Synthesis of Alkyl-Terminated Silicon Nanoclusters by a Solution Route

Abstract

We describe the synthesis and characterization of alkyl-capped nanocrystalline Si (R ˆ-n-Si) prepared by the reaction of SiCl 4 with Mg 2 Si in ethylene glycol dimethyl ether (glyme) and surface-terminated with various alkyl groups, R ˆ-n-Si (R ) methyl, ethyl, n-butyl, and n-octyl). This reaction produces crystalline nanoparticles with surfaces that can be chemically modified. The resultant crystalline nanoparticles can be suspended in organic solvents or isolated as a powder. The nanoclusters were characterized by transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction (SAED), and Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, UV-vis absorption, and photoluminescence spectroscopy. The average cluster size depends on the reflux time of Mg 2 -Si with SiCl 4 , which provided nanoclusters with an average size of 2-5 nm. HRTEM confirms the presence of crystalline nanoclusters, and SAED is consistent with diamond-structured silicon. FTIR spectra are consistent with alkyl surface termination and show very little or no evidence for oxygen on the surface of the nanoclusters, depending on the surface alkyl group. The alkyl termination can be removed by reaction in air at 450 °C, and a Si-O stretch is observed in the FTIR spectra. EPR spectroscopy is consistent with crystalline Si nanoclusters and shows no signal at 4 K. The optical absorption spectra show an absorption edge between 260 and 240 nm, depending on the surface alkyl group, while a strong UV-blue photoluminescence between 315 and 520 nm is observed.

Surface brightens up Si quantum dots: direct bandgap-like size-tunable emission

“…21 Magnesium silicide (Mg 2 Si) was oxidized with bromine (Br 2 ) in refluxing n-octane during 3 days. Formed bromine-terminated Si-QDs were passivated using n-butyllithium, resulting in n-butyl-terminated Si-QDs.…”

Optical Biosensing and Bioimaging With Porous Silicon and Silicon Quantum Dots (Invited Review)

“…Early examples belonging to this approach is the use of precipitation reaction using molecular precursors [113,114]. Early examples were represented by the use of Zintl salts which yield blue fluorescent silicon nanocrystals [114][115][116].…”

“…Early examples belonging to this approach is the use of precipitation reaction using molecular precursors [113,114]. Early examples were represented by the use of Zintl salts which yield blue fluorescent silicon nanocrystals [114][115][116]. Unsurprisingly, the use of surfactants seems to improve the monodispersity of the particles when a high quality micelle is formed, as demonstrated by the reduction of halogenated silane aided by phase transfer agents [101,113,[117][118][119][120].…”

Fabrication of Si nanopowder and application to hydrogen generation and photoluminescent material

“…These methods require expensive materials such as SiH 4 , and moreover, the fabrication rate of Si nanopowder is considerably low. The Si nanopowder can also be produced using chemical methods, eg reduction of SiCl 4 using eg C 8 K [9], and Mg 2 Si, [10]. The chemical method are also time-consuming, and requires expensive reactant materials.…”