Silicon is a key material in the microelectronics industry. Recently, there has been great interest in nanocrystalline phases of silicon due to their size dependent electronic and optical properties.[1] Nanoparticles with physical dimensions less than the bulk Bohr exciton radius of silicon (4 nm) typically display intense photoluminescence due to quantum size effects and have potential use both in optoelectronic devices [2][3][4] and as fluorescent biomarkers. [5,6] In the case of crystalline silicon nanoparticles, the photoluminescence (PL) will shift to higher energies as the average size of the nanoparticles is reduced. [7,8] Particle sizes of the order of ∼ 1 nm have been termed "ultrabright" and show an intense emission in the blue region of the visible spectrum. [9][10][11] In addition to a dependence on the particle size, the photoluminesence of silicon nanoparticles is also influenced by the nature of the passivating layer on the particle surface. [12][13][14][15] Passivation of the surface provides chemical stability to air-oxidation and Ostwald ripening and also ties down defect states at the surface caused by dangling bonds. Successful passiviation of the silicon surface has been recently achieved by chemically inert alkyl groups. A surface passivated with strong Si-C bonds is chemically stable and the effective band gap of the silicon nanoparticle is relatively unperturbed by the alkyl passivation.[16] Alkyl passivated nanoparticles have been previously produced by chemical and electrochemical etching of bulk silicon, [17][18][19][20] the reduction of halosilanes, [21,22] the oxidation of metal silicides, [23,24] and the thermal decomposition of silanes in the gas phase [25][26][27] and supercritical fluids.[28] Each of these approaches requires the use of highly reactive or corrosive chemicals and often requires the modification of unstable hydrogen or halogen terminated surfaces. [29,30] Direct approaches, commonly involving the mechanical scribing of silicon in the presence of reactive organic reagents, have found success in the patterning of silicon surfaces though reaction of a freshly exposed surface with the organic reagent. [31][32][33][34] However, these techniques are limited to large and regular surfaces, and are not practical for use with nanoparticles. Here we describe a novel top-down procedure for the synthesis of stable alkyl/alkenyl passivated silicon nanoparticles using high energy ball milling (HEBM). [35] The main advantage of this mechanochemical approach is the simultaneous production of silicon nanoparticles and the chemical passivation of the particle surface by alkyl/alkenyl groups covalently linked through strong Si-C bonds. The overall procedure for production of alkyl/alkenyl passivated silicon nanoparticles is illustrated in Figure 1. A milling vial is loaded under inert atmosphere with non-spherical millimeter-sized pieces of semiconductor-grade silicon and either an alkene or alkyne. Stainless steel milling balls are added to the vial, which is then sealed and placed in...

Silicon nanoparticles are useful materials for optoelectronic devices, solar cells and biological markers. The synthesis of air-stable nanoparticles with tunable optoelectronic properties is highly desirable. The mechanochemical synthesis of silicon nanoparticles via high-energy ball milling produces a variety of covalently bonded surfaces depending on the nature of the organic liquid used in the milling process. The use of the C 8 reactants including octanoic acid, 1-octanol, 1-octaldehyde and 1-octene results in passivated surfaces characterized by strong Si-C bonds or strong Si-O bonds. The surfaces of the nanoparticles were characterized by infrared spectroscopy and nuclear magnetic resonance spectroscopy. The nanoparticles were soluble in common organic solvents and remarkably stable against agglomeration and air oxidation. The luminescence and optical properties of the nanoparticles were very sensitive to the nature of their passivating surface.

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