Raman spectroscopy of PbS nanocrystalline semiconductors

We have studied the effect of crystalline size and surface roughness on Raman intensity for PbS nanocrystalline semiconductors of different crystalline sizes prepared by an electrochemical route. Rutherford back scattering spectroscopy provides the estimation of surface roughness, thickness, and composition of the PbS samples. The Raman spectrum shows a low-frequency wing at similar to 205 cm(-1) besides the characteristic first order longitudinal optical phonon mode at similar to 210 cm(-1) when excited with a laser of wavelength 514.5 nm. The observed variation of the Raman shifts, widths, and intensities of these two peaks have been discussed as a function of crystalline size. The low frequency wing is identified as a surface phonon mode. In addition to these two peaks, a peak at 271 cm(-1) and another at 415 cm(-1) are observed in good agreement with earlier reported results. [S0163-1829(98)02947-6].