Javier Vela-Becerra (Iowa State University)


Location: B01 McCourtney Hall

ABSTRACT:  A better understanding of the atomic, molecular, and phase evolution aspects of nucleation and growth of colloidal nanocrystals are critical to achieving their true potential in technologically-relevant applications. For example, we have studied how the chemical structure and reactivity of a family of commercially available organophosphite precursors affect the selective preparation of Ni, Ni12P5, and Ni2P nanophases through separate mechanistic pathways. Interestingly, nanocrystals of Ni2P readily hydrogenate nitrate to ammonia near ambient conditions with high selectivity. In two other examples, we have learned to synthesize complex multinary semiconductors such as I-II4-V3 pnictides and I-V-VI2 dichalcogenides (I = alkali metal; II = divalent transition metal; V = pnictide element; VI = chalcogenide). Key features in these systems include the utilization of highly reducing alkali hydride synthetic precursor, which enables to formation of metallic (Cd, Sb, or Bi) seeds that are required for the heterogeneous nucleation of the multinary nanophases. Computations and Pair Distribution Function (PDF) analysis of X-ray diffraction data reveal the presence of short- and long-range ordering, coloring patterns, and polymorphism in these systems. Infrared and solid-state NMR spectroscopy reveal the presence of specific ligands and binding motifs on the nanocrystal surfaces. Further nanostructuring and ligand engineering may enable the preparation of efficient energy conversion devices based on NaSbS2, NaBiS2, and other relatively biocompatible multinary semiconductors.

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