Surface Plasmon\nModulation in Cu<sub>3–<i>x</i></sub>P Nanocrystals

We demonstrate modulation of the surface plasmon resonance\nin nonstoichiometric\ncopper phosphide nanocrystals using spectroelectrochemical methods.\nApplication of an anodic potential resulted in a blue-shift of the\nsurface plasmon resonance and an incremental increase in its extinction\ncoefficient. Conversely, upon application of a cathodic potential,\nthe surface plasmon band red-shifted and reduced in intensity. These\nchanges were found to be reversible over multiple cycles of anodic\nand cathodic potential steps. We also discuss how the postsynthetic\nligand treatment impacts the surface plasmon peak and the structure\nof Cu<sub>3–<i>x</i></sub>P nanocrystals. For example,\nthe addition of alkylthiols resulted in the chemical decomposition\nof the nanocrystals. This work demonstrates how the surface plasmon\npeak in Cu<sub>3–<i>x</i></sub>P can be used to probe\nchanges in the structure and carrier density in these nanocrystals.