Internal Structure of InP/ZnS Nanocrystals Unraveled by High-Resolution Soft X-ray Photoelectron Spectroscopy

Abstract

High-energy resolution photoelectron spectroscopy (DeltaE < 200 meV) is used to investigate the internal structure of semiconductor quantum dots containing low Z-contrast elements. In InP/ZnS core/shell nanocrystals synthesized using a single-step procedure (core and shell precursors added at the same time), a homogeneously alloyed InPZnS core structure is evidenced by quantitative analysis of their In3d(5/2) spectra recorded at variable excitation energy. When using a two-step method (core InP nanocrystal synthesis followed by subsequent ZnS shell growth), XPS analysis reveals a graded core/shell interface. We demonstrate the existence of In-S and S(x)-In-P(1-x) bonding states in both types of InP/ZnS nanocrystals, which allows a refined view on the underlying reaction mechanisms.

Economic and Size-Tunable Synthesis of InP/ZnE (E = S, Se) Colloidal Quantum Dots.

“…In this mixture, InCl3 is the actual indium precursor and ZnCl2 is added to facilitate the shell growth and it also proves to reduce the size dispersion of the InP QDs. Note that, as already mentioned by other authors, 13,14 adding Zn at the beginning of the reaction does not automatically produce In(Zn)P alloys.To form InP QDs, the (amino)3P is injected at high temperature, where we prefer tris(diethylamino)phosphine (DEA)3P because of its low price and its boiling point (240 °C) being higher than the reaction temperature (180 °C). After injection, the initially colorless reaction mixture turns dark red within ≈20 min.…”

“…In this mixture, InCl3 is the actual indium precursor and ZnCl2 is added to facilitate the shell growth and it also proves to reduce the size dispersion of the InP QDs. Note that, as already mentioned by other authors, 13,14 adding Zn at the beginning of the reaction does not automatically produce In(Zn)P alloys.…”

Temperature dependent recombination dynamics in InP/ZnS colloidal nanocrystals

“…It has been suggested 8 and later observed 17 that the shell grown under such conditions is likely to be an alloy of InP and ZnS, resulting in gradual potential transition across the interface between the core and shell rather than abrupt InP/ZnS junction. Such an interface may be vulnerable to the formation of defects responsible for non-radiative recombination.…”

Tri(pyrazolyl)phosphane als Vorstufen für die Synthese von stark emittierenden InP/ZnS‐Quantenpunkten

“…This is in agreement with published XPS (X-ray photoelectron spectroscopy) data following a two-step approach for the synthesis of InP/ZnS QDs. [20] Additional XAS (X-ray absorption spectroscopy) measurements by Cho et al [21] revealed that the In-Zn bond becomes more pronounced with increasing ZnS shelling time. This was attributed to additional bonding between the slow growing InP/ZnS core/shell interface.…”