Study on nucleation and growth of Ag nanoparticles prepared by radio-frequency sputtering on highly oriented pyrolytic graphite and amorphous carbon

The initial growth process of silver nanoparticles on highly oriented pyrolytic graphite (HOPG) and amorphous carbon $\mathrm{(a-}\mathrm{C})$ was studied. Scanning tunneling microscopy was used for analysis of the nanoparticles formed on HOPG. Transmission electron microscopy was employed to study the growth procedure on $\mathrm{a-}\mathrm{C}.$ The number densities ${\mathrm{(D}}_n)$ of silver nanoparticles on both HOPG and $\mathrm{a-}\mathrm{C}$ remain constant at a very early stage, then both decrease with deposition time and have a saturated value. The $D_n$ decrease suggests migration followed by impingement. We found evidence of migration of 5 nm particles on $\mathrm{a-}\mathrm{C}.$ Interpretations are given to explain the impingement and shape change of the silver nanoparticles.