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Modulation of Low-Frequency Acoustic Vibrations in Semiconductor Nanocrystals through Choice of Surface Ligand A. Jolene Mork, Elizabeth M. Y. Lee, Nabeel S Dahod, Adam P. Willard, and William A Tisdale J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.6b01659 • Publication Date (Web): 04 Oct 2016 Downloaded from http://pubs.acs.org on October 4, 2016
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The Journal of Physical Chemistry Letters
Modulation of Low-Frequency Acoustic Vibrations in Semiconductor Nanocrystals through Choice of Surface Ligand A. Jolene Mork1, Elizabeth M.Y. Lee2, Nabeel S. Dahod2, Adam P. Willard1, William A. Tisdale2* 1. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 2. Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139 AUTHOR INFORMATION Corresponding Author *
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ABSTRACT:
Recent experimental and theoretical results have highlighted the surprisingly dominant role of acoustic phonons in regulating dynamic processes in nanocrystals. While it has been known for many years that acoustic phonon frequencies in nanocrystals depend on their size, strategies for tuning acoustic phonon energy at a given fixed size were not available. Here, we show that acoustic phonon frequencies in colloidal quantum dots (QDs) can be tuned through choice of the surface ligand. Using low-frequency Raman spectroscopy, we explore the dependence of the ℓ = 0 acoustic phonon resonance in CdSe QDs on ligand size, molecular weight, and chemical functionality. Based on these aggregated observations, we conclude that the primary mechanism for this effect is mass loading of the QD surface, and that interactions between ligands and with the surrounding environment play a comparatively minor yet non-negligible role. TOC GRAPHIC
KEYWORDS: Raman Spectroscopy, Phonons, Quantum Dot, Alkanethiol, Benzylmercaptan
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Advancements in the synthesis of colloidal semiconductor nanocrystals, also known as quantum dots (QDs), have led to improvements in their monodispersity,1 quantum yield,2 and photostability,3 paving the way for the incorporation of these materials into optoelectronic devices.4-6 While considerable progress has been made in the control of QD electronic properties,7-10 the intentional engineering of vibrational properties is less developed. The low-frequency acoustic vibrations (
