Quantum dots (QDs) have attracted significant interest in various areas during past several decades. Due to excellent size-tunable optical and electronic properties, they become ideal building blocks in photovoltaics, photocatalysis, light emitting and biological imaging. Nevertheless, QDs are highly dynamic and reactive species, it is very challenging to acquire useful information about structure from traditional structural analysis method, such as microscopy (SEM, TEM, AFM etc.), spectroscopy (IR, Absorbance, XPS etc.) and powder XRD. In principle, solid state NMR can be an ideal method because of its ability to characterize molecules, solids, surfaces and intersurfaces. However, solid state NMR suffers from intrinsic low sensitivity, while normally acquired 1D spectrum provides limited information and more informative 2D spectrum is very time-consuming. Thus, in order to extract useful information from solid state NMR spectrum, orders of magnitude of signal enhancement is a necessity. In the past twenty years, dynamic nuclear polarization (DNP) enhanced magic angle spinning (MAS) NMR spectroscopy has been applied to greatly enhance NMR signal by factor of 10 to 100, which corresponds to shortening of the experiment time by 2 – 4 orders of magnitude. This enables rapid acquisition of NMR spectra of QDs, which was considered infeasible in previous study. In our study, we focused on optimization of DNP sample preparation in order to achieve high sensitivity, then applied these conditions to CdS QDs, Si nanocrystals etc. For example, by applying 113Cd-113Cd correlation spectrum in CdS QDs system, we have unveiled the role of surface capping ligands and different Cd sites.

Characterization of quantum dots using dynamic nuclear polarization (DNP) surface enhanced NMR spectroscopy (SENS) to achieve high sensitivity

2019 Spring National Meeting

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