2ND-ORDER RAMAN-SPECTRA OF NANOSTRUCTURES

Phonon states of nanostructures such as porous Si layers and small Ge particles are studied by the second-order Raman scattering. The sizes of particles are estimated to be a few to ten nanometer's. The damping of the 2TO band is much larger than the TO(Gamma) line. Surface phonon lines are observed at frequencies close to the Lucas mode and the S-8/S-8' mode of flat crystalline surfaces. The high frequency edge of the 2TO band shifts by a few cm(-1) reflecting confinement of the bulk phonons into a small volume.