Phase changes in Ge nanoparticles

Butyl-capped crystalline germanium (Ge) nanoparticles were synthesized at room temperature in dimethoxyethane by reduction of GeCl ₄ with Na(naphthalide) and subsequent reaction with butyl Grignard. The nanoparticles were isolated in hexane and characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), elemental analysis, and X-ray powder diffraction (XRD). The product from this room-temperature reaction was heated under vacuum at temperatures of 200-600°C at 50°C intervals. The product obtained from the 300°C treatment was soluble in hexane, while the products from temperatures greater than 300°C were not. SAED was consistent with crystalline Ge from the initial synthesis at room temperature and amorphous Ge for the product heated under vacuum to 300°C. X-ray powder diffraction of the 300°C product shows the transition from amorphous to crystalline nanoparticles occurring between 550 and 600°C. TEM shows that the nanoparticles remain dispersed and nonaggregated up to 600°C. Differential scanning calorimetry (DSC) shows a crystallization exotherm at 561°C and a melting endotherm at 925°C for nanoparticles with average diameter of 8 nm.