Mn-implanted Si was investigated using transmission electron microscopy to gain insight into the structure of the implanted region. Diffraction contrast images, selected area diffraction patterns, and high resolution images of the samples were acquired before and after postimplant annealing at 800 degrees C. The images of the annealed samples revealed the formation of nanometer size precipitates distributed throughout the implanted region. Analysis of the selected area diffraction pattern determined that the most prominent lattice spacing of the crystallites is 2.15 angstrom. This spacing indicates that the most probable phase of the crystallites is MnSi1.7 and this is consistent with the Mn:Si binary phase diagram. This phase is paramagnetic at room temperature with a Curie temperature of 47 K and cannot readily account for the high Curie temperature of the material. (c) 2006 American Vacuum Society.