Formation of almost delta-layered nanoparticles in SiO2 thin film on Si substrate by metal negative-ion implantation

Two formation methods of delta-layered metal nanoparticles in thermally grown thin SiO2 layer on Si substrate were investigated: (1) gold negative-ion implantation at low-energy for nanoparticle formation at a shallow depth of the oxide layer and (2) thermal diffusion after silver negative-ion implantation for formation at a deep depth. Gold negative ions were implanted at 1, 15 and 35 keV to SiO2/Si. At the low-energy implantation at 1 keV, the almost delta-layer of Au nanoparticles (about 8 nm in diameter) was obtained at a shallow depth of 5 nm after annealing at 900 °C. For formation at deep depth, silver negative-ions were implanted at 10 keV and 1 × 1015 ions/cm2 to 25-nm-thick SiO2/Si. After annealing at 700 °C, all formed nanoparticles with 6 nm in diameter aligned at the same deep depth, i.e. almost delta-layered Ag nanoparticles, at the minimum distance of 2 nm from the boundary to Si. It is found from high resolution TEM observation that both almost delta-layered nanoparticles of Au and Ag were single crystals.