Raman scattering experiments are a versatile method to characterize different aspects of nanostructures.
We present Raman spectra from CdSe nanorods of various sizes and discuss features that can be extracted from them.
In particular the nanorod diameter can be estimated from the frequency of the radial breathing mode, similar to carbon nanotubes. ab-initio calculations of CdSe nanowires indicate the presence of this fully symmetric vibrational mode which's frequency is highly diameter dependent. This mode can be characterized by Raman spectroscopy and is especially interesting for very small structures. The RBM frequency rises for decreasing diameter, which makes it experimentally easier to detect, while other suitable techniques like high resolution transmission electron microscopy become more sophisticated. Another discussed feature is the exciton-phonon coupling strength. The coupling strength in nanorods can be deduced from the integrated intensities of the Raman bands and their overtones. Simultaneous measurement of the fundamental and overtone allows the study of e.g. the size dependence of the coupling strength. We find an increasing coupling strength for decreasing nanorod diameter in the diameter regime from 2-10 nm, while still being lower than the coupling strength in bulk material. This is explained within a model for spherical nanocrystals. Couplings to higher frequency phonons increase for smaller structures while the coupling strength compared to bulk material is reduced due to the decreased Coulomb interaction and confinement effects.

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