In situ Raman scattering studies of the amorphous and crystalline Si nanoparticles

We report on in situ studies of the vibrational properties of Si nanoparticles and ultrathin layers grown by dc magnetron sputtering in ultrahigh vacuum on amorphous MgO and Ag buffer layers. The average thickness of the Si layers ranged from monolayer coverage up to 200 angstroms. Transmission electron microscopy has been used to determine size and shape of the Si nanoparticles. Changes in the phonon spectra of Si nanoparticles during the crystallization process have been studied by interference enhanced Raman scattering technique. Marked size-dependences in the phonon density of states and the relaxation of the k-vector conservation with decrease in size of the Si nanoparticles have been detected. The transition between crystalline-and amorphous-like behavior takes place in the particles with an average number of Si atoms equal to (7±2)×10².