Berlin 2015 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 9: Quantum dots: Optical properties

HL 9.9: Vortrag

Montag, 16. März 2015, 12:15–12:30, EW 203

Random-alloying induced optical fingerprints in colloidal quantum dots — •Daniel Mourad¹, Tangi Aubert², Antoine Guille², Edouard Brainis², Zeger Hens², and Gabriel Bester¹ — ¹Institut für Physikalische Chemie, Universität Hamburg — ²Physics and Chemistry of Nanostructures, Ghent University

Monodisperse, homogeneously alloyed quantum dots (QDs), which can be grown by means of colloidal synthesis, allow for a tayloring of the absorption/emission properties by variation of the composition. However, distinguishing a random alloy from, e.g., a core/shell nanocrystal is difficult and requires advanced characterization tools such as Raman spectroscopy [Aubert et al., Chem. Mater. 25(12), 2388 (2013)]. We show that randomly alloyed Cd(Se,S) QDs exhibit fingerprints of random alloying in their absorption spectrum. Furthermore, we demonstrate that a stochastical empirical tight-binding scheme can reproduce these features without additional free parameters and link them to symmetry breaking intrinsic to random alloying [Mourad et al., Chem. Mater., DOI: 10.1021/cm5035408]. When complemented by many-particle calculations in the configuration interaction framework, excited-state properties like the bowing of the optical gap are also in very good agreement with the experiment. Since symmetry breaking is inherent to random alloys, our method may provide a general framework where theory can be used to predict random alloying fingerprints in absorption spectra of different nanomaterials. We discuss the effects of size variations, different composition profiles and further material systems.