Competing processes during the production of metal nanoparticles by pulsed laser deposition

In this work we report on the competition between growth, implantation, and sputtering effects during the production of metal nanoparticles (NPs) by pulsed laser deposition. The production sequence involves first the deposition of an amorphous (a-)Al ₂O ₃ layer onto which gold NPs are produced. They are subsequently covered by a-Al ₂O ₃ and this sequence is repeated five times. The resulting nanocomposite films have metal contents per layer in a broad range: 1-9×10 ¹⁵ at cm ^-2. The results clearly show the formation of two NP layers per layer of gold deposited, the deepest one consisting of NPs produced by metal implanted into the a-Al ₂O ₃ layer, which is acting as a substrate, and the other one consisting of NPs grown on the a-Al ₂O ₃ surface. The high kinetic energy of a significant fraction of the Au species present in the plasma and the high fluxes (10 ¹⁶-10 ¹⁸ at cm ^-2 s ^-1) at the substrate plays an essential role in the nucleation and growth of the NPs. The competition between surface growth and sputtering at high fluence induces a self-regulation of the NP dimensions that narrows the size distributions.