UC San Diego

Colloidal copper phosphide (Cu3−xP) nanocrystals are attractive electronic materials due to their ability to support excess delocalized holes, with both synthesis and dynamic redox modulation allowing tuning of localized surface plasmon resonance (LSPR) absorption in the near-IR. This dissertation presents developments in the colloidal syntheses and post-synthetic redox chemistries of high-quality Cu3−xP nanoplatelets with the attainment of tunable nanocrystallite lateral sizes, LSPR energies, compositions, and optoelectronic properties. A one-pot, colloidal synthesis of Cu3−xP nanoplatelets with copper halide salt and aminophosphine in the presence of oleylamine is presented in Chapter 2. The reactivity of an in situ copper-phosphorus precursor is modulated by varying precursor composition and coordinating solvent ratio to tune nanocrystal lateral size. Oleylamine-to-aminophosphine molar ratio is found to alter particle nucleation activity and access atom-efficient size tuning. By modulating precursor reactivity, the syntheses presented in Chapter 2 are used to access nanocrystals with lateral sizes of 6.1–23 nm and LSPR energies of 709–861 meV. The low polydispersity, size- and LSPR-tunability and colloidal stability make aminophosphine-synthesized Cu3−xP nanocrystals promising candidates for investigations into factors governing their LSPR energy, around which the findings of the subsequent chapter are based. Three copper-coupled redox chemistries are presented in Chapter 3 which allow post-synthetic modulation of the delocalized hole concentrations and corresponding LSPR absorption in colloidal Cu3−xP nanocrystals. Changes in the structural, optical, and compositional properties are evaluated by powder X-ray diffraction, electronic absorption spectroscopy, 31P magic-angle spinning solid-state nuclear magnetic resonance spectroscopy and elemental analysis. The redox chemistries are shown to access nanocrystals with LSPR energies of 660–890 meV, a larger range than has been possible through synthetic tuning. The largest structural and LSPR modulation is achieved through the use of a divalent metal halide and trioctylphosphine, with the smallest reported unit-cell volume (295.2 Å3) and most downfield 31P chemical shift (+346 ppm) reported for P63cm Cu3−xP. In Chapter 4, the platform for systematic mechanistic investigations developed in Chapter 2 is extended to use copper phosphide as a model system for the study of aminopnictine precursor chemistry and the elucidation of metal pnictide nanocrystal formation mechanisms. Preliminary findings are presented for the investigation of the synthetic roles of copper salt counteranion and aminophosphine amide identity.