Study of CdS nanocrystallites by AFM and Raman scattering spectroscopy

We have studied the surface roughness and its effect on Raman intensity for CdS nanocrystalline semiconductors of different crystalline size. Atomic force microscopy (AFM) and Rutherford backscattering spectroscopy (RBS) experiments show that the roughness increases with increasing sample thickness. The Raman scattering experiment shows a shoulder at a low frequency wing (295 cm−1) along with the 1LO (first order longitudinal) phonon mode at 305 cm−1. We found that as the crystalline size decreases the intensity of the 1LO line increases. The intensity ratio of the shoulder and the 1LO peak reaches saturation after a certain thickness/crystalline size which can be understood by taking the surface roughness as well as the crystalline size into account.