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The nucleation and structure of silicon nanocrystals formed by differentpreparation conditions and silicon concentration (28 - 70 area %) have beenstudied using Transmission Electron Microscopy (TEM), Energy Filtered TEM(EFTEM) and Secondary Ion Mass Spectroscopy (SIMS). The nanocrystals wereformed after heat treatment at high temperature of a sputtered 10 nm thicksilicon rich oxide on 3 nm SiO$_2$ layer made by Rapid Thermal Oxidation (RTO)of silicon. Nanocrystals precipitate when the excess silicon concentrationexceeds 50 area %. Below this percentage amorphous silicon nanoclusters werefound. In-situ heat treatment of the samples in the TEM showed that thecrystallization requires a temperature above 800$^o$C. The nanocrystalsprecipitate in a 4 nm band, 5 nm from the Si substrate and 4 nm from theSiO$_2$ sample surface. The silicon nucleates where the excess Si concentrationis the highest. The top surface has less excess Si due to reaction with oxygenfrom the ambient during annealing. The SiO$_2$-RTO layer is more Si rich due toSi diffusion from the SiO$_2$-Si layer into RTO. Twinning and stacking faultswere found in nanocrystals with 4-10 nm in diameter. These types of defects mayhave large effects upon the usability of the material in electronic devices.Both single and double twin boundaries have been found in the nanocrystals byhigh resolution transmission electron microscopy (HRTEM). Image simulationswere carried out in order to obtain more information about the defects andnanocrystals. The stacking faults are extrinsic and located in the twinboundaries.

Characterization of amorphous and crystalline silicon nanoclusters in ultra thin silica layers