The synthesis of two-dimensional arrays of Si nanocrystals in an HfO 2 matrix has been achieved by deposition of HfO 2/SiO/HfO 2 multilayer structures followed by high temperature (1100 C) thermal treatment in nitrogen atmosphere. Silicon out-diffusion from the SiO layer through the HfO 2 films has been shown to be the limiting factor in the formation of the Si nanocrystals. Suitable strategies have been identified in order to overcome this limitation. Si nanocrystal formation has been achieved by properly adjusting the thickness of the SiO layer.