Aluminum nanocrystals are emerging as a more sustainable alternative to noble metal nanoparticles due to a combination of its abundance and desirable optical and plasmonic properties. One key challenge for the wider adoption of aluminum-based colloidal materials is the demonstration of size-, shape-, and facet-controlled growth. Al nanocrystals are unique in their requirement of a catalyst to nucleate nanocrystal growth, to our knowledge. However, the catalyst ligands can also play a dominant role in controlling the growth of specific crystalline facets, and can determine the morphology of the nanocrystalline product. For example, the Ti-based AlH3-reducing catalyst Tebbe’s reagent was shown to produce {100}-faceted nanocubes. We examine this reaction in greater detail, observing the presence of cyclopentadienyl moieties on Al nanocube surfaces through the use of surface-enhanced Raman and IR spectroscopies in the particle growth environment. We then alter the cyclopentadienyl ligands of this catalyst to allow for pure {111} facets to be expressed, giving access to octahedral, decahedral, and icosahedral morphologies. Changing the central atom of a Tebbe’s reagent analogue from Ti to V has a direct effect on AlH3 binding and reduction rates, leading to highly anisotropic one and two-dimensional structures. This allows for further modifications of the resulting Al nanocrystal structure from {100} bars to high-aspect ratio nanowires and nanoplates. The emergence of the AlH3-reducing catalyst as shape-directing ligand allows for realization of aluminum as an earth-abundant alternative for metallic plasmonics and nanophotonics.

Mechanisms for anisotropic growth of aluminum nanocrystals

ACS Spring 2022

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