Understanding the growth of RuO 2 colloidal nanoparticles over a solid support: An atomic force microscopy study

•Single deposition of RuO2 colloids on mica leads to amorphous supported clusters.•Small sharp-pointed clusters and nanorod-like assemblies are formed after calcination.•Disaggregation of particles occurs during the reduction treatment under hydrogen.•Double coating calcined RuO2-mica leads to larger nanorods with stepped surfaces.•This geometry would expose highly active sites for ammonia synthesis reaction.