahydrofuran (THF)), HPLC grade hexane, and HPLC grade water were purchased from Aldrich which was used as supplied. All glassware was silonated for 1-2 hours with a 2% solution of dichlorodimethylsilane in toluene, then rinsed with toluene and hexane, and dried at 120 oC overnight prior to use.
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Synthesis: Magnesium silicide (Mg2Si) was prepared by heating elemental magnesium flakes with elemental silicon powder at 750 oC for 3 days in a sealed tantalum tube, which was sealed in an evacuated quartz ampule [16]
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