Surface Plasmon Modulation in Cu_3–xP Nanocrystals

We demonstrate modulation of the surface plasmon resonance in nonstoichiometric copper phosphide nanocrystals using spectroelectrochemical methods. Application of an anodic potential resulted in a blue-shift of the surface plasmon resonance and an incremental increase in its extinction coefficient. Conversely, upon application of a cathodic potential, the surface plasmon band red-shifted and reduced in intensity. These changes were found to be reversible over multiple cycles of anodic and cathodic potential steps. We also discuss how the postsynthetic ligand treatment impacts the surface plasmon peak and the structure of Cu_3–xP nanocrystals. For example, the addition of alkylthiols resulted in the chemical decomposition of the nanocrystals. This work demonstrates how the surface plasmon peak in Cu_3–xP can be used to probe changes in the structure and carrier density in these nanocrystals.