Probing Surface Defects of InP Quantum Dots Using Phosphorus Kα and Kβ X-ray Emission Spectroscopy

Abstract

Synthetic efforts to prepare indium phosphide (InP) quantum dots (QDs) have historically generated emissive materials with lower than unity quantum yields. This property has been attributed to structural and electronic defects associated with the InP core as well as the chemistry of the shell materials used to overcoat and passivate the InP surface. Consequently, the uniformity of the core-shell interface plays a critical role. Using X-ray emission spectroscopy (XES) performed with a recently developed benchtop spectrometer, we studied the evolution of oxidized phosphorus species arising across a series of common, but chemically distinct, synthetic methods for InP QD particle growth and subsequent ZnE (E = S or Se) shell deposition. XES afforded us the ability to measure the speciation of phosphorus reliably, quantitatively, and more efficiently (with respect to both the quantity of material required and the speed of the measurement) than with traditional techniques, i.e., X-ray photoelectron spectroscopy and magic angle spinning solid state nuclear magnetic resonance spectroscopy. Our findings indicate that even with deliberate care to prevent phosphorus oxidation during InP core synthesis, typical shelling approaches unintentionally introduce oxidative defects at the core-shell interface, limiting the attainable photoluminescence quantum yields. Disciplines

Elucidating the Location of Cd2+ in Post-synthetically Treated InP Quantum Dots Using Dynamic Nuclear Polarization 31P and 113Cd Solid-State NMR Spectroscopy

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Synthesis of In₃₇P₂₀(O₂CR)₅₁ Clusters and Their Conversion to InP Quantum Dots

“…. Surface defects, oxidation, and alloying are critical factors still under intense research that will require significant innovation for optimized InP architectures 19,20,21,22,23,24 . The atomically precise nature of clusters, such as In 37 P 20 (O 2 CR) 51 , makes them ideal platforms for probing the consequences of many post-synthetic surface modifications.…”

Spherically bent mica analyzers as universal dispersing elements for X‐ray spectroscopy

“…At synchrotron light sources, this includes high-energy resolution fluorescence detection to decrease core-hole lifetime broadening, resonant inelastic X-ray scattering, and both resonant and nonresonant X-ray emission spectroscopy (XES; Bergmann & Glatzel, 2009;de Groot, 2001;Gallo & Glatzel, 2014;Glatzel & Bergmann, 2005;Henderson, De Groot, & Moulton, 2014;Pollock & DeBeer, 2011). There is also a renewed and growing trend to perform nonresonant XESX-ray emission spectroscopy in the laboratory (Holden et al, 2017;Holden, Seidler, & Cheah, 2018;Jahrman, Seidler, & Sieber, 2018;Mortensen et al, 2017;Mortensen, Seidler, Ditter, & Glatzel, 2016;Seidler et al, 2014;Stein et al, 2018).…”