The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Here, a comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of nanoparticle thin films. Both surface morphology and internal thin film structure are examined to provide an understanding of particle attachment and reorganization during growth. Under equilibrium conditions, single crystalline, multilayer thin films can be synthesized over 500 × 500 μm<sup>2</sup> areas on lithographically patterned templates, whereas deposition under kinetic conditions leads to the rapid growth of glassy films. Importantly, these superlattices follow similar patterns of crystal growth demonstrated in atomic thin film deposition, but utilize a “soft,” elastically malleable building block. This key difference results in these colloidal thin films exhibiting significant strain tolerance when subjected to heteroepitaxial growth with a lattice mismatch. Calculations of interaction potentials, small-angle X-ray scattering data, and electron microscopy images show that the oligomer corona surrounding a particle core can deform and rearrange to store elastic strain up to ±7.7% lattice mismatch, substantially exceeding the ±1% mismatch tolerated by atomic thin films. Importantly, these DNA-coated particles dissipate strain both elastically through a gradual and coherent relaxation/broadening of the mismatched lattice parameter and plastically (irreversibly) through the formation of dislocations or vacancies. These data also suggest that the DNA cannot be extended as readily as compressed, and thus the thin films exhibit distinctly different relaxation behavior in the positive and negative lattice mismatch regimes. These observations provide a more general understanding of how utilizing rigid building blocks coated with compressible polymeric materials can be used to control nano- and microstructure through “soft heteroepitaxy."

"Soft" epitaxy in DNA-nanoparticle thin films

256th National Meeting (2018)

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