In a recent study, which was published in Nanotechnology, the authors have exploited the size-tunability of nanorods made from the direct band-gap compound semiconductor CdSe to study the influence of changing size and shape on the optical phonons in such nanostructures.

The researchers performed low-temperature Raman scattering experiments on several nanorod samples. The most prominent Raman active phonons are longitudinal optical phonons and surface optical phonon modes. Both can be well separated and their behaviour with changing dimensions is quite different.

The longitudinal optical phonons experience a confinement if the diameter of the nanorod is reduced. This results in a changed frequency of the confined phonons and is independent of the nanorod's length and consistent with theory.

The frequency of the surface vibrations depends on the shape of the nanorod. It neither solely depends on the length nor the diameter but the ratio of both, the aspect ratio. This is the reason why the fundamental Raman band, which is the sum of both contributions, has a different shape and position for nanorods of different sizes.

As photonic devices are promising applications for the nanorods, the reasearchers aim to investigate the impact of these results on the luminescence properties of such structures, which are influenced by the behavior of the optical phonons.