We report the control of nucleation sites for Ni-mediated crystallization of a-Si. It was shown that the self-organization of Ni atoms at the pressure-induced indentation sites on a-Si can be possible during thermal annealing without selective Ni contact or patterning. We have succeeded in forming Ni segregation sites (SSs) on a-Si by pressing a SiO2 coated steel tip-array, where the nucleation starts. Any mechanical damage, such as peeling off and crack, was not found in the a-Si by atomic force microscope (AFM) inspection, when the tip-pressing pressures are in the range of 31-94 MPa. By controlling nucleation sites, the poly-Si with well-aligned rectangular grains of 20 mu m x 40 mu m have been achieved for the first time. (c)\ 2006 Elsevier B.V. All rights reserved.