This report deals with the study of the plastic deformation processes of semi-crystalline polymers at the micrometric and nanometric scales by atomic force microscopy. Capturing images from the same locus of the sample as a function of strain allows in situ observation of the processes. New experimental findings regarding initiation, growth and coalescence of crazes in poly(I-butene) are reported. The benefits of the technique are emphasized in comparison with previous studies carried Out by transmission electron microscopy on ultra-thin films of various semi-crystalline polymers. The present situation is claimed to be closely representative of bulk deformation owing to the much greater sample thickness in comparison with the characteristic craze size. The occurrence of crazes oblique to the principal tensile stress is discussed in terms of triaxiality of the local stress field within the spherulites. (c) 2007 Elsevier Ltd. All rights reserved.