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

We report on in situ studies of the vibrational properties of Si nanopartic les and ultrathin layers grown by de magnetron sputtering in ultrahigh vacu um on amorphous MgO and Ag buffer layers. The average thickness of the Si l ayers ranged from monolayer coverage up to 200 Angstrom. Transmission elect ron microscopy has been used to determine size and shape of the Si nanopart icles. Changes in the phonon spectra of Si nanoparticles during the crystal lization process have been studied by interference enhanced Raman scatterin g technique. Marked size-dependences in the phonon density of states and th e relaxation of the k-vector conservation with decrease in size of the Si n anoparticles have been detected. The transition between crystalline-and amo rphous-like behavior takes place in the particles with an average number of Si atoms equal to (7 +/- 2) X 10(2). (C) 2000 Elsevier Science Ltd. All ri ghts reserved.