Size, shape anisotropy, and distribution of Cu nanocrystals prepared by pulsed laser deposition

Films consisting of Cu nanocrystals (NCs) embedded in an Al ₂ O ₃ matrix have been fabricated by pulsed laser deposition employing alternate ablation of Cu and Al ₂ O ₃ targets. The mean diameter of the Cu NCs in the film plane is varied from 2 to 5 nm by increasing the number of pulses on the Cu target during deposition. It is observed that as the NCs become larger their average separation and shape anisotropy in the film plane increase. The mean diameter of the NCs in the direction perpendicular to the film plane (NCs height) is always smaller than that in the film plane, showing that the NCs are oblate ellipsoids. These results show that the NCs are formed by nucleation on the substrate surface followed by coalescence as the surface coverage of Cu increases, promoted by the high kinetic energy involved in the laser deposition process.