Optical phonon modes in ordered core-shell CdSe/CdS nanorod arrays

We investigate the optical phonons in "dot-in-a-rod" core-shell CdSe/CdS nanorods at wavelengths resonant with the optical transitions either in the core or in the shell. At a wavelength above the CdS band gap, only CdS phonon modes were detected. In contrast, at excitation in resonance with the core transitions, we observed phonon modes of both the CdSe core and the CdS shell. In laterally ordered nanorod assemblies, the CdS longitudinal-optical phonon mode manifested a low-energy shoulder that could be related to higher-order longitudinal-optical phonon modes. Furthermore, we report on surface-optical modes that originate from the tracklike superstructure of the nanorod assemblies.