Controlling Crystal Texture in Programmable Atom Equivalent Thin Films

DNA
is a powerful tool in the directed assembly of nanoparticle
based superlattice materials, as the predictable nature of Watson–Crick
base pairing allows DNA-grafted particles to be programmably assembled
into unit cells that arise from the complete control of nanoparticle
coordination environment within the lattice. However, while the local
environment around each nanoparticle within a superlattice can be
precisely dictated, the same level of control over aspects of crystallite
structure at the meso- or macroscale (e.g., lattice orientation) remains
challenging. This study investigates the pathway through which DNA-functionalized
nanoparticles bound to a DNA-functionalized substrate reorganize upon
annealing to synthesize superlattice thin films with restricted orientation.
Preferential alignment with the substrate occurs because of the energetic
stabilization of specific lattice planes at the substrate interface,
which drives the aligned grains to nucleate more readily and grow
through absorption of surrounding grains. Crystal orientation during
lattice reorganization is shown to be affected by film thickness,
lattice symmetry, DNA sequence, and particle design. Importantly,
judicious control over these factors allows for rational manipulation
over crystalline texture in bulk films. Additionally, it is shown
that this level of control enables a reduction in nanoscale symmetry
of preferentially aligned crystallites bound to an interface through
anisotropic thermal compression upon cooling. Ultimately, this investigation
highlights the remarkable interplays between nanoscale building blocks
and mesoscale orientation, and expands the structure-defining capabilities
of DNA-grafted nanoparticles.