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Abstract
The origin of the high-frequency shoulder (HFS) observed above the longitudinal optical (LO) peak around 230 1/cm in the Raman spectra of CdSe quantum dots (QDs) has been a subject of intense debate. We use state-of-the-art ab initio density functional theory applied to small CdSe QDs with various realistic surface passivations and find an intense Raman signal around 230 1/cm, which corresponds to a stretching vibration of a defective twofold coordinated Se atom. We interpret this signal as being the origin of the HFS. Since the signal disappears in fully passivated and defect-free (magic size cluster) structures, it can be used as a fingerprint to distinguish defective from non-defective structures.
Supplementary materials
Title
Supporting Information
Description
The following files are available free of charge.
coord.zip: The Cartesian coordinate (xyz) files for all structures under investigation.
movies.zip: Movies of different vibrational modes.
si.pdf: The supporting information file contains the theoretical description of Raman intensity calculations, comparison of relaxed geometries (with Se-defect bond-lengths) of Cd$_{45}$Se$_{45}$ with MA and TOPO ligands and the Raman spectra of Cd$_{45}$Se$_{45}$\textbackslash CdS-PH core/shell showing the optical region of CdS shell which is not shown in the main text.
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