Careful preparation of the iron nano-particle catalyst for carbon nanotubes (CNTs) fabrication has crucial importance for initial growth of multi-wall carbon-nanotubes (MWCNTs). Thin iron layer was thermally deposited in a high vacuum onto the surface of the SiO2/Si wafer at about 300 K. The sample was heated up to 700℃ in a hydrogen atmosphere, and then the sample was heated once again at750℃ in ethylene atmosphere. After hydrogen treatment continuous Fe layer was changed into many well separated Fe nano-peaks. AFM, SEM and HR-TEM studies of deposited MWCNTs allow us to propose a growth mechanism for long, straight MWCNTs.