Investigation of oxidation inhibition properties of vaporized self-assembled multilayers on copper nanopowders

Stability against oxidation was investigated for vaporized self-assembled multilayers on nano-sized Cu powders. 100 nm-sized copper powders were coated with 1-octanethiol to make a passivation layer against oxidation. As a result, the surface resistivity of the coated and uncoated nano-sized copper powders differed by two orders of magnitude. XPS analysis was used to monitor changes in the amount of sulfur and oxygen on the surface of octanethiol-coated Cu nano powders over a period of time. While sulfur was detected for up to 75 days, the amount of oxygen increased dramatically after 35 days, indicating sign of partial oxidation. Furthermore, HR-TEM images showed that the octanethiol film was consistently 10 nm thick, for up to 35 days. After 35 days exposure to the air, the octanethiol film was partially damaged and its diffraction pattern detected the presence of Cu2O. Based on these findings, vaporized octanethiol coating protected the copper nano powders from oxidation for up to 35 days. Therefore this oxidation inhibition property of VSAMs coating method on Cu powders achieves a great milestone toward inkjet printing technology.