Annealing-induced highly-conductive and stable Cu-organic composite nanoparticles with hierarchical structures

To obtain high stability and electrical properties simultaneously is crucial for applications of Cu nanomaterials in microelectronics. In this work, multi-crystalline Cu nanoparticles were synthesized in the presence of PVP and SDS. Each as-grown particle was capped by a non-crystalline organic layer. The capped particles were only slightly oxidized after being stored under harsh ambient conditions for 3 months. Annealing at 250 °C and 500 °C in Ar was used to lower the electrical resistivity by five to six orders of magnitude. After being annealed at 250 °C, the original capping layer changed into a shell layer of thinner and uniform thickness. Although the electrical properties improved, oxidation of Cu into Cu₂O was found during storage. Highly conductive and stable Cu-organic composite nanoparticles with hierarchical structures were obtained by heat treatment at 500 °C. The organics did not decompose completely but reacted with Cu to form a crystalline inner shell with a bcc structure and a non-crystalline outer shell. Small crystalline particles of 3-10 nm precipitated out within the outer shell layer and self-assembled on the surfaces of the Cu particle cores. The hierarchical Cu nanoparticles underwent no obvious enlargement and showed potential for fabricating electrical interconnections, sensors, and bionic structures.