Characterization of Si nanocrystals by different TEM-based techniques

Silicon nanocrystals (Si-nc) embedded in SiO2 matrix and obtained by ion implantation (50 keV, 1.0×1017 Si/cm2) were characterized by means of three different transmission electron microscopy (TEM) techniques: Dark Field (DF), Scanning TEM Annular Dark Field (STEM-ADF) and Z contrast. The strengths and weaknesses of each technique for the characterization of the Si-nc were evaluated and discussed. DF imaging, which has the best contrast, was chosen to give the average Si-nc size evaluated to 5.6 nm. On the other hand, STEM-ADF, which is only sensitive to the crystalline phase, provided an evaluation of the Si-nc density of 3.27×1017 nc/cm3. Finally, comparison between the STEM-ADF and Z contrast imaging permitted to evaluate the amorphous phase remaining after the annealing to around 12%.