Controlled thicknesses of vaporized self-assembled multilayers on copper nanopowders under ultra-high vacuum (UHV)

Copper nanoparticles were coated with 1-octanethiol self-assembled monolayers (SAMs) using the dry-coating method for oxidation prevention. In this study, thicknesses of 1-octanethiol SAMs were successfully controlled, and the stability of SAMs as a passivation layer on copper nanoparticles was examined. Thicknesses of 1-octanethiol SAMs varied with vacuum levels and coating cycles. Under low-vacuum conditions, the thickness was 10 nm, regardless of the coating conditions. In contrast, various thicknesses resulted under ultra-high vacuum (UHV) and ranged from 4 nm to 10 nm. SAMs that were nearly a monolayer thick (4 nm) resulted from two coating cycles of 1.5 min, and the oxidation inhibition period was 15 days. Thus, the dry-coating method successfully controlled the thicknesses of SAMs with satisfactory oxidation inhibition properties under ultra-high vacuum.