Nanostructure of Atmospheric Plasma Polymerized Films Measured by X-ray Reflectivity

Plasma polymerization is a facile method of depositing robust films on a wide variety of substrates without the volatile organic solvents associated with conventional coatings. Films plasma polymerized in vacuum have been widely studied, but deposition using atmospheric plasma polymerization is less cumbersome. However, while the nanoscale structure of films deposited in vacuum has been studied some, little is known of the nanoscale structure of the films deposited in the more complex atmospheric conditions. X-ray reflectivity measurements reveal that films deposited using hexamethyldisiloxane (HMDSO) precursor often have depth profiles of scattering length density (SLD) consisting of a center ("bulk") region where the SLD is uniform with depth, a 4-8 nm thick transition region at the substrate and a 3-10 nm thick layer with distinct structure next to air. Deposition rate and SLD in the film center change with plasma power, but these characteristics are also sensitive to changes in ambient humidity. At higher humidity deposition rate and film interior SLD are less sensitive to power level.