Pressure compression of CdSe nanoparticles into luminescent nanowires

Oriented attachment (OA) of synthetic nanocrystals is emerging as an effective means of fabricating low-dimensional nanoscale materials. However, OA relies on energetically favorable nanocrystal facets to grow nanostructured materials. Consequently, nanostructures synthesized through OA are generally limited to a specific crystal facet in their final morphology. We report our discovery that high-pressure compression can induce consolidation of spherical CdSe nanocrystal arrays, leading to unexpected one-dimensional semiconductor nanowires that do not exhibit the typical crystal facet. In particular, in situ high-pressure synchrotron x-ray scattering, optical spectroscopy, and high-resolution transmission electron microscopy characterizations indicate that by manipulating the coupling between nanocrystals through external pressure, a reversible change in nanocrystal assemblies and properties can be achieved at modest pressure. When pressure is increased above a threshold, these nanocrystals begin to contact one another and consolidate, irreversibly forming one-dimensional luminescent nanowires. High-fidelity molecular dynamics (MD) methods were used to calculate surface energies and simulate compression and coalescence mechanisms of CdSe nanocrystals. The MD results provide new insight into nanowire assembly dynamics and phase stability of nanocrystalline structures.