Raman and infrared studies of CdSe/CdS core/shell nanoplatelets

TL;DR

This study combines experimental Raman and infrared spectroscopy with first-principles calculations to analyze vibrational properties of CdSe/CdS core/shell nanoplatelets, revealing phonon behaviors and surface effects.

Contribution

It provides a detailed vibrational analysis of CdSe/CdS nanoplatelets using combined experimental and theoretical approaches, highlighting surface damping and phonon mode characteristics.

Findings

Confirmation of two-mode phonon behavior in nanostructures

Identification of vibrational modes and their damping characteristics

Observation of surface relaxation effects influencing phonon frequencies

Abstract

The vibrational spectroscopy of semiconductor nanostructures can provide important information on their structure. In this work, experimental Raman and infrared spectra are compared with vibrational spectra of CdSe/CdS core/shell nanoplatelets calculated from first principles using the density functional theory. The calculations confirm the two-mode behavior of phonon spectra of nanostructures. An analysis of the experimental spectra reveals the absence of modes with a high amplitude of vibrations of surface atoms, which indicates their strong damping. Taking into account the difference in the damping of different modes and their calculated intensities, all bands in the spectra are unambiguously identified. It is found that the frequencies of longitudinal optical modes in heterostructures are close to the frequencies of LO phonons in bulk strained constituents, whereas the frequencies of transverse modes can differ significantly from those of the corresponding TO phonons. It is shown that an anomalous thickness dependence of CdS TO mode is due to a noticeable surface relaxation of the outer Cd layer in the nanostructure.