A detailed model for the three-dimensional growth of a screw dislocation and a gamma-branching of a lamella of elastomeric polypropylene (ePP) is proposed. The crystallization of a thin film was followed with in situ scanning force microscopy (SFM). Nucleation and growth of individual defects were observed with high temporal and spatial resolution. To identify the three-dimensional volume structure, the defects were examined with nanotomography, which is a layer-by-layer imaging technique based on SFM.