XAFS Study of Inorganically Coated Colloidal Quantum Dots

ACEBRÓN, MARÍA; HERRERA, FACUNDO C.; MIZRAHI, MARTÍN; REQUEJO, FÉLIX G.; JUAREZ, BEATRIZ H.

Campinas

Congreso; 27th Annual Users Meeting; 2017

CNPEM-LNLS

The dielectric nature of organic ligands capping semiconductor colloidal nanocrystals (NCs) makes them incompatible with optoelectronic applications. For this reason, these ligands are regularly substituted through ligand-exchange processes by shorter (even atomic), or inorganic ones. In this work, an alternative path is proposed to obtain inorganically coated NCs. Differently to a regular ligand exchange processes, the here reported method produces core-shell NCs simultaneously to the removal of the original organic shell. The insulating organic ligands and the higher solubility in polar media turnsthese structures very attractive for their further integration into optoelectronic devices. In this work two different sulfur precursors were used, namely: thioacetamide (TA) and thiocarbamide (TC) which, despite of their structural similarities, yield NCs with different optical properties and thickness coverages. The nature of the inorganic shell has been elucidated by X-ray Absorption Near Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS). XAS experiments were measured at the SXS (S and Cd edges) and XAFS2 (Zn and Se edges) beamlines at the LNLS (Laboratorio Nacional de Luz Sincrotron), Campinas, Brazil. According to the S-K edge spectra a combination of sulfides and sulfates seems feasible, although out of these spectra, clear identification to ZnS and/or CdS cannot be ascribed univocally and the contribution of Cd or Zn sulfides and sulfates cannot be distinguishable from these results. samples drastically differ from CdSO4. Cd XANES spectra corresponding to our samples are very close to the already reported for CdS.[1][1] G. Van der Snickt, J. Dik, M. Cotte, K. Janssens, J. Jaroszewicz, W. De Nolf, J. Groenewegen, L. Van der Loeff, Analytical Chemistry 2009, 81, 2600.