Size effects investigated by Raman spectroscopy in Bi nanocrystals

Abstract

Bismuth nanocrystals, embedded in amorphous germanium thin films and synthesized by pulsed-laser deposition, are investigated by Raman spectroscopy. Raman spectra are strongly dependent upon the size of the deposited nanocrystals. For the larger nanocrystals, two peaks corresponding to the optical phonons A1g and Eg can be observed. As the size of the particles decreases, the Eg mode shifts to higher frequencies while the A1g mode shifts to lower frequencies. Such behavior is a result of the curvature of the respective phonon-dispersion curves in Bi. A third size-dependent low-frequency mode has also been observed and attributed to acoustic phonons confined in Bi nanocrystals. ©1999 The American Physical Society.