Energy landscape of self-assembled superlattices of PbSe nanocrystals

Zewei Quan; Di Wu; Jinlong Zhu; Wiel H Evers; James M Boncella; Laurens D A Siebbeles; Zhongwu Wang; Alexandra Navrotsky; Hongwu Xu

doi:10.1073/pnas.1408835111

Energy landscape of self-assembled superlattices of PbSe nanocrystals

Proc Natl Acad Sci U S A. 2014 Jun 24;111(25):9054-7. doi: 10.1073/pnas.1408835111. Epub 2014 Jun 9.

Authors

Zewei Quan¹, Di Wu², Jinlong Zhu³, Wiel H Evers⁴, James M Boncella⁵, Laurens D A Siebbeles⁶, Zhongwu Wang⁷, Alexandra Navrotsky⁸, Hongwu Xu⁹

Affiliations

¹ Earth and Environmental Sciences Division andMaterials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545;
² Peter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit, University of California, Davis, CA 95616;
³ Los Alamos Neutron Science Center, Los Alamos National Laboratory, Los Alamos, NM 87545;
⁴ Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, 2628 BL, Delft, The Netherlands;Kavli Institute for Nanoscience, Delft University of Technology, 2628 CJ, Delft, The Netherlands; and.
⁵ Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545;
⁶ Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, 2628 BL, Delft, The Netherlands;
⁷ Cornell High Energy Synchrotron Source, Wilson Laboratory, Cornell University, Ithaca, NY 14853.
⁸ Peter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit, University of California, Davis, CA 95616; anavrotsky@ucdavis.edu hxu@lanl.gov.
⁹ Earth and Environmental Sciences Division and anavrotsky@ucdavis.edu hxu@lanl.gov.

Abstract

Self-assembly of nanocrystals (NCs) into superlattices is an intriguing multiscale phenomenon that may lead to materials with novel collective properties, in addition to the unique properties of individual NCs compared with their bulk counterparts. By using different dispersion solvents, we synthesized three types of PbSe NC superlattices--body-centered cubic (bcc), body-centered tetragonal (bct), and face-centered cubic (fcc)--as confirmed by synchrotron small-angle X-ray scattering. Solution calorimetric measurements in hexane show that the enthalpy of formation of the superlattice from dispersed NCs is on the order of -2 kJ/mol. The calorimetric measurements reveal that the bcc superlattice is the energetically most stable polymorph, with the bct being 0.32 and the fcc 0.55 kJ/mol higher in enthalpy. This stability sequence is consistent with the decreased packing efficiency of PbSe NCs from bcc (17.2%) to bct (16.0%) and to fcc (15.2%). The small enthalpy differences among the three polymorphs confirm a closely spaced energy landscape and explain the ease of formation of different NC superlattices at slightly different synthesis conditions.

Keywords: PbSe nanocrystal superlattices; ligand interaction; thermodynamics.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.