In this work we use atomic force microscopy to investigate the influence of the annealing temperature on the formation of nano-clusters in our growth technique for carbon nanotubes. Cluster formation is carried out just before in situ growth of carbon nanotubes from a methane feedstock by means of catalytic chemical vapor deposition where the clusters act as the catalyst. Since cluster size and distribution are directly connected to diameter and amount of the grown carbon nanotubes, respectively, the cluster formation process is of great interest.