More recent work explores the self-assembly of size-controlled, ligand-stabilized metal nanocrystals from solution into well-ordered monolayer sheets.  This effort is done in close collaboration with Xiao-Min Lin (Center for Nanoscale Materials, Argonne National Lab), who also synthesizes the nanocrystals our group uses.  We established drop casting techniques that can self-assemble long-range ordered monolayers and demonstrated the interplay of kinetic and energetic mechanisms driving the assembly process [3].  While investigating the electronic transport properties of mono- and multi-layers of close-packed metal nanocrystals [4-6], we discovered in 2006 that the monolayers also have remarkable tensile strength (with moduli in the GigaPascal range) [7] and now mostly focus on the mechanical properties of freely suspended nanoparticle sheets.  Our most recent work in this direction explores molecular transport through such sheets (for use as ultrathin filtration membranes) [8] and the controlled manipulation of the sheets’ properties by electron and ion beams [9].

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1. Terry L. Morkved and H. M. Jaeger, "Thickness-Induced Morphology Changes in Lamellar Diblock Copolymer Ultrathin Films", Europhys. Lett. 40, 643 (1997).

2. Ward A. Lopes and H. M. Jaeger, "Hierarchical Self-Assembly of Metal Nanostructures on Diblock Copolymer Scaffolds", Nature 414, 735 (2001). An image from this work was used as inaugural cover for Nature Nanotechnology.

3. Terry P. Bigioni et al., “Kinetically-Driven Self-Assembly of Highly-Ordered Nanocrystal Monolayers”, Nature Materials 5, 265-270 (2006).

4. Raghuveer Parthasarathy et al., "Electronic Transport in Metal Nanocrystals Arrays: The Effect of Structural Disorder on Scaling Behavior", Phys. Rev. Lett. 87, 186807 (2001).

5. Raghuveer Parthasarathy et al., “Percolating Through Networks of Random Thresholds: Finite Temperature Electron Tunneling in Metal Nanocrystal Arrays”, Phys. Rev. Lett. 92, 076801 (2004).

6. Thu B. Tran et al., “Sequential tunneling and inelastic cotunneling in nanoparticle arrays”, Phys. Rev. B 7, 075437 (2008).

7. Klara E. Mueggenburg et al., "Elastic membranes of close-packed nanoparticle arrays", Nature Materials 6, 656-660 (2007).

8. Jinbo He et al., “Diffusion and Filtration Properties of Self-Assembled Gold Nanocrystal Membranes”, Nano Letters 11, 2430–2435 (2011).

9. Pongsakorn Kanjanaboos et al., “Strain Patterning and Direct Measurement of Poisson’s Ratio in Nanoparticle Monolayer Sheets”, Nano Letters 11, 2567–2571 (2011)

Metal-inorganic hybrid nanostructures combine the electronic, optical or magnetic properties of nanoparticles with the flexibility offered by an embedding matrix of organic molecules. We have been focusing on the ultrathin, 2D limit of such nanoparticle-based structures.  Earlier projects in our lab investigated diblock copolymers as a means for self-assembling hybrid nanostructures with controlled features in the 10-100 nanometer regime.   We discovered new morphologies in ultrathin diblock copolymer films that exhibit lateral, in-plane patterns of alternating domains with both blocks at the film surface [1], and showed how this can be used for selective decoration with metal nanoparticles [2].