Using in situ high-resolution transmission electron microscopy, we observe that, while annealed at 550 degrees C in the TEM, a Ni-deposited amorphous silicon thin film is crystallized, which is preceded by the formation of NiSi2 precipitates. In addition to the NiSi2 precipitates, manometer-sized Ni particles, single crystalline or multiply twinned, form. Their unusual formation is attributed to beam heating effect by beam irradiation during the observations. Unlike the NiSi2 precipitates, no crystallization occurs around the Ni nanoparticles. (c) 2006 American Vacuum Society.