Synthesis of Germanium Nanocrystals in High Temperature Supercritical Fluid Solvents

Abstract

Crystalline germanium (Ge) nanocrystals were synthesized by arrested precipitation in supercritical hexane and octanol at 400∼550 °C and 20.7 MPa in a continuous flow reactor. Two Ge precursors were explored, diphenylgermane (DPG) and tetraethylgermane (TEG), which undergo thermolysis to crystalline Ge under these conditions. Octanol is added to control particle growth, which appears to serve as a capping ligand that binds to the particle surface through an alkoxide linkage. The nanocrystals were characterized by high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), FTIR spectroscopy, and X-ray diffraction (XRD). The average nanocrystal diameter could be changed over a wide range, from ∼2 nm to ∼70 nm, by varying the reaction temperature and precursor concentration. Relatively size-monodisperse nanocrystals could be produced, with standard deviations about the mean diameter as low as ∼10%. UV−visible absorbance and photoluminescence (PL) spectra of Ge nanocrystals in the 3 to 4 nm diameter size range exhibit optical absorbance and PL spectra blue-shifted by approximately 1.7 eV relative to the band gap of bulk Ge, with quantum yields up to 6.6%.

Spontaneous Growth and Chemical Reduction Ability of Ge Nanoparticles

“…2b shows UV-vis spectra (ranging from 190 nm to 800 nm) of Ge NPs suspended in deionized water with different aging time under ambient temperature in darkness. The absorbance increases gradually with decreasing wavelength3940, however, there is no characteristic absorption band edges corresponding to that for bulk Ge294142 and those for other solution chemistry-synthesized Ge NPs reported previously434445. As we know, the optical absorption properties measured under the transmission mode is effective when the particle sizes in the suspension are below the size for complete optical absorption.…”

Solvothermal synthesis of monodisperse self-assembly CeO2 nanospheres and their enhanced blue-shifting in ultraviolet absorption

“…Three peaks at 2970, 2930 and 2874 cm −1 are characteristic of C-H stretching modes for CH 2 and CH 3 groups and the peaks at 1087 and 1052 cm −1 are characteristic of C-OH stretching modes for alcohol. These typical peaks indicate that the sample is coated by n-butanol [37,38]. Attractively, the peak located at 480 cm −1 owing to Ce-O stretching band exhibits great shifting than previous reports [19,39].…”

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

“…A number of different synthetic approaches have been reported, including the metathesis reaction of GeCl 4 with Zintl salts, [8][9][10][11][12] reduction of NaGe by ammonium bromide 13 and high temperature decomposition of organogermane precursors. [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.…”