Abstract
In this study, a novel phenomenon of forming monodispersed Co nanoparticles at room temperature on a single-crystal Si3N4 dielectric thin film is presented. Results of very narrow size distributions with an average size of ~30 Co atoms have been obtained. We have found that cobalt clusters deposited on Si3N4 are stable with respect to cluster agglomeration/coalescence and thermal decomposition. Also, we have confirmed that the average size of Co clusters is independent of the deposition time and insensitive to the magnitude of the deposition flux. Therefore, their areal density can be controlled by the deposition time. The motivation for using a single-crystal Si3N4 support is two-fold. First, the dielectric support reduces chemical intermixing and electronic coupling (Si3N4 is an excellent diffusion barrier with a bandgap energy of 4-5 eV) between metal clusters and the substrate compared with situations using semiconductor or metal surfaces. Second, the defect-free Si3N4 surface provides us a unique opportunity to study the formation of metal clusters without the influence of surface defects. Consequently, quantum effect can play an important role in the size control.