Size Dependence of Doping via Vacancy Formation in Copper Sulfide Nanocrystals

Colloidal semiconductor nanocrystals (SC NCs) are becoming fundamental building blocks in novel systems and devices. Controlling the electronic properties of SC NC based devices through fine tuning of the NC dimensions and doping plays a key role in the prospect of implementing them in advanced transistors, photodiodes and photodetectors. Here, I studied size effect on doping process in copper (I) sulfide quantum-dots (Cu₂S QDs) via vacancy formation.

The effect on doping via vacancy formation in Cu₂S QDs, was examined through their redox reaction with iodine. X-ray absorption spectroscopy (XAS, measured at the synchrotron), along with additional materials characterization methods were employed to identify the doping effects leading to transformation from the stoichiometric Cu₂S phase to Cu depleted Cu_2-xS phase and the formation of the new copper (I) iodide (CuI) phase. In addition, the evolution of a localized surface plasmon resonance (LSPR) was correlated with the addition of free charge carriers due to Cu vacancy formation, and allowed to extract their concentrations. The chemical efficiency of the reaction shows higher efficiency for the larger QDs. This behavior is attributed to the interplay of vacancy formation energy, which decreases with size, and the nucleation and growth of the CuI phase on the QD surface that is favored on the well-defined facets of the larger QDs. This doping process allowed tuning the plasmonic properties of the QDs by varying the size and the iodine concentration and demonstrated a wide range of plasmonic frequencies for the Cu₂S QDs.

• Elimelech, O.; Liu, J.; Plonka, A. M.; Frenkel, A. I.; Banin, U; "Size Dependence of Doping by a Vacancy Formation Reaction in Copper Sulfide Nanocrystals". Angew. Chemie - Int. Ed. 2017, 56 (35), 10335.