High Yield of Germanium Nanocrystals Synthesized from Germanium Diiodide in Solution

High chemical yields, up to 73%, were achieved for germanium (Ge) nanocrystals synthesized in solution with germanium diiodide (GeI 2 ) and LiAlH 4 as a reducing agent in tri- n -octylphosphine (TOP) or tri- n -butylphosphine (TBP). Ge nanocrystals were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Reactions in TOP at 300 °C yielded Ge nanocrystals with moderate size polydispersity and good crystallinity with average diameters that could be manipulated by varying the precursor concentration from ∼3 to ∼11 nm. High chemical yields are enabled by the high reactivity of GeI 2, high GeI 2 solubility in alkyl phosphines, and relatively mild reaction temperature, which minimizes byproduct formation and solvent degradation. Compared to reactions carried out in TOP with the same concentration of GeI 2, nanocrystals synthesized in TBP at 240 °C exhibit larger size and broader size distribution. The presence of alkyl groups in the FTIR spectra, the small and controllable particle diameters, and a lack of significant Ge oxidation revealed by XPS indicate that the nanocrystals were chemically passivated with an organic layer.