Preparation and oxidation behavior of Ag-coated Cu nanoparticles less than 20 nm in size

This study examines the oxidation behavior of Ag-coated Cu (Cu@Ag) nanoparticles (NPs) less than 20 nm in size synthesized using a solvothermal method and an immersion process with varying Ag shell quality. First, the mechanism for the formation of Cu NPs is discussed with respect to increasing reaction temperature and time. It was found that La Mer's model and the digestive-ripening mechanism affected the size and the morphology of the Cu NPs. Spherical Cu NPs were first observed after 15 min at 240 °C. Moreover, Cu@Ag NPs synthesized with varying immersion temperatures were observed by elemental mapping and line profile imaging using scanning transmission electron microscopy. The average thickness and density of the Ag shell increased with increasing immersion temperature. Based on the results, we evaluated the anti-oxidation property of samples immersed at 80 and 150 °C using high-temperature X-ray diffraction. The sample immersed at 150 °C exhibited an enhanced anti-oxidation property mainly as a result of the thicker and denser Ag shell. In particular, we observed a difference in the amount of free Ag NPs as a result of dewetting as the Ag shell structure changed. The anti-oxidation property of Cu@Ag NPs was strongly dependent on the Ag shell quality.