Real time in situ hot stage transmission electron microscopy observations were carried out to characterize the crystallization behavior of a Co65Si15B14Fe4Ni2 amorphous alloy. It was found that the crystallization in the thin foil was highly thickness dependent. The crystallization occurred quickly at 400 degrees C in the thin regions (similar to 80 nm) and slowly in thicker regions (similar to 250 nm). The crystallization product was found to be cobalt with either hexagonal closed packed or face centered cubic crystal structure. The crystal morphology was that of nanosized spheres, faulted elongated crystals and irregular highly faulted crystal clusters; the morphology varied with the local thickness. Quantitative analysis of the thickness dependence of precipitate size and nucleation density indicated that: the precipitate size increased continuously with an increase in thickness; the nucleation density decreased sharply with increasing thickness. The thickness dependence of the crystallization products was analyzed in terms of surface mobility and strain effects. Crystallization in thin foils and conventional samples was compared. (c) 2006 Elsevier B.V. All rights reserved.