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Synthesis of Germanium Nanocrystals in High Temperature Supercritical Fluid Solvents

2004; American Chemical Society; Volume: 4; Issue: 5 Linguagem: Inglês

10.1021/nl049831j

1530-6992

Xianmao Lu, Kirk J. Ziegler, Ali Ghezelbash, Keith P. Johnston, Brian A. Korgel,

Quantum Dots Synthesis And Properties

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%.