Monoclinic copper(I) selenide nanocrystals and copper(I) selenide/palladium heterostructures: Synthesis, characterization, and surface-enhanced raman scattering performance

We have developed a simple and facile approach to the fabrication of monoclinic Cu₂Se nanocrystals and Cu₂Se/Pd heterostructures. [(C₂H₅)₄N]₂[CuCl₄] was chosen as the copper source and SeO₂/terpineol was used as the Se^-II precursor for the generation of hexagonal CuSe and cubic Cu_2-xSe through the "hot-injection" and "one-pot" methods, respectively. Both CuSe and Cu_2-xSe could be further transformed into monoclinic Cu₂Se through heat treatment with trioctylphosphine (TOP) at 220 C. Cu₂Se/Pd as well as CuSe/Pd and Cu_2-xSe/Pd were readily obtained by simply mixing copper selenides and Pd(NO₃)₂ in a 2-propanol solution. The Pd nanoparticles were distributed on the surface of the copper selenides. The effect of certain reaction parameters on the formation of copper selenides was studied. The amount of terpineol used played an important role in the phase-selective synthesis of CuSe and Cu_2-xSe. The surface-enhanced Raman scattering (SERS) performance of the heterostructures was investigated with 4-mercaptopyridine (4-Mpy) as a probe molecule. Owing to the strong synergistic effects between Cu₂Se and Pd, Cu₂Se/Pd showed greater SERS performance than pure Pd or Cu₂Se. Moreover, compared to those of CuSe/Pd and Cu_2-xSe/Pd, Cu₂Se/Pd exhibited the highest SERS sensitivity to 4-Mpy with a detection limit as low as 1.0×10^-9 M, which revealed its phase- and composition-dependent characteristics. This Cu₂Se/Pd heterostructure exhibits potential applications in the chemical and biological sensing fields.