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      Energetics of polar and nonpolar facets of PbSe nanocrystals from theory and experiment.

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          Abstract

          Surface energies of the distinct facets of nanocrystals are an important factor in the free energy and hence determine the nanocrystal morphology, chemical and physical properties, and even interparticle dipole interactions. Here we investigate the stability and atomic structure of polar and nonpolar PbSe surfaces by combining first-principles calculations with high-resolution transmission electron microscopy (TEM). For uncapped surfaces, the calculations predict that the nonpolar {100} surface is the most stable with a surface energy of 0.184 J m(-2), while the nonpolar {110} and reconstructed {111}-Pb surfaces have surface energies of 0.318 J m(-2) and 0.328 J m(-2), respectively. Fully polar {111} surfaces are structurally unstable upon relaxation. These findings are in good agreement with TEM observations showing that capped nanocrystals have a nearly spherical, multifaceted morphology, while cubical shapes with predominantly {100} facets are obtained when the capping molecules are removed through heating in vacuum. During this process, however, also multipolar surfaces can temporarily exist just after the removal of the surfactants. These metastable {111} surfaces consist of ribbon-like nanodomains, whereby the ribbons are alternating in polarity. The calculations confirm that these multipolar surfaces are energetically more favorable than fully polar surfaces. The consequences for capped nanocrystals (a dominant Pb-oleate termination) and nanocrystal fusion (a shorter interaction range of dipole interactions) are discussed.

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          Author and article information

          Journal
          ACS Nano
          ACS nano
          American Chemical Society (ACS)
          1936-086X
          1936-0851
          Jan 26 2010
          : 4
          : 1
          Affiliations
          [1 ] Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, NL-2628 CJ Delft, The Netherlands.
          Article
          10.1021/nn9013406
          20099911
          ba1041c7-7a5d-43a7-8b9d-db6a38a91969

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