Seed-Mediated Growth of Oxidation-Resistant Copper Nanoparticles

Coppernanoparticles (CuNPs) are of interest due to their localizedsurface plasmon resonance, conductive properties, and the low costof copper; however, achieving CuNPs with controlled sizes that areresistant to surface oxidation from the environment is still an ongoingchallenge. We synthesized CuNPs with tunable sizes ranging from 20to 80 nm based on a seed-mediated growth process using polyvinylpyrrolidone(PVP) as a stabilizing agent. This synthetic strategy offered advantagesof using lower reaction temperatures, controlled particle size throughtuning the reaction medium, and protection from oxidation by the PVPstabilizing agent. The PVP polymer length influenced both the CuNPoptical properties and overall shape, with longer PVP allowing forbetter control over particle shape and size and the shorter lengthsproducing polydisperse particles with broader spectra. The size wasfurther controlled through addition of acetic acid, which resultedin larger particle sizes. Wide angle X-ray scattering measurementsindicated that the particles were composed of copper with no oxidepresent and the crystallite sizes were comparable to the overall particlesize. The ultraviolet-visible extinction peak positions ofthe particles showed limited dependence on the overall particle size.By examining the extinction and true absorbance measurements, we determinedthat all CuNPs had a true absorption peak due to interband transitionsat around 590 nm and peaks observed at longer wavelengths were dueto scattering effects from near field coupling of the particles. Finally,the particles were shown to be resistant to oxidation and remainedstable over time, which suggests that this strategy is promising forformation of large copper particles that do not oxidize.