Facile Synthesis of Germanium Nanoparticles with Size Control: Microwave versus Conventional Heating

Abstract

A facile size-controlled synthesis (microwave/ conventional) of quasi-spherical germanium nanoparticles is reported. Oleylamine serves as a solvent, a binding ligand, and a reducing agent in the synthesis. Reactions were carried out with microwave-assisted heating, and the results have been compared with those produced by conventional heating. Germanium iodides (GeI 4 , GeI 2 ) were used as the Ge precursor, and size control in the range of 4−11 nm was achieved by controlling the ratio of Ge 4+ /Ge 2+ in the precursor mix. Longer reaction times and higher temperatures were also observed to have an effect on the nanoparticle size distribution. Microwave heating resulted in crystalline nanoparticles at lower temperatures than conventional resistive heating because of the ability of germanium iodides to convert electromagnetic radiation directly to heat. The reported approach for germanium nanoparticle preparation avoids the use of strong reducing agents (LiAlH 4 , n-BuLi, NaBH 4 ) and HF for etching and, thus, can be considered simple, safe, and amenable to industrial-level scaleup. The as-prepared nanoparticles are a stable dispersion (hexane or toluene) for weeks when stored under an inert atmosphere (N 2 /Ar). The stability of the colloidal dispersion was observed to be dependent on the nanoparticle size, with smaller nanoparticles exhibiting longer stability. On exposure to ambient conditions, oxidation occurs over a period of time and results in slow precipitation of the nanoparticles. The nanoparticles have been characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and spectroscopic techniques (UV-Vis-NIR, FTIR, Raman).

Size and emission color tuning in the solution phase synthesis of highly luminescent germanium nanocrystals

“…The wide variety of synthetic strategies reported, together with broad particle size distributions, different ligand passivation strategies and varying degrees of surface oxidation have all contributed to the lack of consensus. 1,9,29,[33][34][35] The underlying mechanism is usually described in terms of quantum size effects where the electronhole pairs are well confined within the nanocrystal core, a surface chemistry model that emphasizes the importance of species at the nanocrystal surface, or a combination of both. The marked size dependency observed in the UV-Vis absorption spectra shown in Figure 4 agrees well with the quantum confinement model.…”

“…[14][15][16][17][18][19][20][21] Other methods include thermal co-reduction of Ge(II) and amido based precursors, 6,22,23 aqueous phase reduction of GeO 2 powders by NaBH 4 , 24 and other high temperature chemical reduction methods. [25][26][27][28][29][30][31] However, disadvantages associated with these methods include synthetically involved precursor synthesis, long reaction times, high temperatures and pressures, and extensive post synthetic purification procedures. 1,29 As well as the variation in size distribution, morphology and surface chemistries reported above, significant inconsistencies also exist in the photophysical properties of these nanostructures, precluding a detailed understanding of their size-dependent characteristics.…”

“…[25][26][27][28][29][30][31] However, disadvantages associated with these methods include synthetically involved precursor synthesis, long reaction times, high temperatures and pressures, and extensive post synthetic purification procedures. 1,29 As well as the variation in size distribution, morphology and surface chemistries reported above, significant inconsistencies also exist in the photophysical properties of these nanostructures, precluding a detailed understanding of their size-dependent characteristics. One promising approach towards scalable preparation of size monodisperse Ge NCs is the solution phase reduction of germanium halides within inverse micelles at room temperature.…”

Efficient one-pot synthesis of monodisperse alkyl-terminated colloidal germanium nanocrystals

“…A number of different solution phase synthetic approaches have been reported, including the metathesis reaction of GeCl 4 with Zintl salts (Taylor et al 1999) and high temperature decomposition of organogermane precursors (Hoffman and Veinot 2012;Lu et al 2005). Other methods include thermal co-reduction of amido based precursors (Gerung et al 2005), aqueous phase reduction of GeO 2 powders by NaBH 4 (Wu et al 2011), and other high temperature chemical reduction methods Muthuswamy et al 2012;Ruddy et al 2010). Disadvantages associated with these methods include long reaction times, high temperatures and pressures, and extensive post synthetic purification procedures (Muthuswamy et al 2012;Vaughn II and Schaak 2013).…”

“…Other methods include thermal co-reduction of amido based precursors (Gerung et al 2005), aqueous phase reduction of GeO 2 powders by NaBH 4 (Wu et al 2011), and other high temperature chemical reduction methods Muthuswamy et al 2012;Ruddy et al 2010). Disadvantages associated with these methods include long reaction times, high temperatures and pressures, and extensive post synthetic purification procedures (Muthuswamy et al 2012;Vaughn II and Schaak 2013).…”