Direct determination of grain sizes, lattice parameters, and mismatch of porous silicon

High-resolution transmission electron microscopy and digital image processing were used to investigate in detail the structure of porous silicon (PS). It was found that PS is composed of rounded Si nanocrystals with characteristic sizes between 21 and 80 Angstrom, embedded into an amorphous matrix and with no preferential orientation. We have determined that the size distribution of the nanocrystals can be fitted to a Gaussian distribution centered at 45.89 Angstrom. Furthermore, the structure of the individual Si grains was studied, which allowed us to determine that the interplanar distance varies from 3.17 to 3.41 Angstrom, with Gaussian distribution centered at 3.24 Angstrom. Finally, the lattice parameter of the individual Si grains that compose PS was also measured, showing a Gaussian distribution centered at 5.61 Angstrom. The origin of the structure of PS is also discussed. (C) 2002 American Institute of Physics.