Monodisperse Copper Chalcogenide Nanocrystals: Controllable Synthesis and the Pinning of Plasmonic Resonance Absorption

Controllable synthesis of copper chalcogenide nanocrystals (NCs), including desired geometry, composition and surrounding environment, is of high significance for the modulation of their optoelectronic response and the corresponding applications. Herein, copper nitride nanopartides have been used as uncontaminated copper precursors to synthesize copper chalcogenide NCs with high monodispersity through a one-pot strategy. In this protocol, the sizes and compositions of NCs can be readily controlled by varying the ratio of the precursors. For Cu2-xS NCs with different diameters, the size variations are all smaller than 5.6%. Furthermore, the plasmonic properties of the copper chalcogenide NCs are investigated under a steady state by tuning the plasmonic resonance absorption band to a limiting condition (denoted pinning phenomena). It is observed that the pinning frequency increases (from 1.09 to 1.23 eV) with the increment of the NC size (from 5.4 +/- 0.3 to 11.1 +/- 0.4 nm), explained by introducing surface scattering. Meanwhile, the frequencies of ternary alloyed copper sulfide selenide NCs blue-shift from 0.90 to 1.00 eV with the increase of selenium content from 11% to 66%, which is related to the effective mass of free carriers. Additionally, the plasmonic absorption bands of Cu2-xS NCs encapsulated by two single-layer graphene pin at 1525-1550 nm during the oxidation process, which is influenced by both the dielectric constant and redox potential of the surrounding environment. This study demonstrates the controllable synthesis and precise fundamental plasmonic properties of the copper chalcogenide NCs, ensuring the potential plasmonic-related techniques with high efficiency, accuracy and excellent spatial resolution.