Correlating Superlattice Polymorphs to Internanoparticle Distance, Packing Density, and Surface Lattice in Assemblies of PbS Nanoparticles

Wang, Zhongwu; Schliehe, Constanze; Bian, Kaifu; Dale, Darren; Bassett, William A.; Hanrath, Tobias; Klinke, Christian; Weller, Horst

doi:10.1021/nl400084k

Cited by 110 publications

(184 citation statements)

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“…Thus, disassembly occurs presumably because of an entropic driving force. As shown in Table 1, the ΔH x values of all three superlattices are on the order of 2 kJ/mol of NCs, comparable to the energy of van der Waals interactions (23,25,26). The bcc superlattice has the highest ΔH x and thus is energetically the most stable.…”

Section: Resultsmentioning

confidence: 87%

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Energy landscape of self-assembled superlattices of PbSe nanocrystals

Quan

Zhu

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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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.PbSe nanocrystal superlattices | thermodynamics | ligand interaction S elf-assembly of colloidal nanocrystals (NCs) not only is a fascinating phenomenon, but also offers a promising route for design and fabrication of novel materials (1, 2). NCs possess unique size-and shape-dependent structures and properties that differ from those of their bulk counterparts (3). Analogous to formation of a crystal from constituent atoms/ions, highly uniform NCs can self-assemble into periodically ordered structures, referred to as superlattices or "artificial crystals." In addition to the unique properties of individual NCs, these NC superlattices manifest new collective behavior [such as electronic, plasmonic, magnetic, and catalytic properties (4)] through near-field coupling of neighboring NCs (5). In the past two decades, various NC superlattices were developed successfully via the controlled assembly of colloidal nanoparticles (2,(6)(7)(8)(9)(10)(11)(12)(13)(14), and, at the same time, extensive simulation efforts have been devoted to understanding this complicated process and to predict the assembly patterns (15-17). To achieve rational design of NC superlattices, however, it is essential to have a fundamental understanding of the mechanisms underlying their formation, including their energetics of formation and polymorphism, which form the focus of this study.Colloidal NCs usually are composed of a hard inorganic core and a soft shell of organic molecules. The organic shell helps stabilize the inorganic core, allows the formation of an almost monodisperse size distribution of NCs, and enables dispersion of NCs in an organic solvent. NC superlattices can be synthesized, starting with well-dispersed NCs in a solvent via slow and controlled solvent evaporation. We chose PbSe as a model system because of the relative ease of preparing NC building blocks. In addition, PbSe NC superlattic...

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Section: Resultsmentioning

confidence: 87%

“…( Fig. S4), suggesting good translational coherence and large domains of nucleated supercrystals (22,23).…”

Section: Resultsmentioning

confidence: 98%

Energy landscape of self-assembled superlattices of PbSe nanocrystals

Quan

Zhu

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Optimized photovoltaics require precise control over the optical properties, transport properties, and chemical potential of the semiconductor active layer, 3 and despite the disorder and heterogeneity present within nanocrystal films, the effective medium properties can be approximated as uniform when the length scale of interest is much larger than that of the nanoscale variations. 4 The optical properties of a nanocrystal film, including permittivity, absorption coefficient and bandgap, are dramatically altered with nanocrystal size and capping ligand. 5−8 Quantitative understanding of the size dependent optical properties of individual nanocrystals has emerged from the ability to synthesize samples of high monodispersity in solution.…”

Section: ■ Introductionmentioning

confidence: 99%

Postsynthetic Doping Control of Nanocrystal Thin Films: Balancing Space Charge to Improve Photovoltaic Efficiency

Engel

Alivisatos

2013

Chem. Mater.

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A semiconductor nanocrystal film is a unique class of nanocomposite, whose collective properties are determined by those of its constituents. Colloidal synthetic methods offer precise size control and finely tuned optical properties via quantum confinement, while recent improvements in charge transport through films have led to a variety of optoelectronic applications. However, understanding the role of defects and impurities in doping, crucial for optimizing device performance, has remained more elusive. In this perspective, we review recent progress in understanding and controlling the doping of semiconductor nanocrystal thin films, with a special focus on its relevance to photovoltaic applications. We highlight an array of postsynthetic techniques based on stoichiometric control, metal impurity incorporation, and electrochemical charging. We conclude with a review of the state of the art for nanocrystal photovoltaics, and propose the use of controlled doping and charge balance as a pathway to higher device efficiencies.

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“…The latter superlattice transformation does not involve significant rotation and tilting of NCs. Instead, NCs simply chase the well-known Bain deformation route 12 Conclusion. In summary, through controlling the solvent evaporation, we have grown large single supercrystal grains from Pt NC suspensions in hexane.…”

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confidence: 99%

An Obtuse Rhombohedral Superlattice Assembled by Pt Nanocubes

Li¹,

Bian²,

Wang

et al. 2015

Nano Lett.

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100

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We grew large single three-dimensional supercrystals from colloidal Pt nanocubes (NCs) suspended in hexane. A synchrotron-based two circle diffractometer was used to obtain an unprecedented level of detail from full sets of small/wide-angle X-ray scattering (SAXS/WAXS) patterns. Automatic indexing and simulations of X-ray patterns enabled detailed reconstruction of NC translation and shape orientation within the supercrystals from atomic to mesometric levels. The supercrystal has an obtuse rhombohedral (Rh) superlattice with space group R3m and a trigonal cell angle of 106.2°. Individual NCs orient themselves in a manner of atomic Pt[111] parallel to superlattice Rh[111]. We analyzed the superlattice structure in context of three spatial relationships of proximate NCs including face-to-face, edge-to-edge, and corner-to-corner configurations. Detailed analysis of supercrystal structure reveals nearly direct corner-to-corner contacts and a tight interlocking NC structure. We employed the correlations between strain and lattice distortion and established the first structural correlating mechanism between five superlattice polymorphs to elucidate the superlattice transformations and associated developing pathways. Together, the experimental and modeling results provide comprehensive structural information toward controlling design and efficient materials-processing for large fabrication of nanobased functional materials with tailored structures and desired properties.

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Correlating Superlattice Polymorphs to Internanoparticle Distance, Packing Density, and Surface Lattice in Assemblies of PbS Nanoparticles

Cited by 110 publications

References 51 publications

Energy landscape of self-assembled superlattices of PbSe nanocrystals

Energy landscape of self-assembled superlattices of PbSe nanocrystals

Postsynthetic Doping Control of Nanocrystal Thin Films: Balancing Space Charge to Improve Photovoltaic Efficiency

An Obtuse Rhombohedral Superlattice Assembled by Pt Nanocubes

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