Direct Synthesis of Novel Cu 2– x Se Wurtzite Phase

Herein, we report the unprecedented direct synthesis of a recently discovered metastable wurtzite phase of Cu2–xSe. Nanocrystals of Cu2–xSe were synthesized employing dodecyl diselenide as the selenium source and ligand. Optical characterization performed with UV–vis–NIR spectroscopy in solution showed a broad plasmonic band in the NIR. Structural characterization was performed with X-ray diffraction (XRD) and transmission electron microscopy. Variable-temperature XRD analysis revealed that the wurtzite nanocrystals irreversibly transform into the thermodynamic cubic phase at 151 °C. Replacement of dodecyl diselenide with dodecyl selenol yielded cubic phase Cu2–xSe, allowing for polymorphic phase control. An aliquot study was performed to gain insight into the mechanism of phase selectivity. The direct synthesis of this novel wurtzite phase could enable the discovery of new phenomena and expand the vast application space of CuxSey compounds.