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Ligand-Mediated Phase Control in Colloidal AgInSe2 Nanocrystals

preprint
submitted on 07.12.2019 and posted on 13.12.2019 by Bryce A. Tappan, Matthew Horton, Richard Brutchey
Synthetic studies of colloidal nanoparticles that crystallize in metastable structures represent an emerging area of interest in the development of novel functional materials, as metastable nanomaterials may exhibit unique properties when compared to their counterparts that crystallize in thermodynamically preferred structures. Herein, we demonstrate how phase control of colloidal AgInSe2 nanocrystals can be achieved by performing reactions in the presence, or absence, of 1-dodecanethiol. The thiol plays a crucial role in formation of metastable AgInSe2 nanocrystals, as it mediates an in-situ topotactic cation exchange from an orthorhombic Ag2Se intermediate to a metastable orthorhombic phase of AgInSe2. We provide a detailed mechanistic description of this cation exchange process to structurally elucidate how the orthorhombic phase of AgInSe2 forms. Density functional theory calculations suggest that the metastable orthorhombic phase of AgInSe2 is metastable by a small margin, at 10 meV/atom above the thermodynamic ground state. In the absence of 1-dodecanethiol, a mixture of Ag2Se nanocrystal intermediates form that convert through kinetically slow, non-topotactic exchange processes to yield the thermodynamically preferred chalcopyrite structure of AgInSe2. Finally, we offer new insight into the prediction of novel metastable multinary nanocrystal phases that do not exist on bulk phase diagrams.

Funding

DE-FG02-11ER46826

DE-AC02-05CH11231

History

Email Address of Submitting Author

brutchey@usc.edu

Institution

University of Southern California

Country

United States

ORCID For Submitting Author

0000-0002-7781-5596

Declaration of Conflict of Interest

No conflict of interest.

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in Chemistry of Materials

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