Electron and Phonon Confinement and New Surface Phonon Modes in CdSe-CdS Core-Shell Nanocrystals

TL;DR

This study investigates the optical and vibrational properties of CdSe-CdS core-shell nanocrystals, confirming their structure and revealing unique phonon confinement and surface phonon modes through experimental and theoretical analysis.

Contribution

The paper provides experimental confirmation of core-shell structures and analyzes electron and phonon confinement effects in CdSe-CdS nanocrystals using optical and vibrational spectroscopy.

Findings

Confirmation of core-shell structure via TEM analysis

Observation of blue shift indicating electron confinement

Identification of surface phonon modes matching theoretical models

Abstract

Optical and vibrational properties of bare and CdS shelled CdSe nanocrystalline particles are investigated. To confirm the formation of such nanocrystals in our samples we estimate their average particle sizes and size distributions using TEM measurements. From the line profile analysis of the images the core-shell structure in the particles has been confirmed. The blue shift in optical absorption spectra, analyzed using theoretical estimates based on the effective bond order model, establishes the electron confinement in the nanoparticles. Unique characteristics of the nanocrystals (which are absent in the corresponding bulk material), such as confinement of optical phonons and the appearance of surface phonons, are then discussed. Making use of the dielectric response function model we are able to match the experimental and theoretical values of the frequencies of the surface phonons. We believe that our studies using optical probes provide further evidence on the existence of core-shell structures in CdSe-CdS type materials.