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.

A solution synthesis of crystalline Ge nanoparticles (nc-Ge ) is reported. The metathesis reaction of NaGe with excess GeCl 4 in glyme solvents produces nc-Ge. Metathesis reactions between KGe and excess GeCl 4 or GeCl 2 :(dioxane) in glyme and Mg 2 Ge and excess GeCl 4 in diglyme and triglyme were also investigated. The surface of these nanoparticles is terminated with alkyl groups by reaction with alkyl Li and Grignard reagents. The alkyl-terminated crystalline Ge nanoparticles (R ˆ-nc-Ge) were characterized by Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, powder X-ray diffraction, UV-vis absorption spectroscopy, photoluminescence, and photoluminescence excitation spectroscopy. The optical properties of R ˆ-nc-Ge made by this method agree with predictions from quantum confinement models.

Nanoparticles of indium oxide, a transparent conducting oxide with a band gap close to GaN, were synthesized by pulsed laser ablation of a pure indium metal target. X-ray diffraction and transmission electron microscopy confirmed that nanocrystalline indium oxide particles with a mean diameter of 6.6 nm with a cubic crystal structure were formed. Photoluminescence spectroscopy shows a strong emission peak at 3.78 eV with a weak size dependence.

Nanometer-sized silicon particles have been produced by ultrasonic dispersion of thin sections of porous silicon (PS) in organic solvents. The particles have been characterized by HRTEM (high-resolution transmission electron microscopy), FTIR (Fourier transform infrared) spectroscopy, and fluorescence spectroscopy. HRTEM shows both aggregates of and monodispersed crystallite particles of Si. The larger aggregates range in size from 20 to 50 nm and are made up of small crystallites with diameters of 2-10 nm. Monodispersed crystallites ranged in size from 2-10 nm. All the particles have an amorphous layer of SiO 2 . The photoluminescence (PL) spectrum shows two peaks: a red peak at around 680 nm, which is typical for PS and a blue peak between 415 and 446 nm, which is not typical for as-prepared PS. As a function of increased excitation intensity, the blue peak grows at the expense of the red. This is discussed in light of photoluminescence lifetime data. The red luminescence is attributed to quantum confinement. The blue luminescence is attributed to either extremely small Si crystallites or (Si(II)) 0 defects embedded in the oxide matrix.