Germanium nanoparticle nucleation was studied in organized arrays on HfO2 using a SiO2 thin film mask with similar to 20-24nm pores and a 6 x 10(10) cm(-2) pore density. Poly (styrene-b-methyl methacrylate) diblock copolymer was employed to pattern the SiO2 film. Hot wire chemical vapor deposition at 800 K produced Ge nanoparticles using 6-19 monolayer Ge exposures. By seeding adatoms on HfO2 at room temperature before growth, nanoparticle density is approximately one particle per pore. (c) 2006 American Vacuum Society.