We investigate the deposition of SiOx, films by dual ion beam sputtering system with emphasis on secondary ion beam irradiation effect. We observe the intense photoluminescence (PL) from SiOx samples with apparent oxygen contents, x(app), in the narrow range of 1,1 <= x(app)<= 1.4, after post-deposition annealing at 1100 degrees C. This indicates the formation of Si nanocrystals as evidenced by cross-sectional transmission electron microscope (TEM) image. Ar ion beam irradiation changes PL peak positions in ion-beam exposed region. This effect is utilized for achieving the area-selective formation of Si nanocrytals by inserting a shadow mask in secondary ion beam during deposition. (c) 2004 Elsevier B.V. All rights reserved.