Two-dimensional (2-D) arrays of silicon nanocrystals were fabricated in thermally grown SiO2 films by 1 keV 28Si+ ion implantation and subsequent thermal annealing. The nanocrystals characteristics (size, shape, and spatial distribution) as a function of the implanted dose and annealing conditions were investigated by transmission electron microscopy. The nanocrystals were located at a tunneling distance from the oxide surface. With increasing size, the nanocrystals changed from quasi-spheres to faceted platelets. With a reduction in the implantation dose and the annealing temperature, the size of the nanocrystals decreased, their size distribution became more narrow, while their spatial arrangement remained 2-D.