An electron microscopy study of the growth of Ge nanoparticles in SiO2

Ion implantation followed by high temperature annealing can be used to synt hesize group IV semiconducting nanoparticles in SiO2. The density and the s ize distribution of these nanocrystals obviously depend on the implantation and annealing conditions. While their size can be measured by "classical" transmission electron microscopy techniques, their density cannot because n o diffraction occurs in the amorphous matrix. In this letter, we use electr on energy loss spectroscopy to overcome this problem. We have measured the evolution of the size distribution, the density, and the atomic fraction oc cupied by the Ge precipitates during annealing. We show that the nanocrysta ls grow in size and reduce their density, while the overall number of atoms they contain remains constant. This observation proves that the nanopartic les undergo a conservative ripening during annealing. (C) 2000 American Ins titute of Physics. [S0003-6951(00)03325-8].