Facile Synthesis of GermaniumNanoparticles with SizeControl: Microwave versusConventional Heating.

A facile size-controlled synthesis (microwave/conventional)of quasi-spherical germanium nanoparticles is reported.Oleylamineserves as a solvent, a binding ligand, and a reducing agent in thesynthesis. Reactions were carried out with microwave-assisted heating,and the results have been compared with those produced by conventionalheating. Germanium iodides (GeI4, GeI2) wereused as the Ge precursor, and size control in the range of 4–11nm was achieved by controlling the ratio of Ge4+/Ge2+in the precursor mix. Longer reaction times and higher temperatureswere also observed to have an effect on the nanoparticle size distribution.Microwave heating resulted in crystalline nanoparticles at lower temperaturesthan conventional resistive heating because of the ability of germaniumiodides to convert electromagnetic radiation directly to heat. Thereported approach for germanium nanoparticle preparation avoids theuse of strong reducing agents (LiAlH4, n-BuLi, NaBH4) and HF for etching and, thus, can be consideredsimple, safe, and amenable to industrial-level scaleup. The as-preparednanoparticles are a stable dispersion (hexane or toluene) for weekswhen stored under an inert atmosphere (N2/Ar). The stabilityof the colloidal dispersion was observed to be dependent on the nanoparticlesize, with smaller nanoparticles exhibiting longer stability. On exposureto ambient conditions, oxidation occurs over a period of time andresults in slow precipitation of the nanoparticles. The nanoparticleshave been characterized by powder X-ray diffraction (PXRD), transmissionelectron microscopy (TEM), and spectroscopic techniques (UV-Vis-NIR,FTIR, Raman). [ABSTRACT FROM AUTHOR]