We propose an original approach called a "stencil-masked ion implantation process" for performing a spatially localized synthesis of a limited number of Si nanocrystals within a thin SiO2 layer. In this process, the SiO2 layer is irradiated with 1 keV silicon ions through a stencil mask containing apertures (from 100 nm to 2 mu m), and subsequently thermally annealed to create Si nanocrystals. Scanning electron microscopy images show that the implanted areas mimic the mask geometry. Energy-filtered transmission electron microscopy and photoluminescence spectroscopy studies confirm that only the implanted areas are Si nanocrystal rich and fight emitting. The smaller nanocrystal size detected near the edges of the implanted areas is attributed to dose reduction effects. This feature leads to a blueshift of the PL energy. Electrical properties of the structures produced are investigated using Al gate MOS capacitors. Room temperature I-V and I-t characteristics exhibit discrete current peaks that are associated with single-electron charging of the nanocrystals and electrostatic interaction of the trapped charges with the tunnelling current. (C) 2007 Elsevier Ltd. All rights reserved.